3D-Printed Scaffolds Promote Angiogenesis by Recruiting Antigen-Specific T Cells

The immune response after implantation is a primary determinant of the tissue-repair effects of threedimensional(3D)-printed scaffolds.Thus,scaffolds that can subtly regulate immune responses may display extraordinary functions.Inspired by the angiogenesis promotion effect of humoral immune response,we covalently combined mesoporous silica micro rod(MSR)/polyethyleneimine(PEI)/ovalbumin(OVA)self-assembled vaccines with 3D-printed calcium phosphate cement(CPC)scaffolds for local antigen-specific immune response activation.With the response activated,antigen-specific CD4+T helper2(Th2)cells can be recruited to promote early angiogenesis.The silicon(Si)ions from MSRs can accelerate osteogenesis,with an adequate blood supply being provided.At room temperature,scaffolds with uniformly interconnected macropores were printed using a self-setting CPC-based printing paste,which promoted the uniform dispersion and structural preservation of functional polysaccharides oxidized hyaluronic acid(OHA)inside.Sustained release of OVA was achieved with MSR/PEI covalently attached to scaffolds rich in aldehyde groups as the vaccine carrier.The vaccine-loaded scaffolds effectively recruited and activated dendritic cells(DCs)for antigen presentation and promoted the osteogenic differentiation of bone marrow mesenchymal stem cells(BMSCs)in vitro.When embedded subcutaneously in vivo,the vaccine-loaded scaffolds increased the proportion of Th2 cells in the spleen and locally recruited antigenspecific T cells to promote angiogenesis in and around the scaffold.Furthermore,the result in a rat skull defect-repair model indicated that the antigen-specific vaccine-loaded scaffolds promoted the regeneration of vascularized bone.This method may provide a novel concept for patient-specific implant design for angiogenesis promotion.

Regulated macrophage immune microenvironment in 3D printed scaffolds for bone tumor postoperative treatment

The 3D printing technique is suitable for patient-specific implant preparation for bone repair after bone tumor resection.However,improving the survival rate due to tumor recurrence remains a challenge for implants.The macrophage polarization induction to M2-type tumor-associated macrophages(TAMs)by the tumor microenvironment is a key factor of immunosuppression and tumor recurrence.In this study,a regenerative scaffold regulating the macrophage immune microenvironment and promoting bone regeneration in a dual-stage process for the postoperative treatment of bone tumors was constructed by binding a colony-stimulating factor 1 receptor(CSF-1R)inhibitor GW2580 onto in situ cosslinked hydroxybutylchitosan(HBC)/oxidized chondroitin sulfate(OCS)hydrogel layer covering a 3D printed calcium phosphate scaffold based on electrostatic interaction.The hydrogel layer on scaffold surface not only supplied abundant sulfonic acid groups for stable loading of the inhibitor,but also acted as the cover mask protecting the bone repair part from exposure to unhealthy growth factors in the microenvironment at the early treatment stage.With local prolonged release of inhibitor being realized via the functional material design,CSF-1R,the main pathway that induces polarization of TAMs,can be efficiently blocked,thus regulating the immunosuppressive microenvironment and inhibiting tumor development at a low therapeutic dose.At the later stage of treatment,calcium phosphate component of the scaffold can facilitate the repair of bone defects caused by tumor excision.In conclusion,the difunctional 3D printed bone repair scaffold regulating immune microenvironment in stages proposed a novel approach for bone tumor postoperative treatment.

Synergy effects of Asperosaponin Ⅵ and bioactive factor BMP-2 on osteogenesis and anti-osteoclastogenesis

Osteoporosis is a reduction in skeletal mass due to the decrease of osteogenic ability and the activation of the osteoclastic function.Inhibiting bone resorption and accelerating the new bone formation is a promising strategy to repair the bone defect of osteoporosis.In this study,we first systematically investigated the roles of Chinese medicine Asperosaponin Ⅵ(ASP Ⅵ)on osteogenic mineralization of BMSCs and osteoclastogenesis of BMMs,and then explored the synergistic effect of ASP Ⅵ and BS(BMP-2 immobilized in 2-N,6-O-sulfated chitosan)on bone formation.The result showed that ASP Ⅵ with the concentration lower than 10^(-4) M contributed to the expression of osteogenic gene and inhibited osteoclastic genes RANKL of BMSCs.Simultaneously,ASP Ⅵ significantly reduced the differentiation of mononuclear osteoclasts in the process of osteoclast formation induced by M-CSF and RANKL.Furthermore,by stimulating the SMADs,TGF-β1,VEGFA,and OPG/RANKL signaling pathways,ASBS(ASP Ⅵ and BS)substantially enhanced osteogenesis,greatly promoted angiogenesis,and suppressed osteoclastogenesis.The findings provide a new perspective on osteoporosis care and prevention.

3D bioprinting of cell-laden constructs for regenerative medicine

Human tissue consists of various tissue-specific cells,extracellular matrix components and microstructures,and growth factors.With promising multi-cell and multi-material integration manufacturing feature,3D extrusion bioprinting has shown outstanding application potential in the field of regenerative medicine.For functional tissue regeneration,bioprinted constructs not only play the role of a cell-delivery system,but also serve as an important host niche for cell proliferation and work.In order to meet the specific requirements of different tissue regeneration,development of bio-inks that provide tissue-specific biophysical cues and biochemical microenvironments is an important research topic.Furthermore,reconstruction of tissues with anisotropic structure,such as articular cartilage and meniscus,largely depend on the design of 3D bioprinting path for accurate arrangement of specific bio-inks.This review summarizes the advanced designs of tissue-specific 3D bioprinting of cell-laden constructs for functional regeneration of skeletal and locomotor systems such as bone,cartilage,skeletal muscle,and blood vessels via the collaboration of bio-ink and printing processes.It may provide a basis for synergistic design for functional regenerative constructs bioprinting in the future.