Engineering bone-implant integration with photofunctionalized titanium microfibers

There are significant challenges in regenerating large volumes of bone tissue, and titanium implant therapy is extremely difficult or contraindicated when there is no supporting bone. Surface conditioning of titanium implants with UV light immediately prior to use, or photofunctionalization, improves the speed and degree of bone-implant integration. Here, we hypothesized that photofunctionalized titanium microfibers are capable of promoting bone ingrowth into the microfiber scaffold to improve bone-implant integration in bone defects. Titanium implants (1 mm in diameter, 2 mm in length) enfolded with 0.7 mm-thick titanium microfibers were placed into 2.4-mm diameter osteotomy in rat femurs. Titanium microfibers and implants were photofunctionalized by treatment with UV light for 12 min using a photo device immediately prior to surgery. Photofunctionalized microfibers and implants were hydrophilic, while as-made microfiber-enfolded implants were hydrophobic. Implant anchorage strength was 2.5 times and 2.2 times greater for photofunctionalized microfiber-enfolded implants than as-made ones at weeks 2 and 4 of healing, respectively. Robust bone formation was only seen at the implant surface of photofunctionalized microfiber-enfolded implants. Bone formation as measured by the Ca/Ti ratio was 5 to over 20 times greater for photofunctionalized than as-made microfiber scaffolds. The Ca/P ratio was 1.55-1.65 in the tissue produced in photofunctionalized microfibers and 1.1-1.3 in tissue in as-made microfibers. In vitro, the number of attached osteoblasts and their alkaline phosphatase activity, both near zero on as-received microfibers, were significantly increased on photofunctionalized microfibers. In conclusion, bone ingrowth occurred in photofunctionalized titanium microfiber scaffolds, enabling successful bone-implant integration when the microfiber-enfolded implants were placed in a site without primary bone support. The combined use of titanium microfibers and photofunctionalization may provide a novel and effective strategy to regenerate and integrate bone in a wider range of applications.