Enhanced osteogenic differentiation in 3D hydrogel scaffold via macrophage mitochondrial transfer

Yoda1-Loaded Microfibrous Scaffolds Accelerate Osteogenesis through Piezo1-F-Actin Pathway-Mediated YAP Nuclear Localization and Functionalization

Yoda1 has been recognized as an effective pharmacological intervention for the treatment of critical bone defects. However, the local delivery strategy of Yoda1 is uncommon, and the underlying mechanism through which Yoda1 enhances osteogenesis has been poorly investigated. Here, we propose utilizing electrohydrodynamic (EHD)-printed microfibrous scaffolds as a drug carrier for loading Yoda1 through a polydopamine (PDA) coating, and the synthetic mechanisms for enhancing bone regeneration are explored. Yoda1 was successfully loaded on the surface of the EHD-printed microfibrous scaffolds with the assistance of PDA. The results of in vitro experiments demonstrated that the Yoda1-loaded microfibrous scaffold group exhibited a more than 2-fold increase in COL-I protein levels compared to the control group. Additionally, the expression levels of osteogenic indicators such as ALP, Runx2, and OCN genes were significantly increased by 2-4-fold compared to those in the control group. We revealed that Yoda1 can effectively activate the Piezo1-F-actin pathway, thereby facilitating YAP nucleation and promoting lysine histone acetylation. Consequently, this mechanism enhanced the functionality of YAP nucleation and upregulated the expression of COL-I. Moreover, when implanted in vivo, the Yoda1-loaded microfibrous scaffold group could promote macrophage M2 polarization, thereby enhancing bone regeneration at defect sites. It is believed that the localized release of Yoda1 via EHD-printed PCL scaffolds might represent a promising strategy for the clinically precise treatment of bone defects.

From powerhouse to modulator: regulating immune system responses through intracellular mitochondrial transfer

Mitochondria are traditionally known as the cells' powerhouses; however, their roles go far beyond energy suppliers. They are involved in intracellular signaling and thus play a crucial role in shaping cells' destiny and functionality, including immune cells. Mitochondria can be actively exchanged between immune and non-immune cells via mechanisms such as nanotubes and extracellular vesicles. The mitochondria transfer from immune cells to different cells is associated with physiological and pathological processes, including inflammatory disorders, cardiovascular diseases, diabetes, and cancer. On the other hand, mitochondrial transfer from mesenchymal stem cells, bone marrow-derived stem cells, and adipocytes to immune cells significantly affects their functions. Mitochondrial transfer can prevent exhaustion/senescence in immune cells through intracellular signaling pathways and metabolic reprogramming. Thus, it is emerging as a promising therapeutic strategy for immune system diseases, especially those involving inflammation and autoimmune components. Transferring healthy mitochondria into damaged or dysfunctional cells can restore mitochondrial function, which is crucial for cellular energy production, immune regulation, and inflammation control. Also, mitochondrial transfer may enhance the potential of current therapeutic immune cell-based therapies such as CAR-T cell therapy.

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.

Dual-crosslinkable alginate hydrogel with dynamic viscoelasticity for chondrogenic and osteogenic differentiation of mesenchymal stem cells

Tissue engineering presents an advanced approach for cartilage and bone tissue repair, with cells serving as a crucial component of the treatment process. The viscoelasticity, a defining fundamental mechanical property, significantly influences cellular behavior. The majority of current research has primarily focused on comparing static elastic and viscoelastic hydrogels with varying stress relaxation rates, while neglecting the inherent dynamic viscoelastic properties of native tissues. Herein, we developed a dynamic viscoelastic hydrogel system employing modified sodium alginate hydrogels to explore the impact of the transfer of viscoelasticity and elastic mechanical properties on the behavior and fate of mesenchymal stem cells (MSCs). The results demonstrated that a viscoelastic environment facilitates greater cell proliferation and spreading. Moreover, extended exposure to the viscoelastic environment resulted in significantly enhanced secretion of osteogenic/chondrogenic extracellular matrix (ECM), upregulates differentiation-specific gene expression, and supports nuclear localization of Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ). This study elucidates the mechanical microenvironment required for MSC differentiation, enriching the theoretical foundation for the design of optimized scaffold in cartilage and bone tissue engineering applications.

Revolutionizing bone defect healing: the power of mesenchymal stem cells as seeds

Bone defects can arise from trauma or pathological factors, resulting in compromised bone integrity and the loss or absence of bone tissue. As we are all aware, repairing bone defects is a core problem in bone tissue engineering. While minor bone defects can self-repair if the periosteum remains intact and normal osteogenesis occurs, significant defects or conditions such as congenital osteogenesis imperfecta present substantial challenges to self-healing. As research on mesenchymal stem cell (MSC) advances, new fields of application have emerged; however, their application in orthopedics remains one of the most established and clinically valuable directions. This review aims to provide a comprehensive overview of the research progress regarding MSCs in the treatment of diverse bone defects. MSCs, as multipotent stem cells, offer significant advantages due to their immunomodulatory properties and ability to undergo osteogenic differentiation. The review will encompass the characteristics of MSCs within the osteogenic microenvironment and summarize the research progress of MSCs in different types of bone defects, ranging from their fundamental characteristics and animal studies to clinical applications.