Formation of Anisotropic Structure of Porous Vertebral Implants by Compacting Spongy Titanium Powder through the Elastic Punch Facing

摘要

Porous cervical and thoracic vertebrae implants of the so called CVPI system (Cervical VertebraePorous Implant) and ThVPI system (Thoracic Vertebrae Porous Implant) has been developed inBelarus. Their manufacturing process includes the application of spongy titanium powder of TPP (titaniumporous powder) grade which has been used for over 15 years in the production of porous insertsof hip joint endoprostheses of the SLPS (self-locking porous system) system and is approved for usein clinical practice by the Ministry of Health. The specific structural peculiarity of the implants of CVPIand ThVPI systems is the anisotropy of their pore structure: the porosity of the implants is maximal atsupporting surfaces and minimal at lateral surfaces. Such structure provides initial stable fixation, fastosseointegration of the implant, and minimal injury of adjacent soft tissue. A technology for the implants’production has been developed. Titanium powder is poured into a metal matrix; elastic gasketsare placed between the punch and the powder; bilateral pressing occurs at a pressure of 8-20 MPa;the compact is sintered in vacuum at 1190-1230 °C for 1.5-2.0 hours and calibrated by height and lateralsurface with simultaneous formation of chamfer on the edge between lateral flanks and plane surfacesof the implants. The presence of elastic gaskets between the punches and the pressed chargeallows to achieve a controlled pressure distribution on the surface of spongy powder particles, avoidingtheir crushing and significantly reducing their plastic deformation in the surface layer. This leads toretention of clearly pronounced pore sizes and porosity on the sample surface in comparison to theinternal volume of the product. At the same time, the contact of the pressed powder particles at thelateral flanks with the rigid metal matrix results in anisotropic compaction resulting in the anisotropy ofproperties (porosity, pore sizes) at plane surfaces, lateral surfaces and bulk volume of the implant.