Surface modification tailors the characteristics of biomimetic coatings nucleated on starch-based polymers

This work describes the influence of surface pretreatments over the nucleation and growth of an apatite layer, formed by a biomimetic process, on which a bioactive glass is used as a precursor of the calcium-phosphate (Ca-P) formation on the materials surface. SEVA-C, a corn starch-based biodegradable blend, was used as substrate. The surfaces were pretreated during various periods by: (i) physical methods, namely ultraviolet radiation (u.v.), and over exposure to ethylene oxide sterilization (EtO); and (ii) chemical methods, namely potassium hydroxide (KOH) and acetic anhydride (CH₃CO)₂ etchings. The surface modifications, performed before the production of the biomimetic coatings, resulted in a faster formation of Ca-P nuclei during the first stages of SBF immersion, particularly in the case of the KOH etching. In this case, it was possible to observe a decrease in the average surface roughness, as measured by laser profilometry, and an increase of the hydrophilicity of the material, which was evident from a clear increment in the water-uptake ability and quantified by contact angle measurements. With this treatment it was possible not only to reduce the induction period for the formation of a well defined and dense apatite-like layer, as observed by scanning electron microscopy (SEM), but also to improve the adhesion of the Ca-P layer to the substrate, as confirmed by the adhesion strength tests. For all the studied pre-treatments, the composition of the films, analyzed by energy dispersive spectroscopy (EDS) and identified by thin-film X-ray diffraction (TF-XRD), seems to be very similar to that of human bone apatites.