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About this book

With the prospect of revolutionizing specific technologies, this book highlights the most exciting and impactful current research in the fields of cellulose-based superabsorbent hydrogels with their smart applications. The book assembles the newest synthetic routes, characterization methods, and applications in the emergent area. Leading experts in the field have contributed chapters representative of their most recent research results, shedding light on the enormous potential of this field and thoroughly presenting cellulose-based hydrogel functioning materials.
The book is intended for the polymer chemists, academic and industrial scientists and engineers, pharmaceutical and biomedical scientists and agricultural engineers engaged in research and development on absorbency, absorbent products and superabsorbent hydrogels. It can also be supportive for undergraduate and graduate students.

Table of Contents

Frontmatter

Fundamentals of Cellulose, Superabsorbents, and Hydrogels

Frontmatter

1. Cellulosic Hydrogels: A Greener Solution of Sustainability

Hydrogels are insoluble three-dimensional cross-linked polymeric network that swells in presence of water and other fluids. They can hold plenty of water compared to its own mass. The absence of dissolution attraction toward water is due to hydrophilic nature of the polymeric chain. Hydrophilicity arises because of holding hydrophilic functional groups in the chain. Highest portion of the world production of hydrogels is petrochemical based which is neither renewable nor biocompatible. In spite of some drawbacks like nondegradability, synthetic hydrogels are superior to natural one in water absorbency, diversification in chemicals, and longer service life. Taking into consideration sustainability factor, scientists are interested in preparation of hydrogels from renewable cellulosic sources. As cellulose possesses intrinsic nature of degradability, biocompatibility, and nontoxicity, also available in nature, and some cellulose derivatives show smart behavior, cellulose-based hydrogels can be an alternative to synthetic petrochemical-derived hydrogels. Numerous research articles concerning the synthesis and utilization of hydrogels in different fields have been published, and still restless labor is giving for the betterment of the product quality. It is a crying need to make available and adequate information on synthesis and characterization of cellulosic hydrogels for individual researchers. For this the specific aim of this paper is to accumulate some crucial information which will cover synthesis, detailed classification, characterization, and technological feasibility of application about hydrogels of renewable source. As of consequence, the research on hydrogel concerning current environmental issues will reach to its target of making the greener solution of sustainability. In addition, recent trend of hydrogel research is also discussed in this review.

Md. Ibrahim H. Mondal, Md. Obaidul Haque

2. Recent Advances of Multifunctional Cellulose-Based Hydrogels

Cellulose is an abundant and renewable natural resource with biodegradability and nontoxicity. Furthermore, cellulose and cellulose derivatives also have unique properties such as hydrophilicity, mechanical strength, biocompatibility, and tunable functionality due to the strong versatile hydrogen bonding. Cellulose-based hydrogels are prepared by physical or chemical cross-linking of cellulose derivatives with various functional molecules, which covalently bind different functional molecules and form a highly porous hydrogel, with three-dimensional network structure consisting of nanofibrillar-regenerated cellulose Nanofibrillar regenerated cellulose . Such cellulose-based hydrogels have great advantages due to high water-holding capacityWater-holding capacity, abundance, biodegradable biocompatibility and nontoxicity, which can be applied as superabsorbent in wastewater treatmentWastewater treatment (such as oil, heavy metals, dye, organic pollutants), as superabsorbent biomaterialsSuperabsorbent biomaterials, in pharmaceutical and biomedical field, in personal care and hygiene products, and tissue engineering and wound dressing. Moreover, they have also been used in catalysis, sensors, luminescence, and energy storage. This chapter will introduce the smart applications of cellulose-based hydrogels including native cellulose, cellulose derivatives, and cellulose-composite hydrogels. Among those, we will focus our discussion herein on the adsorption application of cellulose-based hydrogels. Most excellent research works are highlighted in this chapter, and cellulose-based hydrogels will be expected to be applied in agriculture, food, environment, industry, medical care, and personal health field. At last, we also give a prospect on cellulose-based hydrogels in the future.

Jiajun Mao, Shuhui Li, Jianying Huang, Kai Meng, Guoqiang Chen, Yuekun Lai

3. Structure-Property Relationships in Cellulose-Based Hydrogels

Hydrogels are widely used for different biomedical applications, due to their ability to absorb, retain, and release water solutions in a reversible manner and in response to specific environmental stimuli. The review is focused on the preparation methods, main characteristics, as well as biomedical applications of hydrogels prepared from the most abundant biopolymers on earth, cellulose. The chapter emphasizes the latest developments in the design and manufacture of cellulose-based hydrogels. The preparation of hydrogels without covalent cross-links (physical hydrogels) and with covalent cross-links (chemical hydrogels) is discussed. The behavior of gels upon coagulation and the swelling capacity in water were analyzed. A systematic investigation into the structure and physical-chemical properties of cellulose-based hydrogels was performed in order to describe the relationships between the network structure and gel properties. The degree of cross-linking of the hydrogels, the morphology of the three-dimensional (3D) matrices, the bulk geometry, and the description by different complementary techniques which offered insight into structure-property relationships of hydrogels are reviewed. The sorption properties of cellulose-based hydrogels and the effect of the design parameters of hydrogels on their biomedical applications are also discussed.

Diana Elena Ciolacu

4. Cellulose Solubility, Gelation, and Absorbency Compared with Designed Synthetic Polymers

Swelling and solubility of polymers, and in particular cellulose, are controlled by interactions, molecular symmetry, chain flexibility, and order/disorder. Theory is used to explain and predict which liquid systems, polymer structures, and chemical modifications form gels and polymer solutions. Extension of these principles leads to super-absorbent polymers. Cellulose is not water soluble, though some water systems can dissolve cellulose, particularly alkaline or strongly hydrogen-bonding solutions. Less hydrophilic derivatives such as methyl cellulose dissolve in water; while with increasing substitution with methyl groups, cellulose becomes soluble in organic solvents such as dichloromethane. Sometimes temperature can enhance solubility or gelation; alternatively adjusting chemistry through functional group modification to reach an optimum between intermolecular versus solvation interactions will create exceptional changes in absorbency. The solvation power can be increased by adding strongly ionic, hydrogen bonding or acid–base solutes such as lithium chloride, urea, or sodium hydroxide. Synthetic polymers have been designed and commercialized with specific solubility, solution rheology, gelation, and absorbency for many applications. Synthetic water-absorptive polymers begin with the choice of monomer(s), molar mass, and chain architecture. Cellulose is separated with exact structure that can be derivatized, grafted, or modified to change its native resistance to super-absorbency, gelation, or dissolving in water. Molecular modeling and simulation are used to evaluate parameters that will describe super-absorbent character. This review explores and evaluates the chemistry and structural symmetry of celluloses and synthetic polymers, leading to solubility, and gelation leading to super-absorbency. Cellulose is emphasized and compared with synthetic polymers where chemistries are designed and created at all levels of structure.

Robert A. Shanks, Isaac R. M. Pardo

5. Review of the Mechanistic Roles of Nanocellulose, Cellulosic Fibers, and Hydrophilic Cellulose Derivatives in Cellulose-Based Absorbents

Cellulose – either in solid form or as a highly hydrophilic chemical derivative of cellulose – can serve multiple and synergistic roles in the preparation of absorbent materials to meet the requirements of diverse absorbent products. Progress in the preparation of nanocellulose products, including nanocrystalline cellulose (CNC), nanofibrillated cellulose (NFC), and bacterial cellulose (BC), is opening up new possibilities for the reinforcement of hydrogels. Conventional cellulosic fibers, including kraft pulp fibers (e.g., fluff pulp), mechanically pulped lignocellulosic fibers, and recycled paper fibers can provide a structure to fine-tune the mechanical and drainage properties of products that can include superabsorbent materials. Carboxymethylcellulose (CMC) is an especially strong candidate for preparation of the swellable phase of a hydrogel. The high content of carboxylic acid groups in CMC gives rise to a strong swelling tendency, especially at neutral to alkaline pH values. The uptake of water can be understood based on concepts of osmotic pressure, in addition to any salinity in the fluid that is being absorbed. The swelling can be adjusted by the choice and amount of a cross-linking agent. Notably, some of the needed cross-linking effect can be optionally provided by nanocellulose or conventional cellulosic fibers. Combinations of solid cellulose entities and water-soluble cellulose-based polyelectrolytes can be used to prepare completely bio-based products that offer an alternative to the presently available disposable absorbents, which are based mainly on petroleum-based superabsorbent hydrogels. Chemical and physical aspects of cellulose and its derivatives also help determine what happens during drying of absorbent products; some swelling ability may be lost irreversibly due to highly organized hydrogen bonding and coalescence of the cellulose-based macromolecular chains. Since cellulose can be involved in both the structural and chemical aspects of highly absorbent products, there will be unique mechanistic roles governing water uptake, water holding, and even the environmental impacts of cellulose-based absorbent products.

Martin A. Hubbe

6. Novel Superabsorbent Cellulose-Based Hydrogels: Present Status, Synthesis, Characterization, and Application Prospects

Over the past century, hydrogels have emerged as an effective material for an immense variety of applications. This contribution provides a brief overview of recent progress in cellulose-based superabsorbent hydrogels, fabrication approaches, materials, and promising applications. Firstly, hydrogels fabricated directly from various polymerization processes are presented. Secondly, we review on the stimuli-responsive hydrogels such as the role of temperature, electric potential, pH, and ionic strength to control the role of hydrogel in different applications. Also, the synthesis route and its formation mechanism for the production of smart superabsorbent, macro- and nano-hydrogels are addressed. In addition, several applications and future research in cellulose-based superabsorbent hydrogels are also discussed in this chapter.

You Wei Chen, Siti Hajjar Binti Hassan, Mazlita Yahya, Hwei Voon Lee

7. Benefits of Renewable Hydrogels over Acrylate- and Acrylamide-Based Hydrogels

In recent years, renewable/biodegradable polymer-based hydrogels have attracted great interest in the field of hydrogel research and development. The reasons of this interest are their applications in versatile fields including personal care products; drug delivery systems; wound healing; tissue engineering; industrial, pharmaceutical, and biomedical, agricultures; water treatments; food packaging; etc. Other important reasons are the problems caused by synthetic sources to the environment. Therefore, it is our demand to develop natural materials that can be biocompatible and biodegradable with the environment, and important efforts are focused on finding alternatives to replace the synthetic one. Furthermore, renewable hydrogels display unique properties such as biodegradability, biocompatibility, stimuli-responsive characteristics and biological functions. Natural hydrogels are often based on polysaccharide or protein chains. Due to the hydrophilic structure of polysaccharides, they have a good property to form hydrogel. There are various polysaccharides like starch, cellulose, sodium alginate, chitosan, guar gum, carrageenan, etc. that have been focused and used for the preparation of environmental friendly hydrogels. Among them, cellulose and its derivatives revealed distinctive benefits because they are the most abundant natural polysaccharide having low cost and better biodegradability and biocompatibility. Protein chains, which form natural hydrogels, are collagen, silk, keratin, elastin, resilin, and gelatin. On the other hand, many synthetic polymers/copolymers also form hydrogel like poly(vinyl alcohol), polyacrylamide, poly(ethylene oxide), poly(ethylene glycol), etc. Synthetic polymer-based hydrogels have one benefit of chemical strength than natural counterpart due to the slower degradation rate of the hydrolyzable moieties. However, biorenewable polymers usually present higher biocompatibility compared to synthetic polymers, as they undergo enzyme-controlled biodegradation by human enzymes (e.g., lysozyme) and produce biocompatible by-products. This chapter focused on the advantages of biorenewable hydrogels over synthetic (acrylate- and acrylamide-based) hydrogels.

Abul K. Mallik, Md. Shahruzzaman, Md. Nurus Sakib, Asaduz Zaman, Md. Shirajur Rahman, Md. Minhajul Islam, Md. Sazedul Islam, Papia Haque, Mohammed Mizanur Rahman

8. Cellulose-Based Superabsorbent Hydrogels

Hydrogels are polymeric three-dimensional networks able to absorb and release water solutions. Sometimes, this behavior is reversed in response to definite environmental stimuli, i.e., temperature, pH, ionic strength, etc. Such stimuli-responsive behavior makes hydrogels attractive candidates for the design of “smart” devices, applicable in a variety of technological fields. In particular, when concerning either ecological or biocompatibility issues, the biodegradability of the hydrogel network, combined with the control of the degradation rate, may add more value to the developed device. Development of new products and materials, particularly those which are based on renewable organic resources using innovative sustainable processes, represents an increasing interest in both academic and industrial research. Cellulose and its derivatives – with numerous hydroxyl groups – have established to be flexible materials with unique chemical structure which provides a good platform for the creation of hydrogel networks with distinctive properties with respect to swelling ability and sensibility to external stimuli. Consequently, cellulose-based hydrogels are attractive materials, biodegradable, biocompatible, and low cost, which exhibit properties that make them promising in many applications, particularly in biomedical and environmental applications. This article reviews the design and the applications of cellulose-based hydrogels, which are extensively investigated due to cellulose availability in nature, the intrinsic degradability of cellulose, and the smart behavior displayed by some cellulose derivatives.

Abdulraheim M. A. Hasan, Manar El-Sayed Abdel-Raouf

9. Stimuli-Responsive Cellulose-Based Hydrogels

Stimuli-responsive hydrogels can spontaneously change their physical and chemical properties in response to changes in the external environment, and they have potential applications in numerous fields as demonstrated in many reports. Cellulose is the most abundant polysaccharide in the natural world, and cellulosic polymers have been considered to be outstanding candidates as building blocks for stimuli-responsive hydrogels with great potential applications for absorption, separation, in the biomedical field, as well as other fields. The main purpose of this chapter is to demonstrate the significance of these materials and provide representative examples regarding the combination of stimuli-responsive hydrogels and cellulosic polymers. Inspired by the merits of both cellulose and stimuli-responsive hydrogels, in this chapter, we will also individually discuss some of the superior properties of stimuli-responsive cellulose-based hydrogels relative to a fossil-based hydrogel, including bulk hydrogels, microgels/nanogels, and injectable hydrogels that respond to stimuli such as heat, pH, ionic strength, light, electric field, magnetic fields, or shear, as well as their major applications. Furthermore, the typical strategies for the preparation of hydrogels (i.e., chemical cross-linking and physical cross-linkingPhysical cross-linking), as well as the mechanisms that drive the ability of these hydrogels to respond to various stimuli (i.e., heat, pH, light, special chemicals, electric fields, magnetic fields, and shear), will also be briefly presented in this chapter. This chapter might be useful for the development of novel stimuli-responsive cellulose-based hydrogels with high performance.

Lei Miao, Min Zhang, Yuanyuan Tu, Shudong Lin, Jiwen Hu

10. Enzyme-Responsive Hydrogels

In an enzymatically responsive system, a suitable enzyme is used as a stimulus for a control release or delivery at a specifically targeted site where that enzyme is designed in such a way that can work at certain controlled conditions (such as temperature, pH). Enzyme-responsive hydrogels prepared from cellulose along with other materials have suitable macromolecular networks and can work in controlled environment. Specifically designed enzymatic stimuli-responsive system, one of the highly explored techniques, popularly explored to add a triggerable agent (such as a polymer or a lipid) that can encapsulate the active component in a protective manner. Usually, this active agent is responsive to degradation or swelling when it reaches at the target site. An enzymatic stimulus-responsive system is highly attractive field of research due to its many potential applications (e.g., in controlled release, drug delivery, and other areas of life and material sciences). This chapter gives a brief overview on the design and uses of enzyme-responsive hydrogels based on cellulose and other polymers for their various applications in different fields including in controlled drug delivery and other areas of biomedical and material sciences.

Shah M. Reduwan Billah, Md. Ibrahim H. Mondal, Sazzad H. Somoal, M. Nahid Pervez, Md. Obaidul Haque

11. Cotton Cellulose-Derived Hydrogels with Tunable Absorbability: Research Advances and Prospects

Cotton is an important, worldwide cash crop and is considered as a ubiquitous resource offering the purest form of cellulose in nature. By far, the most industrially exploited natural resources containing cellulose are wood and cotton. Cellulose derived from either wood or cotton has the same chemical structure. Hydrogels are jellylike materials consisting of substantially hydrophilic cross-linked network filled with water. Upon replacing water with air, hydrogels are able to form aerogels. Cellulose and its derivatives can be used to prepare hydrogels with tailored absorbability and adsorbability. In the first section of this review, we discuss recent progress in the dissolution of high molecular weight cotton-derived cellulose as the dissolution of cellulose is an important step in preparing cellulose-based hydrogels. In the second section, we focus on the preparation of various cotton cellulose-based hydrogels and their derivatives by physical, chemical, and photocatalytic processes and their current applications. The third section includes the preparation and application of cellulose-based aerogels, which are a specific dry form of hydrogels. Overall, this review covers recent research developments in cotton cellulose-based hydrogels and their broad spectrum of applications in agriculture, environment, energy, health, and medicine.

Yang Hu, Rohan S. Dassanayake, Sanjit Acharya, Noureddine Abidi

12. Adsorption Mechanism of Cellulose Hydrogel by Computational Simulation

In this chapter, different adsorption mechanisms of cellulose hydrogel will be investigated. For this aim, computational simulation will be used. On an atomistic scale, cellulose hydrogel has different hydrogen bond properties. The OH groups can only act as hydrogen bond acceptors, but due to the negative charge density, there are still more water molecules assembled around adsorbents. Besides intermolecular hydrogen bonding, it has some hydrophobic properties. It means that some hydrophobic materials can be adsorbed on the surface of cellulose hydrogel at specific conditions. Most force fields for this simulation are empirical and consist of a summation of bonded forces associated with chemical bonds, bond angles, and bond dihedrals and nonbonded forces associated with van der Waals forces and electrostatic charge. Empirical potentials represent quantum mechanical effects in a limited way through ad hoc functional approximations.

Ali Jebali

13. Multifunctional Hydrogels

Hydrogels are cross-linked three-dimensional polymeric networks which can absorb a great quantity of water and keep mechanically stable without dissolution. Due to the biocompatibility and biodegradability, biological hydrogels have been wildly investigated and used in various fields, such as adsorption materials, shape memory materials, self-healing materials, sensor units, super capacitor, drug carriers, and so on. In this chapter, we would focus on some of the upper aspects and give a brief introduction.

Min Xu, Hailong Huang

Synthesis of Cellulose-Based Hydrogels

Frontmatter

14. Synthesis of Cellulose-Based Hydrogels: Preparation, Formation, Mixture, and Modification

Cellulose is the most abundant biopolymer, and it has been used in different areas because of its unique properties as various fibril structures and sizes that affect tensile characteristic of the polymer. To increase its features and/or add a new property to cellulose, preparation and modification methods have been deeply investigated and reported. This chapter is classified into four different sections: preparation, formation, mixture, and modifications of cellulose. The preparation method of cellulose (including bacterial cellulose) is important, because it directly effects to fibril formation and structure. In addition to this, depending on usage area, cellulose is necessary to prepare as whisker, fibril, and nano-formations to sustain desired polymer structure. To increase the targeted property of cellulose hydrogel, different kinds of polymers such as polyvinyl alcohol and polyethylene glycol are mixed with cellulose during the preparation of hydrogel. However, cellulose hydrogels still need to improve its physical abilities. Therefore, various modifications have been developed for cellulose and its hydrogel. The most fundamental derivatives are methyl cellulose, hydroxypropyl cellulose, and carboxymethyl cellulose. In addition to this, in recent years, stimuli-responsive and superabsorbent polymers have become more popular. Swelling behavior of hydrogels can be changed by pH, temperature, composition of solvent, and electric field in stimuli-responsive polymers that are available to use in pharmaceutical, bioengineering, and tissue engineering areas. Superabsorbent hydrogels have the ability to absorb water up to several hundred times of their dried weight that can be used in bioengineering, agricultural, tissue engineering areas, and sanitary products. The reaction mechanisms and configurations of mixtures were clearly illustrated in this chapter. Groundbreaking and latest studies were discussed via the hydrogel properties based on analysis of X-ray diffraction (XRD), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transformation infrared spectroscopy (FTIR), tensile at break, tensile stress, and Young’s modulus.

Neslihan Kayra, Ali Özhan Aytekin

15. Modification of Cellulose

With increasing concerns about synthetic polymers for the environment, the application of natural polymers, especially cellulose due to abundance, biodegradability, nontoxicity, and high functionality, is increasing. For inducing the desired properties of cellulose, it’s necessary to manipulate the cellulose structure. Therefore, the modification of cellulose becomes important. The modification of cellulose is introducing organic and inorganic compounds on the polymer. A significant variation in the cellulose properties can be observed with the binding of polymers. Also, mineralization of cellulose has attracted a great deal of attention in recent years. This chapter investigated all of these modifications on cellulose.

Sajjad Keshipour, Ali Maleki

16. Synthesis and Properties of Hydrogels Prepared by Various Polymerization Reaction Systems

Among all biomass, cellulose is the most abundant renewable polysaccharide in nature, accounting for approximately 40% of the lignocellulosic biomass. The ability of cellulose to absorb enormous amounts of water has prompted the large use of cellulose in preparation of various hydrogels. Cellulose-based hydrogels are generally synthesized by two steps, (i) solubilization of cellulose fibers or powder and (ii) physical and/or chemical cross-linking, in order to obtain a three-dimensional network of hydrophilic polymer chains. The physical synthesizing method includes ionic interaction, hydrophobic interaction, and hydrogen bond formation, whereas the chemically cross-linked hydrogel preparation involves different polymerization techniques such as chain-growth polymerization, irradiation polymerization, and step-growth polymerization. Further, another technique such as bulk polymerization is also used to form gels mainly using lactic acid as monomer. Indeed, the high density of free hydroxyl groups present in the cellulose structure permits them to undergo functionalization/chemical modification, which allows producing cellulose derivatives. The properties of cellulosic hydrogels change based on the different environmental stimuli. The external stimulus includes pH, temperature, light, electric or magnetic field, mechanical stress, etc. The responses of the hydrogel based on the exposure to different stimuli are discussed in this chapter. However, the cellulose hydrogels basically have good biocompatibility and non-toxicity combined with relevant mechanical properties. They showed highest absorption capacity, the swelling/deswelling behavior, and its rate depends on various factors such as particle size, porosity, solvent concentration, cross-linking density, etc. The swell behavior is addressed using various kinetic models such as Fickian, non-Fickian, and Flory. Further, biodegradation, mechanical, and rheological properties variation with respect to cross-linking density and other parameters (shape, pore size, reinforcement, etc.) and stimuli are considered and discussed.

Nalini Ranganathan, R. Joseph Bensingh, M. Abdul Kader, Sanjay K. Nayak

17. Polymer Reaction Engineering Tools to Tailor Smart and Superabsorbent Hydrogels

Experimental and theoretical tools to describe and tailor polymer network formation processes are here addressed. Although a special emphasis is given to the synthesis, characterization, and applications of smart and superabsorbent polymers, other networks with higher cross-linker contents are also prospected. Purely synthetic and cellulose-based hydrogels are both considered in this research. The reactor type (e.g., batch or continuous flow micro-reactor), polymerization process (e.g., bulk, inverse suspension, or precipitation polymerization), and polymerization mechanism (e.g., classic free radical polymerization or reversible deactivation radical polymerization RDRP) are highlighted as possible tools to change the morphology and the molecular architecture of polymer networks and hydrogels. The tailoring of cellulose-synthetic hybrid materials is also addressed through the use of RAFT-mediated polymer grafting. Case studies showing the applications of the synthesized materials are presented, namely, molecularly imprinted hydrogel particles for retention of aminopyridines, molecularly imprinted polymers for polyphenols, caffeine or 5-fluorouracil selective uptake/release, as well as modified cellulose adsorbents for polyphenol retention. Cellulose-based hydrogels are also considered as possible vehicles for polyphenol-controlled release. The mechanisms of liberation of polyphenols from these materials are analyzed, namely, when supercritical CO2 is used in the hydrogel impregnation process.

Catarina P. Gomes, Rolando C. S. Dias, Mário Rui P. F. N. Costa

18. Superabsorbent Aerogels from Cellulose Nanofibril Hydrogels

Deep eutectic solvents (DESs) are promising green chemicals that can function as solvents, reagents, and catalysts in many applications because of their biodegradability, ready availability, and low toxicity. Here, a DES of choline chloride–urea was used as a non-hydrolytic pretreatment medium to obtain cellulose nanofibril (CNF) hydrogels from recycled cellulose pulps (boxboard, milk containerboard, and fluting) and virgin birch cellulose pulp using a mechanical Masuko grinder. The mechanical disintegration of DES-pretreated cellulose fibers resulted in highly viscous, gel-like cellulose nanofibril hydrogels with shear thinning behavior. According to transmission electron microscope (TEM) imaging, the nanofibrils had widths from 2 to 80 nm, possessed the initial cellulose I crystalline structure, and had a crystallinity index of 53–56%. The nanofibril hydrogels obtained were further used to produce low-cost, ultralight, highly porous, hydrophobic, and reusable superabsorbing aerogels that were used as efficient sponges to absorb oil and chemicals. The nanofibril sponges prepared by the consequent hydrophobic modification (silylation) of CNF hydrogels and freeze-drying had ultralow density (0.003 g/cm3) and high porosity (up to 99.8%). The sponges exhibited excellent oil/water absorption selectivity and ultrahigh oil (marine diesel oil, kerosene, gasoline, motor oil, castor oil, or linseed oil) and organic solvent (dimethyl sulfoxide, chloroform, n-hexane, toluene, acetone, or ethanol) absorption capacity. The nanofibril aerogels showed particular selectivity for marine diesel oil absorption from an oil–water mixture and possessed ultrahigh absorption capacities of up to 143 g/g, which were much higher than the commercial absorbent materials (i.e., polypropylenes) (9–27 g/g) used as references. Additionally, the absorbed oil could be recovered by means of simple mechanical squeezing, and the superabsorbent could be reused for at least 30 cycles.

Ossi Laitinen, Terhi Suopajärvi, Juho Antti Sirviö, Henrikki Liimatainen

19. Nanocomposite Hydrogels Obtained by Gamma Irradiation

During the past decades hydrogels have gained considerable interest and reviewed from different points of view, because of their unique properties. The hydrogel 3D structure, porosity, swelling behavior, stability, gel strength, as well as biodegradability, nontoxicity, and biocompatibility are properties which are widely variable and easily adjusted, making them suitable for many versatile applications, especially in the field of medicine and biotechnology. Generally, hydrogels possess the huge potential to be used as a matrix for incorporation of different types of nanoparticles. Namely, hydrogels in the swollen state provide free space between cross-linked polymer chains, in which the nucleation and growth of nanoparticles occurs. In this way, the carrier-hydrogel system acts as a nanoreactor that also immobilizes nanoparticles and provides easy handling with obtained hydrogel nanocomposites. It is well known that the properties of nanocomposite materials are dependent on the method of synthesis. Among various techniques, the radiation-induced synthesis offers a number of advantages over the conventional physical and chemical methods. Radiolytic method is a highly suitable way for formation of three-dimensional polymer network, i.e., hydrogels, as well as for generation of nanoparticles in a solution (especially metal nanoparticles). This method provides fast, easy, and clean synthesis of hydrogel nanocomposites. Moreover, and probably the most important from the biomedical point of view, is the possibility of simultaneous formation of nanocomposite hydrogel and its sterilization in one technological step. Despite all the mentioned advantages of radiolytic method, there are not so many investigations related to nanocomposite materials based on nanoparticles incorporated in a hydrogel matrix.

Aleksandra Radosavljević, Jelena Spasojević, Jelena Krstić, Zorica Kačarević-Popović

20. Effect of Irradiation for Producing the Conductive and Smart Hydrogels

This review presents the past and current efforts with a brief description on the featured properties of conductive and smart hydrogel fabricated from biopolymers and natural ones for different applications. Many endeavors have been exerted during the past 10 years for developing new smart hydrogels. This review mainly focuses on the effect of different irradiation methods for improving the properties of smart hydrogels. As the hydrogels with single component have low mechanical strength, recent trends have offered composite or hybrid hydrogel membranes to achieve the best properties. So this chapter provides the reader good information about the irradiation effects on producing the smart conductive hydrogels and perspective on further potential developments.

Sheila Shahidi

21. Cellulose-Based Composite Hydrogels: Preparation, Structures, and Applications

In this chapter, cellulose-based composite hydrogels were summarized in three categories according to the components. S Epichlorohydrin (ECH) ynthetic polymer/cellulose composite hydrogels combine the advantages of synthetic polymers and cellulose. Soluble cellulose derivatives are feasible to construct the composite hydrogels with polyacrylamide, polyvinyl alcohol, polyacrylic acid, and so on. The composite hydrogels are normally applied as superabsorbents for heavy metal ions and dyes because the abundant functional groups in the hydrogels can act as binding sites. Due to most of the crosslinked polymeric hydrogels suffering from poor mechanical performance, low breaking strain, and sensitivity to fracture, cellulose nanocrystal can be combined into the hydrogels to enhance the mechanical properties significantly in order to obtain the mechanically strong, tough, or highly stretchable nanocomposite hydrogels. Natural macromolecules/cellulose composite hydrogels have a great potential for applications in tissue engineering, drug delivery, sensors, and purification for their excellent biocompatible, biodegradable, and nontoxic properties. Cellulose hydrogels have high mechanical strength and good permeability for liquids, gases, and electrolytes, the composite hydrogels which combine cellulose and extracellular matrixes are very promising scaf folds for the tissue repair and regeneration. Chitosan, alginate, and other polysaccharides are popular natural macromolecules for the composite hydrogels. Inorganics/cellulose composite hydrogels have recently received considerable attentions in both academic research and industrial application due to their excellent hybrid properties. Montmorillonite, clay, and bentonite are traditional inorganic minerals to fabricate the composite hydrogels as superabsorbents for water treatment, personal care, and agriculture. Nanoparticles of ZnO and Ag are also incorporated into the cellulose hydrogels to render the antimicrobial activity to biomedical materials. Recently, the novel cellulose-based composite hydrogels with graphene oxide, carbon nanotube, and carbon dots show potential applications in supercapacitors and biosensors.

Liying Qian

22. Surface Functionalization of Nanocellulose-Based Hydrogels

Nanocellulose is the nanostructured product or extract from the native cellulose found in plants, animals, and bacteria. Three main types of nanocellulose may be identified as cellulose nanocrystals (CNCs), nanofibrillated cellulose (NFC), and bacterial nanocellulose (BNC). Due to the very high surface-to-volume ratio, nanocellulose tends to form hydrogels with exceptionally high water content (>90 wt%). Surface modifications of those nanostructured materials can, e.g., improve their compatibility with different matrices, enable control of water absorption, and release and bring desired chemical functionality expanding utilization of such hydrogel in (bio)nanotechnology-related applications. Various objects including small molecules of biomedical relevance, nano- or microparticles serving as drug carriers, protective/semipermeable coatings, or polymer brushes can be attached onto the surfaces of nanocellulose-based materials in order to prepare various functional nanocomposites. Such composite materials have been successfully applied in, e.g., wound healing and regenerative medicine. Chemical approaches for surface functionalization of nanocellulose-based hydrogels are systematically described in this chapter, together with properties of such formed hydrogel materials and examples of their applications.

Joanna Lewandowska-Łańcucka, Anna Karewicz, Karol Wolski, Szczepan Zapotoczny

Characterization Tools and Techniques of Hydrogels

Frontmatter

23. Characterization Techniques of Hydrogel and Its Applications

Over the past few decades, advances in hydrogel technologies have spurred development in the personal care products and medical, pharmaceutical, and agricultural field aspects due to their unique biocompatibility, flexible methods of synthesis, range of constituents, and desirable physical characteristics. Hydrogels are hydrophilic, three-dimensional hydrophilic polymeric networks, capable of absorbing large quantities of water, biological fluids and simulating biological tissue when they get swollen due to chemical or physical cross-linking of individual polymer chains. Hydrogels are characterized by the nature of their constituent polymers, making them synthetic, natural, or hybrid. The use of natural polymers in hydrogel synthesis is advantageous in biomedical applications due to their biodegradability and nontoxicity, whereas synthetic polymers are hydrophobic, possessing strong covalent bonds within their matrix, which allow for more durability and mechanical strength. In order to design hydrogels with the desired performance and structure, characterization of hydrogel requires different tools and techniques that includes swelling, sol-gel analysis, differential scanning calorimetry, thermal gravimetric analysis, X-ray diffraction analysis, gel permeation chromatography, atomic force microscopy, and scanning electron microscopy. In this chapter, we focused and discussed about the properties, preparation methods, characterization techniques, and their most significant and current biomedical applications of hydrogels with the patents.

M. Azeera, S. Vaidevi, K. Ruckmani

24. Thermal Behavior of Bacterial Cellulose-Based Hydrogels with Other Composites and Related Instrumental Analysis

Hydrogel is a network of polymer chains that are hydrophilic and able to absorb and release large amount of water in a reversible manner. At present, synthetic and natural hydrogels have been extensively studied due to their responsive properties toward specific environmental stimuli such as pH, temperature, and ionic strength. This includes hydrogel from natural cellulose obtained by bacterial fermentation. The capability of hydrogel for transmitting and resulting in a useful response is termed as the smartness ability of the material. Studies on thermal behavior and performance allow fabrication of hydrogels that exhibit smart properties such as with temperature sensitivity or ideally dual (pH/temperature) sensitivity. The designed hydrogel can be characterized thermally using instrumental analyses, for example, the Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), Thermomechanical Analysis (TMA), and Thermogravimetric Analysis (TGA). These allow evaluation on the glass transition temperature, melting temperature, degree of crystallinity, and mechanical properties of the fabricated hydrogels. Furthermore, understanding thermal behavior of the hydrogels can help to elucidate the effect of the preparation technique and treatment on properties of the hydrogels. This gives advantages on producing hydrogel with required properties for defined application. In this work, thermal characterization of bacterial cellulose-based hydrogels and its composites using related instrumental analyses were discussed.

Norhayati Pa’e, Mohd Harfiz Salehudin, Nor Diana Hassan, Aishah Mohd Marsin, Ida Idayu Muhamad

25. Structure Response for Cellulose-Based Hydrogels via Characterization Techniques

Hydrogels are three-dimensional cross-linked polymeric networks capable of imbibing substantial amounts of water or biological fluids and are widely used in biomedical applications, especially in pharmaceutical industry as drug delivery systems. Although their solvent content can be over 99%, hydrogels still retain the appearance and properties of solid materials, and the structural response can include a smart response to environmental stimuli (pH, temp, ionic strength, electric field, presence of enzyme, etc.) These responses can include shrinkage or swelling. Cellulose-based hydrogels are one of the most commonly used materials and extensively investigated due to the widespread availability of cellulose in nature. Cellulose is the most abundant renewable resource on earth that is intrinsically degradable. Additionally, the presence of hydroxyl groups results in fascinating structures and properties. Also, cellulose-based hydrogels with specific properties can be obtained by combining it with synthetic or natural polymers. This chapter surveys different characterization for cellulose hydrogels and the structure-response relationship. As such we would describe the techniques involved for characterizing cellulose-based hydrogels and their response in terms of their morphology such as polarized optical microscopy (POM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), their stability by thermal properties (often with differential scanning calorimetry, DSC), and structure response such as Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). In addition, we give a focus on measuring the mechanical properties of superabsorbent hydrogels giving examples with cellulose where applicable. Finally, we describe the techniques for analyzing biological techniques and the applications with cellulose.

Marcelo Jorge Cavalcanti de Sá, Gabriel Goetten de Lima, Francisco Alipio de Sousa Segundo, Michael J. D. Nugent

26. Morphological Characterization of Hydrogels

Hydrogels are physically or chemically cross-linked polymer networks that are able to absorb large amounts of water. They can be classified into different categories depending on various parameters including the preparation method, the charge, and the mechanical and structural characteristics. The morphological structures are differed from hydrogel compositions to preparation method, fabrication techniques, type of hydrophobic substitutes, etc. This chapter addresses an overview of the morphological characterization of hydrogels and impact of these properties in various potential applications of hydrogels. In a first part, morphological characterizations of hydrogels directly prepared from native materials are described. In a second part, morphological characterizations of hydrogels prepared from different derivatives of native materials by physical as well as chemical cross-linking strategies are introduced. In a third part, morphological characterizations of composite type hydrogels including blending composites, polyelectrolyte complexes, and interpenetrating polymer networks (IPNs) are discussed. In a final part, morphological characterizations of inorganic nanoparticles incorporated hybrid hydrogels are described.

Md. Shirajur Rahman, Md. Minhajul Islam, Md. Sazedul Islam, Asaduz Zaman, Tanvir Ahmed, Shanta Biswas, Sadia Sharmeen, Taslim Ur Rashid, Mohammed Mizanur Rahman

27. Elastic Modulus Measurement of Hydrogels

Hydrogels have been employed for a wide variety of applications, and their mechanical properties need to be modulated based on the applications. In particular, the Young’s modulus, or elastic modulus, of hydrogels is a critical property for understanding their mechanical behaviors. In principle, the Young’s modulus of a hydrogel can be measured by finding a relationship between a force applied to the hydrogel and the resultant deformation of the hydrogel. On a macroscale, Young’s modulus is usually obtained by measuring the stress-strain curves of a hydrogel specimen through the compression method or the tensile method and then finding the slope of the curve. Also, the shear modulus of a hydrogel is measured using a rheometer with parallel plates and then converted into Young’s modulus considering Poisson’s ratio. On a mesoscale, the elastic modulus can be measured by the imaging-based indentation methods which measure the indentation depth of a hydrogel sample deformed by a static ball indenter on the gel. The measured indentation depth is converted to the Young’s modulus of the hydrogel via a contact mechanics model. The mesoscale indentation method and pipette aspiration method are also available. On a microscale, the elastic modulus is usually measured using the atomic force microscopy (AFM)-based indentation method. A hydrogel specimen is locally indented by a sharp or colloidal tip of an AFM probe, and the Young’s modulus of the hydrogel is obtained by fitting an appropriate indentation model against the recorded force-distance curves. An appropriate elastic modulus measurement method needs to be chosen depending on the application, length scale and expected elastic property of the hydrogels.

Donghee Lee, Haipeng Zhang, Sangjin Ryu

Applications of Biocompatible Hydrogels

Frontmatter

28. Strategies in Improving Properties of Cellulose-Based Hydrogels for Smart Applications

Hydrogels are three-dimensional polymeric networks that are able to absorb and retain large volumes of water. Chemical or physical crosslinks are required to avoid dissolution of the hydrophilic polymer chains into the aqueous phase. Because of their sorption capacity, super absorbing hydrogels have been extensively used as water-retaining devices, mainly in the field of personal hygiene products and in agriculture. Moreover, in recent years, the possibility to modulate their sorption capabilities by changing the external conditions (e.g., pH, ionic strength, temperature) has suggested their innovative application as smart materials, drug delivery devices, actuators, and sensors. The presence of the polyelectrolyte NaCMC in the hydrogel network provides a Donnan equilibrium with the external solution, thus modulating material’s sorption capacity in relation to the external solution ionic strength and pH. An important focus of the research in this field is the material’s biodegradability. This material was obtained by chemical crosslinking of cellulose polyelectrolyte derivatives, carboxymethylcellulose (CMC) and hydroxyethylcellulose (HEC), using small difunctional molecules as crosslinkers (divinyl sulfone, DVS) which covalently bound different polymer molecules in a 3D hydrophilic network. Among the biopolymers, cellulose is of special interest due to its abundance and, hence, easy availability. It is easily derivatized to different cellulosics which can be used to obtain functionalized hydrogel beads for ion exchange and affinity chromatography. Various cellulose derivatives having nitrogen or sulfur-containing groups have been prepared, and their metal ion absorption behavior has been examined. Metal ions are reported to partition between cellulosics and liquid phase. However, the use of cellulose as membrane material is not fully realized due to low stability and poor interactions in water. These drawbacks can be improved by crosslinking, radiation grafting, and surfactant adsorption. In the current chapter, we have focused on the smart applications of cellulose-based hydrogels including drug delivery systems, absorption behavior, and swelling mechanism and their prospects.

Farzaneh Sabbagh, Ida Idayu Muhamad, Norhayati Pa’e, Zanariah Hashim

29. Cellulose-Based Hydrogel for Industrial Applications

Cellulose-based superabsorbent hydrogels can absorb and retain huge amounts of water or aqueous solutions. They have a wide range of industrial applications including (a) hygienic and bio-related uses (more specifically in disposable diapers); (b) agricultural uses (such as water reserving in soil, soil conditioning, and controlled release of agrochemicals); (c) pharmaceutical dosage forms; (d) separation technology; (e) textile, leather, and paper industries (such as in wastewater treatment); (f) water-swelling rubbers; (g) soft actuators/valves; (h) electrical applications; (i) construction, packaging, and artificial snow; (j) sludge/coal dewatering; and (k) fire extinguishing gels. Many new advanced technologies are evolving by the day to cope with rigorous industrial-scale applications to ensure improved technical feasibilities. This chapter will briefly cover some of the selected aspects of cellulose-based hydrogels and their industrial applications.

Shah M. Reduwan Billah, Md. Ibrahim H. Mondal, Sazzad H. Somoal, M. Nahid Pervez

30. Cellulose-Based Absorbents for Oil Contaminant Removal

With the rapidly increasing exploitation, transportation, and utilization of fossil oils, oil spillage accidents occur frequently worldwide. Oil pollution can lead to a serious loss of valuable resources on coastal and marine ecosystems during a long period. Besides, industrial waste oil may have a broad impact on city ecological environments and human health. It is thus urgently required to solve oil pollution efficiently. Generally, current strategies are classified into three groups: (1) burning the oil spill in situ, (2) dispersing the oil in water by adding dispersants to facilitate nature degradation, and (3) extracting the oil from the water. The last method seems the “greenest” because both the absorbent and the oil can be recycled. Among the absorbents, cellulose-based absorbents are the first choices due to their environmental friendliness of renewability and biodegradability, good mechanical properties, low density, high porosity, high absorption capacity, and cost-effectiveness. In this chapter, we intend to demonstrate the following aspects of cellulose-based absorbents, including (1) raw materials: properties and pretreatments, (2) fabrication of the various absorbents, (3) characterization of the structure and properties, (4) cellulose-related absorbents and other applications, and (5) discussions and future scope. This work aims to draw a full outline of the cellulose absorbents to date and to promote the understanding and developing of these materials in the future.

Wang Liao, Yu-Zhong Wang

31. Cellulose-Based Hydrogels as Smart Corrosion Inhibitors

This chapter describes briefly the cellulose-based hydrogel definition, classifications, cross-linked structure of hydrogels and types of polymers used in tailor-made hydrogel. In addition, it describes a brief overview of hydrogel-based on cellulose, definitions, methods of preparation, and applications as smart corrosion inhibitors as discussed in some detailed in the text. Finally, this study provides us the use of polymeric hydrogels as corrosion inhibitors. Corrosion problems have driven out to be progressively serious and reached out to different fields. However, corrosion inhibitors are usually not satisfactory due to bad performance during the mixing process, hydrolyze weather, and decompose during working process. These problems settled by solid corrosion inhibitor, which will release under control. Hydrogel can have the capacity to hold many liquids and characterized by a soft rubbery consistency like living tissues, making them a perfect substance for a variety of applications. In this manner, hydrogels utilized as smart carriers for controlled release of corrosion inhibitors.

Reem K. Farag, Ahmed A. Farag

32. Cellulose-Based Hydrogels for Water Treatment

Lakes, rivers, sea, groundwater, drinking water basins, etc. are the main water sources which can increasingly be polluted by commercial and industrial establishments or human activities. The most existing types of contaminants that pollute these water sources are dye-containing effluents and toxic heavy metals which they affect living being’s life catastrophically. Various methods have been applied to get rid of these kinds of toxic pollutants from water sources such as reverse osmosis, chemical precipitation, membrane filtration, coagulation, ion exchange, electrochemical treatment, and adsorption. Among these methods, adsorption is quite effective and economic method for the removal of toxic pollutants. Hydrogels that can be described as 3D network of hydrophilic polymer chains cross-linked chemically or physically which are able to soak and release a significant amount of water while preserving their network structure from dissolution in aqueous media, and they can be applied in many fields including tissue engineering, drug delivery, wound dressing, food, cosmetics, contact lenses, sensors, and water treatment. Hydrogels are excellent candidate to remove toxic pollutants by adsorption due to their high absorption capacity, porous structure, rich functional groups, and relatively low crystallinity. These hydrogels can be composed of petroleum-derived synthetic polymers, natural occurring materials, or composition of both synthetic and natural materials. Hydrogels that prepared from natural materials are preferred by their low cost and biodegradability and easily available from plenty of resources. To prepare hydrogels, a wide range of synthetic and natural materials have been used, such as cellulose, chitin, and chitosan for natural materials; polyethylene glycol and poly(sodium acrylate) for synthetic materials can be given as an example. Among them, cellulose is a well-known naturally found linear homopolymer having consecutive glucose units connected by glucosidic bond. The use of cellulose-based hydrogels is gaining popularity because of their several advantages such as environmental friendliness, biodegradability, biocompatibility, nontoxicity, easy availability, high abundance, low cost, and thermal and chemical stability for water treatment applications. Therefore, cellulose-based hydrogels have been attracted much attention in both academic and industrial applications including drug delivery, hygiene products, medicine, and water purification technologies. Among these applications, the use of cellulose-based hydrogels for water treatments has been discussed in this chapter.

Ilker Yati, Soner Kizil, Hayal Bulbul Sonmez

33. Cellulose-Based Hydrogels for Agricultures

The cellulose-based hydrogel characteristics such as biodegradability and biocompatibility mark its suitability toward agriculture application. In agriculture, the hydrogels are specifically used as water reservoirs, phyto-pharmaceuticals (protected cultivations, soilless cultivations, and open-field cultivations), pesticide release, and nutrient release to the soil. The hydrogels are impregnated by fertilizer components (e.g., soluble phosphate, potassium ions, nitrogen compounds), and those chemicals which are trapped in a polymer network cannot be immediately washed out by water but gradually released into the soil and then absorbed by plants. The hydrogels are classified as two classes, i.e., soluble and insoluble hydrogels. The soluble variety is used to reduce irrigation erosion in fields. The insoluble variety is used in gardens, nurseries, and landscapes to reduce frequency of watering. They are produced either in the form of powder or of a bulky material with a well-defined shape and a strong memory of its shape after swelling. The material can be charged with small molecules, such as nutrients, to be released under a controlled kinetic. The main advantage is controlled release of water, longtime maintaining soil humidity, increase of soil porosity, and therefore better oxygenation of plant roots. The agricultural hydrogel behavior depends on various factors such as temperature, relative humidity, soil type, stress, etc. The performance of the gels is evaluated through different techniques like moisture retention, nutrition release rate, biodegradation rate, relative humidity, and temperature maintained in the soil. Several studies reveal that the amount of moisture retained in the soil is dependent on the concentration of the cellulose-based superabsorbent matrices. Those SAPs/hydrogels were used in specific agriculture application such as nutrient release, conservation of land, and drought stress reduction due to several advantages. The advantage of cellulose-based hydrogels include eco-friendliness, high water holding capacity, low cost, and biodegradability. Moreover, their application helps reduce irrigation water consumption, causes lower death rate of plants, improves fertilizer retention in soil, and increases plant growth rate.

Nalini Ranganathan, R. Joseph Bensingh, M. Abdul Kader, Sanjay K. Nayak

34. Cellulose-Based Hydrogel Films for Food Packaging

The use of fossil-based plastic in food packaging has increased the plastic-based waste, carbon footprint, and global warming, which has led to the development of alternatives such as hydrogels for biodegradable stringent food packaging industries. Hydrogels consist of biopolymers having three dimensional networks can trap a large quantity of water and formulation of cellulose-based hydrogels have laid high impact for food packaging application with improved biodegradability, biocompatibility, mechanical properties, plasticizing effect, etc. Cellulose hydrogels can be imparted as thin layers onto the polymers to improve its wettability, appearance, degradability, and resistance towards environmental agents. Cellulose-based hydrogels are mainly formulated from cellulose, bacterial cellulose, and its derivatives. Further, use of cellulose and its derivatives with gelatin, low-methoxyl pectin, polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG), protein, etc., provide a better property for packaging food products. Various bioactive compounds such as silver nanoparticles and other antioxidants, antifungal agents can be embedded onto hydrogel films to improve its properties. Use of cellulose hydrogel as packaging material mainly depends on its hydrophilicity, swelling property, molecular weight, stability, physical, mechanical and chemical properties. Cellulose hydrogels generally consist of various chemistry of hydrogels such as physical cross-linking, chemical cross-linking, interpenetrating hydrogels, which find significant importance in biodegradable food packaging. Dry hydrogels from biopolymers can be used individually or in conjugate with others. However, use of individual polymers for making hydrogel creates problems in hydration which enhance water-polymer interactions than polymer-polymer interactions. In contrast, blending and composites of polymers help in enhancing interactions between polymer-polymer matrices than water-polymer matrices. The tailored properties of blends or composites of hydrogel can be formed through electrostatic interactions between opposite charges, formation of cross-links through covalent bond, formation of physical networks, and interpenetrating polymer networks.

Tabli Ghosh, Vimal Katiyar

35. Moisture Sorption Isotherm and Isosteric Heat of Sorption Characteristics of PVP-CMC Hydrogel Film: A Useful Food Packaging Material

Hydrogels are polymeric materials possessing a three-dimensional network structure and can absorb a large quantity of liquid water. Recently, hydrogel-based polymeric materials are being focused and encouraged as they are breathable and maintain the shelf life of fresh fruit and vegetables. A hydrogel film was prepared using synthetic polymer, polyvinylpyrrolidone (PVP), and biopolymer, carboxymethyl cellulose (CMC) and agar, along with polyethylene glycol and glycerol as plasticizer to create a breathable and biodegradable film termed as “PVP-CMC” hydrogel film. In general, hydrogel film provides poor but composition- and structure-dependent moisture resistance in normal atmosphere. Further, interaction among the plasticized ingredients, which are dependent on its ultimate moisture content, controls the physical and mechanical properties of the film. Therefore, it is important to know moisture sorption characteristics of each hydrogel film. The “PVP-CMC” hydrogel film exhibited a tendency to adsorb/desorb moisture depending on environmental relative humidity and temperature during storage. Hence, the general features and the equilibrium relationship between moisture contents of “PVP-CMC” hydrogel film at different temperatures (25, 35, 45 and 55 °C) and relative humidities (≈ 10–90%) of the environment in which the film generally resides, i.e., moisture sorption isotherm (MSI), will be discussed in this chapter. The isosteric heat of sorption at different moisture contents of “PVP-CMC” hydrogel film will also be discussed.

Nabanita Saha, Madhusweta Das, Dipali S. Shinde, Antonin Minařík, Petr Saha

36. Cellulose-Based Hydrogels for Pharmaceutical and Biomedical Applications

Hydrogels, the hydrophilic polymers, exhibit a three-dimensional network that can swell and retain the water molecules or any liquid in its structure, ten to 1000 times higher than its normal weight. The chemical cross-linking, physical entanglement, hydrogen bonds, and the ionic bonds are responsible to achieve the network of hydrogels. Hydrogels based on natural polymers like chitosan and cellulose are of great interest because of their abundant availability and biocompatibility and biodegradability. Natural polymer-based hydrogels have been used extensively in biomedicine, bioengineering, agriculture, and horticulture such as drug delivery, food, cosmetics, high water-absorbing resin, contact lenses, corneal implant, and substitutes for the skin, tendons, ligaments, cartilage, and bone due to their excellent hydrophilicity, permeability, compatibility, and low friction coefficient. Hydrogels specially cellulose ethers possess a remarkable combination of important properties for pharmaceutical and biomedical applications, e.g., as carriers for drug targeting, sustained release of drugs, vaccine bullets, and materials for the disintegration of matrix tablets. For the treatment of severe skin burns and in the regeneration of cardiac, vascular, neural, and cartilage bone tissues, these cellulose derivatives are very useful. In this regard bioactive hydrogels can be properly designed to induce at least partial skin regeneration. Cellulose-based hydrogels cross-linked with hyaluronic acid induce a good proliferation of keratinocytes, as a result of a scratch wound model in in vitro culture. Literature data have proposed the use of CMC- and HEC-based hydrogels as water absorbents in treating edemas. Hydrogels are also used as water absorbents for various applications in personal hygiene products or as biomedical devices, like soft contact lenses, lubricating surface coatings, phantoms for ultrasound-based imaging, etc.

Ananya Barman, Mahuya Das

37. Cellulose-Based Hydrogels for Wound Healing

Wound healing is a dynamic process involving several intra/extracellular mechanisms, which are triggered by cutaneous injuries. Wound repair consists of three separate but overlapping phases, i.e., inflammationInflammation, formation of new tissue, and remodeling. Although wound healing is an innate ability of every multicellular organismMulticellular organism, specific precautions are required in some particular cases. One important aspect of wound management is maintaining a good level of moisture. It has been acknowledged by the medical community that an optimal level of hydration leads to increased healing rates, reduces pain, and improves cosmesis. In this context, it is essential to know the nature of the wound in order to choose the most suitable wound dressing. For instance, in the presence of a dry wound, where additional hydration is necessary, the use of highly hydrated hydrogels can allow the autolytic debridement of necrotic tissue when its surgical removal is not feasible. The ability to trap water up to thousand times their dry weight turns these materials into valid alternatives for wound healing applications. The use of cellulose-based hydrogels has become popular owing to their great degree of biocompatibility, low-cost, and biodegradability. Recently, different strategies have been investigated for the development of more efficient wound dressings, for instance, the introduction of antibacterial features using a combination of antibiotics and/or antibacterial polymers. Along with plant-derived cellulose, the use of bacterial cellulose membranes as wound dressings and skin substitutes is attracting considerable interest due to their innate hydrogel structure as well as their high chemical purity and mechanical properties. This chapter will present an overview of the most recent studies on cellulose-based hydrogels for wound healing applications, as well as the most recent outcomes of research in this field.

Isabel Orlando, Ipsita Roy

38. Blended Gels of Sodium Carboxymethyl Cellulose Incorporating Antimicrobials for Absorbance and Wound Healing Applications

Wound healing is frequently enhanced by the application of dressings which maintain a moist environment and provide for absorption of exudates. In many cases, dressings with antibacterial properties are considered beneficial, while barrier properties and mechanical integrity are also important. This chapter initially reviews the role of natural and herbal antimicrobial products including propolis, honey, and Punica granatum (pomegranate) as potential constituents for wound care biohydrogels. The applicability of a wide variety of polysaccharides, including carboxymethyl celluloses, in wound care biomaterials is then considered. Sodium carboxymethyl cellulose (NaCMC) is able to form hydrogels by chemical crosslinking. Where a combination of properties is desired, blending with other polymers may be advantageous. The chapter concludes by examining recent progress with systems that incorporate a natural antimicrobial (propolis) within blended cryogels of NaCMC and poly (vinyl alcohol). PVA and its blends can form strong and relatively stiff hydrogels by a physical crosslinking process which occurs during freeze-thawing cycles. Crystallites are formed which anchor the polymer chains, creating a polymer network that can swell in the presence of fluids or exudates. Such composite gels retain acceptable mechanical properties even when loaded with up to 30% propolis. Dressings containing 15% propolis or more were effective against S. aureus and also exhibited high fluid uptake. Hydrogels containing NaCMC therefore have significant potential to meet the requirements for an effective wound care dressing, particularly when blended with natural antimicrobials and embedded in robust hydrogel matrices such as those of PVA cryogels.

Renata Nunes Oliveira, Garrett Brian McGuinness

39. Cellulose-Based Hydrogels as Biomaterials

Hydrogels are three-dimensional hydrophilic network structures that vary greatly in swelling/shrinkage properties against minor changes such as light density, solvent composition, ionic strength, pH, and temperature. Cellulose-based hydrogels are derived from natural sources which are biodegradable and low-immunologic. These hydrogels are produced in four different ways: those obtained directly from native cellulose (including bacterial cellulose), those derived from cellulose derivatives (methyl cellulose, carboxymethyl cellulose, hydroxy methyl cellulose, etc.), those obtained with other polymers as a composite, and finally those obtained from cellulose-inorganic hybrids. Cellulose hydrogels and its derivatives have many desirable properties such as high water retention capacity, high crystallinity, fine fiber network, easy formability, and high tensile strength. In addition, some cellulose derivatives exhibit intelligent behavior against physiological variables such as pH and ionic strength. Cellulose-based hydrogels have advantages such as better biocompatibility, less latent toxicity, and lower cost than the most synthetic polymer hydrogels. Because of these advantages, cellulose-based hydrogels are preferred to be used in industrial pharmaceutics and biomedical fields. This chapter will discuss applications of cellulose-based hydrogels in pharmaceutical industry and biomedical fields such as drug release systems, wound healing, and tissue engineering. In addition, future prospects on cellulose-based hydrogels will be addressed.

Serdar Sezer, İsa Şahin, Kevser Öztürk, Vildan Şanko, Zeynep Koçer, Ümran Aydemir Sezer

40. Cellulose-Based Hydrogels in Topical Drug Delivery: A Challenge in Medical Devices

Drug delivery is a difficult task in the field of dermal therapeutics mainly in the treatment of burns, ulcers, and wounds. Therefore, fundamental research and the development of novel advanced biomaterials as hydrogels are ongoing to overcome these issues. Currently, several approaches are starting to emerge aiming the stabilization of drug loaded in hydrogel material by increasing the mutual interactions between the polymers, the polymers, and the drug and by covalently cross-linking the polymers during hydrogel formation. Hydrogels provide mechanical support and control over architecture, topography, and biochemical characteristics that make them functionally appropriate to biomedical materials. In this regard, cellulose-based biomaterials can be considered as a gold standard for many topical pharmaceutical applications because of their versatility in fabrication, biodegradability, and biocompatibility. In open wounds, a curative ideal hydrogel is proposed for occlusion and maintenance of the moist environment. Healing through the wet medium has comparative advantages such as preventing dehydration of tissue leading to cell death, stimulating epithelization and formation of granulation tissue, facilitating the removal of necrotic tissue and fibrin, serving as a protective barrier against microorganism, and avoiding excessive fluid loss and can still take drugs. On the other hand, another recent challenge is the use of hydrogel in the manufacture of microneedles. The microneedles are able to, with little force, penetrate effectively in the tissues, maintaining the continuous contact, without causing damages in the tissue, providing a high force of adhesion. These devices may be an alternative to the infection-resistant staples used in surgeries to attach skin grafts to patients with severe wounds resulting from burns and to be used in drug release. In this chapter, we discuss recent developments in cellulose-based hydrogels with respect to drug delivery and current applications in the new devices and research settings for infections, inflammations, skin burns, and wound treatment.

Andreza Maria Ribeiro, Mariana Magalhães, Francisco Veiga, Ana Figueiras

41. Cellulose-Based Nanosupports for Enzyme Immobilization

Integration of biocatalysts and nanoscale materials offer multiple advantages over micro-scaled heterogeneous biocatalysts. Apart from providing reusability and sustainability of the enzyme, the use of nanosupports is aimed at increasing the surface area available for biocatalyst immobilization and improving the yields in bioconversions through better biocatalyst mobility and less diffusional problems. Among many nanomaterials for enzyme immobilization, cellulose stands out as biocompatible, biodegradable, and environmentally-friendly regarding its biological source. In this chapter, we discuss the steady advancement in utilizing different nanostructured cellulosic materials for enzyme immobilization. We address the use of hybrid materials that include cellulose and improve the properties of the heterogeneous biocatalyst. The methodologies for functionalization and integration of enzymes on nanocellulose hydrogels are discussed including covalent linkage through chemical modification, entrapment, and cross-linking. We consider its applications to biomedicine, food industry, and environmental science with a special emphasis on the impact of the enzymatic properties caused after immobilization on cellulosic supports.

Erienne Jackson, Sonali Correa, Lorena Betancor

42. Bacterial Cellulose-Based Hydrogels: Synthesis, Properties, and Applications

There is an importunate effort taking place worldwide to obtain the innovative hydrogels either from natural, synthetic, or mixed type polymers, ever since the breakthrough invention of the first hydrogel of polyhydroxy ethyl methacrylate. Predominantly the cellulose-based hydrogels attracted the attention of researchers due to its renewable, biodegradable biopolymeric nature. In comparison to plant cellulose (PC), the bacterial cellulose (BC) has been preferred due to its pure fibrous biomaterial nature, high crystallinity, ultrafine three-dimensional nanostructure network, high water absorption, superior mechanical properties, biocompatibility, and biodegradability. These promising valuable properties of BC exploit its use especially in hydrogel form in a variety of technological fields like a development of new bacterial cellulose-based hydrogels. The present review focused on its current synthesis methods and use in biomedicine, pharmaceutical, environment, agriculture, etc. In recent years BC itself and in combination have become the subject of intensive studies for the synthesis of hydrogels in search of properties and applications of BC-based hydrogels. On the whole, the review after introducing BC production and its properties discusses the synthesis of BC-based smart hydrogels with various composite materials, formation mechanism, and improved characters. The latest use of BC-based hydrogels in both well-established and innovative high-tech fields is emphatically reviewed. The review concludes with the need for future research with some suggestions for BC-based hydrogels to be commercialized as a smart biomaterial.

Bhavana V. Mohite, Sunil H. Koli, Satish V. Patil

43. Importance of Multi-Stakeholder Initiatives in Applications of Bacterial Cellulose-Based Hydrogels for Sustainable Development

Currently, there is a wide range of consensus and awareness regarding whether nature can help or provide feasible solutions to achieve more inclusive and sustainable growth in a smart, “engineered” way. Similarly, for sustainable development the appearance of multi-stakeholder initiatives (MSIs) among companies, governments, and civil society organizations is also remarkable as they enable them to motivate and share knowledge, expertise, technology, and financial resources. This crucial idea arises in relation to how nature-based solutions provide sustainable, cost-effective, multi-purpose, and flexible alternatives for various objectives. For example, applications of bacterial cellulose (BC), which is synthesized by various bacteria, have great potential in a number of fields, such as food, biomedical material, cosmetics, healthcare, paper making, and other applications, but has a mostly untapped potential for contributing to cellulose-based hydrogels – that is, its smart applications. This work adds detailed discussion of aspects of MSIs (science, policy, business, and society, including small and medium-sized enterprises [SMEs] and public and private investors) relating to BC and BC-based hydrogels (BHs) and the various novel applications that promote the innovative, multi-purpose, dynamic capability intended for commercially exploitable BC and BC-based biocomposite products, in the form of hydrogen. To exploit new and emerging research opportunities for BC and BHs, this work reveals the significance of building an innovative platform such as the European Knowledge-Based Bio-Economy (KBBE) to bring together all of these advancements in cellulose-based hydrogels in simulated pathways for novel applications.

Nibedita Saha, Nabanita Saha, Tomas Sáha, Petr Saha

44. Antimicrobial Food Pads Containing Bacterial Cellulose and Polysaccharides

Antimicrobial food packaging is one of the major innovations in the field of packaging technology. To extend food shelf life and to contribute to the consumer’s health are the main challenges of the new technology. Absorbent pads are widely used in food industry in order to preserve sensorial characteristics of packaged fresh or refrigerated food products, such as meat or poultry and also fruit and vegetables which could generate exudates during storage time. Cellulose and cellulose-derived materials are already used as components in food pads architecture. To tailor an antimicrobial food pad using natural antimicrobial agents is also a challenge which could be achieved. The aim of this chapter is to give an overview of antimicrobial packaging, underlying especially the role of natural antimicrobial agents and biopolymers. Examples are focused on cellulose and its derivative uses. In the second part of this chapter, we propose new composite hydrogels composed of bacterial cellulose and other polysaccharides as xanthan and carboxymethylcellulose, hydrogels which could act as superabsorbent of moisture and fluids exuded from packaged fresh food products. As antimicrobial substances we have tested potassium sorbate and thyme essential oil. The samples impregnated with thyme essential oil were tested against four microbial strains: Escherichia coli, Bacillus subtilis, Candida utilis (Torula), and Penicillium hirsutum.

Marta Stroescu, Gabriela Isopencu, Cristina Busuioc, Anicuta Stoica-Guzun

45. Cellulose-Based Hydrogel for Personal Hygiene Applications

Personal hygiene product is an inseparable part of urban society. It has given comfort, reliability, and flexibility to sick people, women, and children. The hygiene items containing superabsorbent polymer (hydrogels) for absorbing large amount of body fluids are the attractive inventions of modern science. The hydrogels swell and imbibe body fluids in the presence of hydrophilic functional groups in the polymeric backbone. Current trend of using acrylate-based superabsorbent in hygiene products is creating significant portion of urban garbage. This pile up is not only shrinking land sites but also harming a lot to the environment due to non-degradability of superabsorbent materials existing in the core of hygiene product. In spite of high water-holding capacity of petrochemical-based superabsorbent polymer, it has a hidden curse on nature of non-degradability and health risk. Cellulose is the most abundant biocompatible matter on this earth which basically originated from plants. It is also naturally occurring long chain polymer that plays a vital role in food cycle in animal kingdom. Besides this cellulose, its derivatives have large application in various fields. As cellulose and its etherified and esterified derivatives have attractive physicochemical and mechanical properties, hydrogels synthesized from cellulose and its derivative can be alternative to synthetic superabsorbent polymer. Cellulose-based hydrogels have found application in various fields like agriculture, biomedical, tissue engineering, wound dressing, pharmaceuticals, etc. Among various applications, some products are available in the market, and some are in research level. Due to fast swelling and other extraordinary properties (i.e., biocompatible and biodegradable), cellulosic materials (cellulose-originated hydrogels) can be applied in personal hygiene product so that superabsorbent from nonrenewable materials is partially or completely replaced. In this chapter, history of using superabsorbent in hygiene product, brief discussion on hydrogel synthesis, health and environment risk related to non-cellulosic absorbent materials, suitability of cellulose-based hydrogels over available acrylate hydrogels, and recommendation for development have been discussed.

Md. Obaidul Haque, Md. Ibrahim H. Mondal

Other Bio-Based Hydrogels and Their Applications

Frontmatter

46. Synthetic Hydrogels and Their Impact on Health and Environment

Hydrogels have been discovered nearly 60 years ago and due to their permeability to water systems, they have become very important materials for use in comparison to other polymers. Hydrogels are materials first rationally designed for use in human medicine, and they find important usage in various areas, for example, in products for personal care, pharmaceutical, agriculture, and environmental protection. Especially interesting is the class of stimuli-sensitive hydrogels, due to their properties to respond to changes in pH, temperature, and ionic strength of the surrounding medium, whereby changes exist in the network structure, for example, swelling properties. Hydrogels have significant applications: in diagnosis, as substrates or implants in tissue engineering, as drug delivery carriers, and in cosmetics. Water pollution by heavy metals and dyes is a major environmental problem because of toxicity to the living world, bioaccumulation, and bio-non-degradability. Adsorption of heavy metals, radioactive elements, and dyes using the hydrogels is an effective way for their removal. The mechanism of heavy metals and dye ions removal using hydrogels could be explained by the physical adsorption, hydrogen bonding, complexation, and/or chelation and ion exchange. The pollutants adsorption process using hydrogels has some important advantages compared to conventional techniques: high adsorption capacity for removal of pollutants from aqueous solutions, binding ability, and reusability (regeneration). Hydrogels have applications in some systems for the controlled and sustained release of pesticides and fertilizers, so reducing the contamination of the soil and surface water by these agrochemicals.

Ljubiša B. Nikolić, Aleksandar S. Zdravković, Vesna D. Nikolić, Snežana S. Ilić-Stojanović

47. Polysaccharide-Based Superabsorbents: Synthesis, Properties, and Applications

Traditional absorbent hydrogels are based on the copolymerization of petroleum-based synthetic vinyl monomers such as acrylic acid, methacrylic acid, and acrylamide derivatives. Nevertheless, these materials are usually expensive, poorly degradable, and non-environmentally friendly. On the contrary, natural polysaccharides display significant advantages such as availability, low production cost, nontoxicity, biocompatibility, and biodegradability. Accordingly, polysaccharides emerge as an interesting sustainable alternative to traditionally employed polymers. In addition, polysaccharides can easily form hydrogels by chemical or Physical crosslinking physical crosslinking (including hydrogen bonding and ionic interactions) or a combination of both, which makes the crosslinking of natural polysaccharides a versatile and promising approach for superabsorbent hydrogel (SAH) production. Therefore, in the last years, numerous polysaccharides including starch, cellulose, alginate, chitosan, and guar gum, among others, have been employed in SAH fabrication. Polysaccharide-based SAHs have been used in agriculture, hygiene products, waste treatment, crack mitigation in building applications, tissue engineering, and controlled release, for biomedical and soil conditioning applications. Despite of the evident commercial and environmental advantages of polysaccharide-based SAHs, they also display some drawbacks that make them continue appearing as a challenge research field. In this sense, although the biodegradability of polysaccharide-based hydrogels is a key characteristic for some applications because it avoids pollution-related issues and enables enhanced controlled release, at the same time, it could delay the development of longtime sustained release systems. Moreover, polysaccharide crosslinking leads to hydrogels with poor mechanical stability which is another associated disadvantage of these types of materials that needs to be overcome. Therefore an increasing amount of investigations about new synthetic approaches to improve the properties of polysaccharide-based hydrogels have been reported in the last years. In this chapter, the recent progress of this type of hydrogels is reviewed. The synthetic methods employed to obtain SAHs from the most common polysaccharides and the main properties of these materials with a special emphasis on swelling and mechanical properties are studied. Furthermore, the applications of SAHs have been summarized highlighting the most outstanding and promising uses.

Leyre Pérez-Álvarez, Leire Ruiz-Rubio, Erlantz Lizundia, José Luis Vilas-Vilela

48. Biodegradable Hydrogels for Controlled Drug Delivery

Hydrogels are three-dimensional cross-linked polymeric networks that can imbibe large amount of water or biological fluids. The ability of hydrogel to absorb water appears due to the presence of hydrophilic groups such as –OH, –CONH, –CONH2, –COOH, and –SO3H, along the polymer chain. Depending on the pendant functional groups, hydrogels have the ability to respond to their environmental changes such as pH, ionic strength, or temperature. The high water content and soft texture of these hydrogels translate them into a biocompatible material. This property renders the hydrogel similar to biological tissues and consequently minimizes inflammation once implanted or injected in the body. Biodegradable hydrogels are further adding advantages of degradation of the matrix into innocuous biocompatible products that can be eliminated after serving, thus eliminating the necessity of their removal. The degree of biodegradation can be controlled by manipulating the cross-linking with suitable precursors. Their mechanical property can also be tailored to have structural stability followed by extended release of cargo molecules. Their flexibility and minimally invasive administration are useful characteristics for their increased application in biomedical fields. Biodegradable hydrogels as controlled release systems are investigated to improve the temporal and spatial presentation of drug in the body, to protect drug from physiological degradation or elimination and to improve patient compliance. Hence the author has made an attempt to discuss biodegradable polymers of natural and synthetic origin, the biodegradation mechanisms, hydrogel engineering strategies, drug-hydrogel interactions, and release kinetics and mechanisms of such hydrogels to attain controlled delivery of drugs to different site of action in this chapter.

Nilimanka Das

49. Polysaccharide-Aloe vera Bioactive Hydrogels as Wound Care System

Wound care is an essential aspect of any trauma or surgical procedure. Designing an ideal wound healing system requires moist wound bed, proper exudate absorption, optimal diffusion of gases and minimum microbial invasion at the wound site which play a pivotal role. Therefore, choice of an ideal wound dressing is an essential step toward it contributing to the acceleration of wound repair and regeneration as well as prevention from microbial infection. This chapter is dedicated to the development of polysaccharide (PS)-based hydrogels for wound care system by incorporating herbal bioactive agents such as aloe vera which would provide deep insights into the designing aspect of the dressing by incorporation of features of the natural system. The healing aspect and tissue regeneration by PS or its combination with other natural polymers and aloe vera are discussed in the chapter.

Surabhi Singh, Sadiya Anjum, Jincy Joy, Bhuvanesh Gupta

50. Synthesis and Applications of Carbohydrate-Based Hydrogels

Carbohydrate-based hydrogels are cross-linked three-dimensional structures of polymers, utilized for several purposes such as cell culturing, regenerative medicine, agriculture, contact lenses, biosensors, drug delivery, and tissue developing technology. The primary aim of this chapter is to review the literature regarding the classification of the carbohydrate-based hydrogels on the basis of their chemical structure, synthesis, and viability of their utilization. It also involved technologies adopted for hydrogel manufacturing. Hydrogels are most of the times manufactured from polar monomeric units. Based on the substrate material, they can be classified into natural polymer hydrogels, synthetic polymer hydrogels, and combinations of the two classes. Different fabrication processes such as polymerization, grafting, physical and chemical cross-linking, solution polymerization, and polymerization by irradiation are being discussed in this chapter. The synthesis of hydrogels is based on required applications. So this chapter also includes applications of carbohydrate-based hydrogels.

Sarah Farrukh, Kiran Mustafa, Arshad Hussain, Muhammad Ayoub

51. Smart Biopolymer Hydrogels Developments for Biotechnological Applications

Natural-based polyelectrolytes, especially polysaccharides, have received increasing attention in biomedical and pharmaceutical fields due to biodegradability, biocompatibility, natural abundance, unique chemical structures and physicochemical/biological properties, and the ability to form hydrogels. A class of hydrogel which changes its shape, surface characteristics, and solubility or undergoes formation of an intricate molecular self-assembly or phase or conformational transition with external stimuli, such as pH, temperature, ionic strength, solvent composition, the presence of salt ions, light, or electric field, is considered to be a “smart” hydrogel (also referred to as stimuli-responsive hydrogel). These kinds of hydrogels have been proposed for biotechnological applications, such as the delivery of therapeutic agents, tissue engineering, flow control, sensors/diagnostic devices, and actuators. Among these hydrogels, alginate and chitosan biopolymers have been categorized as pH-sensitive, temperature-sensitive, as well as dual pH- and temperature-responsive hydrogels and were discussed in this chapter.

Ahmed M. Omer, Tamer M. Tamer, Randa E. Khalifa, Samar A. Gaber, Mohamed S. Mohy Eldin

52. Polylactic Acid-Based Hydrogels and Its Renewable Characters: Tissue Engineering Applications

Derived from renewable sources, polylactic acid (PLA) is a thermoplastic aliphatic polyester, which is biodegradable and bioactive and being explored for various applications. PLA being hydrophobic in nature, often needs to be used in combination with a hydrophilic moiety in order to form hydrogels. PLA based hydrogels have found significant attention in biomedical applications. Hydrogels resemble the structure of many tissues and can be delivered to the patient using minimally invasive surgery along with their ease of processability which makes them potential scaffold materials. PLA is often considered a suitable candidate for scaffolds due to its biocompatible and bioresorbable nature. The current chapter highlights the importance of PLA based hydrogels in biomedical applications with significant focus on scaffolds for the treatment of damaged tissues. The essential criteria for selection of suitable materials to be used in combination with PLA for tissue engineering applications is presented, which would mimic the host tissue structure and allow the natural regeneration of tissue. Several case studies involving the use of PLA based hydrogels in tissue regeneration with their significant outcomes have been discussed. Furthermore, the investigations on cytotoxicity, cell adhesion, and proliferation are outlined for identifying the scope of these materials in tissue engineering applications.

Neha Mulchandani, Arvind Gupta, Vimal Katiyar

53. Protein-Based Hydrogels

Hydrogels have the capability to absorb large amounts of water or biological fluids into their three-dimensional hydrophilic polymer networks. These attractive materials are used to develop food additives, superabsorbents, wound dressing compounds, pharmaceuticals, and biomedical implants and also applied in tissue engineering, regenerative medicines, and controlled-release process. Hydrogels can be obtained from synthetic and/or natural resources. Synthetic hydrogels exhibit high water absorption capacities and proper mechanical strengthMechanical strength, although their applications are being limited because of low biocompatibility and biodegradability as well as the toxicity arisen from unreacted monomers remained in the gel structure. Natural hydrogels are often derived from polysaccharides and proteins. Protein-based hydrogels have substantial advantages such as biocompatibility, biodegradability, tunable mechanical properties, molecular binding abilities, and intelligent responses to external stimuli such as pH, ionic strength, and temperature. Therefore, this kind of hydrogels is known as smart biomaterials for controlled release, tissue engineering, regenerative medicine, and other applications. Protein can be converted to hydrogel using physical, chemical, or enzymatic treatments. To improve their mechanical properties, hybrid hydrogels are synthesized by combining natural polymers with synthetic ones. The main approach to obtain hybrid hydrogels is grafting natural polymers with synthetic one and vice versa. This chapter intends to look over protein-based hydrogels. After brief introduction of protein and its structure, the properties of proteins and peptides used to develop hydrogels, as well as their preparation methods are discussed. The potential applications of these polypeptide-based hydrogels in the fields of superabsorbent development, tissue engineering, and controlled release are reported. Characterization methods for protein-based hydrogels are covered in the final section to determine rheological properties, morphology, and thermal stability.

Reza Panahi, Mahsa Baghban-Salehi

54. Gelatin-Based Hydrogels

Hydrogels are crosslinked polymers that are able to absorb large amount of water, permit solutes within their swollen matrices, and provide sustained delivery of absorbed solutes. The use of various types of functional biopolymers as scaffold materials in hydrogels has become of great interest not only as an underutilized resource but also as a new functional material of high potential in various fields. Among them, gelatin has been considered as highly potential candidate to be utilized as hydrogel component because of its hydration properties such as swelling and solubility; gelling behavior such as gel formation, texturizing, thickening, and water-binding capacity; and surface behavior like emulsion and foam formation, stabilization, adhesion and cohesion, protective colloid function, and film-forming capacity. In addition, its properties of biocompatibility, low toxicity, antimicrobial activity, and biodegradability make it suitable for diversified biomedical applications. Many works have been reported in various scientifically reputable journals and publications worldwide that seem to have potential or satisfactory contribution of gelatin-based hydrogels. Numerous fields of application of gelatin hydrogels include, not limited to, usage as safer release system in agrochemicals, nutrient carriers for plants, drug and cell carrying devices, bioadhesives, wound healing, tissue engineering, etc. The purpose of this chapter is to compile the recent information on developments in gelatin-based hydrogel preparation, as well as new processing conditions and potential novel or improved applications.

Taslim Ur Rashid, Sadia Sharmeen, Shanta Biswas, Tanvir Ahmed, Abul K. Mallik, Md. Shahruzzaman, Md. Nurus Sakib, Papia Haque, Mohammed Mizanur Rahman

55. Collagen-Based Hydrogels and Their Applications for Tissue Engineering and Regenerative Medicine

A promising solution for soft tissue regeneration is tissue engineering, a multidisciplinary field of research which involves the use of biomaterials, growth factors, and stem cells in order to repair, replace, or regenerate tissues and organs damaged by injury or disease. The success of tissue engineering (TE) depends on the composition and microstructure of the used scaffolds. Ideally, scaffolds have to be similar to natural tissues. Collagen is the major component of the extracellular matrixExtracellular matrix of most soft tissues. The interactions between collagen and cells are vital in the wound healing process and in adult tissue remodeling, collagen being able to support differentiation and maintenance of cellular phenotype. As a natural molecule, collagen possesses the major advantage of being biodegradable, biocompatible, easily available, and highly versatile and presents low antigenicity. This chapter aims to present an overview on the structure, properties, and biomedical applications of collagen hydrogels. Moreover, it introduces the reader to the latest research in the field of tissue engineering related to collagen. It also displays the results we obtained as a joint bioengineering group on collagen hydrogels designed for soft (ATE) or cartilage tissue engineering (CTE) applications: type I collagen hydrogels improved with either silk sericin (CollSS) or with pro-chondrogenic factors – hyaluronic acid and chondroitin sulfate (CollSSHACS). Results indicated in both cases the positive influence of sericin on the interaction between cells and the surface of the hydrogels. In the absence of HA and CS, specific chondrogenic inducers, CollSS hydrogel is adapted for soft tissue reconstruction, whether the addition of HA and CS transforms CollSSHACS into a suitable hydrogel formula for semihard tissue repair via modern strategies in tissue engineering and regenerative medicine.

Sorina Dinescu, Madalina Albu Kaya, Leona Chitoiu, Simona Ignat, Durmus Alpaslan Kaya, Marieta Costache

56. Chitosan-Based Hydrogels: Preparation, Properties, and Applications

Chitosan is a hydrophilic polysaccharide obtained by partial deacetylation of chitin, which is one of the most popular biopolymers. Chitosan is well known for its favorable properties including biocompatibility, biodegradability, antibacterial, and biological activity, as well as its renewable character. Thanks to those features chitosan’s popularity in various applications ranging from food industry to tissue engineering is constantly growing. The following chapter will more closely consider fabrication, properties, and specific applications of chitosan-based hydrogel networks. Methods for chitosan preparation will be summarized, followed by detailed characterization of chitosan properties. Strategies for their improvement and fabrication of chitosan derivatives will be discussed as well. Next, attention will be drawn to preparation of chitosan-based hydrogels via chitosan crosslinking. Both chemical and physical crosslinking methods will be considered with special emphasis on comparison between the two crosslinking methods and recent advancements in application of novel biocompatible crosslinkers. This chapter will also take a closer look at formation of stimuli-responsive (especially pH- and temperature-sensitive systems) and injectable hydrogels. Utilization of chitosan hydrogels in tissue engineering will be highlighted together with different techniques for fabrication and construction of three-dimensional scaffolds. Finally, other applications of chitosan-based hydrogels and their composites will be summarized.

Patrycja Domalik-Pyzik, Jan Chłopek, Kinga Pielichowska

57. Chitosan-Based Polyelectrolyte Complex Hydrogels for Biomedical Applications

Chitosan is produced by deacetylation of chitin, a structural element in the exoskeleton of crustaceans and insects, which is the second most abundant natural biopolymer after cellulose. Chitosan has found applications in many primary industries such as: agriculture, paper, textiles, pharmacology, cosmetology, and wastewater treatment. There is a major interest in using chitosan for biomedical applications due to its generous properties including biocompatibility, low toxicity, hemostatic potential, good film-forming character, anti-infectional activity, and susceptibility to enzymatic degradation. The property of chitosan which will be in detail discussed in this chapter refers to its ability to form polyelectrolyte complexes due to the presence of amine groups in its repetitive unit. Therefore, chitosan in aqueous acid solution reacted with anionic polysaccharides such as: carboxymethylcellulose, xanthan, alginate, carrageenan, gellan, oxychitin and oxypullulan, chondroitin and hyaluronan, poly(galacturonic acid), poly(L-glutamic acid) as well as synthetic polyanions such as poly(acrylic acid) to give polyelectrolyte complexes. One major advantage of polyelectrolyte complexes for biomedical use is their superior biocompatibility in respect with other formulations which are using synthetic crosslinkers to obtain stable hydrogels. The aim of this chapter is to describe the process of chitosan complexation with other natural and synthetic polyanions, the factors that influence the formation and stability of these polyelectrolyte complexes and the potential applications in biomedical field.

Silvia Vasiliu, Stefania Racovita, Marcel Popa, Lacramioara Ochiuz, Catalina Anisoara Peptu

58. Interpenetrating Polymer Network Hydrogels of Chitosan: Applications in Controlling Drug Release

ChitosanChitosanInterpenetrating polymer network hydrogelsInterpenetrating polymer network hydrogels is a natural polysaccharide obtained by alkaline deacetylation of chitin. It is cationic in ionic nature. Because of its biocompatibility and biodegradability, chitosan is employed as a drug carrier material in the development of various kinds of drug delivery. However, the extensive use of chitosan as a drug delivery carrier material is limited by its rapid dissolution in the acidic pH of the stomach, and this causes restrictions in controlling drug release from chitosan-based oral dosage forms. To overcome this limitation, modifications of chitosan to develop hydrogel systems are being investigated by researchers. Among these modified chitosan-based hydrogel systems, interpenetrated polymer network (IPN) hydrogels have enhanced mechanical properties at gastric pH, as well as improved control of drug release over a longer period. This chapter describes the preparations and properties, in terms of drug-releasing performance, of various chitosan-based IPN hydrogels for controlling drug release.

Dilipkumar Pal, Amit Kumar Nayak, Supriyo Saha

59. Techno–Economic Analysis of Chitosan-Based Hydrogels Production

Currently, hydrogels have different applications due to its excellent water absorption capacity such as biomedical applications, absorbent materials manufacturing, chemical industries, and agroindustry industries. The hydrogels can be produced from natural, synthetic, or a combination of both sources. One of the most studied raw materials for the obtaining of hydrogels is chitosan, which is a linear polysaccharide that is composed of D-glucosamine and N-acetyl-D-glucosamine. Thanks to its structural and chemical properties, hydrogels based on this biopolymer are viable for biomedical applications. In this context, the aim of this chapter is to evaluate the preparation of chitosan-based hydrogels from process design point of view. An overview about chitosan-based hydrogels, main applications, description of the production process, and trends in this topic is presented. Additionally, the production of chitosan-based hydrogel using the interaction of hydrogen bonds technology is simulated in Aspen Plus generating the mass and energy balances in order to realize the technical and economic assessment of the process. The simulation shows that the even if the hydrogels from chitosan are economically feasible, there are a number of possibilities to improve the technology (to reduce the energy consumption or to improve the yields).

Jimmy Anderson Martínez Ruano, Carlos Andrés Taimbu de la Cruz, Carlos Eduardo Orrego Alzate, Carlos Ariel Cardona Alzate

60. Silk-Based Hydrogels for Biomedical Applications

Among the naturally occurring fibers, silk occupies a special position due to its properties. Silk fibroins, the unique proteins of silkworm fibers, are high-molecular-weight block copolymers consisting of a heavy (~370 kDa) and a light (~26 kDa) chain with varying amphiphilicity linked by a single disulphide bond. Bombyx mori silk is the most characterized silkworm silk. Researchers have investigated fibroin as one of the promising resources of biotechnology and biomedical materials due to its other unique properties including excellent biocompatibility, favorable oxygen permeability, and outstanding biodegradability, and the degradation product can be readily absorbed by the body with minimal inflammatory reaction. Silk hydrogels have been thoroughly studied for potential biotechnological applications due to their mechanical properties, biocompatibility, controllable degradation rates, and self-assembly into β-sheet networks. Hydrogels made from silk proteins have shown a potential in overcoming limitations of hydrogels prepared from conventional polymers. This chapter offers overview of the recent developments in silk protein-based hydrogels, both of fibroin and sericin proteins. It describes the approaches for obtaining silk hydrogels and ideas to improve the existing properties or to incorporate new features in the hydrogels by making composites. Characterization tools and modern bioapplications of the silk hydrogels for tissue engineering and controlled release are also reviewed. A special focus is given to silk fibroin composite hydrogels for bone tissue engineering applications.

Bianca Galateanu, Ariana Hudita, Catalin Zaharia, Mihaela-Cristina Bunea, Eugenia Vasile, Mihaela-Ramona Buga, Marieta Costache

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