Web of Fine Titanium Fibers Created a Three-dimensional Bonding Between Bone and Titanium by the Geometry of Artificial ECM

Previous methods of bone-titanium bonding have been limited their interfaces essentially to the two-dimensional systems, which provide very limited spaces for osteoblasts to exert active bone formation, leading long time for achieving bone-titanium bonding. Objectives: this study is to create an entirely new method of the bonding, in that bone and titanium coexist three-dimensionally in the "collaboration zone" of about 0.5 mm in thickness. This zone is created by the "titanium web", which composed of fine titanium fibers (diameters: 50-100 microns) molded into an unwoven sheet (Yanagisawa-method, US patent). The idea is based upon geometry of artificial ECM by Kuboki et al.(J Bone Joints Surgery, 2001). Methods: titanium rod (diameter: 1.5-2.0 mm) was wrapped tightly by titanium web and sintered at 1000-1100 centigrade in vacuo for 4 hrs. In the product, titanium web-equipped titanium rod (TWT), the fibers within the web strongly fused together, and the web layer was on the surface of the titanium rod as well. The TWT was cut into a cylindrical form, coated with hydroxyapatite by the method of Osaka (US patent) and implanted into the cranial bone of rabbit. Results: at 4 weeks, histology showed that new bone developed from surrounding calvaria into the entire width of titanium web, reached to the surface of titanium rod. Density of bone in the web was slightly lower than the surrounding calvaria at 4 weeks, but it became equivalent at 6 weeks. In the control experiment of a conventional device of titanium beads-attached titanium rod, bone development reached only on the surface of beads-layer and did not enter the inter-beads spaces at 4 weeks. Conclusion: rapid and effective bone-titanium bonding in TWT was due to the three-dimensional spaces provided by the geometry of the web, which was more feasible environment for osteoblasts than those of conventional devices.