Synthetic extracellular matrix mimic hydrogel improves efficacy of mesenchymal stromal cell therapy for ischemic cardiomyopathy

In silico Mechanics of Stem Cells Intramyocardially Transplanted with a Biomaterial Injectate for Treatment of Myocardial Infarction

PURPOSE

Biomaterial and stem cell delivery are promising approaches to treating myocardial infarction. However, the mechanical and biochemical mechanisms underlying the therapeutic benefits require further clarification. This study aimed to assess the deformation of stem cells injected with the biomaterial into the infarcted heart.

METHODS

A microstructural finite element model of a mid-wall infarcted myocardial region was developed from ex vivo microcomputed tomography data of a rat heart with left ventricular infarct and intramyocardial biomaterial injectate. Nine cells were numerically seeded in the injectate of the microstructural model. The microstructural and a previously developed biventricular finite element model of the same rat heart were used to quantify the deformation of the cells during a cardiac cycle for a biomaterial elastic modulus (Einj) ranging between 4.1 and 405,900 kPa.

RESULTS

The transplanted cells' deformation was largest for Einj = 7.4 kPa, matching that of the cells, and decreased for an increase and decrease in Einj. The cell deformation was more sensitive to Einj changes for softer (Einj ≤ 738 kPa) than stiffer biomaterials.

CONCLUSIONS

Combining the microstructural and biventricular finite element models enables quantifying micromechanics of transplanted cells in the heart. The approach offers a broader scope for in silico investigations of biomaterial and cell therapies for myocardial infarction and other cardiac pathologies.

Research and application of hydrogel-encapsulated mesenchymal stem cells in the treatment of myocardial infarction

Myocardial infarction (MI) stands out as a highly lethal disease that poses a significant threat to global health. Worldwide, heart failure resulting from MI remains a leading cause of human mortality. Mesenchymal stem cell (MSC) therapy has emerged as a promising therapeutic approach, leveraging its intrinsic healing properties. Nevertheless, pervasive issues, including a low cell retention rate, suboptimal survival rate, and incomplete differentiation of MSCs, present formidable challenges for further research. The introduction and advancement of biomaterials have offered a novel avenue for the exploration of MSC therapy in MI, marking considerable progress thus far. Notably, hydrogels, among the representative biomaterials, have garnered extensive attention within the biomedical field. This review delves into recent advancements, specifically focusing on the application of hydrogels to augment MSC therapy for cardiac tissue regeneration in MI.

Role of Treg cell subsets in cardiovascular disease pathogenesis and potential therapeutic targets

In the genesis and progression of cardiovascular diseases involving both innate and adaptive immune responses, inflammation plays a pivotal and dual role. Studies in experimental animals indicate that certain immune responses are protective, while others exacerbate the disease. T-helper (Th) 1 cell immune responses are recognized as key drivers of inflammatory progression in cardiovascular diseases. Consequently, the CD4+CD25+FOXP3+ regulatory T cells (Tregs) are gaining increasing attention for their roles in inflammation and immune regulation. Given the critical role of Tregs in maintaining immune-inflammatory balance and homeostasis, abnormalities in their generation or function might lead to aberrant immune responses, thereby initiating pathological changes. Numerous preclinical studies and clinical trials have unveiled the central role of Tregs in cardiovascular diseases, such as atherosclerosis. Here, we review the roles and mechanisms of Treg subsets in cardiovascular conditions like atherosclerosis, hypertension, myocardial infarction and remodeling, myocarditis, dilated cardiomyopathy, and heart failure. While the precise molecular mechanisms of Tregs in cardiac protection remain elusive, therapeutic strategies targeting Tregs present a promising new direction for the prevention and treatment of cardiovascular diseases.

Injectable hydrogel-based combination therapy for myocardial infarction: a systematic review and Meta-analysis of preclinical trials

INTRODUCTION

This study evaluates the effectiveness of a combined regimen involving injectable hydrogels for the treatment of experimental myocardial infarction.

PATIENT CONCERNS

Myocardial infarction is an acute illness that negatively affects quality of life and increases mortality rates. Experimental models of myocardial infarction can aid in disease research by allowing for the development of therapies that effectively manage disease progression and promote tissue repair.

DIAGNOSIS

Experimental animal models of myocardial infarction were established using the ligation method on the anterior descending branch of the left coronary artery (LAD).

INTERVENTIONS

The efficacy of intracardiac injection of hydrogels, combined with cells, drugs, cytokines, extracellular vesicles, or nucleic acid therapies, was evaluated to assess the functional and morphological improvements in the post-infarction heart achieved through the combined hydrogel regimen.

OUTCOMES

A literature review was conducted using PubMed, Web of Science, Scopus, and Cochrane databases. A total of 83 papers, including studies on 1332 experimental animals (rats, mice, rabbits, sheep, and pigs), were included in the meta-analysis based on the inclusion and exclusion criteria. The overall effect size observed in the group receiving combined hydrogel therapy, compared to the group receiving hydrogel treatment alone, resulted in an ejection fraction (EF) improvement of 8.87% [95% confidence interval (CI): 7.53, 10.21] and a fractional shortening (FS) improvement of 6.31% [95% CI: 5.94, 6.67] in rat models, while in mice models, the improvements were 16.45% [95% CI: 11.29, 21.61] for EF and 5.68% [95% CI: 5.15, 6.22] for FS. The most significant improvements in EF (rats: MD = 9.63% [95% CI: 4.02, 15.23]; mice: MD = 23.93% [95% CI: 17.52, 30.84]) and FS (rats: MD = 8.55% [95% CI: 2.54, 14.56]; mice: MD = 5.68% [95% CI: 5.15, 6.22]) were observed when extracellular vesicle therapy was used. Although there have been significant results in large animal experiments, the number of studies conducted in this area is limited.

CONCLUSION

The present study demonstrates that combining hydrogel with other therapies effectively improves heart function and morphology. Further preclinical research using large animal models is necessary for additional study and validation.

Pulmonary decellularized extracellular matrix (dECM) modified polyethylene terephthalate three-dimensional cell carriers regulate the proliferation and paracrine activity of mesenchymal stem cells

Introduction: Mesenchymal stem cells (MSCs) possess a high degree of self-renewal capacity and in vitro multi-lineage differentiation potential. Decellularized materials have garnered considerable attention due to their elevated biocompatibility, reduced immunogenicity, excellent biodegradability, and the ability to partially mimic the in vivo microenvironment conducive to cell growth. To address the issue of mesenchymal stem cells losing their stem cell characteristics during two-dimensional (2D) cultivation, this study established three-dimensional cell carriers modified with lung decellularized extracellular matrix and assessed its impact on the life activities of mesenchymal stem cells. Methods: This study employed PET as a substrate material, grafting with polydopamine (PDA), and constructing a decellularized extracellular matrix (dECM) coating on its surface, thus creating the PET/PDA/dECM three-dimensional (3D) composite carrier. Subsequently, material characterization of the cellular carriers was conducted, followed by co-culturing with human umbilical cord mesenchymal stem cells in vitro, aiming to investigate the material's impact on the proliferation and paracrine activity of mesenchymal stem cells. Results and Discussion: Material characterization demonstrated successful grafting of PDA and dECM materials, and it had complete hydrophilicity, high porosity, and excellent mechanical properties. The material was rich in various ECM proteins (collagen I, collagen IV , laminin, fibronectin, elastin), indicating good biocompatibility. In long-term in vitro cultivation (14 days) experiments, the PET/PDA/dECM three-dimensional composite carrier significantly enhanced adhesion and proliferation of human umbilical cord-derived mesenchymal stem cells (HUCMSCs), with a proliferation rate 1.9 times higher than that of cells cultured on tissue culture polystyrene (TCPS) at day 14. Furthermore, it effectively maintained the stem cell characteristics, expressing specific antigens for HUCMSCs. Through qPCR, Western blot, and ELISA experiments, the composite carrier markedly promoted the expression and secretion of key cell factors in HUCMSCs. These results demonstrate that the PET/PDA/dECM composite carrier holds great potential for scaling up MSCs' long-term in vitro cultivation and the production of paracrine factors.

The origin, progress, and application of cell-based cardiac regeneration therapy

Cardiovascular disease (CVD) has become a severe threat to human health, with morbidity and mortality increasing yearly and gradually becoming younger. When the disease progresses to the middle and late stages, the loss of a large number of cardiomyocytes is irreparable to the body itself, and clinical drug therapy and mechanical support therapy cannot reverse the development of the disease. To explore the source of regenerated myocardium in model animals with the ability of heart regeneration through lineage tracing and other methods, and develop a new alternative therapy for CVDs, namely cell therapy. It directly compensates for cardiomyocyte proliferation through adult stem cell differentiation or cell reprogramming, which indirectly promotes cardiomyocyte proliferation through non-cardiomyocyte paracrine, to play a role in heart repair and regeneration. This review comprehensively summarizes the origin of newly generated cardiomyocytes, the research progress of cardiac regeneration based on cell therapy, the opportunity and development of cardiac regeneration in the context of bioengineering, and the clinical application of cell therapy in ischemic diseases.

Insight into Heart-Tailored Architectures of Hydrogel to Restore Cardiac Functions after Myocardial Infarction

With permanent heart muscle injury or death, myocardial infarction (MI) is complicated by inflammatory, proliferation and remodeling phases from both the early ischemic period and subsequent infarct expansion. Though in situ re-establishment of blood flow to the infarct zone and delays of the ventricular remodeling process are current treatment options of MI, they fail to address massive loss of viable cardiomyocytes while transplanting stem cells to regenerate heart is hindered by their poor retention in the infarct bed. Equipped with heart-specific mimicry and extracellular matrix (ECM)-like functionality on the network structure, hydrogels leveraging tissue-matching biomechanics and biocompatibility can mechanically constrain the infarct and act as localized transport of bioactive ingredients to refresh the dysfunctional heart under the constant cyclic stress. Given diverse characteristics of hydrogel including conductivity, anisotropy, adhesiveness, biodegradability, self-healing and mechanical properties driving local cardiac repair, we aim to investigate and conclude the dynamic balance between ordered architectures of hydrogels and the post-MI pathological milieu. Additionally, our review summarizes advantages of heart-tailored architectures of hydrogels in cardiac repair following MI. Finally, we propose challenges and prospects in clinical translation of hydrogels to draw theoretical guidance on cardiac repair and regeneration after MI.

Role of Biomaterials in Cardiac Repair and Regeneration: Therapeutic Intervention for Myocardial Infarction

Heart failure or myocardial infarction (MI) is one of the world's leading causes of death. Post MI, the heart can develop pathological conditions such as ischemia, inflammation, fibrosis, and left ventricular dysfunction. However, current surgical approaches are sufficient for enhancing myocardial perfusion but are unable to reverse the pathological changes. Tissue engineering and regenerative medicine approaches have shown promising effects in the repair and replacement of injured cardiomyocytes. Additionally, biomaterial scaffolds with or without stem cells are established to provide an effective environment for cardiac regeneration. Excipients loaded with growth factors, cytokines, oligonucleotides, and exosomes are found to help in such cardiac eventualities by promoting angiogenesis, cardiomyocyte proliferation, and reducing fibrosis, inflammation, and apoptosis. Injectable hydrogels, nanocarriers, cardiac patches, and vascular grafts are some excipients that can help the self-renewal in the damaged heart but are not understood well yet, in the context of used biomaterials. This review focuses on the use of various biomaterial-based approaches for the regeneration and repair of cardiac tissue postoccurrence of MI. It also discusses the outlines of cardiac remodeling and current therapeutic approaches after myocardial infarction, which are translationally important with respect to used biomaterials. It provides comprehensive details of the biomaterial-based regenerative approaches, which are currently the focus of the research for cardiac repair and regeneration and can provide a broad outline for further improvements.

Mesenchymal Stromal Cells Combined With Elastin-Like Recombinamers Increase Angiogenesis In Vivo After Hindlimb Ischemia

Hindlimb ischemia is an unmet medical need, especially for those patients unable to undergo vascular surgery. Cellular therapy, mainly through mesenchymal stromal cell (MSC) administration, may be a potentially attractive approach in this setting. In the current work, we aimed to assess the potential of the combination of MSCs with a proangiogenic elastin-like recombinamer (ELR)–based hydrogel in a hindlimb ischemia murine model. Human bone marrow MSCs were isolated from four healthy donors, while ELR biomaterials were genetically engineered. Hindlimb ischemia was induced through ligation of the right femoral artery, and mice were intramuscularly injected with ELR biomaterial, 0.5 × 10⁶ MSCs or the combination, and also compared to untreated animals. Tissue perfusion was monitored using laser Doppler perfusion imaging. Histological analysis of hindlimbs was performed after hematoxylin and eosin staining. Immunofluorescence with anti–human mitochondria antibody was used for human MSC detection, and the biomaterial was detected by elastin staining. To analyze the capillary density, immunostaining with an anti–CD31 antibody was performed. Our results show that the injection of MSCs significantly improves tissue reperfusion from day 7 (p = 0.0044) to day 21 (p = 0.0216), similar to the infusion of MSC + ELR (p = 0.0038, p = 0.0014), without significant differences between both groups. After histological evaluation, ELR hydrogels induced minimal inflammation in the injection sites, showing biocompatibility. MSCs persisted with the biomaterial after 21 days, both in vitro and in vivo. Finally, we observed a higher blood vessel density when mice were treated with MSCs compared to control (p<0.0001), but this effect was maximized and significantly different to the remaining experimental conditions when mice were treated with the combination of MSCs and the ELR biomaterial (p < 0.0001). In summary, the combination of an ELR-based hydrogel with MSCs may improve the angiogenic effects of both strategies on revascularization of ischemic tissues.

Recent Advances in Cardiac Tissue Engineering for the Management of Myocardium Infarction

Myocardium Infarction (MI) is one of the foremost cardiovascular diseases (CVDs) causing death worldwide, and its case numbers are expected to continuously increase in the coming years. Pharmacological interventions have not been at the forefront in ameliorating MI-related morbidity and mortality. Stem cell-based tissue engineering approaches have been extensively explored for their regenerative potential in the infarcted myocardium. Recent studies on microfluidic devices employing stem cells under laboratory set-up have revealed meticulous events pertaining to the pathophysiology of MI occurring at the infarcted site. This discovery also underpins the appropriate conditions in the niche for differentiating stem cells into mature cardiomyocyte-like cells and leads to engineering of the scaffold via mimicking of native cardiac physiological conditions. However, the mode of stem cell-loaded engineered scaffolds delivered to the site of infarction is still a challenging mission, and yet to be translated to the clinical setting. In this review, we have elucidated the various strategies developed using a hydrogel-based system both as encapsulated stem cells and as biocompatible patches loaded with cells and applied at the site of infarction.

Translational Applications of Hydrogels

Advances in hydrogel technology have unlocked unique and valuable capabilities that are being applied to a diverse set of translational applications. Hydrogels perform functions relevant to a range of biomedical purposes-they can deliver drugs or cells, regenerate hard and soft tissues, adhere to wet tissues, prevent bleeding, provide contrast during imaging, protect tissues or organs during radiotherapy, and improve the biocompatibility of medical implants. These capabilities make hydrogels useful for many distinct and pressing diseases and medical conditions and even for less conventional areas such as environmental engineering. In this review, we cover the major capabilities of hydrogels, with a focus on the novel benefits of injectable hydrogels, and how they relate to translational applications in medicine and the environment. We pay close attention to how the development of contemporary hydrogels requires extensive interdisciplinary collaboration to accomplish highly specific and complex biological tasks that range from cancer immunotherapy to tissue engineering to vaccination. We complement our discussion of preclinical and clinical development of hydrogels with mechanical design considerations needed for scaling injectable hydrogel technologies for clinical application. We anticipate that readers will gain a more complete picture of the expansive possibilities for hydrogels to make practical and impactful differences across numerous fields and biomedical applications.

Injectable hydrogels for vascular embolization and cell delivery: The potential for advances in cerebral aneurysm treatment

Cerebral aneurysms are vascular lesions caused by the biomechanical failure of the vessel wall due to hemodynamic stress and inflammation. Aneurysmal rupture results in subarachnoid hemorrhage often leading to death or disability. Current treatment options include open surgery and minimally invasive endovascular options aimed at secluding the aneurysm from the circulation. Cerebral aneurysm embolization with appropriate materials is a therapeutic approach to prevent rupture and the resultant clinical sequelae. Metallic platinum coils are a typical, practical option to embolize cerebral aneurysms. However, the development of an alternative treatment modality is of interest because of poor occlusion permanence, coil migration, and coil compaction. Moreover, minimizing the implanted foreign materials during therapy is of importance not just to patients, but also to clinicians in the event an open surgical approach has to be pursued in the future. Polymeric injectable hydrogels have been investigated for transcatheter embolization and cell therapy with the potential for permanent aneurysm repair. This review focuses on how the combination of injectable embolic biomaterials and cell therapy may achieve minimally invasive remodeling of a degenerated cerebral artery with promise for superior outcomes in treatment of this devastating disease.

Regenerative Medicine for the Treatment of Ischemic Heart Disease; Status and Future Perspectives

Cardiovascular disease is now the leading cause of adult death in the world. According to new estimates from the World Health Organization, myocardial infarction (MI) is responsible for four out of every five deaths due to cardiovascular disease. Conventional treatments of MI are taking aspirin and nitroglycerin as intermediate treatments and injecting antithrombotic agents within the first 3 h after MI. Coronary artery bypass grafting and percutaneous coronary intervention are the most common long term treatments. Since none of these interventions will fully regenerate the infarcted myocardium, there is value in pursuing more innovative therapeutic approaches. Regenerative medicine is an innovative interdisciplinary method for rebuilding, replacing, or repairing the missed part of different organs in the body, as similar as possible to the primary structure. In recent years, regenerative medicine has been widely utilized as a treatment for ischemic heart disease (one of the most fatal factors around the world) to repair the lost part of the heart by using stem cells. Here, the development of mesenchymal stem cells causes a breakthrough in the treatment of different cardiovascular diseases. They are easily obtainable from different sources, and expanded and enriched easily, with no need for immunosuppressing agents before transplantation, and fewer possibilities of genetic abnormality accompany them through multiple passages. The production of new cardiomyocytes can result from the transplantation of different types of stem cells. Accordingly, due to its remarkable benefits, stem cell therapy has received attention in recent years as it provides a drug-free and surgical treatment for patients and encourages a more safe and feasible cardiac repair. Although different clinical trials have reported on the promising benefits of stem cell therapy, there is still uncertainty about its mechanism of action. It is important to conduct different preclinical and clinical studies to explore the exact mechanism of action of the cells. After reviewing the pathophysiology of MI, this study addresses the role of tissue regeneration using various materials, including different types of stem cells. It proves some appropriate data about the importance of ethical problems, which leads to future perspectives on this scientific method.

Bidirectional relationship between cardiac extracellular matrix and cardiac cells in ischemic heart disease

Ischemic heart diseases (IHDs), including myocardial infarction and cardiomyopathies, are a leading cause of mortality and morbidity worldwide. Cardiac-derived stem and progenitor cells have shown promise as a therapeutic for IHD but are limited by poor cell survival, limited retention, and rapid washout. One mechanism to address this is to encapsulate the cells in a matrix or three-dimensional construct, so as to provide structural support and better mimic the cells' physiological microenvironment during administration. More specifically, the extracellular matrix (ECM), the native cellular support network, has been a strong candidate for this purpose. Moreover, there is a strong consensus that the ECM and its residing cells, including cardiac stem cells, have a constant interplay in response to tissue development, aging, disease progression, and repair. When externally stimulated, the cells and ECM work together to mutually maintain the local homeostasis by initially altering the ECM composition and stiffness, which in turn alters the cellular response and behavior. Given this constant interplay, understanding the mechanism of bidirectional cell-ECM interaction is essential to develop better cell implantation matrices to enhance cell engraftment and cardiac tissue repair. This review summarizes current understanding in the field, elucidating the signaling mechanisms between cardiac ECM and residing cells in response to IHD onset. Furthermore, this review highlights recent advances in native ECM-mimicking cardiac matrices as a platform for modulating cardiac cell behavior and inducing cardiac repair.

Bioactive Scaffolds in Stem Cell-Based Therapies for Myocardial Infarction: a Systematic Review and Meta-Analysis of Preclinical Trials

The use of bioactive scaffolds in conjunction with stem cell therapies for cardiac repair after a myocardial infarction shows significant promise for clinical translation. We performed a systematic review and meta-analysis of preclinical trials that investigated the use of bioactive scaffolds to support stem cell-aided cardiac regeneration, in comparison to stem cell treatment alone. Cochrane Library, Medline, Embase, PubMed, Scopus, Web of Science, and grey literature were searched through April 23, 2020 and 60 articles were included in the final analysis. The overall effect size observed in scaffold and stem cell-treated small animals compared to stem cell-treated controls for ejection fraction (EF) was 7.98 [95% confidence interval (CI): 6.36, 9.59] and for fractional shortening (FS) was 5.50 [95% CI: 4.35, 6.65] in small animal models. The largest improvements in EF and FS were observed when hydrogels were used (MD = 8.45 [95% CI: 6.46, 10.45] and MD = 5.76 [95% CI: 4.46, 7.05], respectively). Subgroup analysis revealed that cardiac progenitor cells had the largest effect size for FS, and was significant from pluripotent, mesenchymal and endothelial stem cell types. In large animal studies, the overall improvement of EF favoured the use of stem cell-embedded scaffolds compared to direct injection of cells (MD = 10.49 [95% CI: 6.30, 14.67]). Significant publication bias was present in the small animal trials for EF and FS. This study supports the use of bioactive scaffolds to aid in stem cell-based cardiac regeneration. Hydrogels should be further investigated in larger animal models for clinical translation.

Polymeric Biomaterials for the Treatment of Cardiac Post-Infarction Injuries

Cardiac regeneration aims to reconstruct the heart contractile mass, preventing the organ from a progressive functional deterioration, by delivering pro-regenerative cells, drugs, or growth factors to the site of injury. In recent years, scientific research focused the attention on tissue engineering for the regeneration of cardiac infarct tissue, and biomaterials able to anatomically and physiologically adapt to the heart muscle have been proposed as valuable tools for this purpose, providing the cells with the stimuli necessary to initiate a complete regenerative process. An ideal biomaterial for cardiac tissue regeneration should have a positive influence on the biomechanical, biochemical, and biological properties of tissues and cells; perfectly reflect the morphology and functionality of the native myocardium; and be mechanically stable, with a suitable thickness. Among others, engineered hydrogels, three-dimensional polymeric systems made from synthetic and natural biomaterials, have attracted much interest for cardiac post-infarction therapy. In addition, biocompatible nanosystems, and polymeric nanoparticles in particular, have been explored in preclinical studies as drug delivery and tissue engineering platforms for the treatment of cardiovascular diseases. This review focused on the most employed natural and synthetic biomaterials in cardiac regeneration, paying particular attention to the contribution of Italian research groups in this field, the fabrication techniques, and the current status of the clinical trials.

In Vivo Retention Quantification of Supramolecular Hydrogels Engineered for Cardiac Delivery

Recent advances in the field of cardiac regeneration show great potential in the use of injectable hydrogels to reduce immediate flush-out of injected factors, thereby increasing the effectiveness of the encapsulated drugs. To establish a relation between cardiac function and retention of the drug-encapsulating hydrogel, a quantitative in vivo imaging method is required. Here, the supramolecular ureido-pyrimidinone modified poly(ethylene glycol) (UPy-PEG) material is developed into a bioactive hydrogel for radioactive imaging in a large animal model. A radioactive label is synthesized, being a ureido-pyrimidinone moiety functionalized with a chelator (UPy-DOTA) complexed with the radioactive isotope indium-111 (UPy-DOTA-¹¹¹ In) that is mixed with the hydrogel. Additionally, bioactive and adhesive properties of the UPy-PEG hydrogel are increased by supramolecular introduction of a UPy-functionalized recombinant collagen type 1-based material (UPy-PEG-RCPhC1). This method enables in vivo tracking of the nonbioactive and bioactive supramolecular hydrogels and quantification of hydrogel retention in a porcine heart. In a small pilot, cardiac retention values of 8% for UPy-PEG and 16% for UPy-PEG-RCPhC1 hydrogel are observed 4 h postinjection. This work highlights the importance of retention quantification of hydrogels in vivo, where elucidation of hydrogel quantity at the target site is proposed to strongly influence efficacy of the intended therapy.

A low-temperature-printed hierarchical porous sponge-like scaffold that promotes cell-material interaction and modulates paracrine activity of MSCs for vascularized bone regeneration

Mesenchymal stem cells (MSCs) secrete paracrine trophic factors that are beneficial for tissue regeneration. In this study, a sponge-like scaffold with hierarchical and interconnected pores was developed using low-temperature deposition modeling (LDM) printing. Its effects on the cellular behavior, especially on the paracrine secretion patterns of MSCs, were comprehensively investigated. We found that compared with the scaffolds printed via the fused deposition modeling (FDM) technique, the LDM-printed sponges enhanced the adhesion, retention, survival, and ingrowth of MSCs and promoted cell-material interactions. Moreover, the paracrine functions of the cultured MSCs on the LDM-printed sponges were improved, with significant secretion of upregulated immunomodulatory, angiogenic, and osteogenic factors. MSCs on the LDM-printed sponges exert beneficial paracrine effects on multiple regenerative processes, including macrophage polarization, tube formation, and osteogenesis, verifying the enhanced immunomodulatory, angiogenic, and osteogenic potential. Further protein function assays indicated that focal adhesion kinase (FAK), downstream AKT, and yes-associated-protein (YAP) signaling might participate in the required mechanotransductive pathways, through which the hierarchical porous structures stimulated the paracrine effects of MSCs. In a rat distal femoral defect model, the MSC-laden LDM-printed sponges significantly promoted vascularized bone regeneration. The results of the present study demonstrate that the hierarchical porous biomimetic sponges prepared via LDM printing have potential applications in tissue engineering based on their cell-material interaction promotion and MSC paracrine function modulation effects. Furthermore, our findings suggest that the optimization of biomaterial properties to direct the paracrine signaling of MSCs would enhance tissue regeneration.

Injectable Hydrogels for Improving Cardiac Cell Therapy-In Vivo Evidence and Translational Challenges

Cell therapy has the potential to regenerate cardiac tissue and treat a variety of cardiac diseases which are currently without effective treatment. This novel approach to treatment has demonstrated clinical efficiency, despite low retention of the cell products in the heart. It has been shown that improving retention often leads to improved functional outcome. A feasible method of improving cell graft retention is administration of injectable hydrogels. Over the last decade, a variety of injectable hydrogels have been investigated preclinically for their potential to improve the effects of cardiac cell therapy. These hydrogels are created with different polymers, properties, and additional functional motifs and differ in their approaches for encapsulating different cell types. Only one combinational therapy has been tested in a clinical randomized controlled trial. In this review, the latest research on the potential of injectable hydrogels for delivery of cell therapy is discussed, together with potential roadblocks for clinical translation and recommendations for future explorations to facilitate future translation.

Mapping current research and identifying hotspots on mesenchymal stem cells in cardiovascular disease

BACKGROUND

Mesenchymal stem cells (MSCs) have important research value and broad application prospects in the cardiovascular disease. This study provides information on the latest progress, evolutionary path, frontier research hotspots, and future research developmental trends in this field.

METHODS

A knowledge map was generated by CiteSpace and VOSviewer analysis software based on data obtained from the literature on MSCs in the cardiovascular field.

RESULTS

The USA and China ranked at the top in terms of the percentage of articles, accounting for 34.306% and 28.550%, respectively. The institution with the highest number of research publications in this field was the University of Miami, followed by the Chinese Academy of Medical Sciences and Harvard University. The research institution with the highest ACI value was Harvard University, followed by the Mayo Clinic and the University of Cincinnati. The top three subjects in terms of the number of published articles were cell biology, cardiovascular system cardiology, and research experimental medicine. The journal with the most publications in this field was Circulation Research, followed by Scientific Reports and Biomaterials. The direction of research on MSCs in the cardiovascular system was divided into four parts: (1) tissue engineering, scaffolds, and extracellular matrix research; (2) cell transplantation, differentiation, proliferation, and signal transduction pathway research; (3) assessment of the efficacy of stem cells from different sources and administration methods in the treatment of acute myocardial infarction, myocardial hypertrophy, and heart failure; and (4) exosomes and extracellular vesicles research. Tissue research is the hotspot and frontier in this field.

CONCLUSION

MSC research has presented a gradual upward trend in the cardiovascular field. Multidisciplinary intersection is a characteristic of this field. Engineering and materials disciplines are particularly valued and have received attention from researchers. The progress in multidisciplinary research will provide motivation and technical support for the development of this field.

Progressive Reinvention or Destination Lost? Half a Century of Cardiovascular Tissue Engineering

The concept of tissue engineering evolved long before the phrase was forged, driven by the thromboembolic complications associated with the early total artificial heart programs of the 1960s. Yet more than half a century of dedicated research has not fulfilled the promise of successful broad clinical implementation. A historical account outlines reasons for this scientific impasse. For one, there was a disconnect between distinct eras each characterized by different clinical needs and different advocates. Initiated by the pioneers of cardiac surgery attempting to create neointimas on total artificial hearts, tissue engineering became fashionable when vascular surgeons pursued the endothelialisation of vascular grafts in the late 1970s. A decade later, it were cardiac surgeons again who strived to improve the longevity of tissue heart valves, and lastly, cardiologists entered the fray pursuing myocardial regeneration. Each of these disciplines and eras started with immense enthusiasm but were only remotely aware of the preceding efforts. Over the decades, the growing complexity of cellular and molecular biology as well as polymer sciences have led to surgeons gradually being replaced by scientists as the champions of tissue engineering. Together with a widening chasm between clinical purpose, human pathobiology and laboratory-based solutions, clinical implementation increasingly faded away as the singular endpoint of all strategies. Moreover, a loss of insight into the healing of cardiovascular prostheses in humans resulted in the acceptance of misleading animal models compromising the translation from laboratory to clinical reality. This was most evident in vascular graft healing, where the two main impediments to the in-situ generation of functional tissue in humans remained unheeded–the trans-anastomotic outgrowth stoppage of endothelium and the build-up of an impenetrable surface thrombus. To overcome this dead-lock, research focus needs to shift from a biologically possible tissue regeneration response to one that is feasible at the intended site and in the intended host environment of patients. Equipped with an impressive toolbox of modern biomaterials and deep insight into cues for facilitated healing, reconnecting to the “user needs” of patients would bring one of the most exciting concepts of cardiovascular medicine closer to clinical reality.

Human mesenchymal stromal cells and derived extracellular vesicles: Translational strategies to increase their proangiogenic potential for the treatment of cardiovascular disease

Mesenchymal stromal cells (MSCs) offer great potential for the treatment of cardiovascular diseases (CVDs) such as myocardial infarction and heart failure. Studies have revealed that the efficacy of MSCs is mainly attributed to their capacity to secrete numerous trophic factors that promote angiogenesis, inhibit apoptosis, and modulate the immune response. There is growing evidence that MSC‐derived extracellular vesicles (EVs) containing a cargo of lipids, proteins, metabolites, and RNAs play a key role in this paracrine mechanism. In particular, encapsulated microRNAs have been identified as important positive regulators of angiogenesis in pathological settings of insufficient blood supply to the heart, thus opening a new path for the treatment of CVD. In the present review, we discuss the current knowledge related to the proangiogenic potential of MSCs and MSC‐derived EVs as well as methods to enhance their biological activities for improved cardiac tissue repair. Increasing our understanding of mechanisms supporting angiogenesis will help optimize future approaches to CVD intervention.

Host macrophage response to injectable hydrogels derived from ECM and α-helical peptides

Tissue engineering materials play a key role in how closely the complex architectural and functional characteristics of native healthy tissue can be replicated. Traditional natural and synthetic materials are superseded by bespoke materials that cross the boundary between these two categories. Here we present hydrogels that are derived from decellularised extracellular matrix and those that are synthesised from de novo α-helical peptides. We assess in vitro activation of murine macrophages to our hydrogels and whether these gels induce an M1-like or M2-like phenotype. This was followed by the in vivo immune macrophage response to hydrogels injected into rat partial-thickness abdominal wall defects. Over 28 days we observe an increase in mononuclear cell infiltration at the hydrogel-tissue interface without promoting a foreign body reaction and see no evidence of hydrogel encapsulation or formation of multinucleate giant cells. We also note an upregulation of myogenic differentiation markers and the expression of anti-inflammatory markers Arginase1, IL-10, and CD206, indicating pro-remodelling for all injected hydrogels. Furthermore, all hydrogels promote an anti-inflammatory environment after an initial spike in the pro-inflammatory phenotype. No difference between the injected site and the healthy tissue is observed after 28 days, indicating full integration. These materials offer great potential for future applications in regenerative medicine and towards unmet clinical needs. STATEMENT OF SIGNIFICANCE: Materials play a key role in how closely the complex architectural and functional characteristics of native healthy tissue can be replicated in tissue engineering. Here we present injectable hydrogels derived from decellularised extracellular matrix and de novo designed α-helical peptides. Over 28 days in the rat abdominal wall we observe an increase in mononuclear cell infiltration at the hydrogel-tissue interface with no foreign body reaction, no evidence of hydrogel encapsulation and no multinucleate giant cells. Our data indicate pro-remodelling and the promotion of an anti-inflammatory environment for all injected hydrogels with evidence of full integration with healthy tissue after 28 days. These unique materials offer great potential for future applications in regenerative medicine and towards designing materials for unmet clinical needs.

Tuning Tissue Ingrowth into Proangiogenic Hydrogels via Dual Modality Degradation

The potential to control the rate of replacement of a biodegradable implant by a tissue would be advantageous. Here, we demonstrate that tissue invasion can be tuned through the novel approach of overlaying an enzymatically degradable hydrogel with an increasingly hydrolytically degradable environment. Poly(ethylene glycol) (PEG) hydrogels were formed from varying proportions of PEG-vinyl sulfone and PEG-acrylate (PEG-AC) monomers via a Michael-type addition reaction with a dithiol-containing matrix-metalloproteinase-susceptible peptide cross-linker. Swelling studies showed that PEG hydrogels with similar initial stiffnesses degraded more rapidly as the PEG-AC content increased. The replacement of subcutaneously implanted PEG hydrogels was also found to be proportional to their PEG-AC content. In addition, it would in many instances be desirable that these materials have the ability to stimulate their neovascularization. These hydrogels contained covalently bound heparin, and it was shown that a formulation of the hydrogel that allowed tissue replacement to occur over 1 month could trap and release growth factors and increase neovascularization by 50% over that time.

A Preliminary Computational Investigation Into the Flow of PEG in Rat Myocardial Tissue for Regenerative Therapy

Myocardial infarction (MI), a type of cardiovascular disease, affects a significant proportion of people around the world. Traditionally, non-communicable chronic diseases were largely associated with aging populations in higher income countries. It is now evident that low- to middle-income countries are also affected and in these settings, younger individuals are at high risk. Currently, interventions for MI prolong the time to heart failure. Regenerative medicine and stem cell therapy have the potential to mitigate the effects of MI and to significantly improve the quality of life for patients. The main drawback with these therapies is that many of the injected cells are lost due to the vigorous motion of the heart. Great effort has been directed toward the development of scaffolds which can be injected alongside stem cells, in an attempt to improve retention and cell engraftment. In some cases, the scaffold alone has been seen to improve heart function. This study focuses on a synthetic polyethylene glycol (PEG) based hydrogel which is injected into the heart to improve left ventricular function following MI. Many studies in literature characterize PEG as a Newtonian fluid within a specified shear rate range, on the macroscale. The aim of the study is to characterize the flow of a 20 kDa PEG on the microscale, where the behavior is likely to deviate from macroscale flow patterns. Micro particle image velocimetry (μPIV) is used to observe flow behavior in microchannels, representing the gaps in myocardial tissue. The fluid exhibits non-Newtonian, shear-thinning behavior at this scale. Idealized two-dimensional computational fluid dynamics (CFD) models of PEG flow in microchannels are then developed and validated using the μPIV study. The validated computational model is applied to a realistic, microscopy-derived myocardial tissue model. From the realistic tissue reconstruction, it is evident that the myocardial flow region plays an important role in the distribution of PEG, and therefore, in the retention of material.

Hydrogel-Nanoparticles Composite System for Controlled Drug Delivery

Biodegradable poly(ethylene glycol)-block-poly(-lactic acid) (PEG-b-PLA) nanoparticles (NPs) were prepared by nanoprecipitation with controlled dimension and with different electric charges, as monitored by dynamic light scattering (DLS). Then NPs were loaded within hydrogels (HG) developed for biomedical applications in the central nervous system, with different pore sizes (30 and 90 nm). The characteristics of the resulting composite hydrogel-NPs system were firstly studied in terms of ability to control the release of small steric hindrance drug mimetic. Then, diffusion-controlled release of different charged NPs from different entangled hydrogels was studied in vitro and correlated with NPs electric charges and hydrogel mean mesh size. These studies showed different trends, that depend on NPs superficial charge and HG mesh size. Release experiments and diffusion studies, then rationalized by mathematical modeling, allowed us to build different drug delivery devices that can satisfy different medical needs.

Differential Proteomic Analysis Predicts Appropriate Applications for the Secretome of Adipose-Derived Mesenchymal Stem/Stromal Cells and Dermal Fibroblasts

The adult stem cell secretome is currently under investigation as an alternative to cell-based therapy in regenerative medicine, thanks to the remarkable translational opportunity and the advantages in terms of handling and safety. In this perspective, we recently demonstrated the efficient performance of the adipose-derived mesenchymal stem/stromal cell (ASC) secretome in contrasting neuroinflammation in a murine model of diabetic neuropathy, where the administration of factors released by dermal fibroblasts (DFs) did not exert any effect. Up to now, the complex mixture of the constituents of the conditioned medium from ASCs has not been fully deepened, although its appropriate characterization is required in the perspective of a clinical use. Herein, we propose the differential proteomic approach for the identification of the players accounting for the functional effects of the cell secretome with the aim to unravel its appropriate applications. Out of 967 quantified proteins, 34 and 62 factors were found preponderantly or exclusively secreted by ASCs and DFs, respectively. This approach led to the recognition of distinct functions related to the conditioned medium of ASCs and DFs, with the former being involved in the regulation of neuronal death and apoptosis and the latter in bone metabolism and ossification. The proosteogenic effect of DF secretome was validated in vitro on human primary osteoblasts, providing a proof of concept of its osteoinductive potential. Besides discovering new applications of the cell type-specific secretome, the proposed strategy could allow the recognition of the cocktail of bioactive factors which might be responsible for the effects of conditioned media, thus providing a solid rationale to the implementation of a cell-free approach in several clinical scenarios involving tissue regeneration.