Design Strategies and Biomimetic Approaches for Calcium Phosphate Scaffolds in Bone Tissue Regeneration

Abstract

Bone is a complex biologic tissue, which is extremely relevant for various physiological functions, in addition to movement, organ protection, and weight bearing. The repair of critical size bone defects is a still unmet clinical need, and over the past decades, material scientists have been expending efforts to find effective technological solutions, based on the use of scaffolds. In this context, biomimetics which is intended as the ability of a scaffold to reproduce compositional and structural features of the host tissues, is increasingly considered as a guide for this purpose. However, the achievement of implants that mimic the very complex bone composition, multi-scale structure, and mechanics is still an open challenge. Indeed, despite the fact that calcium phosphates are widely recognized as elective biomaterials to fabricate regenerative bone scaffolds, their processing into 3D devices with suitable cell-instructing features is still prevented by insurmountable drawbacks. With respect to biomaterials science, new approaches maybe conceived to gain ground and promise for a substantial leap forward in this field. The present review provides an overview of physicochemical and structural features of bone tissue that are responsible for its biologic behavior. Moreover, relevant and recent technological approaches, also inspired by natural processes and structures, are described, which can be considered as a leverage for future development of next generation bioactive medical devices.

Keywords: 3D scaffolds; biomimetics; biomineralization; biomorphic transformations; bone regeneration; hydroxyapatite; ion doping.

Figure 1

Pictorial illustration of the hydroxyapatite crystal structure and chemical signaling to bone cells.

Figure 2

Relevant challenges in the development of biomimetic scaffolds for bone regeneration.

Figure 3

Three-dimensional hybrid scaffolds by bio-inspired mineralization processes for regeneration of osteocartilaginous tissues (left) and SEM micrograph showing multi-layered structure (right).

Figure 4

Biomimetic injectable bone cements (left) and SEM micrograph showing the typical needle and plate-like morphology (right).

Figure 5

Hierarchically organized biomorphic scaffolds for regeneration of load-bearing bones (left) and SEM micrograph showing the macroscopic longitudinal channels mimicking the osteon (right).