Wood-Derived Hydrogels\nfor Osteochondral Defect Repair

Repairing cartilage tissue is a serious global challenge.\nHerein,\nwe focus on wood skeletal structures that are highly porous for cell\npenetration yet have load-bearing strength, and aim to synthesize\nwood-derived hydrogels with the ability to regenerate cartilage tissues.\nThe hydrogels were synthesized by wood delignification and the subsequent\nintercalation of citric acid (CA), which is involved in tricarboxylic\nacid cycles and essential for energy production, and <i>N</i>-acetylglucosamine (NAG), which is a cartilage glycosaminoglycan,\namong cellulose microfibrils. CA and NAG intercalation increased the\namorphous region of the cellulose microfibrils and endowed them with\nflexibility while maintaining the skeletal structure of the wood.\nConsequently, the CA-NAG-treated wood hydrogels became twistable and\nbendable, and the acquired stiffness, compressive strength, water\ncontent, and cushioning characteristics were similar to those of the\ncartilage. In rabbit femur cartilage defects, CA-NAG-treated wood\nhydrogels induced the differentiation of surrounding cells into chondrocytes.\nConsequently, the CA-NAG-treated wood hydrogels repaired cartilage\ndefects, whereas the collagen scaffolds, delignified wood materials,\nand CA-treated wood hydrogels did not. The CA-NAG-treated wood hydrogels\nexhibit superior structural and mechanical characteristics over conventional\ncellulose-fiber-containing scaffolds. Furthermore, the CA-NAG-treated\nwood hydrogels can effectively repair cartilage on their own, whereas\nconventional natural and synthetic polymeric materials need to be\ncombined with cells and growth factors to achieve a sufficient therapeutic\neffect. Therefore, the CA-NAG-treated wood hydrogels successfully\naddress the limitations of current therapies that either fail to repair\narticular cartilage or sacrifice healthy cartilage. To our knowledge,\nthis is the pioneer study on the utilization of thinned wood for tissue\nengineering, which will contribute to solving both global health and\nenvironmental problems and to creating a sustainable society.