Nonbiodegradable polymers

The third general class of polymers used as matrices for drug delivery are the nonbiodegradable polymers. Because these polymers are essentially inert in the body, they can be used for applications in which extended drug delivery is required. Also, because of their inertness, they will remain in the body indefinitely after the drug is depleted unless they are removed. 

Ethylene vinyl acetate has also found major applications in drug delivery. These copolymers used in drug release normally contain 30-50 wt% of vinyl acetate. They have been commercialized by the Alza Corporation for the delivery of pilocarpine over a one-week period (Ocusert) and the delivery of progesterone for over one year in the form of an intrauterine device (Progestasert). Ethylene vinyl acetate has also been evaluated for the release of macromolecules such as proteins. The release of proteins form these polymers is by a porous diffusion and the pore structure can be used to control the rate of release (3). Similar nonbiodegradable polymers such as the polyurethanes, polyethylenes, polytetrafluoroethylene and poly(methyl methacrylate) have also been used to deliver a variety of different pharmaceutical agents usually as implants or removal devices. 

Table IV. Examples of Nonbiodegradable Polymers Used in Drug Delivery...

As shown in the tables, both biodegradable and nonbiodegradable polymers have been used as matrix for... 

Ven der Giessen W, Lincoff AM, Schwartz RS, et al, Marked inflammatory sequelae to implantation of biodegradable and nonbiodegradable polymers in porcine coronary arteries, Circulation 1996 94 1690-1697. 

Fischell TA, Carter AJ, Laird JR, The beta-particle-emitting radioisotope stent (isostent) animal studies and planned clinical trials. Am J Cardiol I 996 78 45-50, van der Giessen WJ, Lincoff AM, Schwartz RS, et al. Marked inflammatory sequelae to implantation of biodegradable and nonbiodegradable polymers in porcine coronary arteries. Circulation 1996 94 1690-1697. 

G. Verreck, I. Chim, J. Rosenblatt, J. Peeters, A.V. Dijck, J. Mensch, M. Noppe, M.E. Brewster. 2003. Incorporation of drugs in an amorphous state into electrospun nanofibers composed of a waterinsoluble, nonbiodegradable polymer. J. Control. Release, 92. pp.349. 

Despite of the encouraging potential of polymeric nano/microparticles, formulating a marketable peptide-delivery system still remains a major challenge. In this chapter, we have attempted to review the prospects and problems associated with polymeric nano/microparticles toward oral peptide delivery. Polymers are classified under three different categories (1) synthetic biodegradable polymers, (2) synthetic nonbiodegradable polymers, and (3) natural- and protein-based polymers (Table 57.2). 

PLA has also been blended with other nonbiodegradable polymers, such as poly(methyl methacrylate), acrylonitrile-butadiene-styrene, and Hytrel (from DuPont). Note that some polymers such as PE and PP are not compatible with PLA and cannot be used for compounding, unless special compatibilizers are used. 

A composite material is a two-phase or multiphase compact material with its components (phases) separated by interfaces which can be formed naturally or be manmade. One of the composite material phases is the matrix (phase I). It exists in the solid (crystalline or amorphous) state of aggregation. Within the matrix, particles are distributed discretely. This is phase II or disperse phase [23]. Biocomposites are composite materials made from natural fiber and petroleum-derived nonbiodegradable polymers like PP, PE, and epoxies or biopolymers like poly lactic acid (PLA), cellulose esters. Composite materials derived from biopolymer and synthetic fibers such as glass and carbon come under biocomposites. Biocomposites derived from plant-derived fiber (natural/biofi-ber) and crop/bioderived plastics (biopolymer/bioplastic) are likely more ecofriendly, and such biocomposites are sometimes termed green composites [24]. 

In a reported in vitro study of blood and cellular response to saturated AA-PEAs, the proliferation of endothelial cells adhered to SPEA substrates was much higher than on nonbiodegradable polymers like poly(n-butyl methacrylate) or polyethylene vinyl acetate copolymer (DeHfe et a/., 2005). 

The nonbiodegradable polymers used in matrix systems include hy-droxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, PEO, PAA, and various PHEMA derivatives. The most common biodegradable copolymer used is PGLA. 

Blending of PLA with nonbiodegradable polymers has been mainly conducted to overcome the drawbacks of PLA such as low heat deflection temperature (HDT), fragility, and poor barrier properties. A second objective to produce these blends is to create specific morphologies for medical applications. A more recent objective has been to increase the bio-based content of these polymer blends. Among the main polymer families that have been blended with PLA, polyolefins [3-7],... 

TABLE 16.1 Summary of the Mechanical Properties of Nonbiodegradable Polymer and PLA Blends... 

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