In this study, we developed a novel in vitro model to study how microstructured and hydrophilic titanium implants impact bone remodeling for dental and orthopaedic applications. Our approach intersects biomaterials and systems physiology, revealing for the first time that implant surface properties are capable of regulating the communication among the cells involved in remodeling of primary bone during osseointegration. We believe that the basic research presented in our manuscript will provide important knowledge in our understanding of factors that impact implant success. Furthermore, it provides a solid foundation for the development of materials that enable rapid osseointegration and earlier loading times for implants in bone that has been compromised by trauma or disease.

No abstract

No abstract

Successful osseointegration of an endosseous implant involves migration and differentiation of mesenchymal stem cells (MSCs) on the implant surface. Micro-structured, hydrophilic titanium surfaces direct MSCs to undergo osteoblastic differentiation in vitro, in the absence of media additives commonly used in cultures grown on tissue culture polystyrene (TCPS). This process involves non-canonical Wnt5a, in contrast to canonical Wnt3a typically credited with osteoblastic differentiation on TCPS. Wnt proteins have been implicated in morphological development and tissue patterning, suggesting that additional Wnts may participate. Here, we demonstrate that Wnt11 is a mediator of osteoblast commitment of MSCs, and increases in a surface-roughness dependent manner. Experiments using cells silenced for Wnt11 indicate that cross-talk between Wnt5a and Wnt11 occurs. Wnt11 potentially acts upstream to Wnt5a, increasing Wnt5a expression and factors associated with osteogenesis. Thus, Wnt11 contributes to peri-implant bone formation distal to the implant surface through a heavily regulated signaling cascade of autocrine/paracrine proteins.

Establishment of a patent vasculature at the bone-implant interface plays a significant role in determining overall success of orthopaedic and dental implants. Osteoblasts produce vascular endothelial growth factor-A (VEGF-A), an important regulator of angiogenesis during bone formation and healing, and the amount secreted is sensitive to titanium (Ti) surface microtopography and surface energy. The purpose of this study was to determine if surface properties modulate cellular response to VEGF-A. MG63 osteoblast-like cells were transfected with shRNA targeting VEGF-A at >80% knockdown. Cells stably silenced for VEGF-A secreted reduced levels of osteocalcin, osteoprotegerin, FGF-2, and angiopoietin-1 when cultured on grit-blasted/acid-etched (SLA) and hydrophilic SLA (modSLA) Ti surfaces and conditioned media from these cultures caused reduced angiogenesis in an endothelial tubule formation assay. Treatment of MG63 cells with 20 ng/mL rhVEGF-A165 rescued production in silenced cells and increased production of osteocalcin, osteoprotegerin, FGF-2, and angiopoietin-1, with greatest effects on control cells cultured on modSLA. Addition of a neutralization antibody against VEGF receptor 2 (VEGFR2; Flk-1) resulted in a significant increase in VEGF-A production. Overall, this study indicates that VEGF-A has two roles in osseointegration: enhanced angiogenesis and an autocrine/paracrine role in maturation of osteoblast-like cells in response to Ti surface properties.