ABSTRACT
Biomaterials are nonviable materials used as medical devices intended to interact with biological systems. They display a combination of properties including chemical, mechanical, physical, and biological properties that render them suitable for safe, effective, and reliable use within a physiological environment. Biomaterials are developed to support damaged tissues, through suitable scaffolds for promoting cell differentiation and proliferation toward the formation of a new tissue (Williams 1987). The basic aim of scaffolds is to provide mechanical, morphological, and biological support for the damaged tissues and to recover them. To be successful, a scaffold should effectively repair the defect it covers without eliciting an adverse tissue reaction while maintaining mechanical and biological integrity for a desired amount of time from a few weeks to several years (Puppi et al. 2010). Natural-based polymers are or resemble the biological macromolecules, which the biological environment is prepared to recognize and deal with metabolically. The ECM is the optimized environment that nature has developed to maintain homeostasis and to direct tissue development (Mano et al. 2007). Owing to their similarity to the ECM macromolecules, natural polymers may serve as potential biomaterials. Natural polymers may also bypass the stimulation of chronic in¥ammation or immunological reactions and toxicities encountered by implants. The degradation of natural polymers is directed by naturally occurring enzymes and/or simple hydrolysis or
10.1 Introduction .......................................................................................................................... 271 10.1.1Historical Background.............................................................................................. 272
10.2Natural Polymers as Biomaterials........................................................................................ 272 10.2.1Polysaccharides as Biomaterials............................................................................... 273
10.2.1.1Cellulose.................................................................................................... 273 10.2.1.2 Starch ......................................................................................................... 276 10.2.1.3Agar-Agarose............................................................................................. 278 10.2.1.4Alginate......................................................................................................280 10.2.1.5Chitin and Chitosan................................................................................... 281 10.2.1.6Hyaluronan/Hyaluronic Acid/Hyaluronate................................................ 282
10.2.2 Proteins as Biomaterials ...........................................................................................286 10.2.2.1Collagen.....................................................................................................286 10.2.2.2Gelatin........................................................................................................288 10.2.2.3Fibrin-Fibrinogen-Fibronectin................................................................... 291
10.3Concluding Remarks............................................................................................................296 Abbreviations .................................................................................................................................297 References...................................................................................................................................... 298
oxidative processes which ensures that the implant degrades completely during normal metabolic processes. Furthermore, the rate of degradation of natural polymers can be modi…ed by chemical cross-linking or other modi…cations to attain a predetermined biodegradation rate. So, with natural polymers, biomaterials can be designed such that they can function biologically at molecular level.
The utilization of natural polymers as biomaterials is dated back to centuries. Ancient Egyptians used animal tendons as sutures. In the …rst century AD, in both Greece and India, physicians used natural biomaterials for surgery to repair mutilations from war. Susrutha, a medical encyclopedia of ancient India, describes a procedure similar to “autograft” which involved the transplantation of a tissue from one part of the body to another in the same individual. The method was used to obtain a prosthetic nose for patients whose nose had been cut off, by using a skin graft from the patient’s cheek, and molded into the new prosthetic nose. Physicians succeeded to keep an open wound at the nose clean and viable, to detach a portion of patient’s skin while maintaining the blood supply as to avoid necrosis and …nally to reattach it to the patient so that it revascularized and the new nose sustained itself (Chari 2003).The Romans were able to perform simple surgical techniques such as repairing damaged ears around the …rst century BC. Due to religious reasons, they did not approve the dissection of both human beings and animals, thus their knowledge was based on the texts of their Greek predecessors (Santoni-Rugiu 2007). At around 1460, physicians performed rhinoplasty in which the skin from arm was used as prosthetic nose (Zimmerman and Veith 1993).
