New starch-based thermoplastic hydrogels for use as bone cements or drug-delivery carriers

The development of new biodegradable hydrogels, based on corn starch/cellul ose acetate blends, produced by free-radical polymerization with methyl met hacrylate monomer (MMA) and/or an acrylic acid monomer (AA), is reported. T he polymerization was initiated by a redox system consisting of a benzoyl p eroxide and 4-dimethlyaminobenzyl alcohol at low temperature. These hydroge ls may constitute an alternative to the materials currently used as bone ce ments or drug-delivery carriers. Swelling studies were carried out, as a fu nction of pH and temperature, in buffered solutions. The xerogels were furt her characterized by Fourier transform-infrared spectroscopy. Tensile and c ompression tests, and dynamic mechanical thermal analysis were used to asse ss the mechanical performance of the developed materials. The fracture surf aces were observed by scanning electron microscopy. The developed materials are sensitive to the pH, showing a clear reversible transition in a relati vely narrow interval of pH, which is just in the range of physiological con ditions. These properties make the materials developed in this study very p romising for biomedical applications. Fickian-type diffusion is the mechani sm predominant in these systems, except for the composition with a higher c oncentration of AA, that corresponds to the most desirable kinetical behavi or for controlled release (case II-transport mechanism). Furthermore, the r esults obtained in the mechanical tests are in the range of those reported for typical PMMA bone cements, showing that it is possible to develop parti ally degradable cements with an adequate mechanical behavior. (C) 1998 Kluw er Academic Publishers.