| Due to the good mechanical properties, in vitro and in vivo biocompatibility, anddegradability, magnesium (Mg) and its alloys have been regarded as the candidate forthe application as the biodegradable bone repair materials recently. However, theclinic use of Mg alloys is mainly restricted owing to the too fast initial corrosion ratein body fluids. Surface modification is an efficient way to protect Mg alloys andcontrol their corrosion behavior. Compared with the conventional coatings materials,mesoporous materials have the narrow distribution of pore size, large specific surfacearea and enhanced surface wettability, which favor for the promotion of biologicalproperties of the substrates. It could be hypothesized that Mg alloys coated withmesoporous coatings would exhibit suitable properties for bone repair.In this paper, mesoporous hydroxyapatite (HA) and mesoporous HA/45S5glass-ceramic composite coatings were respectively prepared on the glass or Mg alloysubstates using a sol-gel dip-coating method, and the process was optimized toprepare the uniform and crack-free coatings. Mesoporous HA with different porestructure was prepared using CTAB or F127as the templates by varing pH value andtemplate concentration. Therein, the mesoporous HA prepared using0.192g/mL ofF127template achieved the mesopores sized in3.17nm, and its pore volume andspecific surface area were0.38cc/g and211.7m2/g. The uniform and crack-freemesoporous coating with the thickness in~1.0μm was prepared on Mg alloysubstrate.Using simulated body fluids (SBF) as the corrosion medium, the influence of theporous structure and composition of the coatings on the corrosion behavior of Mgalloy was studied, and the mechanism of the mesoporous coatings to prevent Mg alloyfrom rapid corrosion was explored. The immersion tests showed that the presence ofmesoporous structure would decline the elastic modulus of the coating and the effectof residual stress on its breakdown, preventing the rapid cracking and peeling of HAcoating in the initial soaking stage and promoted the protection of the mesoporous HAcoating to the substrate. After soaking in SBF for10days, the corrosion rate of themesoporous HA coated Mg alloy was0.050mm/d, revealing that the coated sample has good corrosion resistance. Furthermore, the addition of glass-ceramic into themesoporous coating would decrease the difference of thermal expansion coefficientsbetween the coatings and substrates. Due to the downtrend of the residual stress, themesoporous composite coating didn’t peel after immersed in SBF for10days andprovided the enhanced protection to the substrate, that is, the corrosion rate of themesoporous composite coating coated Mg alloy was decreased to0.012mm/d.Meanwhile, the effect of the mesoporous structure on the surface wettability andbiological properties of the coatings was evaluated. The introduction of mesoporespromoted the specific surface area and surface roughness of the coatings, which led tothe decrease of water contact angle from67.8°to30.1°. In vitro cell assay revealedthat the improved surface area and wettability favored for the adsorption of proteins inculture media, being beneficial for the adhesion, spreading, proliferation ofosteoblasts and bone-related proteins expression. After being cultured for designedperiods, the cell density and proteins concentration in the mesoporous groups weremarkedly higher than those of the non-mesoporous group (*p<0.05).In conclusion, the mesoporous structure could prevent the rapid cracking andpeeling of the coatings, and promote their surface wettability and in vitrocytocompatibility. Therefore, the mesoporous coatings coated Mg alloy, being withgood corrosion resistance and biological properties, could be used as the bone repairmaterials. |
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