Evaluation of the influence of the addition of biodegradable polymer matrices in the formulation of self-curing polymer systems for biomedical purposes

The solid phase of self-curing formulations of poly(methyl methacrylate) was modified by different biodegradable polymer matrices, such as poly(l-lactic acid), poly(β-hydroxybutyrate) and thermoplastic starches (TPSs). The aim of this modification was the acquisition of a short- to medium-term drug delivery system to release bisphosphonates for hard tissue treatment. Different physico-chemical characterization techniques were used in order to determine the influence of these matrices and their mechanical capacity, in vitro behaviour, curing parameters, residual monomer content and surface topography for the preparation of the self-curing formulations. The incorporation of the polyesters did not induce an increase in water uptake capacity of the system due to their apolar aliphatic character. On the other hand, TPSs exhibited values of water absorption up to 15.3%, related with their hydrophilic chemical structure, dependent on the commercial formulation and the particle size distribution of the powder. The modifications of the solid phase led in all cases to a decrease in the mechanical behaviour of the material, although the formulations modified with TPS were in the range of accepted values according to standard specifications. The immersion of TPS formulations in a simulated physiological environment (phosphate buffer solution, pH 7.4, 37 °C) conducted to a surface porosity related with release of plasticizers of the domains of the biodegradable component of the formulation. Finally drug release capacity was studied by loading the material with Ibandronate, observing high dependence with the kind of TPS added, as well as its particle size.