BME MS Defense Seminar: Diana Olvera
Coating of Titanium with Electrically Polarized Hydroxyapatite Modulates Mesenchymal Stem Cell Adhesion
Advisor: Hani Awad
While orthopedic implants are generally successful, they are not without complications due to osseointegration delays that prolong patient recovery after surgery and increase the likelihood of device failure. Success of any orthopedic implant relies on effective integration between the surface of the implant and bone, with no fibrous tissue interface. Titanium alloys are among the most successful implantable materials used for orthopedic applications due to their excellent mechanical strength, corrosion resistance, and superior biocompatibility compared to other metallic biomaterials. However, these alloys fall into a group of bioinert materials and therefore lack the ability to induce robust osseointegration. Titanium implants that have been coated with hydroxyapatite combine the mechanical advantage of the metallic substrate and the biological affinity of the hydroxyapatite surface to bone. Though the tissue growth on the synthetic hydroxyapatite surface is still not as fast as that of natural bone, surface modifications have been widely studied to promote a higher osseointegration. The aim of this study was to investigate the surface characteristics and in vitro effects on cell attachment, focal adhesion, proliferation and differentiation of a novel hydroxyapatite coating technique. The novel hydroxyapatite surface contained yttrium and fluoride dopants that affect crystal growth, promote strong charge storage, and enhance electrical polarization abilities. The findings illustrate how polarization and surface charge influence early stages of cell-surface interaction. Negatively polarized and heated hydroxyapatite promote cell activity while positively polarized and non-polarized hydroxyapatite delays or inhibit their response, respectively. In terms of gene expression, markers of terminal chondrogenic differentiation were upregulated in MSCs cultured on negatively polarized and heated hydroxyapatite in osteogenic medium. In control (growth) culture media, lineage commitment to osteogenesis but no osteoblast differentiation markers were also observed on negatively polarized and heated hydroxyapatite. These data suggest that polarized hydroxyapatite coating of titanium can affect its biointerface properties and merit future investigation in vivo.