Using Decellularized Magnetic Microrobots to Deliver Functional Cells for Cartilage Regeneration.

The use of natural cartilage extracellular matrix (ECM) has gained widespread attention in the field of cartilage tissue engineering. However, current approaches for delivering functional scaffolds for osteoarthritis (OA) therapy rely on knee surgery, which is limited by the narrow and complex structure of the articular cavity and carries the risk of injuring surrounding tissues. This work introduces a novel cell microcarrier, magnetized cartilage ECM-derived scaffolds (M-CEDSs), which are derived from decellularized natural porcine cartilage ECM. Human bone marrow mesenchymal stem cells are selected for their therapeutic potential in OA treatments. Owing to their natural composition, M-CEDSs have a biomechanical environment similar to that of human cartilage and can efficiently load functional cells while maintaining high mobility. The cells are released spontaneously at a target location for at least 20 days. Furthermore, cell-seeded M-CEDSs show better knee joint function recovery than control groups 3 weeks after surgery in preclinical experiments, and ex vivo experiments reveal that M-CEDSs can rapidly aggregate inside tissue samples. This work demonstrates the use of decellularized microrobots for cell delivery and their in vivo therapeutic effects in preclinical tests.

Magnetically Driven Undulatory Microswimmers Integrating Multiple Rigid Segments.

Mimicking biological locomotion strategies offers important possibilities and motivations for robot design and control methods. Among bioinspired microrobots, flexible microrobots exhibit remarkable efficiency and agility. These microrobots traditionally rely on soft material components to achieve undulatory propulsion, which may encounter challenges in design and manufacture including the complex fabrication processes and the interfacing of rigid and soft components. Herein, a bioinspired magnetically driven microswimmer that mimics the undulatory propulsive mechanism is proposed. The designed microswimmer consists of four rigid segments, and each segment is connected to the succeeding segment by joints. The microswimmer is fabricated integrally by 3D laser lithography without further assembly, thereby simplifying microrobot fabrication while enhancing structural integrity. Experimental results show that the microswimmer can successfully swim forward along guided directions via undulatory locomotion in the low Reynolds number (Re) regime. This work demonstrates for the first time that the flexible characteristic of microswimmers can be emulated by 3D structures with multiple rigid segments, which broadens possibilities in microrobot design. The proposed magnetically driven microswimmer can potentially be used in biomedical applications, such as medical diagnosis and treatment in precision medicine.

Automated In Vivo Navigation of Magnetic-Driven Microrobots Using OCT Imaging Feedback.

OBJECTIVE: The application of in vivo microrobot navigation has received considerable attention from the field of precision therapy, which uses microrobots in living organisms. METHODS: This study investigates the navigation of microrobots in vivo using optical coherence tomography (OCT) imaging feedback. The electromagnetic gradient field generated by a home-made electromagnetic manipulation system is magnetically modeled. With this model, the magnetic force acting on the microrobot is calculated, and the relationship between this force and the velocity of the microrobot is characterized. RESULTS: Results are verified through in vitro experiments wherein microrobots are driven in three types of fluid, namely, normal saline, gastric juice, and mouse urine. In vivo experiments are performed to navigate the microrobot in a mouse portal vein in which the OCT imaging system tracks the microrobot in vivo. CONCLUSIONS: Experimental results demonstrate the effectiveness of the proposed approach. The microrobots can be magnetically driven in the in vivo environment using the OCT imaging feedback. SIGNIFICANCE: The significance of this study lies in providing a new method of driving microrobots in vivo.