Calcium Carbonate Microparticles Growth Templated by an Oxadiazole-Functionalized Maleic Anhydride-co-N-vinyl-pyrrolidone Copolymer, with Enhanced pH Stability and Variable Loading Capabilities

The crystallization characteristics of CaCO3 microparticles from supersaturate aqueous solutions in the presence of a conjugate drug-copolymer has been investigated, comparative with particles prepared in similar conditions but without polymer. The polymer conjugate, P(NVP-MA-Ox), is based on poly(N-vinylpyrrolidone-co-maleic anhydride) as support and 2-amino-5-(4-methoxy-phenyl)-1,3,4-oxadiazole. The influence of the polymer/CaCO3 ratio on the microparticles characteristics and the particles' pH stability was deeply investigated by scanning electron microscopy, X-ray diffraction, flow particle image analysis, particles charge density, and electrophoresis. The presence of P(NVP-MA-Ox) as a template in the CaCO3 crystallization process induced the particles stability increase up to the polymer isoelectric point located at pH = 3.4, irrespective of carbonate content in composite particles. The adsorption capacity of the microparticles as a function of their characteristics was tested using methylene blue. The sorption capacity of composite materials increased with the increase of polymer content in the composites, suggesting that the sorption process takes place mainly by electrostatic interactions.