Phenotypic changes in hMSCs induced by contact with titanium surfaces

Objectives: Hydrophilic micro-rough implant topographies with high surface free energy significantly augment osseointegration in endosseous dental and orthopaedic titanium (Ti) implants in vivo. These substrates have previously been shown to have effects on the osteogenic differentiation of committed osteoblasts and also multipotent adult mesenchymal stromal cells (MSCs) in vitro, resulting in earlier differentiation and bone matrix elaboration. These effects may be triggered in the cells with contact to different Ti surfaces. This study examines the differences in cellular adherence and morphology, and how these may influence the expression of “stemness” related genes, to induce enhanced osteogenic differentiation.

Methods: Cellular adherence of human MSCs to polished (P), hydrophobic rough (SLA) and hydrophilic rough (modSLA) Ti surfaces was assessed at very early times by the CyQuant GR assay (Sigma), and morphological differences were studied by electron microscopy. Real time polymerase chain reaction (RTPCR) mini arrays were used to examine transcriptional changes in 96 “stemness” related genes 24 hour (h) and 7 days post seeding. Calcium deposition onto the Ti surfaces was assessed using the Alizarin Red stain.

Results: The findings indicate human MSCs attach at higher numbers to polished rather than rough Ti surfaces through a time course of 5 minute to 24 h. The hMSCs were observed to adapt a stellate morphology on the polished surfaces by 1 hour, while they remained in a stretched form on the rough. Gene expression patterns suggest a relatively early induction of osteogenic commitment by cells on the rough surfaces, which was concomitant with higher levels of calcium mineral deposition.

Conclusions:  The data suggests that uncommitted multipotent hMSCs cells may undergo accelerated osteogenic differentiation due to topographical and chemical stimuli on modified Ti surfaces and that this enhanced differentiation underlies the different clinical efficacies of various Ti surfaces.