Polyhydroxybutyrate-valerate blends

Aliphatic polyesters based on monomers other than a-hydroxyalkanoic acids have also been developed and evaluated as drug delivery matrices. These include the polyhydroxybutyrate and polyhydroxy valerate homo- and copolymers developed by Imperial Chemical Industries (ICI) from a fermentation process and the polycaprolactones extensively studied by Pitt and Schindler (14,15). The homopolymers in these series of aliphatic polyesters are hydrophobic and crystalline in structure. Because of these properties, these polyesters normally have long degradation times in vivo of 1-2 years. However, the use of copolymers and in the case of polycaprolactone even polymer blends have led to materials with useful degradation times as a result of changes in the crystallinity and hydrophobicity of these polymers. An even larger family of polymers based upon hydroxyaliphatic acids has recently been prepared by bacteria fermentation processes, and it is anticipated that some of these materials may be evaluated for drug delivery as soon as they become commercially available. 

Specifically, 70-30 parts poly(hydroxy-butyrate-co-hydroxyvalerate) (4 mol% valerate) or polyhydroxybutyrate was mixed with 30-70 parts PCL in an internal mixer at 100° or 160°C in the presence of 0-0.5 parts DCP or DBP radical initiator. Blends were characterized by SEM, mechanical properties, selective solvent extraction, and FTIR. 

PCL), polylactic acid (PLA), polyhydroxybutyrate-co-valerate (PHBV), and polyesteramide. Some starch-based blends have been commercialized such as Mater-Bi (Novamont) or Bioplast (Biotec). 

Biodegradation experiments of polymer-films in marine and soil environments indicated that, in general and depending on the environment, biodegradation rates for unblended polymers were polyhydroxybutyrate-C(9-valerate > cellophane > chitosan > polycaprolactone. Results from blends are more difficult to interpret since different biodegradation rates of the component polymers and leaching of plasticizers and additives can impact the data [216]. 

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