Structure–property–function relationships in 3D-printed gelatin/cellulose nanocrystals/n-HAP scaffolds for bone tissue repair

The development of biodegradable composite scaffolds with tailored properties holds significant potential for tissue regeneration. In this study, three-dimensional (3D) porous scaffolds composed of gelatin, cellulose nanocrystals (CNC), and nano-hydroxyapatite (n-HAP) were fabricated via extrusion-based 3D printing. Citric acid served as a crosslinker to enhance scaffold stability. Formulations with varying CNC and n-HAP contents were evaluated for rheological behavior, printability, physicochemical characteristics, mechanical performance, and biocompatibility. Increased CNC and n-HAP concentrations improved ink viscosity and viscoelasticity, enabling high-fidelity printing of lattice structures. Covalent crosslinking between gelatin and citric acid was confirmed by FTIR, resulting in enhanced thermal stability as shown by TGA. XRD analysis indicated increased crystallinity, while SEM images revealed a well-dispersed porous architecture with pore sizes of 181-325 μm and porosity of 65-84 %. CNC and crosslinking suppressed swelling (<700 %) and degradation (<11 %) over 4 weeks in phosphate-buffered saline (PBS). The printed scaffolds exhibited compressive moduli of 43 MPa (dry) and 24 MPa (wet), within the range of trabecular (cancellous) bone, indicating suitability for non-load-bearing or low-load-bearing bone tissue applications. Cytocompatibility tests with MG-63 osteoblast-like cells confirmed non-cytotoxicity, and higher n-HAP content enhanced cell viability (up to 140 %) and adhesion, further supporting their potential for bone tissue engineering. These findings highlight the gelatin/CNC/n-HAP scaffold as a promising candidate for bone tissue engineering, combining printability, mechanical integrity, and biological functionality.