Surface coating with carboxymethyl cellulose and calcium-crosslinked carboxymethyl cellulose to enhance 3D-printed hydroxyapatite scaffolds

Achieving simultaneous mechanical reinforcement and preservation of pore architecture remains a fundamental challenge in bone tissue engineering. This screening study investigated the effects of surface coating 3D-printed hydroxyapatite scaffolds with carboxymethyl cellulose (CMC) and calcium-crosslinked CMC (CMC-Ca). Scaffolds were externally coated with 1% CMC, 2% CMC, or CMC-Ca formulations (1:1, 1:2 and 2:1 ratios), and porosity, compressive strength, liquid absorption, degradation and cytocompatibility were evaluated. The surface coatings improved compressive strength and liquid absorption capacity while preserving porosity. Relative to uncoated scaffolds, the 2:1 CMC-Ca coating increased compressive stress at maximum load from 1.98 to 2.46 MPa (about a 24% improvement) and day-1 liquid absorption from 177% to 233% (about a 32% increase), while internal porosity was maintained above 57% by micro-CT. Among all formulations, the 2:1 CMC-Ca coating showed the most favourable combination of mechanical reinforcement, fluid uptake and controlled degradation. In vitro assays using human fetal osteoblasts confirmed good cytocompatibility across all experimental groups. Although this was a preliminary study, these findings indicate that a surface CMC-Ca coating strategy can decouple structural reinforcement from pore design, enhancing the mechanical and functional performance of 3D-printed scaffolds without compromising their internal architecture and offering a tunable modification strategy for future bone tissue engineering applications.