On the importance and mechanisms of burst release in matrix-controlled drug delivery systems

Preparation and characterization of poly(l-lactic acid) foams

http://www.nanoparticles.org/EMU/SurfMod/Wk12/JCR-05-102-313.pdf

Microencapsulation by solvent extraction/evaporation: reviewing the state of the art of microsphere preparation process technology.

Increased and accelerated global economic activities over the past century have led to interlinked problems that require urgent attention. The current patterns of production and consumption have raised serious concerns. In this context, greater emphasis has been put on the concept of sustainable economic systems that rely on technologies based on and supporting renewable sources of energy and materials. Average UK households produce around 3.2 million tonnes of packaging waste annually whereas 150 million tonnes of packaging waste is generated annually by industries in the UK. Hence, the development of biologically derived biodegradable polymers is one important element of the new economic development. Key among the biodegradable biopolymers is a class known as polyhydroxyalkanoates. Polyhydroxyalkanoates (PHAs) are a family of polyhydroxyesters of 3-, 4-, 5- and 6-hydroxyalkanoic acids, produced by a variety of bacterial species under nutrient-limiting conditions with excess carbon. These water-insoluble storage polymers are biodegradable, exhibit thermoplastic properties and can be produced from renewable carbon sources. Thus, there has been considerable interest in the commercial exploitation of these biodegradable polyesters. In this review various applications of polyhydroxyalkanoates are discussed, covering areas such as medicine, agriculture, tissue engineering, nanocomposites, polymer blends and chiral synthesis. Overall this review shows that polyhydroxyalkanoates are a promising class of new emerging biopolymers.

Polyhydroxyalkanoates: biodegradable polymers with a range of applications

Preparation of microspheres by the solvent evaporation technique

Influence of formulation methods on the in vitro controlled release of protein from poly (ester) microspheres

Degradation of poly(ester) microspheres.

Biodegradable microspheres of poly(L-lactide) and copolymers of lactide and glycolide have been prepared by spray drying. Degradation studies of these microspheres using residual mass measurements, viscometry and gel permeation chromatography indicated the entire mass of polyester matrices was maintained for 10, 30 days and 6–10 months for 50:50 and 85:15 copolymers and poly(L-lactide), respectively. The continuous drop in polymer intrinsic viscosity and molecular weight during hydrolysis suggested that matrix degradation began as soon as these microspheres were placed in the buffer and that their degradation proceeded through random-chain scission. Protein release, using bovine serum albumin micro-spheres, showed that release from 50:50 copolymer was independent of polymer molecular weight over a range from 31,000 to 93,000. The release was, however, dependent on the polymer composition and BSA loading in the microspheres. A burst-effect was found in the release study for microspheres prepared from copolymers. The identity and integrity of the released protein was confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis on the release products of polymeric microspheres containing BSA, FPL-R and EcoBacR-Plus vaccines. These results suggested that the release BSA (or vaccine) from polymeric microspheres could be sustained for up to one month.

H.T. Wang

Papers

Influence of formulation methods on the in vitro controlled release of protein from poly (ester) microspheres

Degradation of poly(ester) microspheres.

Controlled Release of Protein and Vaccines from Poly(Ester) Microspheres in Vitro