Degradation controlled release polymers

Processing at 100°C Degradation onset is >200°C Low Tg can limit stability Extrudable at moderate temperatures, >100°C Excellent CR polymer Extrudable at low temperatures, >60°C Excellent controlled release polymer but non-biodegradable... 

Tyrosine-derived polycarbonates have important advantages when used in the design of implantable, degradable controlled release systems. First, all members of this series of polymers are amorphous materials with relatively low glass transition temperatures which are a function of the pendent chain length (Tdhte 1). X-ray diffraction... 

A variety of different formulations for controlled release polymers exist including microparticles, microcapsules and microspheres. Microparticles range in size from 1-200 pm, while particles with a diameter smaller than 1 pm are called nanoparticles. Microcapsules are microparticles which have the substance of interest enclosed in a shell of degradable polymer. Microcapsules however are characterized by a relatively fast release of large amounts of the enclosed substance. Microspheres (Figi 1), on the other hand, are monolithic in structure, Le. have the substance unifomdy distributed within the polymer layer. This distribution results in a more uniform release over longer periods of time. We selected such microspheies prepared from poly(lactide-glycolide) copolymers to develop our sensors. 

The rate of drug release (E) from the eroding matrix is controlled by (a) the chemical properties of the system - the hydrolytic and the neutralizing process at the boundary of the device, catalytic degradation of the polymer and the intrinsic backbone reactivity, and (b) several concomitant physical processes such as water diffusivity, water solubility, water partitioning, etc. 

Poly-j3-malate is readily degraded completely to L-malic acid under both acid and base conditions [108], and it can also be hydrolyzed by enzymes within the cell [105,106]. Recently, several bacteria were isolated which were able to utilize poly-/i-malate as sole carbon source for growth [109]. Because the polymer is biodegradable and bioadsorbable, it is of considerable interest for pharmaceutical applications, especially in controlled-release drug delivery systems [97,98]. Chemical routes to poly-/ -malate are expected to provide materials with various properties [110]. 

Panyam J, Dali MM, Sahoo SK et al (2003) Polymer degradation and in vitro release of a model protein from poly(D, L-lactide-co-glycolide) nano- and microparticles. J Control Release 92 173-187... 

Another aspect related to control release of drugs concerns the type of structures that currently appear to be working. Not unexpectedly, because of compatibility and degradation purposes, most of the effort on the control release formulations includes polymers that have both a hydrophobic and hydrophilic portion with the material necessarily containing atoms in addition to carbon. Another concern is that the products of degradation are not toxic or do not form toxic materials. It has also been found that amorphous materials appear to be better since they are more flexible and permit more ready entrance of potential degrad-ative compounds. 

Polymers from renewable sources have received great attention over many years, predominantly due to the environmental concerns. Potato starch is a promising biopol5mier for various food, pharmaceutical, and biomedical applications because of its higher water solubility that raises its degradability and speed of degradation non-toxicity, easy availability, and abundancy. The role of starch for tissue engineering of bone, bone fixation, carrier for the controlled release... 

Bernkop-Schniirch, A., G.H. Schwarz, and M. Kratzel. 1997. Modified mucoadhesive polymers for the peroral administration of mainly elastase degradable therapeutic (poly)peptidcs. J Control Release 47 113. 

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