Polymer Gels

Research concerning physical hydrogels, their morphological characteristics, swelling ability, and related mechanical properties is of increasing significance over last fifteen years due to their controllable degradability and desirable biocompatibility. Additionally, it is very important that physical crosslinking methods such as freeze-thaw cycling, heat treatment, ionic interactions, hydrophobic interactions, hydrogen bonding interactions, self-assembly stereocomplexation as well as other non-covalent interactions do not require use of chemical crosslinking agents which may induce allergic or toxic side effects. Physical crosslinked hydrogels have found their applications so far in pharmaceutical and medical areas. The engineering applications of physical hydrogels are still limited due to low mechanical toughness and short-term stability. This review explores mainly used physical crosslinking methods with examples of polymers crosslinkable with physical junctions. Special focus is given to methods improving mechanical rigidity of physical hydrogels based on anionic polysaccharides and poly(vinyl alcohol).

Polymer gels are worn in our steadily lives for extended wear lenses, superabsorbent polymers, etc., and more fancy applications are in development. They are among the most interesting and functional materials. Gels are characterized as polymers and their swollen matters with three-dimensional chain structures that are insoluble in any solvents. The capacity of polymer gels to experience considerable swelling and crumpling as an element of their surroundings is a standout among the most admirable properties of these materials. Polymer gels ordinarily contain a lot of portion of solvent, which gives them a singular quality started from a fluid nature. Additionally, they can keep up shape like strong materials, unless extra stress is applied. Subsequently, the mix of flexibility and shape maintenance capacity gives special properties, especially mechanical properties. Gels are wet and moldable and resemble a strong material yet are set up for experiencing considerable distortion. This property is as opposed to most modern materials, for example metals, earthenware production, and plastics, which are dry and hard. This chapter focuses on polymer gels in terms of molecular design, assembly, crosslink formations, and practical application.

Because of the potentially devastating consequences, adequate hemostasis is of paramount importance in all surgical procedures: generalized ooze hemorrhage from the surgical wall cavities, arising from the surface of different organs as liver, kidney, or nervous tissue, can result in considerable blood loss, prolonging surgical times, and with major risk for infection and mortality. Furthermore, hemorrhage may limit visualization in a confined operative field of view, as during endoscopic approaches. Blood-sparing procedures are required for blood loss control to arrest bleeding-related issues and the need for blood transfusions. Classical blood-sparing techniques, such as electrocauterization of the vessels and suturing, are in some cases ineffective. Matrix hemostatic agents are a mixture of a gelatin matrix (bovine or porcine) and a thrombin component mixed together at the time of use. Both components interact synergistically to raise hemostasis and make possible the development of the clot at the bleeding area. In this study, we compare the different hemostatic techniques using the gelatin hemostatic matrix sealant, investigating and reviewing its efficacy and safety in all surgical subspecialties.

Utilization of polysaccharides as precursors to develop new polymer gels has been growing recently due to their superior inherent properties such as biodegradability, chemical activity, biocompatibility, non-toxicity, abundance, and affordable price. This chapter discusses polymer gels in terms of chemical structures, modifications, the main properties of promising polysaccharide precursors, the most common crosslinkers, and methods of crosslinking either by physical or chemical methods along with mode of interactions. It also highlights the different techniques used to characterize and evaluate the performance and functional properties of the fabricated gels as well as their potential applications in different fields. Finally, recent developments and future trends are considered to cope with the growing demands for engineering novel polymer gels for further ecofriendly successful applications.

This chapter focuses on polymeric gel drug delivery systems used for initial immobilization and subsequent controlled release of active pharmaceutical ingredients. The primary focus is on phosphonate-based drugs, which are extensively used for a variety of medicinal applications and pathological conditions. Their most recognizable use is for osteoporosis drugs with the common names: medronate, chlodronate, etidronate, alendronate, zoledronate, obadronate, ibandronate, neridronate, etc. Herein, we present a concise literature overview of this research field, presenting research results on immobilization of phosphonates onto silica-based polymeric gels, with the goal to achieve controlled release of these ingredients into biological fluids.

Hydrogels are promising and innovative drug delivery system that plays a vital role by addressing the problems associated with old and modern therapeutics such as nonspecific effects and poor stability. Hydrogels are extensively being explored as drug delivery systems due to ease of their modifications and ability to efficiently encapsulate therapeutics of diverse nature through simple mechanisms. These are essentially based on hydrophilic polymer networks, with a tendency to imbibe water when placed in an aqueous environment. The affinity to aqueous solutions, superior colloidal properties, inertness in the biological system and the internal aqueous environment, make them suitable for incorporation of bulky drugs for delivery of chemotherapeutics and proteins. Present chapter presents introduction to hydrogel based drug delivery including types of hydrogel, their composition, types of polymerization techniques used for formulation of hydrogel and characterization of hydrogel. Furthermore, stimuli responsive hydrogels and their biomedical applications will be summarized.

In the last few years, many advances have been made in genomic and proteomic sciences using gel-based technologies. Some of these technologies still have valuable applications for genomic and proteomic studies. Two-dimensional gel electrophoresis (2DE), for example, is a protein fractionation technique used to analyze the differential expression of genes and to characterize post-translational modifications. On the other hand, pulsed-field gel electrophoresis (PFGE) is used to determine the size of prokaryotic genomes, for the detection of plasmids, and in epidemiological studies of pathogenic microorganisms. In this context, this chapter aims to describe the functionality of gel-based techniques, such as 2DE and PFGE, as well as their pros and cons, and advances that have been made and their primary applications in the fields of genomics and proteomics of microorganisms.

Vaginal drug delivery is a promising route for the treatment and prevention of local and systemic diseases such as genital herpes or AIDS. Suitable excipients must be selected to optimize the residence time of formulations in vaginal mucosa and could be included in the formulation. Many polymers are excellent choices for the development of vaginal drug delivery systems due to their properties of mucoadhesion, biocompatibility and biodegradability. These polymers swell in the aqueous medium of the vaginal environment and generate a gel layer which allows controlled release of the drug. The thickness and viscosity of the gel layer determine the drug release process. The aim of this chapter is to review the different polymers available for the development of vaginal delivery systems and to describe their physicochemical (swelling, viscosity, mucoadhesion), biopharmaceutical (drug release, biodegradability) and cytotoxic properties.

Polymer gels are constructed by polymeric network structures with cross-linking points, which stably include a large amount of dispersion media, leading to functional soft materials. The specific formation of cross-linking points contributes to exhibiting unique properties of the resulting gels. In this chapter, we focus on the gel formation through non-covalent cross-linking from amylose, a natural polysaccharide. Amylose has a helical conformation, which is able to form two types of complexes, that is, double helix by two amylose chains and inclusion complex with other molecules having suitable structures and sizes. Because a well-defined amylose can be synthesized by enzymatic polymerization by phosphorylase catalysis, the studies on the dynamic gel formation through non-covalent, double helical, and inclusion complexing, cross-linking from amylose has been achieved by means of the enzymatic polymerization field. The resulting gels showed unique properties and functions.

Some coordination biopolymeric metal–alginate ionotropic hydrogel complexes were prepared by the replacement of the Na⁺ counter ions of alginate sol polysaccharide by monovalent silver(I) or polyvalent metal ions forming their corresponding complexes in either granule or hydrogel phases. The type of such phase and the capillary or non-capillary structures property were found to be dependent on the method of preparation and the direction of diffusion of the metal ion toward the alginate sol matrix whether is of upward or downward direction. The net process of exchange leads to the so-called sol-gel transformation to give its respective hydrogel complexes. This process takes place through formation of partially ionic and partially coordinate bonds between the metal ion and the carboxylate and hydroxyl functional groups of alginate, respectively. This kind of chelation forms a sort of bridges in an egg box-like structure. The anisotropic property of the hydrogels is owing to the orientation of the solvent molecules and macromolecular chains toward the chelated metal ions. The geometrical configuration and physicochemical properties of the hydrogel complexes depend on the nature of the metal ions such as the valence and its coordination number as well as on the strength of chelating of the bonds formed. The kinetics and mechanism of sol-gel transformation, electrical conductivity, and thermal decomposition with their evaluated kinetic parameters along with the other physicochemical properties such as FTIR, XRD, morphology, configuration geometry, and rheological properties have been investigated and discussed.

Fundamental definitions, classification, and applications of smart polymer gels are the main discussions of this chapter. Smart polymer gels are polymer network structure which swell or shrink as a response to the changing in surrounding environment. Smart polymer gels are able to absorb high amount of water or biological fluid and release it when particular characteristic such as temperature, light, pH, and electric field of the surrounding medium is changed. Chemical compositions of the main materials of smart polymer gels are the main factors that determine the final properties. Smart polymer gels have an extensive range of application in medical such as drug delivery system, artificial muscle, and actuators. In addition, smart polymer gels are used in water treatment as ions and dyes adsorbents.

This chapter presents some applications of artificial neural networks for modeling the polymer gels. A series of general aspects for this topic (neural networks) is first shortly reviewed, emphasizing the main elements of the modeling methodology. Also, general considerations related to the neuro-evolution are discussed, as an appropriate method for obtaining neural networks in an optimal form. The difficulties related to the modeling of polymerization processes are enumerated as motivation for recommending the empirical techniques. The most important part is represented by a series of examples of applications of the neuro-evolutive techniques for modeling the polyacrylamide-based hydrogels. Some examples have been published, but the last three represent new approaches. They refer, mainly, to polyacrylamide-based hydrogels modeled with neural networks of different types, used individually or aggregated in stacks, or with neural networks developed with an evolutionary algorithm (differential evolution algorithm). An inverse neural network modeling was also performed as a particular optimization. Neuro-evolution, based on neural networks and differential evolution algorithm, was also applied for modeling the release of micromolecular compounds from hydrogels.