Abstract
To improve biocompatibility and mechanical compatibility, post-treatment is necessary for porous scaffolds of bone tissue engineering. Hot isostatic pressing (HIP) is introduced into post-treatment of metal implants to enhance their mechanical properties by eliminating residual stress and pores. Additionally, oxide film formed on the material surface can be contributed to improve its biocompatibility. Ti6Al4V porous scaffolds fabricated by laser-powder bed fusion (L-PBF) process is studied in this paper, their mechanical properties are measured by pressure test, and the macroscopic surface morphology and microstructure are observed by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). After HIP treatment, an oxide layer of 0.8 μm thickness forms on the surface of Ti6Al4V porous scaffolds and the microstructure of Ti6Al4V transforms from α’ phase to α + β dual-phase, as expected. However, the pressure test results of Ti6Al4V porous scaffolds show a definitely different variation trend of mechanical properties from solid parts, unexpectedly. Concerning Ti6Al4V porous scaffolds, the compression stiffness and critical stress improves clearly using HIP treatment, and the fracture morphology shows obvious brittle fracture. Both the strengthening and brittleness transition of Ti6Al4V porous scaffolds result from the formation of an oxide layer and an oxygen atom diffusion layer. The critical stress of Ti6Al4V porous scaffolds can be calculated by fully considering these two strengthening layers. To obtain a porous scaffold with specific mechanical properties, the effect of post-treatment should be considered during structural design.
Highlights
It is a significant challenge that replacement of over critical size bone defects result from trauma and bone diseases in the field of orthopedic and craniofacial surgery [1,2]
Residual stress formed by a high temperature gradient may lead to early cracking
Comparing the results of the as-built and hot isostatic pressing (HIP)-treated Ti6Al4V with the same dimensions, the post-treatment improved the density of the materials, as expected
Summary
It is a significant challenge that replacement of over critical size bone defects result from trauma and bone diseases in the field of orthopedic and craniofacial surgery [1,2]. Titanium and its alloys have been widely applied as orthopedic implant materials for their excellent mechanical properties, biocompatibility and corrosion resistance [5]. The mismatch of mechanical properties between metals and natural bone lead to stress shielding and, result in bone. Porous scaffolds are introduced as bone substitute in view of its controllable mechanical properties to avoid the stress shielding effect and to improve implant material longevity [7,8,9]. The Young’s modulus of these scaffolds should approximate that of the host bone tissues, avoiding potential stress shielding [10]. It is essential and critical to consider the mechanical properties of scaffolds
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