Osteogenic and angiogenic properties of strontium incorporated titanium implants

Abstract

In the current day and age, osteogenic bone implants are important to reduce healing time and infections after bone implantation. To help induce bone formation, the implant surface can be biofunctionalized with different agents. A promising surface modification technique used to treat titanium implants is Plasma Electrolytic Oxidation (PEO). In previous research, strontium has shown to be a bone inducing agent, both in implant surfaces and in culture by stimulating mesenchymal stem cells (MSCs) to form bone. To explore this technique and its merits further, the effect of strontium and PEO combined was investigated by looking at the effect of strontium and strontium-incorporated implants on the viability, metabolic activity and osteogenic differentiation of human MSCs. In these experiments a 1 hour seeding time and 2 hour seeding time group were assessed, in which the cells were able to attach to the implant for 1 or 2 hours in a cell immersion, after which the implants with only the attached cells were cultured further. The implants groups were, based on the strontium concentration in the electrolyte, NT (not treated with PEO), PT, PT + 0.3 M Sr, PT + 0.5 M Sr and PT + 1 M Sr. The effects of strontium on the mutual effects of MSCs and endothelial cells (ECs) were also investigated, since the interaction of these cells is vital in the formation of blood vessels. To investigate these two topics, firstly 5 types of implants surfaces were created and their characteristics were analyzed. Then the effects of these implants on viability, metabolic activity and differentiation of MSCs were assessed. The results showed an increasing viability of MSCs on implants with strontium incorporated into them. Metabolic activity and differentiation improved in MSCs on the two medium strontium concentration incorporated implants, although there were differences between different seeding times of MSCs. Due to differences in morphology of the strontium incorporated implants, and presumably the oxide layer thickness, these results could both be the result of these material characteristics and/or of the strontium release of the implants. In future experiments, the implant characteristics must be created more similarly, so the effect of the single variable strontium can be assessed. Concerning the effects of strontium on the mutual effects of MSCs and ECs, co-culture with MSCs decreased the gene expression of VEGF-A, a marker of early angiogenesis.