Advances in the Development of Gradient Scaffolds Made of Nano-Micromaterials for Musculoskeletal Tissue Regeneration

CBD-conjugated BMP-inhibiting exosomes on collagen scaffold dual-target Achilles tendon repair: Synergistic regeneration and heterotopic ossification prevention

Tendon injuries in the aging population are often complicated by heterotopic ossification (HO), hindering functional recovery. Exosomes from tendon stem/progenitor cells (TSPCs) promote regeneration but may also induce osteogenesis, contributing to HO. Preconditioning with the BMP inhibitor LDN193189 and modification with collagen-binding peptides (CBD) can enhance the tenogenic potential of exosomes while mitigating osteogenic effects. We evaluated the efficacy of a 3D-printed scaffold loaded with LDN-preconditioned, CBD-modified exosomes (3D-CBD@LDN/Exos) derived from CD26+ TSPCs in promoting Achilles tendon repair and preventing HO in aged Sprague-Dawley rats. CD26+ TSPCs were isolated from rat tendons, and exosomes were collected after LDN treatment and subsequently modified with CBD. A scaffold composed of PLGA and collagen I was fabricated via 3D printing and loaded with the exosomes. Rats (20 months old) with 6-mm Achilles tendon defects were randomly assigned to Control, 3D-Exos, 3D-LDN/Exos, or 3D-CBD@LDN/Exos groups, and tendon regeneration was evaluated at 4 and 12 weeks using histology, ECM quantification, micro-CT, and biomechanical testing. At 12 weeks, the 3D-CBD@LDN/Exos group exhibited near-normal histology, enhanced collagen and sGAG deposition, biomechanical properties comparable to native tendons, and significantly reduced HO, indicating that this dual-targeted strategy holds promise for tendon repair.

Tendon regeneration deserves better: focused review on In vivo models, artificial intelligence and 3D bioprinting approaches

Tendon regeneration has been one of the most challenging issues in orthopedics. Despite various surgical techniques and rehabilitation methods, tendon tears or ruptures cannot wholly regenerate and gain the load-bearing capacity the tendon tissue had before the injury. The enhancement of tendon regeneration mostly requires grafting or an artificial tendon-like tissue to replace the damaged tendon. Tendon tissue engineering offers promising regenerative effects with numerous techniques in the additive manufacturing context. 3D bioprinting is a widely used additive manufacturing method to produce tendon-like artificial tissues based on biocompatible substitutes. There are multiple techniques and bio-inks for fabricating innovative scaffolds for tendon applications. Nevertheless, there are still many drawbacks to overcome for the successful regeneration of injured tendon tissue. The most important target is to catch the highest similarity to the tissue requirements such as anisotropy, porosity, viscoelasticity, mechanical strength, and cell-compatible constructs. To achieve the best-designed artificial tendon-like structure, novel AI-based systems in the field of 3D bioprinting may unveil excellent final products to re-establish tendon integrity and functionality. AI-driven optimization can enhance bio-ink selection, scaffold architecture, and printing parameters, ensuring better alignment with the biomechanical properties of native tendons. Furthermore, AI algorithms facilitate real-time process monitoring and adaptive adjustments, improving reproducibility and precision in scaffold fabrication. Thus, in vitro biocompatibility and in vivo application-based experimental processes will make it possible to accelerate tendon healing and reach the required mechanical strength. Integrating AI-based predictive modeling can further refine these experimental processes to evaluate scaffold performance, cell viability, and mechanical durability, ultimately improving translation into clinical applications. Here in this review, 3D bioprinting approaches and AI-based technology incorporation were given in addition to in vivo models.

Tendon regeneration deserves better: focused review on In vivo models, artificial intelligence and 3D bioprinting approaches

Tendon regeneration has been one of the most challenging issues in orthopedics. Despite various surgical techniques and rehabilitation methods, tendon tears or ruptures cannot wholly regenerate and gain the load-bearing capacity the tendon tissue had before the injury. The enhancement of tendon regeneration mostly requires grafting or an artificial tendon-like tissue to replace the damaged tendon. Tendon tissue engineering offers promising regenerative effects with numerous techniques in the additive manufacturing context. 3D bioprinting is a widely used additive manufacturing method to produce tendon-like artificial tissues based on biocompatible substitutes. There are multiple techniques and bio-inks for fabricating innovative scaffolds for tendon applications. Nevertheless, there are still many drawbacks to overcome for the successful regeneration of injured tendon tissue. The most important target is to catch the highest similarity to the tissue requirements such as anisotropy, porosity, viscoelasticity, mechanical strength, and cell-compatible constructs. To achieve the best-designed artificial tendon-like structure, novel AI-based systems in the field of 3D bioprinting may unveil excellent final products to re-establish tendon integrity and functionality. AI-driven optimization can enhance bio-ink selection, scaffold architecture, and printing parameters, ensuring better alignment with the biomechanical properties of native tendons. Furthermore, AI algorithms facilitate real-time process monitoring and adaptive adjustments, improving reproducibility and precision in scaffold fabrication. Thus, in vitro biocompatibility and in vivo application-based experimental processes will make it possible to accelerate tendon healing and reach the required mechanical strength. Integrating AI-based predictive modeling can further refine these experimental processes to evaluate scaffold performance, cell viability, and mechanical durability, ultimately improving translation into clinical applications. Here in this review, 3D bioprinting approaches and AI-based technology incorporation were given in addition to in vivo models.

Bioinspired Paste-Extrusion Printed Microlattices with Natural Bone-Like Porosity and Performance

The structure feature determines its performance. In the field of biological implants, microlattices are commonly used as building blocks for light-weight and adaptive purposes, which however show limitations in biological and mechanical properties as compared with natural bones. Inspired by the efficient mass transfer and high fault tolerance of biological neural networks derived from the hierarchical structure and functional gradient, a bioinspired paste-extrusion printed microlattice (BPPM) structure is developed and its tunable properties are demonstrated. The mechanical properties of non-crossing microlattice structures are first verified outweigh crossing one under equivalent compressive stress. Then, by introducing gradient components and a paste-extrusion 3D printing process, a BPPM structure with a hierarchical porosity, and gradient composites is fabricated. As a result, the BPPM shows the eliminated deformation along the gradient direction, a fine surface roughness (Sa 3.65-15.67 µm), a wide range of porosity (56-78%) and compressive strength (3.44-22.3 MPa), a favorable permeability (3.02 × 103-3.22 × 103D), and good biocompatibility and promoted cell proliferation. This work not only demonstrates the properties of BPPM in a range of natural bones but also provides a robust way to realize it.

3D printing in musculoskeletal interface engineering: Current progress and future directions

The musculoskeletal system relies on critical tissue interfaces for its function; however, these interfaces are often compromised by injuries and diseases. Restoration of these interfaces is complex by nature which renders traditional treatments inadequate. An emerging solution is three-dimensional printing, which allows for precise fabrication of biomimetic scaffolds to enhance tissue regeneration. This review summarizes the use of 3D printing in creating scaffolds for musculoskeletal interfaces, mainly focusing on advanced techniques such as multi-material printing, bioprinting, and 4D printing. We emphasize the significance of mimicking natural tissue gradients and the selection of appropriate biomaterials to ensure scaffold success. The review outlines state-of-the-art 3D printing technologies, varying from extrusion, inkjet and laser-assisted bioprinting, which are crucial for producing scaffolds with tailored mechanical and biological properties. Applications in cartilage-bone, intervertebral disc, tendon/ligament-bone, and muscle-tendon junction engineering are discussed, highlighting the potential for improved integration and functionality. Furthermore, we address challenges in material development, printing resolution, and the in vivo performance of scaffolds, as well as the prospects for clinical translation. The review concludes by underscoring the transformative potential of 3D printing to advance orthopedic medicine, offering a roadmap for future research at the intersection of biomaterials, drug delivery, and tissue engineering.