Collagen Polymers

Surgery to correct refractive errors for the improvement of visual acuity generally aims at changing the corneal curvature. Corneal tissue is mainly constituted of a network of natural collagen polymer with the void volume filled with a special type of aqueous saline solution. A wide variety of laser and nonlaser procedures, such as laser-assisted in situ keratomileusis (LA-SIK), laser-cut channels for intracorneal ring segment (ICRS) implantation, femtosecond lamellar keratoplasty (FLK), intrastromal vision correction, and corneal transplantation have been developed for refractive surgical correction [83, 84]. They include removal of corneal tissue from the surface, removal of corneal tissue from the interior or stroma, and alteration of the corneal mechanical properties to produce a refractive effect. The most popular by far are procedures based on excimer laser ablation of the corneal surface and/or stroma [85]. 

E. H. Harris and S. H. Feairheller, Crosslinking Systems in the Graft Polymerization of Chromium-Tanned Collagen, Polym. Eng. Sci. 17, 287 (1977). IPN formation with tanned leather as network I. Crosslinked acrylics, etc. serve as network II. Mechanical and physical behavior. Swelling behavior. 

Wiederhorn, N. and Beardon, G.V. 1952. Studies concerned with the structure of collagen II. Stress-strain behavior of thermally controlled collagen. /. Polym. Sci. 9 315-325. 

Sionkowska, A., Kozlowska, J., Planecka, A, Skopinska-Wisniewska, J. Photochemical stability of poly(vinyl pyrrolidone) in the presence of collagen. Polym. Degrad. Stab. 93, 2127-2132 (2008)... 

Fibrous proteins can serve as structural materials for the same reason that other polymers do they are long-chain molecules. By cross-linking, interleaving and intertwining the proper combination of individual long-chain molecules, bulk properties are obtained that can serve many different functions. Fibrous proteins are usually divided in three different groups dependent on the secondary structure of the individual molecules coiled-coil a helices present in keratin and myosin, the triple helix in collagen, and P sheets in amyloid fibers and silks. 

Fibrous proteins are long-chain polymers that are used as structural materials. Most contain specific repetitive amino acid sequences and fall into one of three groups coiled-coil a helices as in keratin and myosin triple helices as in collagen and p sheets as in silk and amyloid fibrils. 

Chitosan has been associated with other biopolymers and with synthetic polymer dispersions to produce wound dressings. Biosynthetic wound dressings composed of a spongy sheet of chitosan and collagen, laminated with a gentamicyn sulphate-impregnated polyurethane membrane, have been produced and clinically tested with good results. 

Since the purpose of this book is to describe applications of biodegradable polymers to drug delivery systems, particularly from the perspective of the materials employed, the approach taken in this chapter has been to focus on the natural biodegradable polymers which have been used most extensively as matrices for the delivery of drugs. Consideration was also given to the fact that collagen has not been the subject of any recent reviews. 

Meyer, M., Muhlbach, R., and Harzer, D. (2005). Solubilisation of cattle hide collagen by thermo-mechanical treatment. Polym. Degrad. Stab. 87,137-142. 

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