High-resolution morphometric analysis of human osteoblastic cell adhesion on clinically relevant orthopedic alloys

Understanding the cellular basis of osteoblastic cell-biomaterial interaction is crucial to the analysis of the mechanism of osseointegration, a requirement of long-term orthopedic implant stability. Clinically, the amount of bone ingrowth is variable, and cellular parameters that influence ingrowth have yet to be clearly determined. In this study, two clinically relevant orthopedic alloys, titanium Ti6A14V (Ti) and cobalt-chrome-molybdenum (CC), were used for a comparative analysis of primary human osteoblastic cell adhesion and spreading, where cell adhesion represents the initial interaction between cellular elements and the biomaterial surface. The kinetic profile of adhesion revealed enhanced cell attachment upon rough Ti surfaces relative to rough CC. Using confocal laser scanning microscopy (CLSM), we observed that, during the first 12 h of contact with the substratum, osteoblastic cells were relatively less spread on rough Ti, whereas cells appeared elongated with multiple cellular extensions on rough CC. Focal adhesion contacts, as indicated by vinculin immunostaining, were distributed throughout the cells adhering to Ti, but were relatively sparse and localized to cellular processes on CC. Furthermore, three-dimensional CLSM reconstruction analysis indicated the presence of vinculin at all membrane-to-surface contact points on both Ti and CC. On Ti, these contact points closely followed the surface contour, whereas, on CC, they were restricted to relative topographic peaks only. Actin cytoskeletal reorganization was prominent in cells cultured on Ti, with stress fibers arranged throughout the cell body, whereas, on CC, actin filaments were sparse and localized primarily to cellular extensions. Because cell attachment mechanisms are likely to influence signal transduction and regulation of gene expression, these early differential responses of osteoblastic cells on Ti and CC may have functional implications on subsequent extracellular matrix mineralization and bone ingrowth at the cell-biomaterial interface.