Robocasting of biomimetic hydroxyapatite scaffolds using self-setting inks

Traditional ceramic inks for 3D printing have largely avoided low-temperature self-setting formulations. Prior research has shown that solid freeform fabrication methods often rely on high-temperature sintering or external binders. No prior work had resolved the use of reactive slurries that set at room temperature for scaffold fabrication. This gap motivated exploration of self-setting inks to simplify processing and improve biocompatibility. It was already known that gelatine can act as a crosslinker and support cell adhesion. However, the role of gelatine in delaying setting reactions remained unclear. This paper's contribution is the first demonstration of a bioinspired ink that combines self-setting properties with viscoelasticity. The study introduces a new approach to scaffold fabrication that aligns with biological structures.

The aim of this study was to develop a self-setting ink for robocasting that mimics natural bone structures. The specific problem addressed is the lack of printable inks that can form interconnected pore networks without high-temperature processing. The motivation stems from the need for scaffolds that support cell adhesion and proliferation while maintaining mechanical strength. The researchers propose using alpha-tricalcium phosphate and gelatine to create a reactive slurry. This approach allows for room-temperature setting and eliminates the need for external binders. The goal is to produce scaffolds with a pore size of approximately 300 micrometers. The study also aims to evaluate how gelatine affects mechanical properties and cell behavior. The ultimate objective is to create a scalable method for bone tissue engineering.

The study employed robocasting to print alpha-tricalcium phosphate and gelatine slurries. The inks were formulated to undergo a self-setting reaction at room temperature. A controlled pore network was achieved through precise printing parameters. The resulting scaffolds were analyzed for porosity and crystal structure. Needle-shaped calcium-deficient hydroxyapatite crystals were observed in the matrix. Gelatine retention was confirmed through chemical crosslinking techniques. Mechanical testing measured elastic modulus and compressive strength. Cell adhesion and proliferation were assessed using mesenchymal stem cells. The researchers used scanning electron microscopy to examine pore interconnectivity. The study also evaluated the effect of gelatine on the setting reaction kinetics.

The scaffolds exhibited a pore size of approximately 300 micrometers with full interconnectivity. The microstructure consisted of needle-shaped hydroxyapatite crystals with high surface area. Gelatine was retained through chemical crosslinking, ensuring structural stability. The elastic modulus reached values comparable to trabecular bone. Compressive strength was within the range of human trabecular bone. Gelatine delayed the setting reaction, allowing sufficient printing time. The viscoelastic properties of the ink supported strand integrity during printing. Mesenchymal stem cells adhered and proliferated on the scaffold surface. The setting reaction increased mechanical properties significantly. The study demonstrated that gelatine enhances both structural and biological performance.

The authors propose that this new ink formulation enables the fabrication of biomimetic scaffolds with enhanced mechanical and biological properties. The self-setting reaction eliminates the need for high-temperature processing. The interconnected pore structure supports cell infiltration and nutrient transport. The study suggests that gelatine improves both viscoelasticity and cell adhesion. The researchers propose that the method allows for scalable scaffold design. The findings indicate that the approach aligns with natural bone architecture. The setting reaction increases scaffold strength to match trabecular bone. The authors suggest that this method could be used for bone tissue engineering applications.