Macroporous Granular Hydrogels Functionalized with Aligned Architecture and Small Extracellular Vesicles Stimulate Osteoporotic Tendon-To-Bone Healing

Osteoporotic tendon-to-bone healing (TBH) after rotator cuff repair (RCR) is a significant orthopedic challenge. Considering the aligned architecture of the tendon, inflammatory microenvironment at the injury site, and the need for endogenous cell/tissue infiltration, there is an imminent need for an ideal scaffold to promote TBH that has aligned architecture, ability to modulate inflammation, and macroporous structure. Herein, a novel macroporous hydrogel comprising sodium alginate/hyaluronic acid/small extracellular vesicles from adipose-derived stem cells (sEVs) (MHA-sEVs) with aligned architecture and immunomodulatory ability is fabricated. When implanted subcutaneously, MHA-sEVs significantly improve cell infiltration and tissue integration through its macroporous structure. When applied to the osteoporotic RCR model, MHA-sEVs promote TBH by improving tendon repair through macroporous aligned architecture while enhancing bone regeneration by modulating inflammation. Notably, the biomechanical strength of MHA-sEVs is approximately two times higher than the control group, indicating great potential in reducing postoperative retear rates. Further cell-hydrogel interaction studies reveal that the alignment of microfiber gels in MHA-sEVs induces tenogenic differentiation of tendon-derived stem cells, while sEVs improve mitochondrial dysfunction in M1 macrophages (Mφ) and inhibit Mφ polarization toward M1 via nuclear factor-kappaB (NF-κb) signaling pathway. Taken together, MHA-sEVs provide a promising strategy for future clinical application in promoting osteoporotic TBH.

Review on material parameters to enhance bone cell function in vitro and in vivo

Bone plays critical roles in support, protection, movement, and metabolism. Although bone has an innate capacity for regeneration, this capacity is limited, and many bone injuries and diseases require intervention. Biomaterials are a critical component of many treatments to restore bone function and include non-resorbable implants to augment bone and resorbable materials to guide regeneration. Biomaterials can vary considerably in their biocompatibility and bioactivity, which are functions of specific material parameters. The success of biomaterials in bone augmentation and regeneration is based on their effects on the function of bone cells. Such functions include adhesion, migration, inflammation, proliferation, communication, differentiation, resorption, and vascularization. This review will focus on how different material parameters can enhance bone cell function both in vitro and in vivo.

Bioglass enhances the production of exosomes and improves their capability of promoting vascularization

Recently, exosomes have been extensively applied in tissue regeneration. However, their practical applications are severely restricted by the limited exosome secretion capability of cells. Therefore, developing strategies to enhance the production of exosomes and improve their biological function attracts great interest. Studies have shown that biomaterials can significantly enhance the paracrine effects of cells and exosomes are the main signal carriers of intercellular paracrine communication, thus biomaterials are considered to affect the exosome secretion of cells and their biological function. In this study, a widely recognized biomaterial, 45S5 Bioglass® (BG), is used to create a mild and cell-friendly microenvironment for mesenchymal stem cells (MSCs) with its ion products. Results showed that BG ion products can significantly improve exosome production of MSCs by upregulating the expression of neutral sphingomyelinase-2 (nSMase2) and Rab27a which enhanced the nSMases and Rab GTPases pathways, respectively. Besides, microRNA analysis indicates that BG ion products can modulate the cargoes of MSCs-derived exosomes by decreasing microRNA-342-5p level while increasing microRNA-1290 level. Subsequently, the function of exosomes is modified as their capabilities of promoting the vascularization of endothelial cells and facilitating the intradermal angiogenesis are enhanced. Taken together, BG ion products are confirmed to enhance exosome production and simultaneously improve exosome function, suggesting a feasible approach to improve the practical application of exosomes in regenerative medicine.

In situ activated mesenchymal stem cells (MSCs) by bioactive hydrogels for myocardial infarction treatment

Stem-cell therapy has been proved as a promising strategy for myocardial infarction (MI) treatment. However, the therapeutic efficacy is mainly limited by the cellular activity of transplanted mesenchymal stem cells (MSCs). In this study, a novel bioglass (BG)/γ-polyglutamic acid (γ-PGA)/chitosan (CS) hydrogel was obtained by in situ adding BG to stimulate the imine bond formation. And the effect of the composite hydrogel on MI therapeutic efficacy was evaluated in a rat acute myocardial infarction (AMI) model in vivo and the possible mechanism of the BG/γ-PGA/CS hydrogel for the stimulation of the intercellular interaction between MSCs and cardiomyocytes (CMs) was explored by a MSC and CM co-culture experiment in vitro. The implantation of the MSC loaded BG/γ-PGA/CS composite hydrogel in the mice AMI model showed a significant improvement in the therapeutic efficacy with improved cardiac function, attenuation of heart remodeling, reduced cardiomyocyte apoptosis and accelerated vascularization. The in vitro cell experiments demonstrated that the BG/γ-PGA/CS hydrogel activated the intercellular interaction between MSCs and CMs, which resulted in reduced cell apoptosis and enhanced angiogenesis. Silicate based bioactive hydrogels activated MSCs and cell-cell interactions in cardiac tissue after AMI and significantly enhanced the efficacy, which suggests that this bioactive hydrogel based approach is an effective way to enhance stem-cell therapy.

Multilayer Injectable Hydrogel System Sequentially Delivers Bioactive Substances for Each Wound Healing Stage

Wound healing is a dynamic and complex process that contains several sequential phases. However, most of the current drug delivery systems were designed to treat only one certain phase of wound repair, ignoring the fact that every stage plays critical roles in the wound healing process and those critical stages coordinately work to ensure optimal tissue regeneration. Therefore, a delivery system that can precisely meet the requirements of each wound healing stage is desired to enhance tissue regeneration. In this study, an injectable sodium alginate/bioglass (SA/BG) composite hydrogel was used to carry SA microparticles containing a conditioned medium (CM) of cells (SA_CM). Inside the SA_CM microparticles, poly(lactic-co-glycolic acid) (PLGA) microspheres containing pirfenidone (PFD) were encapsulated (PLGA_PFD). This multilayer injectable hydrogel system (SA/BG-SA_CM-PLGA_PFD) was designed to sequentially deliver bioactive molecules for meeting the bioactivity requirement and timeline of each wound healing stage. First, SA/BG hydrogels could rapidly release BG ionic products in the first 1-3 days to regulate the inflammatory response of the host and initiate the subsequent tissue regeneration. Then, SA_CM hydrogel microparticles could release CM of RAW 264.7 cells stimulated with BG ionic products in 2-7 days to facilitate the formation of the vascularized granulation tissue. Finally, PLGA_PFD microspheres released PFD in 8-20 days to prevent the fibrosis and scar formation in the regenerated skin. Thus, this SA/BG-SA_CM-PLGA_PFD delivery system could restrain host inflammation, accelerate wound healing, and inhibit the fibrosis formation in a diabetic mouse skin damage model, enhancing skin regeneration. As the bioactive components in each layer of the system can be adjusted according to the requirements of different tissue regeneration, this three-layered injectable biomaterial system has a wide application potential in the regenerative medicine field.

Strategies to Improve Nanofibrous Scaffolds for Vascular Tissue Engineering

The biofabrication of biomimetic scaffolds for tissue engineering applications is a field in continuous expansion. Of particular interest, nanofibrous scaffolds can mimic the mechanical and structural properties (e.g., collagen fibers) of the natural extracellular matrix (ECM) and have shown high potential in tissue engineering and regenerative medicine. This review presents a general overview on nanofiber fabrication, with a specific focus on the design and application of electrospun nanofibrous scaffolds for vascular regeneration. The main nanofiber fabrication approaches, including self-assembly, thermally induced phase separation, and electrospinning are described. We also address nanofibrous scaffold design, including nanofiber structuring and surface functionalization, to improve scaffolds' properties. Scaffolds for vascular regeneration with enhanced functional properties, given by providing cells with structural or bioactive cues, are discussed. Finally, current in vivo evaluation strategies of these nanofibrous scaffolds are introduced as the final step, before their potential application in clinical vascular tissue engineering can be further assessed.

Effects of Fiber Alignment and Coculture with Endothelial Cells on Osteogenic Differentiation of Mesenchymal Stromal Cells

Vascularization is a critical process during bone regeneration. The lack of vascular networks leads to insufficient oxygen and nutrients supply, which compromises the survival of regenerated bone. One strategy for improving the survival and osteogenesis of tissue-engineered bone grafts involves the coculture of endothelial cells (ECs) with mesenchymal stromal cells (MSCs). Moreover, bone regeneration is especially challenging due to its unique structural properties with aligned topographical cues, with which stem cells can interact. Inspired by the aligned fibrillar nanostructures in human cancellous bone, we fabricated polycaprolactone (PCL) electrospun fibers with aligned and random morphology, cocultured human MSCs with human umbilical vein ECs (HUVECs), and finally investigated how these two factors modulate osteogenic differentiation of human MSCs (hMSCs). After optimizing cell ratio, a hMSCs/HUVECs ratio (90:10) was considered to be the best combination for osteogenic differentiation. Coculture results showed that hMSCs and HUVECs adhered to and proliferated well on both scaffolds. The aligned structure of PCL fibers strongly influenced the morphology and orientation of hMSCs and HUVECs; however, fiber alignment was observed to not affect alkaline phosphate (ALP) activity or mineralization of hMSCs compared with random scaffolds. More importantly, cocultured cells on both random and aligned scaffolds had significantly higher ALP activities than monoculture groups, which indicated that coculture with HUVECs provided a larger relative contribution to the osteogenesis of hMSCs compared with fiber alignment. Taken together, we conclude that coculture of hMSCs with ECs is an effective strategy to promote osteogenesis on electrospun scaffolds, and aligned fibers could be introduced to regenerate bone tissues with oriented topography without significant deleterious effects on hMSCs differentiation. This study shows the ability to grow oriented tissue-engineered cocultures with significant increases in osteogenesis over monoculture conditions. Impact statement This work demonstrates an effective method of enhancing osteogenesis of mesenchymal stromal cells on electrospun scaffolds through coculturing with endothelial cells. Furthermore, we provide the optimized conditions for cocultures on electrospun fibrous scaffolds and engineered bone tissues with oriented topography on aligned fibers. This study demonstrates promising findings for growing oriented tissue-engineered cocultures with significant increase in osteogenesis over monoculture conditions.

Bioactive Injectable Hydrogels Containing Desferrioxamine and Bioglass for Diabetic Wound Healing

Diabetic wound is hard to heal mainly because of the difficulty in vascularization in the wound area. Accumulating results have shown that desferrioxamine (DFO) can promote secretion of hypoxia inducible factor-1 (HIF-1α), thereby upregulating the expression of angiogenic growth factors and facilitating revascularization. Our preliminary study has demonstrated that Si ions in bioglass (BG) can upregulate vascular endothelial growth factor (VEGF) expression, thus promoting revascularization. It is hypothesized that the combined use of BG and DFO may have a synergistic effect in promoting VEGF expression and revascularization. To prove this, we first determined DFO concentration range that had no apparent cytotoxicity on human umbilical vein endothelial cells (HUVECs). Then, the optimal concentration of DFO promoting tube formation of HUVECs was determined by cell migration and tube formation assays. In addition, we demonstrated that combination use of BG and DFO improved the migration and tube formation of HUVECs as compared with the use of either BG or DFO alone as BG and DFO could synergistically upregulate VEGF expression. Furthermore, a sodium alginate hydrogel containing both BG and DFO was developed, and this hydrogel better facilitated diabetic skin wound healing than the use of either BG or DFO alone as BG and DFO in the hydrogels worked synergistically in promoting HIF-1α and VEGF expression and subsequently vascularization in the wound sites. Therefore, in this study, the synergistic effect in promoting revascularization between BG and DFO was first demonstrated and an injectable hydrogel simultaneously containing BG and DFO was developed for enhancing repair of diabetic chronic skin defects by taking advantages of the synergistic effects of BG and DFO in promoting revascularization. The study opens up a new prospect for the development of skin repair-promoting biomaterials.

Comparison between mandibular and femur derived bone marrow stromal cells: osteogenic and angiogenic potentials in vitro and bone repairing ability in vivo

M-BMSCs contains stronger osteogenic and angiogenic potentials, and better bone repairing ability.