Chapter 5 - Biological metamaterials

Abstract

At present, the design of bone scaffolds cannot balance the combination of suitable porosity and proper mechanical property well, leading to difficulties in simultaneously facilitating bone tissue regeneration and avoiding the stress shielding phenomenon. In this chapter, a topology strategy of designing double-cone struts to reduce stress shielding of diamond-like porous metallic biomaterials while maintaining unvaried porosity is proposed. Porous metallic biomaterials developed from pentamode metamaterials (PMs) were rationally designed to mimic the topological, mechanical, and mass transport properties of human bones. For this chapter, a series of diamond-based PMs with different strut parameters were fabricated from a Ti6Al4V powder by the selective laser melting technique. The PM scaffolds showed a switchable deformation pattern controlled by the slenderness ratio of struts. The double-cone strut topology increases the tortuosity and thereby accelerates the nutrients supply, waste removal, and cell migration to the whole scaffold region and circumambient bone tissue. Biomimetic metallic biomaterials prepared for bone scaffolds have drawn more and more attention in recent years. However, the topological design of scaffolds is critical to cater to multiphysical requirements for efficient cell seeding and bone regeneration, but it remains a significant scientific challenge due to the combination of mechanical and mass-transport properties in conventional scaffolds that lead to poor control toward favorable modulus and permeability combinations. For this chapter, inspired by the microstructure of natural sea urchin spines, biomimetic scaffolds constructed by PMs with hierarchical structural tunability were additively manufactured via selective laser melting. The mechanical and mass-transport properties of scaffolds could be simultaneously tuned by the graded porosity (B/T ratio) and the tapering level (D/d ratio). Compared with traditional metallic biomaterials, our biomimetic PM scaffolds possess graded pore distribution, suitable strength, and significant improvements to cell seeding efficiency, permeability, and impact-tolerant capacity; they also promote in vivo osteogenesis, indicating promising application for cell proliferation and bone regeneration using a structural innovation.