Nondegradable polymers poly

Sasaki et al. [151] prepared nondegradable disc-type ophthalmic inserts of P- blockers using different polymers. They found that inserts made from poly(hydroxypropyl methacrylate) were able to control the release of tilisolol hydrochloride. 

Despite successful results from in vitro studies, however, the clinical applications of systems that are based on polyNlPAAm may be limited, becanse poly-NIPAAm is nondegradable and insoluble. In addition, a major problem of polyNIPAAm-based drug deUvery systems is that thermal treatment is required for controlled destabilization of the micelles and concurrent drug release, which is not always feasible in clinical situations. Therefore, to overcome the disadvantages of polyNIPAAm, controlled biodegradable systems that use polyester block copolymers as thermosensitive polymers have been investigated. 

Poly(ethylene glycol) (PEG) is a nondegradable synthetic polymer that has been extensively studied as a polymer-drug carrier. PEG is hydrophilic and is well tolerated in human. The main disadvantage of PEG is that the polymer backbone is not biodegradable in vivo. PEG has been used to conjugate anticancer drugs such as doxorubicin [311], camptothecin... 

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. 

Nondegradable model polymers such as polystyrene are not realistic therapeutic systems. This approach is difficult to generalize to hydrophilic polymer chain adsorption on biodegradable materials such as poly(lactic acid) (MiiUer, 1991). 

In general, nonabsorbable sutures can retain their tensile strength longer than 2 months [113]. The synthetic polymers used to make nondegradable sutures include polypropylene (PP), polyamides, polyesters such PET and polybutylene terephthalate (PBT), and polyether-ester based on poly(tetramethylene glycol), 1,4-butanediol, and dimethyl terephthalic acid [114]. The base polymer and filament configuration for common nonabsorbable sutures are summarized in Table 8.2. 

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