Nondegradable polymers polyurethanes

One particular hydrophobic polymer, EVAc, has been investigated extensively as a matrix system for protein delivery. This polymer is biocompatible, a major consideration because of the interest in developing systems for human health. Other classes of hydrophobic polymers, like silicone elastomers and polyurethanes, may also be useful for controlled protein delivery, although there are fewer examples available in the literature. Nondegradable, hydrophilic polymers, such as poly(2-hydroxyethyl methacrylate) [p(HEMA)], are also biocompatible but usually release proteins over a relatively short period. However, a few examples oflong-term release of peptides and proteins from hydrophilic polymers are available. Longterm release of peptides from devices that employ cross-linked p(HEMA) as rate-limiting barriers has been reported (Davidson et al, 1988). The use of hydrophilic polymers for protein release is discussed in more detail elsewhere in this volume. 

Recent investigations have developed polyurethane polymers as scaffold materials. Polyurethane is an elastomeric polymer that is typically nondegradable (Table 37.2, Figure 37.2). Positive attributes, such as flexible mechanical strength and biocompatibihty, has led to the synthesis of degradable polyurethanes with nontoxic diisocyanate derivatives [47,94-96]. Studies have shown that polyurethane scaffolds support cell attachment with chondrocytes, bone marrow stromal cells, and cardiomyocytes [96-98]. 

The use of nondegradable synthetic polymers such as silicone (Lundborg et al. 1982 Kakinoki et al. 1995), polyethylene (Madison et al. 1987), polyurethanes (Robinson et al. 1991), Teflon (Lanzetta et al. 

---