Osteogenic Performance Evaluation of Nanoscale Hydroxyapatite Surface Treatment on Porous Titanium Compared to an Untreated Solid Titanium Surface

Introduction: Advances to interbody implant surface characteristics are being pursued to promote integration with the surrounding environment and to ultimately improve clinical outcomes. Surface chemistry and topography profoundly impact the implant-host interface, by influencing protein adsorption, cell response and functionality. This study evaluates the osteogenic performance of a nanoscale hydroxyapatite surface treatment on porous titanium ("treated") compared to untreated solid titanium ("untreated") and tissue culture plastic (TCP) as a control. The performance quantified by evaluating the responses of human mesenchymal stem cells (hMSCs) and human osteoblasts (hOBs).

Methods: The responses of hMSCs and hOBs on treated, untreated, and TCP surfaces were measured using: 1) cell proliferation via MTT assay at 7 days in two media (growth and differentiation), 2) osteogenic differentiation assessed through alkaline phosphatase (ALP) activity at 7 days, and 3) mineralization evaluated using Alizarin Red staining at 7 and 14 days.

Results: The treated surface significantly enhanced cellular activity compared to the untreated surface. MTT assays showed a minimum 1.6-fold increase in cell proliferation for both hMSCs and hOBs on treated surfaces at 7 days. No significant differences were noted between untreated and TCP surfaces.

hMSCs on treated surfaces exhibited 1.81-fold greater ALP activity than TCP and 1.79-fold greater than untreated, while hOBs showed 2.34-fold and 1.38-fold increases, respectively.

Microscopic (qualitative) Alizarin Red observation revealed that the treated surface had more reddish nodular regions than the untreated and TCP surfaces at both time points and for both cell lines. Quantitative analysis confirmed the qualitative analysis, where the treated surface had statistically significantly higher mineralized extracellular matrix than the untreated and TCP surfaces at both times.

Conclusion : In vitro results indicate that nanoscale hydroxyapatite surface treatment on porous titanium enhances osteogenic responses compared to untreated surfaces. Further clinical studies are needed to assess in vivo responses.