Preparation and characterization of poly(epsilon-caprolactone) polymer blends for the delivery of proteins.

A series of ternary blend matrices, based on high- and low-molecular-weight poly(epsilon-caprolactone) (PCL) and a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer (Synperonic L61), has been developed for the delivery of proteins. The inclusion of Synperonic L61 served to enhance the water content of the matrix available for protein diffusion. Blends comprising high-molecular-weight PCL (PCLH) and Synperonic L61 alone were found by scanning electron microscopy to be incompatible over a wide composition range. The addition of a low-molecular-weight PCL (PCLL) enhanced compatibility of the polymeric components. Analysis of the dynamic mechanical and thermal properties of these blends showed a significant shift in the glass transition temperature of the material (-38 to -55 degrees C), as the weight fraction of Synperonic L61 increased to 30 wt%, indicative of limited miscibility of the components in the non-crystalline phase. All ternary blended matrices showed a higher degree of hydration relative to homogeneous PCLH. The maximum water content could be modified by adjusting the weight fraction of Synperonic L61 in the blend. The rate of release of a model protein, bovine serum albumin (BSA), from matrices containing Synperonic L61 was considerably higher than that from PCLH and PCLH/PCLL alone. Analysis of the release mechanisms of BSA from these matrices suggested that, whilst diffusion was the predominant mode of protein transport, the elution of Synperonic L61 from blended matrices during the dissolution caused a notable deviation from Fickian control.