![]() ![]() The concept of minimal surface defined in differential geometry of surfaces is the surface with a mean curvature of zero that can be indefinitely extended in three periodic directions. The porous structure with minimal surfaces can be realised using this method. Because of its specific design, the porosity and the pore architecture can be generated by defining weight functions and spatially dependent porosity function. Triply periodic minimal surfaces (TPMSs), which can exhibit periodicity in three independent directions in three-dimensional (3D) space, have been regarded as an effective tool for designing scaffolds with gradual and regular porous structure. Therefore, designing a porous structure with adequate modulus is critical for the application of titanium alloys in bone tissue repair. Although the higher porosity and pore size, such as 500–1000 μm, are favourable for bone ingrowth, the strength of the implant is constantly decreasing. ![]() Previous studies have shown that the titanium scaffolds with a pore size ranging from 100 to 500 μm and a porosity of approx. The exchange of nutrients and vascularisation are also improved with appropriate porous characteristics (pore size, pore shape and pore size distribution). ![]() Moreover, the porous structure can provide interfacial adhesion between implants and the surrounding bone, which enables an enhanced bonding and a shorter healing time. The interconnected pores generally result in significant osteointegration and better fixation of implants. The modulus is significantly lower in the porous structure, and the stress shielding may be alleviated. To address these issues and to construct a long-lasting implant, the porous design is introduced to mimic the elasticity modulus and yield the strength of the nature bone. In addition, the bone resorption around the implants can lead to an unstable interface between bone and implants, which can be regarded as the high risk for early implantation failure. As a result, the bone tissues can become atrophic and gradually lose the load-bearing capability, which may cause osteoporosis and fracture around the implants. The mismatch of Young's moduli between implants and bone tissues is vital in stress shielding, a universal phenomenon after implantation, which results in the nonhomogeneous stress transfer between the implants and the surrounding bone tissue. Nevertheless, this material is elastic, has low wear resistance and is stiffer than the cortical bone (Young's modulus: 7–30 GPa). Compared with the aforementioned metals, titanium (Young's modulus: 110 GPa) is a low modulus metal, with nonallergenic qualities and excellent biocompatibility, which has been applied in many orthopaedic and dental applications. Metallic biomaterials such as stainless steel (Young's modulus: 190 GPa), cobalt–chromium alloys (Young's modulus: 230 GPa) and tantalum (Young's modulus: 187 GPa) have been used to fabricate implant devices. With the increased population growth and increased life expectancy, a rapid increase in musculoskeletal disorders, fractures and osteoporosis, which gives rise to bone-related medical treatment, has been observed, especially in elderly populations, Over the past decades, a number of artificial implants have been developed, including artificial bones and joints, plates, screws and dental implants. The bone has a prominent role in motion, support and protection of the human body. ![]()
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