Large bone defects remain an unsolved clinical challenge because of the lack of effective vascularization in newly formed bone tissue. 3D bioprinting is a fabrication technology with the potential to create vascularized bone grafts with biological activity for repairing bone defects. In this study, vascular endothelial cells laden with thermosensitive bio-ink were bioprinted in situ on the inner surfaces of interconnected tubular channels of bone mesenchymal stem cell-laden 3D-bioprinted scaffolds. Endothelial cells exhibited a more uniform distribution and greater seeding efficiency throughout the channels. In vitro, the in situ bioprinted endothelial cells can form a vascular network through proliferation and migration. The in situ vascularized tissue-engineered bone also resulted in a coupling effect between angiogenesis and osteogenesis. Moreover, RNA sequencing analysis revealed that the expression of genes related to osteogenesis and angiogenesis is upregulated in biological processes. The in vivo 3D-bioprinted in situ vascularized scaffolds exhibited excellent performance in promoting new bone formation in rat calvarial critical-sized defect models. Consequently, in situ vascularized tissue-engineered bones constructed using 3D bioprinting technology have a potential of being used as bone grafts for repairing large bone defects, with a possible clinical application in the future.

Limb allotransplantation is emerging as a promising solution to the loss of a limb with the development of advanced surgical techniques and new, highly effective immunosuppressive agents. We retrospectively reviewed the records of 15 hand allotransplantations in 12 patients in China which were performed from September 1999 to May 2008. In total, there were 1 bilateral and 5 unilateral hand transplantations, 3 unilateral and 2 bilateral forearm transplantations, and 1 palm and 1 thumb transplantation. The average age of recipients was 34 ± 11.3 years (range, 19-52 years). At 1-year follow-up, all grafts were viable and with good function. Of the 15 hands transplanted, 8 are currently viable (mean follow-up, 52 ± 36.3 months; range, 16-112 months), including all 3 bilateral cases. Reasons for graft failure were rejection and failure of compliance with immunosuppressive therapy. Long-term survival of hand transplantation with appropriate immunosuppression is feasible, and satisfactory functional results have been achieved. Careful pretransplant psychologic and social evaluation, consideration of the financial burden of long-term immunosuppressive medications, and close multispecialty collaboration is critical for good outcomes. Limb rejection was related with immunosuppression use. Further study and experience is required before hand allotransplantation can become a generally recommended treatment.

Injectable hydrogels have long been gaining attention in the bone tissue engineering field owing to their ability to mix homogeneously with cells and therapeutic agents, minimally invasive administration, and seamless defect filling. Despite the advantages, the use of injectable hydrogels as cell delivery carriers is currently limited by the challenge of mimicking the natural microenvironment of the loaded cells, promoting cell proliferation, and enhancing bone regeneration. To overcome these problems, we aimed to develop an injectable and in situ-forming nanocomposite hydrogel composed of gelatin, alginate, and LAPONITE® to mimic the architecture and composition of the extracellular matrix. The encapsulated rat bone marrow mesenchymal stem cells (rBMSCs) survived in the nanocomposite hydrogel, and the gel promoted cell proliferation in vitro. Systematic in vivo research of the biomimetic hydrogel with or without cells was conducted in a critical-size (8 mm) rat bone defect model. The in vivo results proved that the hydrogel loaded with rBMSCs significantly promoted bone healing in rat calvarial defects, compared to the hydrogel without cells, and that the hydrogel did not provoked side effects on the recipients. Given these advantageous properties, the developed cell-loaded injectable nanocomposite hydrogel can greatly accelerate the bone healing in critical bone defects, thus providing a clinical potential candidate for orthopedic applications.