Osteoblast Attachment to Titanium Surfaces as a Function of Surface Charge

Heipp P.S.¹, Chapovsky F.², Brennan D.J.³, Pourezzaei K.⁴, Beard R.B.⁴, Hickok N.², DiNardo N.J.^1,3, Tuan R.S.² and Marcolongo M.^1,5

¹School of Biomedical Engineering
³Deptartment  of Physics
⁴Deptartment  of Electrical and Computer Engineering
⁵Deptartment of Materials Engineering
Drexel University
Philadelphia PA 19104
psheipp@drexel.edu
(215) 895-1283

²Dept. of Orthopaedic Surgery Research,
Thomas Jefferson University
Philadelphia PA

Osseointegration of orthopaedic implants is paramount to the success of the devices for non-cemented hip and knee prostheses. The ability of the surface to stably interact with the extracellular matrix is critical for osseointegration. We examined osteoblast attachment to titanium surfaces in vitro by utilizing an electric field generating device to change the polarity and magnitude of the surface charge. In this way, we have been able to uncouple the effects of surface charge from those of surface chemistry and topography. Titanium surfaces were prepared by RF sputtering onto 4" diameter silicon wafers, then cleaved into 15 mm squares. Electric fields of +/-12.7 V/m and +/- 38.1 V/m were applied and compared to a zero-field control group via parallel plate configuration. SAOS-2 osteoblastic cells were plated on Ti surfaces in DMEM/F12 containing 10% FCS, and allowed to adhere for 6 hours. Cells were then incubated for 30 min in 10 mM 2',7'-bis(2-carboxyethyl)-5-carboxyfluorescein acetoxymethyl ester (BCECF-AM), then lysed in 1% Triton X-100. Adhesion was measured spectrofluorometrically. Our preliminary adhesion assays, osteoblastic cells showed an increase in cell attachment for negatively-charged surfaces with respect to a neutral control group. Bone is reported to have a negative zeta potential. We suggest that negative surface charge induces attachment of osteoblastic cells, perhaps through facilitated attachment of ECM proteins necessary for osteoblastic cell adhesion. Further refinements of the experiment will help us to understand the effect of surface charge on cell adhesion.