Other Natural Polymer Matrices

Quite a few alternative polymer matrices originating directly from nature have been proposed as potential matrices for composite biomaterials. Examples are starch, corn protein, and bacterial synthesized cellulose, and polysaccharides. Starch is 

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A composite material can be defined as a material in which two or more distinct structurally complementary substances are combined to produce structural or functional properties which are different from the individual components. Composites may be either synthetic or natural. Polymer matrix composites are much easier to produce than other composites, because of their low cost, low density and ease of processing. Composites have two phases, a continuous matrix phase and a dispersed phase or reinforcement phase. Polymer composites can be classified according to the nature of the dispersed phase as micro-or nanocomposites. ... 

Natural polymers such as collagen, elastin, and fibrin make up much of the body s native extracellular matrix (ECM), and they were explored as platforms for tissue engineered constructs [34,47 9]. Polysaccharides such as chitosan, starch, alginate, and dextran were also studied for these purposes. Simultaneously, silk fibroin was widely explored for vascular applications due to its higher mechanical properties in comparison to other natural polymers, such as fibrin [48]. The utilization of natural polymers to create tissue-engineered scaffolds has yielded promising results, both in vitro and in vivo, due in part to the enhanced bioactivity provided by materials normally found within the human body [50]. However, their mechanical response is usually below the required values therefore, synthetic polymers have been explored to achieve the desired properties. 

Similarly, a composite of hydroxyapatite and a network formed via cross-linking of chitosan and gelatin with glutaraldehyde was developed by Yin et al. [ 169]. A porous material, with similar organic-inorganic constituents to that of natural bone, was made by the sol-gel method. The presence of hydroxyapatite did not retard the formation of the chitosan-gelatin network. On the other hand, the polymer matrix had hardly any influence on the high crystallinity of hydroxyapatite. 

Enzymes can be immobilized by matrix entrapment, by microencapsulation, by physical or ionic adsorption, by covalent binding to organic or inorganic polymer-carriers, or by whole cell immobilization (5 ). Particularly impressive is the great number of chemical reactions developed for the covalent binding of enzymes to inorganic carriers such as glass, to natural polymers such as cellulose or Sepharose, and to synthetic polymers such as nylon, polyacrylamide, and other vinyl polymers and... 

Materials and processing technologies. The polymers discussed previously for nonenteric coatings such as HPMC (the most widely used), PVP, CMC, and carbomer, xanthin gum, and other naturally occurring polysaccharide polymers may be used for dissolution controlled release matrix systems. Furthermore, conventional processing techniques that were discussed for coating systems also can be used for matrix systems. 

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