Precise Cell Type Electrical Stimulation Therapy Via Force-electric Hydrogel Microspheres for Cartilage Healing

Multifunctional piezoelectric hydrogels under ultrasound stimulation boost chondrogenesis by recruiting autologous stem cells and activating the Ca2+/CaM/CaN signaling pathway

Articular cartilage, owing to the lack of undifferentiated stem cells after injury, faces significant challenges in reconstruction and repair, making it a major clinical challenge. Therefore, there is an urgent need to design a multifunctional hydrogels capable of recruiting autologous stem cells to achieve in situ cartilage regeneration. Here, our study investigated the potential of a piezoelectric hydrogel (Hyd6) for enhancing cartilage regeneration through ultrasound (US) stimulation. Hyd6 has multiple properties including injectability, self-healing capabilities, and piezoelectric characteristics. These properties synergistically promote stem cell chondrogenesis. The fabrication and characterization of Hyd6 revealed its excellent biocompatibility, biodegradability, and electromechanical conversion capabilities. In vitro and in vivo experiments revealed that Hyd6, when combined with US stimulation, significantly promotes the recruitment of autologous stem cells and enhances chondrogenesis by generating electrical signals that promote the influx of Ca2+, activating downstream CaM/CaN signaling pathways and accelerating cartilage formation. An in vivo study in a rabbit model of chondral defects revealed that Hyd6 combined with US treatment significantly improved cartilage regeneration, as evidenced by better integration of the regenerated tissue with the surrounding cartilage, greater collagen type II expression, and improved mechanical properties. The results highlight the potential of Hyd6 as a novel therapeutic approach for treating cartilage injuries, offering a self-powered, noninvasive, and effective strategy for tissue engineering and regenerative medicine.

Conductive and piezoelectric biomaterials: a comprehensive review of load-bearing soft tissue repair

Load-bearing soft tissues, such as tendons, cartilage, and ligaments, withstand substantial mechanical stress and are susceptible to injury, particularly in athletes. The increasing prevalence of these injuries poses a significant challenge, exacerbated by the limitations of traditional treatments, which often lead to lengthy recovery periods and a high risk of recurrence. In recent years, researchers have harnessed the electrical properties of conductive and piezoelectric biomaterials to address challenges in load-bearing soft tissue engineering. These materials facilitate electrical stimulation and/or enable the monitoring of biomechanical properties during motion, with the aim of advancing load-bearing soft tissue regeneration and repair. This review explores the roles and mechanisms of electrical cues in load-bearing soft tissues, highlighting the development and application of two primary types of biomaterials-conductive and piezoelectric materials-in electro-biomechanical sensing and stimulation therapies for load-bearing soft tissue engineering.

HAMA-SBMA hydrogel with anti-inflammatory properties delivers cartilage organoids, boosting cartilage regeneration

Cartilage tissue lacks blood supply, which limits its ability to self-repair. Cartilage organoid (CO) technology, which replicates the structure and function of cartilage, holds significant promise. However, it is essential to maintain cellular function and ensure secure fixation at the site of injury. Therefore, we loaded allogeneic bone marrow mesenchymal stem cells (BMSCs) onto decellularized extracellular matrix microparticles of porcine articular cartilage (CEP) to construct CO-CCO, which demonstrated characteristics of articular cartilage. Additionally, betaine sulfonate methacrylate (SBMA) was incorporated into hyaluronic acid methacrylate (HAMA) to synthesize a novel hydrogel, HAMA-SBMA (HS), characterized by its adhesive properties, promotion of chondrogenesis, and inhibition of inflammation. In Vivo studies revealed that the combination of HS and CCO (HS + CCO) exhibited excellent repair efficacy in both rat and sheep models of cartilage defects. Mechanistically, we found that HS + CCO promoted cartilage repair by activating the Frizzled-related protein (Frzb), which inhibited inflammatory factors and enhanced the expression of the adhesion factor integrin ɑ5β1. This strategy, which combines hydrogels and organoids, enhances cartilage repair, offering substantial potential for clinical applications in cartilage regeneration.

Micromotion-Driven "Mechanical-Electrical-Pharmaceutical Coupling" Bone-Guiding Membrane Modulates Stress-Concentrating Inflammation Under Diabetic Fractures

The use of piezoelectric materials to convert micromechanical energy at the fracture site into electrical signals, thereby modulating stress-concentrated inflammation, has emerged as a promising treatment strategy for diabetic fractures. However, traditional bone-guiding membranes often face challenges in diabetic fracture repair due to their passive and imprecise drug release profiles. Herein, a piezoelectric polyvinylidene fluoride (PVDF) fibrous membrane is fabricated through electrospinning and oxidative polymerization to load metformin (Met) into a polypyrrole (PPy) coating (Met-PF@PPy), creating a "mechanical-electrical-pharmaceutical coupling" system. In a micromotion mechanical environment, Met-PF@PPy converts mechanical energy into electrical signals, activating the electrochemical reduction of PPy and triggering stress-responsive Met release. The generated electrical signals suppress inflammation through M1-to-M2 macrophage polarization and simultaneously enhance osteogenesis. Simultaneously, Met inhibits the NF-κB pathway to reduce pro-inflammatory cytokines while activating the AMPK pathway to promote osteogenesis and angiogenesis. In a diabetic mouse femoral fracture model, Met-PF@PPy significantly reduces inflammatory markers, enhances vascularization, and increases bone mineral density and bone volume fraction by over 30%. This "force-electric-drug coupling" strategy provides an innovative approach for active regulation in diabetic fracture repair and offers a versatile platform for advancing piezoelectric materials in regenerative medicine.

Engineered Stem Cell Clusters for Extracellular Vesicles-Mediated Gene Delivery to Rejuvenate Chondrocytes and Facilitate Chondrogenesis in Osteoarthritis Therapy

Gene therapy offers an ideal potential treatment strategy for osteoarthritis (OA). However, the safe and efficient delivery of therapeutic genes remains highly challenging because of the inactivation in direct delivery of miRNA, low transfection efficiency, and a short half-life. This study introduced a gene therapy strategy using mesenchymal stem cells (MSCs) as a gene delivery platform and achieved the sustained delivery of therapeutic genes via engineered MSCs-derived extracellular vesicles (EVs). The miRNA-874-3p is combined with an exosome-targeting motif and transfected into bone marrow mesenchymal stem cells (BMSCs). The BMSCsmotif+miR874 are then seeded onto hydrogel microspheres, creating the BMSCmotif+miR874/MS system for OA treatment. In vitro experiments demonstrated that miRNA-874-3p not only alleviated inflammation and oxidative stress-induced damage to chondrocytes by downregulating the NF-κB signaling pathway, thereby rejuvenating chondrocytes, but also promoted chondrogenesis in the inflammatory microenvironment. Furthermore, the engineered BMSCs in the system demonstrated prolonged retention in vivo, thereby enabling the sustained delivery of the therapeutic gene, miRNA-874-3p, over an extended duration. In the rat OA model, BMSCmotif+miR874/MS successfully delivered miRNA-874-3p to the articular cartilage and effectively alleviated cartilage degeneration. In conclusion, this EVs-mediated therapeutic gene delivery approach enables miRNA-based gene therapy a viable alternative to surgery for OA treatment and provides a novel option for gene therapy.

Polydopamine Nanocomposite Hydrogel for Drug Slow-Release in Bone Defect Repair: A Review of Research Advances

In recent years, hydrogels have emerged as promising candidates for bone defect repair due to their excellent biocompatibility, high porosity, and water-retentive properties. However, conventional hydrogels face significant challenges in clinical translation, including brittleness, low mechanical strength, and poorly controlled drug degradation rates. To address these limitations, as a multifunctional polymer, polydopamine (PDA) has shown great potential in both bone regeneration and drug delivery systems. Its robust adhesive properties, biocompatibility, and responsiveness to photothermal stimulation make it an ideal candidate for enhancing hydrogel performance. Integrating PDA into conventional hydrogels not only improves their mechanical properties but also creates an environment conducive to cell adhesion, proliferation, and differentiation, thereby promoting bone defect repair. Moreover, PDA facilitates controlled drug release, offering a promising approach to optimizing treatment outcomes. This paper first explores the mechanisms through which PDA promotes bone regeneration, laying the foundation for its clinical translation. Additionally, it discusses the application of PDA-based nanocomposite hydrogels as advanced drug delivery systems for bone defect repair, providing valuable insights for both research and clinical translation.