Creation of microrough surface on sintered bioactive glass microspheres

Bioactive glasses are surface-active, generally silica-based, synthetic materials that form a firm chemical bond to bone. The aim of this study was to further enhance the bioactivity of glasses by creating a microroughness on their surface. Microroughness increases potential surface area for cell attachment and biomaterial-cell interactions. Three bioactive glasses of different composition were studied. Each material was flame-sprayed into microspheres, and a selected fraction of the spheres (250-300 microm) was sintered to form porous bioactive glass specimens. To create microrough surfaces, different acid etching techniques were tested. Atomic force microscopy (AFM) and back-scattered electron imaging of scanning electron microscopy (BEI-SEM) were used to characterize surface roughness. The degree of roughness was measured by AFM. A novel chemical-etching method, developed through intensive screening of different options, was found consistently to create the desired microroughness, with an average roughness value (R(a)) of 0.35-0.52 microm and a root mean-square roughness value (R(rms)) of 0.42-0.64 microm. Microroughening of the glass surface was obtained even in the internal parts of the porous glass matrices. Measured by BEI-SEM, the etching of a bioactive glass surface did not interfere with the formation of the characteristic surface reactions of bioactive glasses. This was confirmed by immersing the etched and control glass bodies in a simulated body fluid and tris(hydroxymethyl) aminomethane/HCl. The etching process did not significantly affect the mechanical strength of the sintered bioactive glass structures. Based on these experiments, it seems possible to create a reproducible microroughness of appropriate size on the surface of porous bioactive glass. The biologic benefits of such a surface treatment need to be validated with in vivo experiments.