Osteogenic differentiation of human mesenchymal stromal cells on surface-modified titanium alloys for orthopedic and dental implants

Surface properties of titanium alloys, used for orthopedic and dental applications, are known to affect implant interactions with host tissues. Osteointegration, bone growth and remodeling in the area surrounding the implants can be implemented by specific biomimetic treatments; these allow the preparation of micro/nanostructured titanium surfaces with a thickened oxide layer, doped with calcium and phosphorus ions. We have challenged these experimental titanium alloys with primary human bone marrow stromal cells to compare the osteogenic differentiation outcomes of the cells once they are seeded onto the modified surfaces, thus simulating a prosthetic device-biological interface of clinical relevance.

A specific anodic spark discharge was the biomimetic treatment of choice, providing experimental titanium disks treated with different alkali etching approaches. The disks, checked by electron microscopy and spectroscopy, were subsequently used as substrates for the proliferation and osteogenic differentiation of human cells. Expression of markers of the osteogenic lineage was assessed by means of qualitative and quantitative PCR, by cytochemistry, immunohistochemistry, Western blot and matrix metalloprotease activity analyses.

Metal surfaces were initially less permissive for cell growth. Untreated control substrates were less efficient in sustaining mineralized matrix deposition upon osteogenic induction of the cells. Interestingly, bone sialo protein and matrix metalloprotease 2 levels were enhanced on experimental metals compared to control surfaces, particularly for titanium oxide coatings etched with KOH.

As a whole, the KOH-modification of titanium surfaces seems to allow the best osteogenic differentiation of human mesenchymal stromal cells, representing a possible plus for future clinical prosthetic applications.