Stimuli-responsive 4D-bioprinted constructs for musculoskeletal tissue regeneration: Shape-morphing mechanisms, cell-laden bioink engineering, and preclinical outcomes.

INTRODUCTION

Musculoskeletal disorders impose a substantial global disability burden. Conventional 3D bioprinting cannot replicate the dynamic, anisotropic architecture of bone, cartilage, skeletal muscle, and cardiac muscle. Four-dimensional (4D) bioprinting addresses this by integrating stimuli-responsive materials into constructs, enabling programmed shape transformation and adaptive behavior following implantation.

METHODS

This narrative review examines primary experimental research on stimuli-responsive 4D-bioprinted musculoskeletal constructs, drawing on in vitro, in vivo, and combined outcomes from leading peer-reviewed journals.

RESULTS

Evidence spans four stimuli modalities - magnetic actuation, near-infrared (NIR) photothermal response, thermoresponsive swelling-shrinking transitions, and shape memory polymer (SMP) recovery - applied across bone, cartilage, skeletal muscle, and cardiac constructs. Bioink formulations from silk fibroin-gelatin composites and alginate-polydopamine inks to GelMA-based hydrogels and polyester SMPs present trade-offs between printability, shape fidelity, and cellular compatibility. Cross-study synthesis identifies stiffness trajectory, architectural anisotropy, and dynamic deformation as primary mechano-biological axes directing cell fate decisions. Preclinical studies document encouraging ossification and chondrogenesis outcomes, though constructs fall short of native tissue mechanical benchmarks.

CONCLUSION

Translational barriers range from fundamental physical constraints - including the mechanical performance gap and stimulus penetration depth limitations - to incremental engineering challenges amenable to near-term resolution. Passive hydration-driven deployment represents the most clinically tractable strategy, while multifunctional bioinks integrating stimuli-responsiveness, bioactive factor presentation, and cell-instructive surface chemistry define the primary material development direction.