Hydroxyapatite (HAp) is one of the most important bioceramics for medical and dental applications, as it possesses excellent biocompatibility and is osteoconductive. Therefore, we have developed novel nanocomposite hydrogels based on HAp and poly(ethylene glycol) (PEG) hydrogels. The gel properties (soft, hydrated and moldable) allow the fabrication of 2D-patterned substrates and 3D-structured scaffolds, which can be further biomineralized to exhibit increased bioactivity and functionality to support the growth of osteoblast cells.
Several PEG-based macromonomers can be selected from our library of multifunctional building blocks, e.g. linear or star-shaped, liquid or solid, with a low or high molecular weight and with the desired functional groups for crosslinking the gels.
Simple mixing of hydroxyapatite nanoparticles (HAp NPs) with the hydrogel precursors then yields novel nanocomposite materials with interesting properties. Nevertheless, even more finely dispersed HAp can be obtained when the PEG-precursors are mixed with salt solutions containing calcium and phosphate ions; in that case, nHAp is formed in situ. The nanocomposite precursor mixtures can be further crosslinked to create stable, new hydrogels with tunable mechanical and swelling properties. Interestingly, the shear mixing of our 8-arm PEG-prepolymer (Mn≈15,000 Da) with salt solutions already resulted in spontaneous gelation.
Fluid precursor mixtures containing minimal amounts of water can be processed by our unique Fill-Molding In Capillaries (FIMIC) method to fabricate surface patterns of bioactive composite materials verses bio-inert regions of pure PEG, which were demonstrated to induce selective cell adhesion. The nanocomposite precursor mixtures with high water content can be structured by freeze-drying into 3D-scaffolds with pore sizes ranging from a few to several hundreds of µm. Within these pores, fibroblasts and osteoblasts exhibited distinctly different cellular morphology.