Fabrication of Elastic 3D Macroporous Scaffolds with Tunable Mechanical Properties for Bone Tissue Regeneration

<b>Abstract:</b><br/>Repairing bone defects or injuries, especially with irregular shapes or at soft tissue insertion sites, presents a significant challenge. Scaffolds that can adapt to such bone defects, present stiffness gradient, and induce osteogenesis are essential for effective bone regeneration. Ceria nanoparticles (CeNPs), polyethyleneimine (PEI), and polyethyleneglycol diglycidyl ether (PEGDE)-based composite macroporous scaffolds with tailored architectures and optimized mechanical attributes and potential for bone regeneration have been demonstrated. We elucidate the physicochemical, mechanical and osteogenic properties of elastic and structurally robust yet deformable 3D macroporous scaffolds developed by freeze-templating PEI-coated ceria nanoparticles. All the designed scaffolds showed interconnected pores with sizes varying between 80-150 µm, overall porosity of ~ 90 %, and interestingly, could undergo compressive strains while exhibiting a zero Poisson’s ratio behaviour. To address the stiffness gradient of the native bone environment, we either varied the composition of CeNPs, PEI, and PEGDE in the scaffolds or crosslinked the free amine-functional groups in the scaffold with glutaraldehyde to increase compressive modulus. E.g. scaffolds comprising 0.02 % and ~ 0.06 % w/v ceria showed an average compressive strength of ~ 1 MPa and ~ 5 MPa, mimicking the cartilage/spongy bone mechanical environment. The scaffolds exhibit excellent elasticity and fast recovery (in ~ 2-3 seconds) from 80 % compressive deformation with intact porous architecture in the wet state. Scaffolded MC3T3-E1 pre-osteoblast bone cells demonstrated enhanced cell proliferation, optimal adhesion and high cell viability, indicating a non-toxic and conducive environment rendered by the designed scaffolds. This was further strengthened by <i>in vivo </i>studies in animal models showing high biocompatibility, low toxicity and non-immunogenicity of the scaffolds. Compared to pristine scaffolds, higher cellular activities with ceria-containing scaffolds indicate that nanoceria promotes efficient osteoblast adhesion and proliferation. This work presents the design and development of mechanically tuneable, elastic and deformable 3D macroporous scaffolds that can be included in bone defects with irregular shapes or at different implant sites with high potential for clinical translation.<br/><br/><b><i>Keywords</i></b><b>:</b> Biomaterials, 3D macroporous scaffold, mechanical properties, osteogenic properties, tissue engineering.