High modulus thermoplastic segmented polyurethane/poly(L-lactide) blends as potential candidates for structural implantable drug delivery systems: I. Structure-properties relationship study

Structural polymers with a high modulus of elasticity have the necessary properties for drug eluting implants which are continuously subjected to long-term loading. The range of polymers that can be used for this purpose is severely limited by the demanding requirements, such as biocompatibility, specific mechanical properties and the capability to control the release rate of incorporated drugs. A new series of blend compositions was developed for these applications, based on a combination of a high modulus thermoplastic segmented polyurethane (TSPU) (shore D hardness) and poly(L-lactide) (PLLA). The microstructures and properties of these blends were characterized by DSC, tensile tester, FTIR, SEM, WAXD, transmitted light microscopy and elastic recovery testing. The two polymers were found to be immiscible, irrespective of the weight ratio between them, but still compatible, although the compatibility was reduced in blends with equal weight ratios or thereabouts. The dispersed phase in any case spontaneously organized into microspheres embedded within the continuous phase. PLLA could recrystallize as both the dispersed and the continuous phases. The ultimate mechanical properties and the elastic load-recovery of the blends were largely dependent on the ratio between the polymers. The ability of these blends to create self-assembled microspheres and the fact that they did not require a compatibilizer or plasticizer point to the potential of these systems to be used for structural implantable drug delivery systems.