Design and Development of Heterogeneous Porous Scaffold—A Review

Abstract

This paper presents a review of the strategies for the design and development of heterogeneous porous scaffolds. Once the lattice structure (scaffold) is designed with the help of computer-aided design (CAD) software, analysis is done to investigate its compressive response with finite element analysis (FEA). The stiffness of the scaffold is calculated and compared with that of a compact bone and validated experimentally with the help of 3D printing of the scaffold. Heterogeneity of both types, i.e. structural and material, helps mimic the structure of human bones as human bones are porous, heterogeneous and anisotropic. Topology optimization of lattice structure is performed to achieve a high surface area to volume ratio of the scaffold so that cell proliferation and vascularization can be increased. Porosity, pore interconnectivity and pore size are varied to achieve the desired properties in the scaffold to match the stiffness of the scaffold with that of humane bone. Metallic biomedical materials that are investigated in the reported works include stainless steel SS 316L (~210 GPa), Co–29Cr–6Mo alloy (~210 GPa), Ti–6Al–4V alloy (~110 GPa) and Mg alloy (~45 GPa). All the above materials have stiffness greater than that of the cancellous bone (0.02–2 GPa) and the cortical bone (3–30 GPa) which creates a stress shielding effect after implantation in the bone. To avoid the stress shielding problem, these materials are made porous to decrease the stiffness of the solid material. Porosity is not only used for reducing the stress shielding effect but is also used for cell proliferation and vascularization. The objective of this review is to reflect on the heterogeneous porous scaffold design process detailing various phases like material and structural heterogeneity. The current literature on the design of heterogeneous porous scaffold is mainly focused on discussing structural heterogeneity and not much focused on material heterogeneity and there is very little work that reports both structural and material heterogeneity. Thus, there is a clear lack of a comprehensive view. This paper acts as a bridge among the main research outcomes available in the literature related to the design optimization and modelling of the heterogeneous porous scaffolds.