Preparation of Modified Sweet Potato Residue-Derived Cellulose Nanocrystal Scaffolds for Bone Tissue Engineering and Study of Their Osteogenic Mechanisms

Precision repair of large-scale clinical bone defects urgently requires bone graft materials that provide both structural mechanical support and high bioinductive activity. This study aims to construct a biomimetic scaffold for bone tissue engineering with a controllable architecture, strong osteoinductive capacity, and excellent mechanical properties. Based on a high-value utilization and functionalization strategy that employs agricultural waste, specifically sweet potato residue (SPR), as a sustainable nanofiller platform, a multifunctional biopolymer scaffold with immunomodulatory properties was successfully developed using 3D printing technology by enhancing the interfacial interactions between cellulose nanocrystals (CNCs) and the hydrophobic polymer matrix.
Firstly, pilot-scale production of cellulose and CNCs was achieved using SPR as the primary raw material. Simultaneously, the economic benefits of producing CNCs from SPR were systematically compared with the commercial acid hydrolysis process using wood pulp. Results indicated that the cellulose content in SPR reached 20.93%. The derived CNCs exhibited a typical rod-like morphology, high crystallinity (61.0%), and exceptional thermal stability (Tmax of 347.88°C). Techno-economic analysis revealed that the total capital investment for commercial CNC production was $227.74 million, whereas the SPR-based process required only $203.34 million. Compared to commercial alternatives, SPR-derived CNCs demonstrated higher economic efficiency and a superior net present value, highlighting excellent economic feasibility and providing high-quality, sustainable nano-reinforcing fillers for composite development.
Secondly, to address the poor interfacial compatibility between CNCs and hydrophobic matrices, three orthogonal grafting strategies were employed for CNCs modification: i) metal-ion mineralization; ii) tannic acid coupling; and iii) silk protein (SP) grafting. Experimental results showed that functionalization significantly enhanced the thermal stability (up to 330°C) and dispersibility of the CNCs while preserving their intrinsic crystalline structure. Furthermore, by modulating surface wettability, the interfacial adhesion of the composites was markedly improved, with the water contact angle reaching 81.70°. Among the evaluated formulations, the incorporation of 7 wt% SP modified CNCs (SP-CNCs) into a polylactic acid (PLA) matrix was identified as the optimal configuration. Subsequently, 3D printing was utilized to fabricate the composite scaffolds. Scanning electron microscopy revealed a more uniform pore size distribution in the composite scaffolds. With increasing functionalized CNCs content, the porosity, equilibrium swelling rate, and pore size of the scaffolds exhibited an initial increase followed by a decrease. Scaffolds prepared at the specific optimal ratio demonstrated superior porosity and a balanced swelling ratio, forming a highly interconnected and stable 3D cross-linked porous network.
Finally, the osteogenic mechanisms of the scaffolds were elucidated at both cellular and animal levels. The 3D-printed PLA scaffold containing 7 wt% SP-CNCs exhibited the best porous structure and mechanical strength, with a compressive modulus of 12.29 MPa and excellent thermal stability (Tmax of 320.30°C). In vitro experiments confirmed that the PLA composite 7 wt% SP-CNCs scaffold possessed exceptional cytocompatibility, significantly promoting the proliferation of rat bone marrow mesenchymal stem cells with a rate of 228.68% ± 26.28%. It also enhanced alkaline phosphatase activity (2.16 ± 0.05 nmol/min/mg), mineralization levels, calcium deposition, and the expression of osteogenic genes. In a rat tibial defect model, micro-CT and histological analyses (H&E, Masson’s trichrome, and Sirius red staining) demonstrated that the scaffold induced significant new bone maturation and tissue integration within 8 weeks, achieving near-complete healing of the bone defect with minimal inflammatory response. KEGG pathway enrichment analysis revealed that the scaffold effectively promoted bone matrix synthesis and cell cycle progression by regulating protein ubiquitination and activating the PI3K-Akt and MAPK signaling pathways.
In summary, this study not only achieves the value-added utilization of agricultural waste but also develops a bone repair material with superior mechanical support and osteoinductive capacity through biomimetic design and precision printing. The findings establish a solid theoretical and experimental foundation for the development of personalized, high-performance bone graft substitutes.