Effect of Molar Mass and Water Solubility of Incorporated Molecules on the Degradation Profile of the Triblock Copolymer Delivery System

The purpose of this study was to investigate the effects of size and type of incorporated model molecules on the polymer degradation and release profile from thermosensitive triblock copolymer based controlled delivery systems. In vitro release of the incorporated molecules demonstrated slow release for risperidone (molecular weight (M-w) = 410.48 Da; partition coefficient (K-o/w) = 3.49), while bovine serum albumin (BSA) (M-w = similar to 66,400 Da; K-o/w = 0.007) and insulin (M-w = 5808 Da; K-o/w = 0.02) showed initial burst release followed by controlled release. The proton NMR, Gel Permeation Chromatography, and Cryo-SEM studies suggest that the size and partition coefficient of incorporated molecules influence the pore size, polymer degradation, and their release. In spite of using a similar polymer delivery system the polymer degradation rate and drug release notably differ for these model molecules. Therefore, size and oil-water partition coefficient are important factors for designing the controlled release formulation of therapeutics from triblock copolymer based delivery systems.