The concept of in situ 3D bio-printing was previously reported, while its realization has still encountered with several difficulties. The present study aimed to report robotic-assisted in situ 3D bio-printing technology for cartilage regeneration, and explore its potential in clinical application. A six-degree-of-freedom (6-DOF) robot was introduced in this study, and a fast tool center point (TCP) calibration method was developed to improve printing accuracy. The bio-ink consisted of hyaluronic acid methacrylate and acrylate-terminated 4-armed polyethylene glycol was employed as well. The in vitro experiment was performed on a resin model to verify the printing accuracy. The in vivo experiment was conducted on rabbits to evaluate the cartilage treatment capability. According to our results, the accuracy of the robot could be notably improved, and the error of printed surface was less than 30 μm. The osteochondral defect could be repaired during about 60 s, and the regenerated cartilage in hydrogel implantation and in situ 3D bio-printing groups demonstrated the same biomechanical and biochemical performance. We found that the cartilage injury could be treated by using this method. The robotic-assisted in situ 3D bio-printing is highly appropriate for improving surgical procedure, as well as promoting cartilage regeneration.

Hydrogels are extensively utilized in stem cell-based tissue regeneration, providing a supportive environment that facilitates cell survival, differentiation, and integration with surrounding tissues. However, designing hydrogels for regenerating hard tissues like bone presents significant challenges. Here, we introduce macroporous hydrogels with spatiotemporally programmed mechanical properties for stem cell-driven bone regeneration. Using liquid-liquid phase separation and interfacial supramolecular self-assembly of protein fibres, the macroporous structure of hydrogels provide ample space to prevent contact inhibition during proliferation. The rigid protein fibre-coated pore shell provides sustained mechanical cues for guiding osteodifferentiation and protecting against mechanical loads. Temporally, the hydrogel exhibits tunable degradation rates that can synchronize with new tissue deposition to some extent. By integrating localized mechanical heterogeneity, macroporous structures, surface chemistry, and regenerative degradability, we demonstrate the efficacy of these stem cell-encapsulated hydrogels in rabbit and porcine models. This marks a substantial advancement in tailoring the mechanical properties of hydrogels for stem cell-assisted tissue regeneration.

Osteoporosis is the most common degenerative orthopedic disease in the elderly. Recently, the therapeutic methods for osteoporosis have shifted towards the regulation of local immunity in bone tissues, which could provide a suitable environment for the positive regulation of bone metabolism, promoting osteogenic differentiation and inhibiting osteoclast differentiation. Our previous work demonstrated that iron oxide nanoparticles (IONPs) could positively regulate bone metabolism in vitro. In this study, we further demonstrated that daily administration of IONPs relieved estrogen deficiency-induced osteoporosis via scavenging reactive oxygen species in vivo. Meanwhile, IONPs promoted the osteogenic differentiation of bone marrow mesenchymal stem cells and inhibited the osteoclast differentiation of monocytes from IONPs treated mice. Besides, alendronate, a clinically used anti-osteoporosis bisphosphate, was employed to precisely deliver the IONPs to the bone tissues and played a synergically therapeutic role. Eventually, we verified the bone targeting ability, therapeutic efficiency, and biocompatibility of the novel bone target iron oxides in ovariectomy-induced osteoporotic mice. By applying BTNPs, the OVX-induced osteoporosis was significantly revised in mice models via the positive regulation of bone metabolism.

Osteoarthritis is a common degenerative joint disease, in which mechanical overloading disrupts subchondral bone remodeling before cartilage degeneration and the osteocytes in the subchondral bone are mainly responsible for mechanosensing. However, their functional role in the early osteoarthritis is still unclear. Here we show that mechanical stress induces osteocytes in subchondral bone to secrete extracellular vesicles that accelerate cartilage metabolic dysregulation in patients with both sexes and male mice. The miR-23b-3p in extracellular vesicles promotes cartilage catabolism and inhibits anabolism by targeting OTUD4, disrupting mitophagy in chondrocytes. Inhibiting miR-23b-3p in osteocytes or chondrocytes reduces cartilage degeneration and osteoarthritis progression in male mice. Together, our findings highlight that osteocyte-derived extracellular vesicles mediate communication with chondrocytes and suggest miR-23b-3p as a potential therapeutic target for osteoarthritis.