Abstract
Surface biofunctionalization is frequently applied to enhance the functionality and longevity of orthopedic implants. Here, we investigated the osteogenic effects of additively manufactured porous Ti6Al4V implants whose surfaces were biofunctionalized using plasma electrolytic oxidation (PEO) in Ca/P-based electrolytes with or without strontium. Various levels of Sr and Ca were incorporated in the oxide layers by using different current densities and oxidation times. Increasing the current density and oxidation time resulted in thicker titanium oxide layers and enhanced the release of Ca2+ and Sr2+. Biofunctionalization with strontium resulted in enhanced pore density, a thinner TiO2 layer, four-fold reduced release of Ca2+, and mainly anatase phases as compared to implants biofunctionalized in electrolytes containing solely Ca/P species under otherwise similar conditions. Different current densities and oxidation times significantly increased the osteogenic differentiation of MC3T3-E1 cells on implants biofunctionalized with strontium, when the PEO treatment was performed with a current density of 20 A/dm2 for 5 and 10 min as well as for a current density of 40 A/dm2 for 5 min. Therefore, addition of Sr in the PEO electrolyte and control of the PEO processing parameters represent a promising way to optimize the surface morphology and osteogenic activity of future porous AM implants.
Highlights
The demand for orthopedic bone implants that last for extensive lifetimes is increasing [1]
Different current densities and oxidation times significantly increased the osteogenic differentiation of MC3T3-E1 cells on implants biofunctionalized with strontium, when the plasma electrolytic oxidation (PEO) treatment was performed with a current density of 20 A/dm2 for 5 and 10 min as well as for a current density of 40 A/dm2 for 5 min
Our results suggest that the osteogenic behavior of the implants may be determined by a combination of surface morphology and Sr ion release, since an unfavorable surface morphology and too high doses of strontium may hamper the osteogenic differentiation of cells and induce apoptosis [65,66,67]
Summary
The demand for orthopedic bone implants that last for extensive lifetimes is increasing [1]. To support the longevity of cementless bone implants, proper fixation between implant and bone tissue is of utmost importance. Such implants are increasingly made using additive manufacturing (AM), as it allows for the free-form fabrication of customized (titanium) implants for a variety of purposes including the treatment of large bony defects [2,3,4]. The highly porous nature of such implants means that they possess vast surface areas, which make these implants prone to infection. Surface biofunctionalization of these AM implants has been, used to prevent implantassociated infections and to stimulate osteogenic properties [7] of AM porous implants. Such biofunctionalization procedures have been found to be challenging
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