Porous ongrowth surfaces alter osteoblast maturation and mineralization

Implant fixation through osseointegration is essential for the success of uncemented total joint arthroplasty, and nature and composition of implant surface play a critical role in this process. Despite widespread use of uncemented implants, the extent of bone ingrowth into implants is generally only a small percentage of the total implant surface. An understanding of the processes whereby bone cells grow into and multiply on porous surfaces is critical for the design and manufacture of implants that maximize ingrowth and implant fixation. A wide variety of implant materials are currently utilized for uncemented total joint arthroplasty, including titanium mesh, cobalt chromium beads, and tantalum deposited on a carbon network. Despite differences in physical and chemical properties of these materials, all have functioned well clinically. Therefore, the goals of this study were to compare and contrast the effects of these materials on the proliferation, phenotypic maturation, and mineralization of osteoblasts. Disks of porous tantalum, titanium mesh, and cobalt chromium beaded surfaces were fabricated and processed employing the same methods used to produce implants, including packaging and sterilization. Preosteoblasts were plated on disks, cellular morphology was evaluated by scanning electron microscopy. Osteoblast proliferation was significantly higher on the porous tantalum compared to other implant surfaces. Alkaline phosphatase activity, osteocalcin secretion, and upregulation of RUNX2 were inversely proportional to the rate of proliferation. Mineralization of osteoblasts paralleled the rate of proliferation. These findings suggest that proliferation of osteoblasts into the interstices of implant materials along with delayed maturation were favorable for increased bone ongrowth and ultimately implant stabilization.