Effects of Pore Morphology and Bone Ingrowth on Mechanical Properties of Microporous Titanium as an Orthopaedic Implant Material

Abstract

Successful bone formation which leads to functional osseointegration is determined by the local mechanical environment around boneinterfacing implants. In this work, a novel porous titanium material is developed and tested and then impact of porosity on mechanical properties as a function of bone ingrowth is studied numerically. A superplastic foaming technique is used to produce CP-Ti material with rounded, interconnected pores of 50% porosity; the pore size and morphology is particularly suitable for bone ingrowth. In order to understand the structure-property relations for this new material, a numerical simulation is performed to study the effect of the porous microstructure and bone ingrowth on the mechanical properties. Using ABAQUS, we create two-dimensional representative microstructures for fully porous samples, as well as samples with partial and full bone ingrowth. We then use the finite element method to predict the macroscopic mechanical properties of the foam, e.g., overall Young's modulus and yield stress, as well as the local stress and strain pattern of both the titanium foam and bone inclusions. The strain-stress curve, stress concentrations and stress shielding caused by the bone-implant modulus mismatch are examined for different microstructures in both elastic and plastic region. The results are compared with experimental data from the porous titanium samples. Based on the finite element predictions, bone ingrowth is predicted to dramatically reduce stress concentrations around the pores. It is shown that the morphology of the implants will influence both macroscopic properties (such as modulus) and localized behavior (such as stress concentrations). Therefore, these studies provide a methodology for the optimal design of porous titanium as an implant material.

Numeric simulation of bone remodelling patterns after implantation of a cementless straight stem

“…As a consequence, physiological influences of the proximal microporous structure of the prosthesis surface must be considered. Li et al [21] found that the proximal properties of their investigated implant encourage bone ingrowth in the plasma-sprayed layer, which mitigates stress concentration and thus the unloading as well as the overloading ratio of bone tissue. Titanium-coated implants will behave differently when bone ingrowth has taken place, particularly in terms of stress shielding [21].…”

“…Li et al [21] found that the proximal properties of their investigated implant encourage bone ingrowth in the plasma-sprayed layer, which mitigates stress concentration and thus the unloading as well as the overloading ratio of bone tissue. Titanium-coated implants will behave differently when bone ingrowth has taken place, particularly in terms of stress shielding [21]. Proliferation of bone cells will increase as another consequence of these coating properties [22].…”

Solid State Foaming of Nickel, Monel, and Copper by the Reduction and Expansion of NiO and CuO Dispersions

“…As recently reviewed, [9] routes for creating porous metals in the solid state may take a variety of forms, including gas entrapment, [10][11][12][13][14] fugitive templating, [15][16][17][18][19] powder injection molding, [20][21][22] and powder or hollow sphere sintering. [23][24][25][26][27] Despite the diverse possibilities in solid state foaming, Ni has been primarily produced through vapor-phase deposition on a polymer template, as described by Paserin et al [28][29][30] Developed and sold under the name INCO-FOAM 1 , the process is capable of large-scale output using a reel-to-reel setup that produces metallic foam sheets 1 m wide and 2000 m long.…”

Preparation and In Vivo Study of Porous Titanium–Polyglycolide Composite

“…The mechanical properties of metallic materials can be controlled by both alloy design [2][3][4] and the construction of an appropriate structure [5][6][7][8] . A porous implant material with an adequate pore structure showing appropriate mechanical properties, a low Young s modulus, and bone ingrowth has long been sought as the ideal bone substitute 9) .…”