Three-dimensional bioprinting of clay-based nanocomposite hydrogel scaffold for bone regneration

Abstract

Bone defects occur in a wide variety of situations such as trauma, developmental deformities, or tumor resection. Reconstruction of bone defects with suitable scaffolds finely fitting the original surrounding bone tissues is one of the important options for patients’ rehabilitation. The emerging three-dimensional printing (3D-printing) and three-dimensional bioprinting (3D-bioprinting) techniques both are strongly dependent on the development of bioinks offer a promising opportunity to customize personalized bioscaffolds for precision and individualized therapy of bone defects. Various degradable or nondegradable scaffold materials have been developed for 3D-printing and 3D-bioprinting. Hydrogels are one sort of attractive scaffolding materials due to their resemblance to extracellular matrices, as well as a broad range of modulus tunability, but their low mechanical properties limit their application in bone tissue engineering. Recently, researcher have tried to incorporate inorganic particles such as hydroxyapatite (HAp) and tricalcium phosphate (TCP) into hydrogels, which not only enhanced the mechanical properties of the hydrogels but also showed osteogenic properties both in vitro and in vivo. But the concentration of the inorganic particles is not easy to control, higher concentration will influence the crosslinking procedure of the hydrogels and lower concentration will not control the viscosity of hydrogels effectively and delamination occurs easily. The key issue for this study is finding out the organic/inorganic hydrogels, which show attractive mechanical properties, facilitate 3D-printing procedure at room temperature, exhibit good biocompatibility, promote new bone formation and even realize 3D-bioprinting. Nanoclay, a kind of inorganic nanoparticles has been used as a physical crosslinker to enhance the mechanical properties of hydrogels. The obtained clay-based nanocomposite hydrogels show good mechanical properties. Recently, researchers have just used the clay-based nanocomposite hydrogels in 3D-printing. One reason is that the addition of nanoclay into the pre-hydrogel solutions can effectively control the viscosity of the solutions to facilitate 3D-printing procedure at room temperature. Another reason is that after adding nanoclay into pre-hydrogel solutions, the solutions show shear-thinning properties which can confirm the formation of stable constructs without collapse just after the extrusion-based 3D-printing. Although nanoclay have been used in 3D-printing, the real application of the clay-based nanocomposite hydrogel scaffolds has not been developed. As nanoclay contains some bioactive ions such as magnesium ions (Mg2+) and silicon ions (Si4+) which can promote osteogenesis effectively, we try to explore the application of clay-based nanocomposite hydrogel scaffolds with good mechanical properties in bone tissue engineering. In our work, we successfully synthesized three kinds of clay-based nanocomposite hydrogels. Poly(4-Acryloylmorpholine) clay-based nanocomposite hydrogel shows attractive mechanical properties and good biocompatibility, promotes osteoblasts differentiation in vitro and stimulates new bone formation in vivo, but the high swelling ratio limits its application in 3D-printing. Poly(N-acryloyl glycinamide) clay-based nanocomposite hydrogel scaffold shows excellent mechanical properties, swelling stability, good biocompatibility and osteogenic properties both in vitro and in vivo, but the toxicity of the N-acryloyl glycinamide (NAGA) monomer limits its application in 3D-bioprinting. Poly(ethylene glycol) clay-based hydrogel system fulfills the 3D-bioprinting, shows high cell viability and well cell distribution, promotes osteoblasts differentiation in vitro, stimulates new bone formation in vivo.