Bioerodible polymer

Poly(orthoesters) represent the first class of bioerodible polymers designed specifically for dmg deUvery appHcations (52). In vivo degradation of the polyorthoester shown, known as the Al amer degradation, yields 1,4-cydohexanedimethanol and 4-hydroxybutyric acid as hydrolysis products (53). 

Hie ester linkage of aliphatic and aliphatic-aromatic copolyesters can easily be cleaved by hydrolysis under alkaline, acid, or enzymatic catalysis. This feature makes polyesters very attractive for two related, but quite different, applications (i) bioresorbable, bioabsorbable, or bioerodible polymers and (ii) environmentally degradable and recyclable polymers. 

Grossman, S. A., Reinhard, C., Colvin, O. M., Chasin, M., Brundrett, R., Tamargo, R., and Brem, H., The intracerebral distribution of BCNU delivered by surgically implanted bioerodable polymers. Submitted. 

The development of a bioerodible implant capable of releasing controlled amounts of a contraceptive steriod from a subcutaneous implant for periods of time ranging from three months to about a year has been in progress for many years. The three principal bioerodible polymers currently in use are copolymers of lactic and glycolic acid (25), poly(e-caprolactone) (26), and poly (ortho esters) (14). The desire to develop such a contraceptive system was the principal motivation for the initial development of the poly(ortho ester) polymer system. 

It has been demonstrated that a variety of different polyphosphazenes can be developed as biomaterials, membranes or hydrogels, bioactive polymers, and bioerodible polymers. As with most new areas of polymer chemistry and biomaterials science, molecular design forms the basis of most new advances, but the rate-controlling step is the testing and evaluation of the materials in both in vitro and in vivo environments. This is particularly true for polyphosphazenes where the availability of research quantities only has limited the... 

Kohn, J., and Langer, R., A new approach to the development of bioerodible polymers for controlled release applications employing naturally occurring amino acids, in Proceeding of the ACS Division of Polymeric Materials. Science and Engineering. American Chemical Society, 1984, Vol. 51, pp. 119-121. 

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. 

DIRECT SYNTHESIS FROM N-SILYL-PHOSPHORAMINES CARBORANYL DERIVATIVES BIOACTIVE AND BIOERODABLE POLYMERS (STEROIDS, DOPAMINE, PROCAINE, ETC.)... 

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

HB Rosen, J Kohn, K Leong, R Langer. Bioerodible polymers for controlled release systems. In DST Hsieh, ed. Controlled Release Systems Fabrication Technology, Vol n. Boca Raton, FL CRC Press, 1988, pp 83-110. 

Bioerodible polymers offer a unique combination of properties that can be tailored to suit nearly any controlled drug delivery application. By far the most common bioerodible polymers employed for biomedical applications are polyesters and polyethers (e.g., polyethylene glycol), polylactide, polyglycolide and their copolymers). These polymers are biocompatible, have good mechanical properties, and have been used in... 

It is important to distinguish between erosion and degradation. Erosion is mass loss from a bioerodible polymer and may be a consequence of polymer dissolution or degradation of the polymer backbone, followed by dissolution of the degradation products. Degradation typically occurs by hydrolysis of the polymer backbone, the kinetics of which is a function of the polymer chemistry. Thus, erosion is the sum of several elementary processes, one of which may be polymer degradation. 

Chickering, D.E.lll, Jacob, J.S., and Mathiowitz, E., Bioadhesive microspheres. 2. Characterization and evaluation of bioadhesion involving hard, bioerodible polymers and soft tissue. Reactive Polymers, 25 189-206 (1995). 

Bioerodible polymers having pendant functional groups are of particular interest, since they are capable of covalent pro-drug formation. Acemoglu [60] prepared... 

Figure 3.21 Bioerodable polymers can be used for the controlled release of pharmaceutical molecules (black clipscs). Ideally, hydrolysis of the implanted matrix polymer should occur at the polymer surface only so that the drug molecules are released at a constant rate—a so-called zero-order release profile.

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

Use of Bioerodible Polymers in Self-Regulated Drug Delivery Systems... 

Heller, J. Baker, R.W. Theory and practice of controlled drug delivery from bioerodible polymers. In Controlled Release of Bioactive Materials Baker, R., Ed. Academic Press New York, 1980 1-17. 

Fig. 26 Cross-sectional view of a bioerosion-regulated hydrocortisone delivery system, a feedback-regulated drug delivery system, showing the drug-dispersed monolithic bioerodible polymer matrix with surface-immobilized ureases. The mechanism of release and time course for the urea-activated release of hydrocortisone are also shown. (From Ref > 1)...

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