Extrusion-based three-dimensional bioprinting of osteochondral scaffolds: Strategies using hydrogel/thermoplastic combinations

Osteochondral defects remain a major clinical challenge due to the complex hierarchical structure, marked mechanical gradients, and distinct biological requirements of cartilage, calcified cartilage, and subchondral bone. Extrusion-based three-dimensional bioprinting has emerged as a promising strategy for osteochondral repair, enabling the spatially controlled deposition of cells, biomaterials, and bioactive factors to fabricate constructs with region-specific compositions and architectures. Among the available material systems, combinations of hydrogels and thermoplastics have attracted increasing attention, as they integrate the favourable biological microenvironment of hydrogels with the mechanical strength, structural stability, and printability of thermoplastics. This synergy makes them particularly suitable for the fabrication of biomimetic osteochondral scaffolds with multiphasic and gradient features. This review systematically summarises the application of hydrogel/thermoplastic combinations in extrusion-based bioprinting for osteochondral repair, with particular emphasis on their role in addressing the structural, mechanical, and biological requirements of osteochondral regeneration. It discusses the design requirements for osteochondral scaffolds, the properties and crosslinking strategies of hydrogel bioinks, the function of thermoplastic frameworks in mechanical reinforcement, and current approaches for constructing multilayered and gradient scaffolds. The review also analyses current limitations, including challenges related to printability, material compatibility, interlayer bonding, degradation mismatch, and long-term functional performance. Overall, this work provides a comprehensive overview of hydrogel/thermoplastic composite systems and highlights their potential to advance the development of clinically relevant bioprinted scaffolds for osteochondral repair.