Mesenchymal Stem Cell‐Laden Nanofibril‐Reinforced Injectable and Self‐Healing Alginate Dialdehyde/Gelatin Hydrogels with Enhanced Mechanical and Chondrogenic Performance In Vitro

ABSTRACT

Injectable hydrogels offer a minimally invasive approach for cartilage repair, enabling precise defect filling and in situ scaffold formation; however, balancing mechanical strength with stem cell viability and chondrogenic differentiation remains challenging. Here, alginate dialdehyde‐gelatin (ADAG) hydrogels are reinforced with cellulose nanofibrils (CNFs) to enhance mechanical performance while retaining injectability, rapid self‐healing, and chondroinductive properties. FTIR spectroscopy confirms efficient Schiff base cross‐linking between ADA and gelatin, with CNF incorporation preserving chemical integrity. SEM imaging revealed a porous, interconnected architecture, with the 9:1 (ADAG: CNF, v/v) hydrogel exhibiting a more homogeneous and compact network structure, similar to ADAG. Optimization identifies 9:1 and 8:2 ratios as maintaining crosslinking density, while 7:3 ratio slightly disrupts uniformity but retains fast gelation (<5 min) and smooth injectability. CNF reinforcement markedly enhanced mechanical properties, as evidenced by increased storage modulus (0.007 MPa) and compressive modulus (0.006 MPa). The hydrogels exhibit high self‐healing efficiency (98%) and support robust proliferation of human bone marrow‐derived mesenchymal stem cells. Biochemical and gene‐expression analyses show enhanced glycosaminoglycan and collagen deposition, upregulation of chondrogenic markers (SOX9, COL2A1, ACAN), and low COL1A1 expression. Overall, CNF‐reinforced ADAG hydrogels combine cytocompatibility, mechanical resilience, injectability, and chondroinductive potential, highlighting suitability for stem cell‐mediated cartilage tissue engineering applications.