Natural polymers collagen

Polymers are substances whose molecules are very large, formed by the combination of many small and simpler molecules usually referred to as monomers. The chemical reaction by which single and relatively small monomers react with each other to form polymers is known as polymerization (Young and Lovell 1991). Polymers may be of natural origin or, since the twentieth century, synthesized by humans. Natural polymers, usually referred to as biopolymers, are made by living organisms. Common examples of biopolymers are cellulose, a carbohydrate made only by plants (see Textbox 53) collagen, a protein made solely by animals (see Textbox 61), and the nucleic acid DNA, which is made by both plants and animals (see Textbox 64). 

Besides the previously mentioned collagen, a wide variety of natural polymers have been involved in the synthesis of bio-nanohybrid materials with potential application in bone repair and dental prostheses. For instance, some recent examples refer to bionanocomposites based on the combination of HAP with alginate [96,97], chitosan [98,99], bovine serum albumin (BSA) [100], sodium caseinate [101], hyaluronic acid [102], silk fibroin [103,104], silk sericin [105], or polylactic add (PLA) [106,107]. These examples illustrate the increasing interest in the subject of HAP-based biohybrid materials, which has led to almost 400 articles appeared in scientific journals in 2006 alone. 

Natural polymers polysaccharides (celullose, starch, pectins, dextrans, agar, agarose, alginate, chitine, chitosan, etc.) and fibrous proteins (collagen, keratine, etc.). 

Gelatin A hydrolysis product of collagen (a natural polymer) Mostly -CO-NH- Major constituent amino acids are glycine, proline, and hydroxyproline... 

Further examples of natural polymers also include collagen, chitosan, and polyhydroxyalkanoates. Additional synthetic polymers include poly(glycolic acid) (PGA), poly(lactic acid) (PLA), copolymers of PGA and PLA, and polydioxananone. 

The use of chemiluminescence technique has expanded to others natural polymers. Recently, Millington et al. reported studies on polymers such as the fibrous proteins wool and feather keratin, silk fibroin, and reconstituted collagen from bovine skin, which revealed new information about their degradation [81]. The potential of CL to analyze the effectiveness of treatments to protect the polymer during processing could contribute to diminish the loss of properties of the types of polymers widely used in textile industry. 

Transformations with immobilized enzymes or cells Often the stability of the biocatalyst can be increased by immobilization and many different enzymes and cells have been immobilized by a variety of different methods. The most popular method for the fixation of whole cells is entrapment or encapsulation with calcium alginate. Other natural gels e.g., carrageenan, collagen, chemically-modified natural polymers e.g., cellulose acetate and synthetic gels and polymers e.g., polyacrylamide or polyhydroxyethylmethacrylate can also be used for this type of immobilization. 

From the perspective of biocompatibility, degradability, and process-ability, synthetic polymers have many advantages over complex natural polymers such as collagen. One class of polymers in particular, polyesters in the family of polylactic acid (PLA), polyglycolic acid (PGA), and copolymers of lactic and glycolic acids (PLGAs), most closely meets the listed criteria. These polymers have been approved by the FDA for in vivo... 

---