The Advantages and Shortcomings of Stem Cell Therapy for Enhanced Bone Healing.

This review explores the regenerative potential of key progenitor cell types and therapeutic strategies to improve healing of complex fractures and bone defects. We define, summarize, and discuss the differentiation potential of totipotent, pluripotent, and multipotent stem cells, emphasizing the advantages and shortcomings of cell therapy for bone repair and regeneration. The fundamental role of mesenchymal stem cells is highlighted due to their multipotency to differentiate into the key lineage cells including osteoblasts, osteocytes, and chondrocytes, which are crucial for bone formation and remodeling. Hematopoietic stem cells (HSCs) also play a significant role; immune cells such as macrophages and T-cells modulate inflammation and tissue repair. Osteoclasts are multinucleated cells that are important to bone remodeling. Vascular progenitor (VP) cells are critical to oxygen and nutrient supply. The dynamic interplay among these lineages and their microenvironment is essential for effective bone restoration. Therapies involving cells that are more than "minimally manipulated" are controversial and include embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). ESCs, derived from early-stage embryos, possess pluripotent capabilities and have shown promise in preclinical studies for bone healing. iPSCs, reprogrammed from somatic cells, offer personalized medicine applications and can differentiate into various tissue-specific cell lines. Minimally manipulative cell therapy approaches such as the use of bone marrow aspirate concentrate (BMAC), exosomes, and various biomaterials for local delivery are explored for their effectiveness in bone regeneration. BMAC, which contains mostly immune cells but few mesenchymal and VPs, probably improves bone healing by facilitating paracrine-mediated intercellular communication. Exosome isolation harnesses the biological signals and cellular by-products that are a primary source for cell crosstalk and activation. Safe, efficacious, and cost-effective strategies to enhance bone healing using novel cellular therapies are part of a changing paradigm to modulate the inflammatory, repair, and regenerative pathways to achieve earlier more robust tissue healing and improved physical function. Impact Statement Stem cell therapy holds immense potential for bone healing due to its ability to regenerate damaged tissue. Nonmanipulated bone marrow aspirate contains mesenchymal stem cells that promote bone repair and reduce healing time. Induced pluripotent stem cells offer the advantage of creating patient-specific cells that can differentiate into osteoblasts, aiding in bone regeneration. Other delivery methods, such as scaffold-based techniques, enhance stem cell integration and function. Collectively, these approaches can improve treatment outcomes, reduce recovery periods, and advance our understanding of bone healing mechanisms, making them pivotal in orthopedic research and regenerative medicine.

Enhanced osteogenesis of mesenchymal stem cells encapsulated in injectable microporous hydrogel.

Delivery of therapeutic stem cells to treat bone tissue damage is a promising strategy that faces many hurdles to clinical translation. Among them is the design of a delivery vehicle which promotes desired cell behavior for new bone formation. In this work, we describe the use of an injectable microporous hydrogel, made of crosslinked gelatin microgels, for the encapsulation and delivery of human mesenchymal stem cells (MSCs) and compared it to a traditional nonporous injectable hydrogel. MSCs encapsulated in the microporous hydrogel showed rapid cell spreading with direct cell-cell connections whereas the MSCs in the nonporous hydrogel were entrapped by the surrounding polymer mesh and isolated from each other. On a per-cell basis, encapsulation in microporous hydrogel induced a 4 × increase in alkaline phosphatase (ALP) activity and calcium mineral deposition in comparison to nonporous hydrogel, as measured by ALP and calcium assays, which indicates more robust osteogenic differentiation. RNA-seq confirmed the upregulation of the genes and pathways that are associated with cell spreading and cell-cell connections, as well as the osteogenesis in the microporous hydrogel. These results demonstrate that microgel-based injectable hydrogels can be useful tools for therapeutic cell delivery for bone tissue repair.

Thermoresponsive and Injectable Pluronic F127 Hydrogel for Loading Adipose-Derived Mesenchymal Stem Cells.

BACKGROUND: Stem cell-based therapies display immense potential in regenerative medicine, highlighting the crucial significance of devising efficient delivery methods. This study centers on a pioneering approach that utilizes Pluronic F127 (PF127) as a thermoresponsive and injectable hydrogel designed for the encapsulation of adipose-derived mesenchymal stem cells (AdMSCs). METHODS: The degradation profile, gelation time, and microstructure of the PF127 hydrogel were thoroughly examined. AdMSCs were isolated, expanded, and characterized based on their multi-lineage differentiation potential. AdMSCs from the third passage were specifically employed for encapsulation within the PF127 hydrogel. Subsequently, the cytotoxicity of the AdMSC-loaded PF127 hydrogel was assessed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and apoptosis assays. RESULTS: Characterized by scanning electron microscopy (SEM), the PF127 hydrogel exhibited a porous structure, indicating its suitability for accommodating AdMSCs and facilitating wound healing. The PF127 hydrogel demonstrated reversible phase transitions, rendering it suitable for in vivo applications. Studies on the gelation time of PF127 hydrogel unveiled a concentration-dependent decrease in gelation time, offering adaptability for diverse medical applications. Analysis of the degradation profile showcased a seven-day degradation period, leading to the decision for weekly topical applications. Cytotoxicity assessments confirmed that AdMSCs loaded into the PF127 hydrogel maintained heightened metabolic activity for up to one week, affirming the safety and appropriateness of the PF127 hydrogel for encapsulating cellular therapeutics. Furthermore, cell apoptosis assays consistently indicated low rates of apoptosis, emphasizing the viability and robust health of AdMSCs when delivered within the hydrogel. CONCLUSIONS: These findings underscore the vast potential of PF127 hydrogel as a versatile and biocompatible delivery system for AdMSCs in the realm of regenerative medicine. Boasting adjustable gelation properties and a remarkable capacity for cell encapsulation, this pioneering delivery system presents a promising path for applications in tissue engineering and wound healing. Ultimately, these advancements propel and elevate the landscape of regenerative medicine.

Four-Arm Polymer-Guided Formation of Curcumin-Loaded Flower-Like Porous Microspheres as Injectable Cell Carriers for Diabetic Wound Healing.

Stem cell injection is an effective approach for treating diabetic wounds; however, shear stress during injections can negatively affect their stemness and cell growth. Cell-laden porous microspheres can provide shelter for bone mesenchymal stem cells (BMSC). Herein, curcumin-loaded flower-like porous microspheres (CFPM) are designed by combining phase inversion emulsification with thermally induced phase separation-guided four-arm poly (l-lactic acid) (B-PLLA). Notably, the CFPM shows a well-defined surface topography and inner structure, ensuring a high surface area to enable the incorporation and delivery of a large amount of -BMSC and curcumin. The BMSC-carrying CFPM (BMSC@CFPM) maintains the proliferation, retention, and stemness of -BMSCs, which, in combination with their sustainable curcumin release, facilitates the endogenous production of growth/proangiogenic factors and offers a local anti-inflammatory function. An in vivo bioluminescence assay demonstrates that BMSC@CFPM can significantly increase the retention and survival of BMSC in wound sites. Accordingly, BMSC@CFPM, with no significant systemic toxicity, could significantly accelerate diabetic wound healing by promoting angiogenesis, collagen reconstruction, and M2 macrophage polarization. RNA sequencing further unveils the mechanisms by which BMSC@CFPM promotes diabetic wound healing by increasing -growth factors and enhancing angiogenesis through the JAK/STAT pathway. Overall, BMSC@CFPM represents a potential therapeutic tool for diabetic wound healing.

Erectile Dysfunction Treatment Using Stem Cell Delivery Patch in a Cavernous Nerve Injury Rat Model.

Erectile dysfunction (ED) is a common and feared complication of radical prostatectomy (RP) for prostate cancer. Recently, tissue engineering for post-prostatectomy ED has been attempted in which controlled interactions between cells, growth factors, and the extracellular matrix (ECM) are important for the structural integrity if nerve regeneration. In this study, we evaluated the effects of a biomechanical ECM patch on the morphology and behavior of human bone marrow-derived mesenchymal stem cells (hBMSCs) in a bilateral cavernous nerve injury (BCNI) rat model. The ECM patch, made of decellularized human fibroblast-derived ECM (hFDM) and a biocompatible polyvinyl alcohol (PVA) hydrogel, was tested with human bone marrow-derived mesenchymal stem cells (hBMSCs) on a bilateral cavernous nerve injury (BCNI) rat model. In vitro analysis showed that the hFDM/PVA + hBMSCs patches significantly increased neural development markers. In vivo experiments demonstrated that the rats treated with the hFDM/PVA patch had higher ICP/MAP ratios, higher ratios of smooth muscle to collagen, increased nNOS content, higher levels of eNOS protein expression, and higher cGMP levels compared to the BCNI group. These results indicate that the hFDM/PVA patch is effective in promoting angiogenesis, smooth muscle regeneration, and nitrergic nerve regeneration, which could contribute to improved erectile function in post-prostatectomy ED.

Biostimulatory Micro-Fragmented Nanofiber-Hydrogel Composite Improves Mesenchymal Stem Cell Delivery and Soft Tissue Remodeling.

Functional microgels are preferred stem cell carriers due to the ease of delivery through minimally invasive injection and seamless integration with the surrounding host tissue. A biostimulatory nanofiber-hydrogel composite (NHC) has been previously developed through covalently crosslinking a hyaluronic acid hydrogel network with surface-functionalized poly (ε-caprolactone) nanofiber fragments. The NHC mimics the microarchitecture of native soft tissue matrix, showing enhanced cell infiltration, immunomodulation, and proangiogenic properties. Here, injectability of the pre-formed NHC is improved by mechanical fragmentation, making it into micro-fragmented NHC (mfNHC) in a granular gel form as a stem cell carrier to deliver mesenchymal stem cells (MSCs) for soft tissue remodeling. The mfNHC shows a similar storage modulus but a significantly reduced injection force, as compared with the corresponding bulk NHC. When injected subcutaneously in a rat model, mfNHC-MSC constructs initiate an elevated level of host macrophage infiltration, more pro-regenerative polarization, and subsequently, improved angiogenesis and adipogenesis response when compared to mfNHC alone. A similar trend of host cell infiltration and pro-angiogenic response is detected in a swine model with a larger volume injection. These results suggest a strong potential for use of the mfNHC as an injectable carrier for cell delivery and soft tissue remodeling.

Equine Platelet Lysate Gel: A Matrix for Mesenchymal Stem Cell Delivery.

A variety of bioscaffolds have been developed as carriers for the delivery of mesenchymal stem cells (MSCs), however, many of them are unable to provide direct cell nourishment, a critical factor for survival and retention of MSCs at the site of delivery. Platelet lysate is a plasma-derived product rich in growth factors that can be turned into a gel matrix following the addition of calcium chloride. Our objective was to characterize growth factor and cytokine release of equine platelet lysate gel (ePL gel) encapsulated with MSCs over time and to measure the viability and proliferation of ePL gel-encapsulated MSCs for up to 14 days. The release of interleukin-1ß (IL-1ß), interleukin-10 (IL-10), transforming growth factor beta (TGF-ß), vascular endothelial growth factor (VEGF), and platelet-derived growth factor BB (PDGF-BB), as well as fibrinogen degradation, were measured from ePL gel with and without equine bone marrow-derived MSCs and compared with MSCs in monolayer. MSC proliferation and viability within the gel were assessed up to 14 days. Compared with monolayer MSC cultures, significantly higher concentrations of IL-1ß, IL-10, and TGF-ß were measured from supernatants collected from ePL gel containing MSCs at various time points. Significantly lower concentrations of PDGF-BB were measured in the supernatant when MSCs were incorporated in ePL gel while VEGF tended to be increased compared with MSCs in monolayer. Incorporation in ePL gel for up to 14 days did not appear to affect viability and proliferation rates of MSCs as these were found to be similar to those measured in monolayer cell culture. ePL gel may have the potential to serve as bioscaffold for MSC delivery since it appears to support the proliferation and viability of MSCs for up to 14 days.

Fast-Curing Injectable Microporous Hydrogel for In Situ Cell Encapsulation.

Injectable hydrogels have previously demonstrated potential as a temporary scaffold for tissue regeneration or as a delivery vehicle for cells, growth factors, or drugs. However, most injectable hydrogel systems lack a microporous structure, preventing host cell migration into the hydrogel interior and limiting spreading and proliferation of encapsulated cells. Herein, an injectable microporous hydrogel assembled from gelatin/gelatin methacryloyl (GelMA) composite microgels is described. Microgels are produced by a water-in-oil emulsion using a gelatin/GelMA aqueous mixture. These microgels show improved thermal stability compared to GelMA-only microgels and benefit from combined photopolymerization using UV irradiation (365 nm) in the presence of a photoinitiator (PI) and enzymatic reaction by microbial transglutaminase (mTG), which together enable fast curing and tissue adhesion of the hydrogel. The dual-crosslinking approach also allows for the reduction of PI concentration and minimizes cytotoxicity during photopolymerization. When applied for in situ cell encapsulation, encapsulated human dermal fibroblasts and human mesenchymal stem cells (hMSCs) are able to rapidly spread and proliferate in the pore space of the hydrogel. This hydrogel has the potential to enhance hMSC anti-inflammatory behavior through the demonstrated secretion of prostaglandin E2 (PGE2) and interleukin-6 (IL-6) by encapsulated cells. Altogether, this injectable formulation has the potential to be used as a cell delivery vehicle for various applications in regenerative medicine.

A Biodegradable Magnetic Microrobot Based on Gelatin Methacrylate for Precise Delivery of Stem Cells with Mass Production Capability.

A great deal of research has focused on small-scale robots for biomedical applications and minimally invasive delivery of therapeutics (e.g., cells, drugs, and genes) to a target area. Conventional fabrication methods, such as two-photon polymerization, can be used to build sophisticated micro- and nanorobots, but the long fabrication cycle for a single microrobot has limited its practical use. This study proposes a biodegradable spherical gelatin methacrylate (GelMA) microrobot for mass production in a microfluidic channel. The proposed microrobot is fabricated in a flow-focusing droplet generator by shearing a mixture of GelMA, photoinitiator, and superparamagnetic iron oxide nanoparticles (SPIONs) with a mixture of oil and surfactant. Human nasal turbinate stem cells (hNTSCs) are loaded on the GelMA microrobot, and the hNTSC-loaded microrobot shows precise rolling motion in response to an external rotating magnetic field. The microrobot is enzymatically degraded by collagenase, and released hNTSCs are proliferated and differentiated into neuronal cells. In addition, the feasibility of the GelMA microrobot as a cell therapeutic delivery system is investigated by measuring electrophysiological activity on a multielectrode array. Such a versatile and fully biodegradable microrobot has the potential for targeted stem cell delivery, proliferation, and differentiation for stem cell-based therapy.

Neural stem cell delivery using brain-derived tissue-specific bioink for recovering from traumatic brain injury.

Traumatic brain injury is one of the leading causes of accidental death and disability. The loss of parts in a severely injured brain induces edema, neuronal apoptosis, and neuroinflammation. Recently, stem cell transplantation demonstrated regenerative efficacy in an injured brain. However, the efficacy of current stem cell therapy needs improvement to resolve issues such as low survival of implanted stem cells and low efficacy of differentiation into respective cells. We developed brain-derived decellularized extracellular matrix (BdECM) bioink that is printable and has native brain-like stiffness. This study aimed to fabricate injured cavity-fit scaffold with BdECM bioink and assessed the utility of BdECM bioink for stem cell delivery to a traumatically injured brain. Our BdECM bioink had shear thinning property for three-dimensional (3D)-cell-printing and physical properties and fiber structures comparable to those of the native brain, which is important for tissue integration after implantation. The human neural stem cells (NSCs) (F3 cells) laden with BdECM bioink were found to be fully differentiated to neurons; the levels of markers for mature differentiated neurons were higher than those observed with collagen bioinkin vitro. Moreover, the BdECM bioink demonstrated potential in defect-fit carrier fabrication with 3D cell-printing, based on the rheological properties and shape fidelity of the material. As F3 cell-laden BdECM bioink was transplanted into the motor cortex of a rat brain, high efficacy of differentiation into mature neurons was observed in the transplanted NSCs; notably increased level of MAP2, a marker of neuronal differentiation, was observed. Furthermore, the transplanted-cell bioink suppressed reactive astrogliosis and microglial activation that may impede regeneration of the injured brain. The brain-specific material reported here is favorable for NSC differentiation and suppression of neuroinflammation and is expected to successfully support regeneration of a traumatically injured brain.

A Magnetically Powered Stem Cell-Based Microrobot for Minimally Invasive Stem Cell Delivery via the Intranasal Pathway in a Mouse Brain.

Targeted stem cell delivery with microrobots has emerged as a potential alternative therapeutic strategy in regenerative medicine, and intranasal administration is an effective approach for minimally invasive delivery of therapeutic agents into the brain. In this study, a magnetically powered stem cell-based microrobot ("Cellbot") is used for minimally invasive targeted stem cell delivery to the brain through the intranasal passage. The Cellbot is developed by internalizing superparamagnetic iron oxide nanoparticles (SPIONs) into human nasal turbinate stem cells. The SPIONs have no influence on hNTSC characteristics, including morphology, cell viability, and neuronal differentiation. The Cellbots are capable of proliferation and differentiation into neurons, neural precursor cells, and neurogliocytes. The Cellbots in the microfluidic channel can be reliably manipulated by an external magnetic field for orientation and position control. Using an ex vivo model based on brain organoids, it is determined that the Cellbots can be transplanted into brain tissue. Using a murine model, it is demonstrated that the Cellbots can be intranasally administered and magnetically guided to the target tissue in vivo. This approach has the potential to effectively treat central nervous system disorders in a minimally invasive manner.

Human amniotic membrane as a delivery vehicle for stem cell-based therapies.

Stem cell-based therapy is known as a regenerative approach for a variety of diseases and tissue injuries. These cells exert their therapeutic effects through paracrine secretions namely extracellular vesicles. To achieve higher therapeutic potential, a variety of delivery routes have been tested in clinical and preclinical studies. Direct cell injection, intra-venous administration, and intra-arterial infusion are widely used methods of stem cells delivery but these methods are associated with several complications. As one of the most popular biological delivery systems, amniotic membrane has been widely utilized to support cell proliferation and differentiation therefore facilitating tissue regeneration without endangering the stem cells' viability. It is composed of several extracellular matrix components and growth factors. Due to these characteristics, amniotic membrane can mimic the stem cell's niche and can be an ideal carrier for stem cell transplantation. Here, we provide an overview of the recent progress, challenges, and future perspectives in the use of amniotic membrane as a delivery platform for stem cells.

Personalized-induced neural stem cell therapy: Generation, transplant, and safety in a large animal model.

In this study, we take an important step toward clinical translation by generating the first canine-induced neural stem cells (iNSCs). We explore key aspects of scale-up, persistence, and safety of personalized iNSC therapy in autologous canine surgery models. iNSCs are a promising new approach to treat aggressive cancers of the brain, including the deadly glioblastoma. Created by direct transdifferentiation of fibroblasts, iNSCs are known to migrate through the brain, track down invasive cancer foci, and deliver anticancer payloads that significantly reduce tumor burden and extend survival of tumor-bearing mice. Here, skin biopsies were collected from canines and converted into the first personalized canine iNSCs engineered to carry TNFα-related apoptosis-inducing ligand (TRAIL) and thymidine kinase (TK), as well as magnetic resonance imaging (MRI) contrast agents for in vivo tracking. Time-lapse analysis showed canine iNSCs efficiently migrate to human tumor cells, and cell viability assays showed both TRAIL and TK monotherapy markedly reduced tumor growth. Using intraoperative navigation and two delivery methods to closely mimic human therapy, canines received autologous iNSCs either within postsurgical cavities in a biocompatible matrix or via a catheter placed in the lateral ventricle. Both strategies were well tolerated, and serial MRI showed hypointense regions at the implant sites that remained stable through 86 days postimplant. Serial fluid sample testing following iNSC delivery showed the bimodal personalized therapy was well tolerated, with no iNSC-induced abnormal tissue pathology. Overall, this study lays an important foundation as this promising personalized cell therapy advances toward human patient testing.

The interaction of stem cells and vascularity in peripheral nerve regeneration.

The degree of nerve regeneration after peripheral nerve injury can be altered by the microenvironment at the site of injury. Stem cells and vascularity are postulated to be a part of a complex pathway that enhances peripheral nerve regeneration; however, their interaction remains unexplored. This review aims to summarize current knowledge on this interaction, including various mechanisms through which trophic factors are promoted by stem cells and angiogenesis. Angiogenesis after nerve injury is stimulated by hypoxia, mediated by vascular endothelial growth factor, resulting in the growth of pre-existing vessels into new areas. Modulation of distinct signaling pathways in stem cells can promote angiogenesis by the secretion of various angiogenic factors. Simultaneously, the importance of stem cells in peripheral nerve regeneration relies on their ability to promote myelin formation and their capacity to be influenced by the microenvironment to differentiate into Schwann-like cells. Stem cells can be acquired through various sources that correlate to their differentiation potential, including embryonic stem cells, neural stem cells, and mesenchymal stem cells. Each source of stem cells serves its particular differentiation potential and properties associated with the promotion of revascularization and nerve regeneration. Exosomes are a subtype of extracellular vesicles released from cell types and play an important role in cell-to-cell communication. Exosomes hold promise for future transplantation applications, as these vesicles contain fewer membrane-bound proteins, resulting in lower immunogenicity. This review presents pre-clinical and clinical studies that focus on selecting the ideal type of stem cell and optimizing stem cell delivery methods for potential translation to clinical practice. Future studies integrating stem cell-based therapies with the promotion of angiogenesis may elucidate the synergistic pathways and ultimately enhance nerve regeneration.

Engineered cell-degradable poly(2-alkyl-2-oxazoline) hydrogel for epicardial placement of mesenchymal stem cells for myocardial repair.

Epicardial placement of mesenchymal stromal cells (MSCs) is a promising strategy for cardiac repair post-myocardial infarction, but requires the design of biomaterials to maximise the retention of donor cells on the heart surface and control their phenotype. To this end, we propose the use of a poly(2-alkyl-2-oxazoline) (POx) derivative, based on 2-ethyl-2-oxazoline and 2-butenyl-2-oxazoline. This POx polymer can be cured rapidly (less than 2 min) via photo-irradiation due to the use of di-cysteine cell degradable peptides. We report that the cell-degradable properties of the resulting POx hydrogels enables the regulation of cell protrusion in corresponding 3D matrices and that this, in turn, regulates the secretory phenotype of MSCs. In particular, the expression of pro-angiogenic genes was upregulated in partially cell-degradable POx hydrogels. Improved angiogenesis was confirmed in an in vitro microfluidic assay. Finally, we confirmed that, owing to the excellent tissue adhesive properties of thiol-ene crosslinked hydrogels, the epicardial placement of MSC-loaded POx hydrogels promoted the recovery of cardiac function and structure with reduced interstitial fibrosis and improved neovascular formation in a rat myocardial infarction model. This report demonstrates that engineered synthetic hydrogels displaying controlled mechanical, cell degradable and bioactive properties are particularly attractive candidates for the epicardial placement of stem cells to promote cardiac repair post myocardial infarction.

Extracellular matrix-based biomaterials as adipose-derived stem cell delivery vehicles in wound healing: a comparative study between a collagen scaffold and two xenografts.

BACKGROUND: Stem cell therapies represent a promising tool in regenerative medicine. Considering the drawbacks of direct stem cell injections (e.g. poor cell localisation), extracellular matrix-based biomaterials (e.g. scaffolds and tissue grafts), due to their compositional biofunctionality and cytocompatibility, are under investigation as potential stem cell carriers. METHODS: The present study assessed the potential of three commercially available extracellular matrix-based biomaterials [a collagen/glycosaminoglycan scaffold (Integra™ Matrix Wound Dressing), a decellularised porcine peritoneum (XenoMEM™) and a porcine urinary bladder (MatriStem™)] as human adipose-derived stem cell delivery vehicles. RESULTS: Both tissue grafts induced significantly (p < 0.01) higher human adipose-derived stem cell proliferation in vitro over the collagen scaffold, especially when the cells were seeded on the basement membrane side. Human adipose-derived stem cell phenotype and trilineage differentiation potential was preserved in all biomaterials. In a splinted wound healing nude mouse model, in comparison to sham, biomaterials alone and cells alone groups, all biomaterials seeded with human adipose-derived stem cells showed a moderate improvement of wound closure, a significantly (p < 0.05) lower wound gap and scar index and a significantly (p < 0.05) higher proportion of mature collagen deposition and angiogenesis (the highest, p < 0.01, was observed for the cell loaded at the basement membrane XenoMEM™ group). All cell-loaded biomaterial groups retained more cells at the implantation side than the direct injection group, even though they were loaded with half of the cells than the cell injection group. CONCLUSIONS: This study further advocates the use of extracellular matrix-based biomaterials (in particular porcine peritoneum) as human adipose-derived stem cell delivery vehicles. Comparative analysis of a collagen scaffold (Integra™ Matrix Wound Dressing) and two tissue grafts [decellularised porcine peritoneum (XenoMEM™) and porcine urinary bladder (MatriStem™)] as human adipose-derived stem cells carriers.

Advances in the Application of Supramolecular Hydrogels for Stem Cell Delivery and Cartilage Tissue Engineering.

Cartilage defects pose a great threat to the health of the aging population. Cartilage has limited self-regeneration ability because it lacks blood vessels, nerves and lymph. To achieve efficient cartilage regeneration, supramolecular hydrogels are used in medical applications and tissue engineering as they are tunable and reversible in nature. Moreover, they possess supramolecular interactions which allow the incorporation of cells. These hydrogels present great potential for tissue engineering-based therapies. This review presents advances in the development of stem cell-laden supramolecular hydrogels. We discuss new possibilities for stem cell therapy and their uses in cartilage tissue engineering. Gray areas and future perspectives are discussed.

Pre-culture of mesenchymal stem cells within RGD-modified hyaluronic acid hydrogel improves their resilience to ischaemic conditions.

The incorporation of the RGD peptide (arginine-glycine-aspartate) into biomaterials has been proposed to promote cell adhesion to the matrix, which can influence and control cell behaviour and function. While many studies have utilised RGD modified biomaterials for cell delivery, few have examined its effect under the condition of reduced oxygen and nutrients, as found at ischaemic injury sites. Here, we systematically examine the effect of RGD on hMSCs in hyaluronic acid (HA) hydrogel under standard and ischaemic culture conditions, to elucidate under what conditions RGD has beneficial effects over unmodified HA and its effectiveness in improving cell viability. Results demonstrate that under standard culture conditions, RGD significantly increased hMSC spreading and the release of vascular endothelial factor-1 (VEGF) and monocyte chemoattractant factor-1 (MCP-1), compared to unmodified HA hydrogel. As adhesion is known to influence cell survival, we hypothesised that cells in RGD hydrogels would exhibit increased cell viability under ischaemic culture conditions. However, results demonstrate that cell viability and protein release was comparable in both RGD modified and unmodified HA hydrogels. Confocal imaging revealed cellular morphology indicative of weak cell adhesion. Subsequent investigations found that RGD was could exert positive effects on encapsulated cells under ischaemic conditions but only if hMSCs were pre-cultured under standard conditions to allow strong adhesion to RGD before exposure. Together, these results provide novel insight into the value of RGD introduction and suggest that the adhesion of hMSCs to RGD prior to delivery could improve survival and function at ischaemic injury sites. STATEMENT OF SIGNIFICANCE: The development of a biomaterial scaffold capable of maintaining cell viability while promoting cell function is a major research goal in the field of cardiac tissue engineering. This study confirms the suitability of a modified HA hydrogel whereby stem cells in the modified hydrogel showed significantly greater cell spreading and protein secretion compared to cells in the unmodified HA hydrogel. A pre-culture period allowing strong adhesion of the cells to the modified hydrogel was shown to improve cell survival under conditions that mimic the myocardium post-MI. This finding may have a significant impact on the use and timelines of modifications to improve stem cell survival in harsh environments like the injured heart.

Stem cell spheroids incorporating fibers coated with adenosine and polydopamine as a modular building blocks for bone tissue engineering.

Although stem cell spheroids offer great potential as functional building blocks for bottom-up bone tissue engineering, delivery of bioactive signals remain challenging. Here, we engineered adenosine-ligand-modified fiber fragments to create a 3D cell-instructive microenvironment for bone. Briefly, the Poly(ι-lactic acid) (PLLA) nanofiber sheet was partially degraded into fragmented fibers (FFs) through aminolysis and adenosine was stably incorporated via one-step polydopamine coating. The SEM and XPS analysis demonstrated that polydopamine assisted adenosine coating efficiency was significantly increased, which led to high coating efficiency of adenosine and its significant retention. The engineered fibers were then assembled into stable spheroids with human-adipose-derived stem cells (hADSCs). The adenosine in the spheroids effectively stimulated A2bR (1.768 ± 0.08) signaling, which further significantly induced the expression of osteogenic markers such as Runx2 (3.216 ± 0.25), OPN (4.136 ± 0.14), OCN (10.16 ± 0.34), and OSX (2.27 ± 0.11) with improved mineral deposition (1.375 ± 0.05 µg per spheroid). In contrast, the adipogenic differentiation of hADSCs was significantly suppressed within the engineered spheroids. Transplantation of engineered spheroids strongly induced osteogenic differentiation of hADSCs in ectopic subcutaneous tissue. Finally, the bone regeneration was significantly enhanced by implanting AP-FF group (59.97 ± 18.33%) as compared to P-FF (27.96 ± 11.14) and defect only (7.97 ± 3.76%). We propose that stem cell spheroids impregnated with engineered fibers enabling adenosine delivery could be promising building blocks for a bottom-up approach to create large tissues for regeneration of damaged bone.