Cellular Dynamics of Neovascularization and Osteoconduction in Peri-Implant Endosseous Wound Healing

Khosravi, Niloufar 1, 2; Maeda, Azusa 2; Mendes, Vanessa 1; Underhill, T.Michael 3; DaCosta, Ralph S. 2; Davies, John E. 1, 4

1. Faculty of Dentistry, University of Toronto; 2. University Health Network, Toronto; 3. University of British Columbia, Vancouver; 4. Institute of Biomaterials and Biomedical Engineering, University of Toronto

Background: Peri-implant wound healing is a multistage regeneration process involving neovascularization and osteoconduction. The latter has been defined as migration and recruitment of osteogenic cells to the implant surface.

Striking advancements have been made in the development of novel implant surfaces to enhance contact osteogenesis. However further studies are required to uncover the regulatory effect of the topographically complex surfaces on these two healing steps at the cellular level.

Hypothesis: Perivascular mesenchymal cells (PMC) are the progenitors of osteogenic cells, and the implant surface topography influences the pattern of peri-implant osteogenesis through controlling the rate and the architecture of microvascular network development following implantation.

Methods: We stablished a platform for intravital tracking and 3D quantification of neovascularization and perivascular cell dynamics. Two-photon fluorescence microscopy was performed from day 3 up to day 43 post-surgery. Perivascular mesenchymal cells were endogenously labeled with tdTomato in our mouse model, the neovasculature and the Ti-implant were visualized with green fluorescein (FITC-Dextran) and Second Harmonic Generation (SHG) respectively. The lateral surface of the Ti implant was either machined or modified with Nanotubes.

Results: The rate of the vascularization was slower around the machined implant surface. The nascent vessel fragments were spatially closer to the nano-surface with significantly higher branching level in the early time points. PMCs appeared at the wound site on day 3, a massive expansion in their population occurred between day 7 to 11. Some of these cells changed morphology and became stabilized on the vessels after day 15, others became osteocytes in the newly formed bone. Comparative analysis of two implant surface types showed that the population of the PMCs was significantly higher in the proximity of the implant surface in the nano treated group between days 3 and 15.

Conclusion: Our results provide evidence that PMCs are brought into the wound site in parallel with the invasion of the site by capillaries. The trafficking of these osteoprogenitor cells in the peri-implant wound microenvironment is controlled by the rate and pattern of the microvascularization, which is enhanced by nano-structurally complex implant surfaces.

Significance: Reengineering endosseous implants based on the findings of this project would possibly help overcome the delayed bone healing associated with diseased conditions and ultimately improve clinical outcomes.