Bioerodable Biological

This subject can be considered in terms of five different types of molecules or materials (a) biologically inert, water-insoluble polymers (b) water-insoluble polymers that bear biologically active surface groups (c) water-swellable polymeric gels, or amphiphilic polymers that function as membranes (d) water-insoluble but bioerodable polymers that erode in aqueous media with concurrent release of a linked or entrapped bioactive molecule and (e) water-soluble polymers that bear bioactive agents as side groups. 

J Heller. Controlled release of biologically active compounds from bioerodible polymers. Biomaterials 1 51, 1980. 

Alkyl monoesters of poly(vinyl methyl ether-maleic anhydride) (PVM-MA) are bioerodible acidic polymers that are used to control drug release. In biological fluids with poor buffering capacity, drug release from the polymers and their dissolution are slowed owing to the lower pH on the polymer surface. We studied whether the release of timolol from matrices of monoisopropyl ester of PVM-MA in vitro and in vivo in rabbits eyes could be affected by disodium phosphate in the matrices. Addition of disodium phosphate to the matrices doubled the release rate of timolol in vitro, but it did not affect the bulk pH of the dissolution medium. On the basis of the timolol concentrations in the tear fluid and in systemic circulation, disodium phosphate seems to accelerate drug release in vivo also. Disodium phosphate probably affects the rate of dmg release by increasing the microenvironmental pH on the polymer surface. 

J. Heller, Controlled Release of Biologically Active Compounds from Bioerodible Polymers, Biomaterials 1, 51 (1980). 

Ng [2,3] prepared bioerodible copoly(ortho esters) consisting of the Step 2 product with monomethyl polyethylene glycol ether termini and 1,4-cyclohex-anedimethanol and either an a-hydroxy carboxylic acid, (II), or A -methyl-di-ethanol amine (III), for use as bioerodible matrices for the sustained release of biologically active agents. Other dioxalane bioerodible analogues were prepared by Ng [4] in an earlier investigation. 

Protection and Deprotection of Pendent Hydroxyl Groups. The presence of hydroxyl oups in the side chains of polyphosphazenes is required for a variety of purposes, including the preparation of water-soluble or bioerodible polymers, and for the introduction of sites for the linkage of biologically active or electro-optical units to the polymer. Two typical approaches are shown in Scheme V. 

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