Determination mechanical properties and permeability of porous titanium alloy bone implants, including under conditions of their interaction with biological fluids

Abstract

Additive manufacturing technologies make it possible to create porous implants with mechanical properties equivalent to natural bone. At the same time, a number of new problems arise, including determining the mechanical properties of such structures. This study is aimed at obtaining the mechanical parameters of porous titanium alloy for bone implants, including under conditions of their interaction with biological fluids. Mechanical properties were obtained for nine types of structures: three types of porosity for each of the three types of structure orientation. The considered porosity of the structures from 41–52 % lies in the porosity range of cancellous bone. Young's modulus was obtained from 10 to 22 GPa and Poisson's ratio was obtained from 0.136 to 0.337, as the results of uniaxial compression test. The Young's moduli of the standard 47 % porosity are closest to the moduli of the cortical bone 15–16 GPa. The structure configuration with the lowest Young's modulus is recommended for the manufacture of implants for patients with high porosity of bone tissue. The experiments considered the interaction of porous structures with biological fluids. Poroelastic effects were not found for structures with pore space filled by collagen under uniaxial compression up to 5000 N. Experiments to determine the permeability were carried out for three types of porosity with the orthogonal orientation of the structure. The permeability coefficient varied from 0.99∙10-10 to 3.6∙10-10 m2 for an aqueous solution of glycerol, simulating blood, and from 1.4∙10-10 to 2∙10-10 m2 for gelatin, simulating collagen formation during primary osteointegration. The results obtained will be useful in developing new approaches to modeling porous implants in biomechanics.