Polylactide synthetic polymers

Selection of a tissue engineering substrate includes a choice between absorbable and nonabsorbable material, as well as a choice between synthetic and naturally derived materials. The most common synthetic polymers used for fibrous meshes and porous scaffolds include polyesters such as polylactide and polyglycolide and their copolymers, polycaprolactone, and polyethylene glycol. Synthetic polymers have advantages over natural polymers in select instances, such as the following i... 

The use of lipids, including lipid-protein membranes, concentric lipid manbranes, and submicron ultrathin lipid membranes is another common approach. Biodegradable synthetic polymers offer another approach. The first one used was polylactide. Many types of polylactides and poly-glycolic acids are now used for artificial cells. Other synthetic biodegradable polymers, such as polyanhydride, also are used. The use of biodegradable artificial cells has become an active field. 

Cell-culture studies have indicated that such structures promote cellular infiltration into the fibrillar network and can become densely populated in a reasonably short time. A number of natural and synthetic polymers have been successfully electrospun into fibrous scaffolds for the purpose collagen, elastin, gelatin, fibrinogen, polyglycolic acid, polylactic acid, polycaprolactone, polylactide-co-glycolide and polylactide-co-caprolac-tone. Recently published work indicates that an electrospun web formed... 

The most common strategy to decrease the price or improve the properties of polylactide to fulfill the requirements of different applications is blending. Polylactide has been blended with degradable and inert polymers, natural and synthetic polymers, plasticizers, natural fibers and inorganic fillers. The most common blends include blends with other polyesters such as polycaprolactone or PLA/starch blends. Usually the compatibility between the two components has to be improved by addition of compatibilizers such as polylactide grafted with starch or acrylic acid (114,115). Recently a lot of focus was concentrated on the development of polylactide biocomposites, nanocomposites and stereocomplex materials. In addition various approaches have been evaluated for toughening of polylactide. 

Figure 2.1 Basic structures for some groups of synthetic polymers commonly employed as degradable materials in medical applications a) polylactide-co-polyglycolides (also commonly used as their homopolymers (i.e., n/m = 0), b) polycaprolactones, c) polydioxanones, d) polyorthoesters, e) polyanhydrides, f) polyalkylcyanoacrylates, g) poly(organo)phosphazenes and h) polyphosphoesters...

It is well known that proliferation or differentiation of nerve or muscle tissue can be enhanced by electrical stimulation, which is in part attributed to the propagation of action potentials upon stimulation. To exploit these physiological events, composites of biodegradable polymers with electroconduc-tive materials have been investigated for effective transmission of electrical signals to the cells cultured on them. PLCL and polyaniline, one of the widely used electrically conductive materials, were mixed to fabricate the nanofiber meshes, illustrating that myotube formation was accelerated when the myoblasts were cultured on polyaniline-containing nanofibers compared to that of PLCL-only nanofibers, even without electrical stimulation (Jun et ah, 2009). Another electroconductive polymer, polypyrrole, was also used as a composite with other synthetic polymers. For example, polypyrrole was incorporated as particles into polylactide scaffolds, and the fibroblasts cultured on them with various intensities of DC current showed controlled proliferation in a current-dependent manner (Shi et al., 2004). 

At the time of writing, the applications of biodegradable polymers are confined mostly to the field of agriculture, where they are used in products with limited lifetimes, such as mulch films and pellets for the controlled release of herbicides. The synthetic polyesters used in medical applications, principally polylactide and poly(lactide-co-glycolide), while claimed to be biodegradable, are degraded in the body mainly, if not entirely, by chemical hydrolysis. There is little evidence that the hydrolysis of these polyesters of a-hydroxyacids can be catalyzed by hydrolase or depolymerase enzymes. 

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