Systemic delivery, using poly matrix

Use of basic excipients. As discussed in Sect. 4.2.4, a typical poly(ortho ester) device will be completely permeated by water in a matter of a few weeks so that the use of acidic excipients is limited to delivery systems having a maximum lifetime of about one month. However, ortho ester linkages are stable in devices containing a base, and very long erosion times are possible if the polymer is stabilized with a base which prevents hydrolysis even though the matrix is completely permeated by water. A plausible mechanism for erosion of devices that contain the base Mg(OH)2 is shown in Fig. 18. According to this mech-... 

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. 

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