Bone-derived MSCs encapsulated in alginate hydrogel prevent collagen-induced arthritis in mice through the activation of adenosine A_(2A/2B)receptors in tolerogenic dendritic cells

Tolerogenic dendritic cells(tol DCs)facilitate the suppression of autoimmune responses by differentiating regulatory T cells(Treg).The dysfunction of immunotolerance results in the development of autoimmune diseases,such as rheumatoid arthritis(RA).As multipotent progenitor cells,mesenchymal stem cells(MSCs),can regulate dendritic cells(DCs)to restore their immunosuppressive function and prevent disease development.However,the underlying mechanisms of MSCs in regulating DCs still need to be better defined.Simultaneously,the delivery system for MSCs also influences their function.Herein,MSCs are encapsulated in alginate hydrogel to improve cell survival and retention in situ,maximizing efficacy in vivo.The three-dimensional co-culture of encapsulated MSCs with DCs demonstrates that MSCs can inhibit the maturation of DCs and the secretion of pro-inflammatory cytokines.In the collagen-induced arthritis(CIA)mice model,alginate hydrogel encapsulated MSCs induce a significantly higher expression of CD39^(+)CD73^(+)on MSCs.These enzymes hydrolyze ATP to adenosine and activate A_(2A/2B)receptors on immature DCs,further promoting the phenotypic transformation of DCs to tol DCs and regulating naive T cells to Tregs.Therefore,encapsulated MSCs obviously alleviate the inflammatory response and prevent CIA progression.This finding clarifies the mechanism of MSCs-DCs crosstalk in eliciting the immunosuppression effect and provides insights into hydrogel-promoted stem cell therapy for autoimmune diseases.

Bioprinting and regeneration of auricular cartilage using a bioactive bioink based on microporous photocrosslinkable acellular cartilage matrix

Tissue engineering provides a promising strategy for auricular reconstruction.Although the first international clinical breakthrough of tissue-engineered auricular reconstruction has been realized based on polymer scaffolds,this approach has not been recognized as a clinically available treatment because of its unsatisfactory clinical efficacy.This is mainly since reconstruction constructs easily cause inflammation and deformation.In this study,we present a novel strategy for the development of biological auricle equivalents with precise shapes,low immunogenicity,and excellent mechanics using auricular chondrocytes and a bioactive bioink based on biomimetic microporous methacrylate-modified acellular cartilage matrix(ACMMA)with the assistance of gelatin methacrylate(GelMA),poly(ethylene oxide)(PEO),and polycaprolactone(PCL)by integrating multi-nozzle bioprinting technology.Photocrosslinkable ACMMA is used to emulate the intricacy of the cartilage-specific microenvironment for active cellular behavior,while GelMA,PEO,and PCL are used to balance printability and physical properties for precise structural stability,form the microporous structure for unhindered nutrient exchange,and provide mechanical support for higher shape fidelity,respectively.Finally,mature auricular cartilage-like tissues with high morphological fidelity,excellent elasticity,abundant cartilage lacunae,and cartilage-specific ECM deposition are successfully regenerated in vivo,which provides new opportunities and novel strategies for the fabrication and regeneration of patient-specific auricular cartilage.

Titanium alloy composited with dual-cytokine releasing polysaccharide hydrogel to enhance osseointegration via osteogenic and macrophage polarization signaling pathways

Titanium alloy has been widely used in orthopedic surgeries as bone defect filling.However,the regeneration of high-quality new bones is limited due to the pro-inflammatory microenvironment around implants,resulting in a high occurrence rate of implant loosening or failure in osteological therapy.In this study,extracellular matrix-mimetic polysaccharide hydrogel co-delivering BMP-2 and interleukin(IL)-4 was composited with 3D printed titanium alloy to promote the osseointegration and regulate macrophage response to create a pro-healing microenvironment in bone defect.Notably,it is discovered from the bioinformatics data that IL-4 and BMP-2 could affect each other through multiple signal pathways to achieve a synergistic effect toward osteogenesis.The composite scaffold significantly promoted the osteoblast differentiation and proliferation of human bone marrow mesenchyme stem cells(hBMSCs).The repair of large-scale femur defect in rat indicated that the dual-cytokinedelivered composite scaffold could manipulate a lower inflammatory level in situ by polarizing macrophages to M2 phenotype,resulting in superior efficacy of mature new bone regeneration over the treatment of native titanium alloy or that with an individual cytokine.Collectively,this work highlights the importance of M2-type macrophages-enriched immune-environment in bone healing.The biomimetic hydrogel–metal implant composite is a versatile and advanced scaffold for accelerating in vivo bone regeneration,holding great promise in treating orthopedic diseases.