Titanium nanotopography induces osteocyte lacunar-canalicular networks to strengthen osseointegration

Osteocyte network architecture is closely associated with bone turnover. The cellular mechanosensing system regulates osteocyte dendrite formation by enhancing focal adhesion. Therefore, titanium surface nanotopography might affect osteocyte network architecture and improve the peri-implant bone tissue quality, leading to strengthened osseointegration of bone-anchored implants. We aimed to investigate the effects of titanium nanosurfaces on the development of osteocyte lacunar-canalicular networks and osseointegration of dental implants. Alkaline etching created titanium nanosurfaces with anisotropically patterned dense nanospikes, superhydrophilicity, and hydroxyl groups. MLO-Y4 mouse osteocyte-like cells cultured on titanium nanosurfaces developed neuron-like dendrites with increased focal adhesion assembly and gap junctions. Maturation was promoted in osteocytes cultured on titanium nanosurfaces compared to cells cultured on machined or acid-etched micro-roughened titanium surfaces. Osteocytes cultured in type I three-dimensional collagen gels for seven days on nano-roughened titanium surfaces displayed well-developed interconnectivity with highly developed dendrites and gap junctions compared to the poor interconnectivity observed on the other titanium surfaces. Even if superhydrophilicity and hydroxyl groups were maintained, the loss of anisotropy-patterned nanospikes reduced expression of gap junction in osteocytes cultured on alkaline-etched titanium nanosurfaces. Four weeks after placing the titanium nanosurface implants in the upper jawbone of wild-type rats, osteocytes with numerous dendrites were found directly attached to the implant surface, forming well-developed lacunar-canalicular networks around the nano-roughened titanium implants. The osseointegration strength of the nano-roughened titanium implants was significantly higher than that of the micro-roughened titanium implants. These data indicate that titanium nanosurfaces promote osteocyte lacunar-canalicular network development via nanotopographical cues and strengthen osseointegration. STATEMENT OF SIGNIFICANCE: The clinical stability of bone-anchoring implant devices is influenced by the bone quality. The osteocyte network potentially affects bone quality and is established by the three-dimensional (3D) connection of neuron-like dendrites of well-matured osteocytes within the bone matrix. No biomaterials are known to regulate formation of the osteocyte network. The present study provides the first demonstration that titanium nanosurfaces with nanospikes created by alkali-etching treatment enhance the 3D formation of osteocyte networks by promoting osteocyte dendrite formation and maturation by nanotopographic cues, leading to strengthened osseointegration of titanium implants. Osteocytes attached to the titanium nanosurfaces via numerous cellular projections. The success of osteocyte regulation by nanotechnology paves the way for development of epoch-making technologies to control bone quality.