RGD-incorporated biomimetic cryogels for hyaline cartilage regeneration

Comparison studies identify mesenchymal stromal cells with potent regenerative activity in osteoarthritis treatment

Osteoarthritis affects 15% of people over 65 years of age. It is characterized by articular cartilage degradation and inflammation, leading to joint pain and disability. Osteoarthritis is incurable and the patients may eventually need joint replacement. An emerging treatment is mesenchymal stromal cells (MSCs), with over two hundred clinical trials being registered. However, the outcomes of these trials have fallen short of the expectation, due to heterogeneity of MSCs and uncertain mechanisms of action. It is generally believed that MSCs exert their function mainly by secreting immunomodulatory and trophic factors. Here we used knee osteoarthritis mouse model to assess the therapeutic effects of MSCs isolated from the white adipose or dermal adipose tissue of Prrx1-Cre; R26tdTomato mice and Dermo1-Cre; R26tdTomato mice. We found that the Prrx1-lineage MSCs from the white adipose tissues showed the greatest in vitro differentiation potentials among the four MSC groups and single cell profiling showed that the Prrx1-lineage MSCs contained more stem cells than the Dermo1 counterpart. Only the Prrx1-lineage cells isolated from white adipose tissues showed long-term therapeutic effectiveness on early-stage osteoarthritis models. Mechanistically, Prrx1-lineage MSCs differentiated into Col2+ chondrocytes and replaced the damage cartilage, activated Col1 expressing in resident chondrocytes, and inhibited synovial inflammation. Transcriptome analysis showed that the articular chondrocytes derived from injected MSCs expressed immunomodulatory cytokines, trophic factors, and chondrocyte-specific genes. Our study identified a MSC population genetically marked by Prrx1 that has great multipotentiality and can differentiate into chondrocytes to replace the damaged cartilage.

A novel cartilage-targeting MOF-HMME-RGD sonosensitizer combined with sonodynamic therapy to enhance chondrogenesis and cartilage regeneration

Articular cartilage regeneration is still a difficult task due to the cartilage's weak capacity for self-healing and the effectiveness of the available therapies. The engineering of cartilage tissue has seen widespread use of stem cell-based therapies. However, efficient orientation of line-specific bone marrow mesenchymal stem cells (BMSCs) to chondrogenesis and maintenance of chondrogenic differentiation challenged stem cell-based therapy. Herein, we developed a Fe-based metal-organic framework (MOF) loaded with hematoporphyrin monomethyl ether (HMME) and cartilage-targeting arginine-aspartate-glycine (RGD) peptide to form MOF-HMME-RGD sonosensitizer to regulate BMSCs chondrogenic differentiation for cartilage regeneration via the modulation of reactive oxygen species (ROS). By using sonodynamic therapy (SDT), the MOF-HMME-RGD demonstrated favorable biocompatibility, could generate a modest amount of ROS, and enhanced BMSCs chondrogenic differentiation through increased accumulation of glycosaminoglycan, an ECM component specific to cartilage, and upregulated expression of key chondrogenic genes (ACAN, SOX9, and Col2a1). Further, transplanted BMSCs loading MOF-HMME-RGD combined with SDT enhanced cartilage regeneration for cartilage defect repair after 8 weeks into treatment. This synergistic strategy based on MOF nanoparticles provides an instructive approach to developing alternative sonosensitizers for cartilage regeneration combined with SDT.

Cryogel Scaffolds for Tissue-Engineering: Advances and Challenges for Effective Bone and Cartilage Regeneration

Critical-sized bone defects and articular cartilage injuries resulting from trauma, osteonecrosis, or age-related degeneration can be often non-healed by physiological repairing mechanisms, thus representing a relevant clinical issue due to a high epidemiological incidence rate. Novel tissue-engineering approaches have been proposed as an alternative to common clinical practices. This cutting-edge technology is based on the combination of three fundamental components, generally referred to as the tissue-engineering triad: autologous or allogenic cells, growth-stimulating factors, and a scaffold. Three-dimensional polymer networks are frequently used as scaffolds to allow cell proliferation and tissue regeneration. In particular, cryogels give promising results for this purpose, thanks to their peculiar properties. Cryogels are indeed characterized by an interconnected porous structure and a typical sponge-like behavior, which facilitate cellular infiltration and ingrowth. Their composition and the fabrication procedure can be appropriately tuned to obtain scaffolds that match the requirements of a specific tissue or organ to be regenerated. These features make cryogels interesting and promising scaffolds for the regeneration of different tissues, including those characterized by very complex mechanical and physical properties, such as bones and joints. In this review, state-of-the-art fabrication and employment of cryogels for supporting effective osteogenic or chondrogenic differentiation to allow for the regeneration of functional tissues is reported. Current progress and challenges for the implementation of this technology in clinical practice are also highlighted.

Editorial: Focus issue on biomaterials approaches to the repair and regeneration of cartilage tissue

Traditional joint replacement surgery faces the risk of enormous trauma and secondary revision while using medication to relieve symptoms can cause bone thinning, weight gain and interference with the patient's pain signalling. Medical research has therefore focused on minimally invasive solutions for implanting tissue-engineered scaffolds to induce cartilage regeneration and repair. In cartilage tissue engineering, there are still technical barriers to seed cells, scaffold construction techniques, mechanical properties, and the regulation of the internal environment on the transplanted material. This issue focuses on the development of cartilage repair, cutting-edge discoveries, manufacturing technologies, and the current technological queries still faced in cartilage regenerative medicine research. The articles in this collection cover the coordination of physical and biochemical signals, genes, and regulations by the extracellular environment.