Timing effect of intramyocardial hydrogel injection for positively impacting left ventricular remodeling after myocardial infarction

Comparative effectiveness of myocardial patches and intramyocardial injections in treating myocardial infarction with a MitoQ/hydrogel system

In cardiac tissue engineering, myocardial surface patches and hydrogel intramyocardial injections represent the two primary hydrogel-based strategies for myocardial infarction (MI) treatment. However, the comparative effectiveness of these two treatments remains uncertain. Therefore, this study aimed to compare the effects of the two treatment modalities by designing a simple and reproducible hydrogel cross-linked with γ-PGA and 4-arm-PEG-SG. To improve mitochondrial damage in cardiomyocytes (CMs) during early MI, we incorporated the mitochondria-targeting antioxidant MitoQ into the hydrogel network. The hydrogel exhibited excellent biodegradability, biocompatibility, adhesion, and injectability in vitro. The hydrogel was utilized for rat MI treatment through both patch adhesion and intramyocardial injections. In vivo results demonstrated that the slow release of MitoQ peptide from the hydrogel hindered ROS production in CM, alleviated mitochondrial damage, and enhanced CM activity within 7 days, effectively inhibiting MI progression. Both hydrogel intramyocardial injections and patches exhibited positive therapeutic effects, with intramyocardial injections demonstrating superior efficacy in terms of cardiac function and structure in equivalent treatment cycles. In conclusion, we developed a MitoQ/hydrogel system that is easily prepared and can serve as both a myocardial patch and an intramyocardial injection for MI treatment, showing significant potential for clinical applications.

Analysis of the mechanism of curcumin against osteoarthritis using metabolomics and transcriptomics

Curcumin, a polyphenolic compound derived from the turmeric plant (Curcuma longa), has been extensively studied for its anti-inflammatory and anti-proliferative properties. The safety and efficacy of curcumin have been thoroughly validated. Nevertheless, the underlying mechanism for treating osteoarthritis remains ambiguous. This study aims to reveal the potential mechanism of curcumin in treating osteoarthritis by using metabolomics and transcriptomics. Firstly, we validated the effect of curcumin on inflammatory factors in human articular chondrocytes. Secondly, we explored the cellular metabolism mechanism of curcumin against osteoarthritis using cell metabolomics. Thirdly, we assessed the differences in gene expression of human articular chondrocytes through transcriptomics. Lastly, to evaluate the essential targets and elucidate the potential mechanism underlying the therapeutic effects of curcumin in osteoarthritis, we conducted a screening of the proteins within the shared pathway of metabolomics and transcriptomics. Our results demonstrated that curcumin significantly decreased the levels of inflammatory markers, such as IL-β, IL-6, and TNF-α, in human articular chondrocytes. Cell metabolomics identified 106 differential metabolites, including beta-aminopropionitrile, 3-amino-2-piperidone, pyrrole-2-carboxaldehyde, and various other components. The transcriptomic analysis yielded 1050 differential mRNAs. Enrichment analysis showed that the differential metabolites and mRNAs were significantly enriched in seven pathways, including glycine, serine, and threonine metabolism; pentose and glucuronate interconversions; glycerolipid metabolism; histidine metabolism; mucin-type o-glycan biosynthesis; inositol phosphate metabolism; and cysteine and methionine metabolism. A total of 23 key targets were identified to be involved in these pathways. We speculate that curcumin may alleviate osteoarthritis by targeting key proteins involved in glycine, serine, and threonine metabolism; inhibiting pyruvate production; and modulating glycolysis.

Hydrogels for the Treatment of Myocardial Infarction: Design and Therapeutic Strategies

Cardiovascular diseases (CVDs) have become the leading global burden of diseases in recent years and are the primary cause of human mortality and loss of healthy life expectancy. Myocardial infarction (MI) is the top cause of CVDs-related deaths, and its incidence is increasing worldwide every year. Recently, hydrogels have garnered great interest from researchers as a promising therapeutic option for cardiac tissue repair after MI. This is due to their excellent properties, including biocompatibility, mechanical properties, injectable properties, anti-inflammatory properties, antioxidant properties, angiogenic properties, and conductive properties. This review discusses the advantages of hydrogels as a novel treatment for cardiac tissue repair after MI. The design strategies of various hydrogels in MI treatment are then summarized, and the latest research progress in the field is classified. Finally, the future perspectives of this booming field are also discussed at the end of this review.

An injectable conductive hydrogel with dual responsive release of rosmarinic acid improves cardiac function and promotes repair after myocardial infarction

Myocardial infarction (MI) causes irreversible damage to the heart muscle, seriously threatening the lives of patients. Injectable hydrogels have attracted extensive attention in the treatment of MI. By promoting the coupling of mechanical and electrical signals between cardiomyocytes, combined with synergistic therapeutic strategies targeting the pathological processes of inflammation, proliferation, and fibrotic remodeling after MI, it is expected to improve the therapeutic effect. In this study, a pH/ROS dual-responsive injectable hydrogel was developed by modifying xanthan gum and gelatin with reversible imine bond and boronic ester bond double crosslinking. By encapsulating polydopamine-rosmarinic acid nanoparticles to achieve on-demand drug release in response to the microenvironment of MI, thereby exerting anti-inflammatory, anti-apoptotic, and anti-fibrosis effects. By adding conductive composites to improve the conductivity and mechanical strength of the hydrogel, restore electrical signal transmission in the infarct area, promote synchronous contraction of cardiomyocytes, avoid induced arrhythmias, and induce angiogenesis. Furthermore, the multifunctional hydrogel promoted the expression of cardiac-specific markers to restore cardiac function after MI. The in vivo and in vitro results demonstrate the effectiveness of this synergistic comprehensive treatment strategy in MI treatment, showing great application potential to promote the repair of infarcted hearts.

New treatment methods for myocardial infarction

For a long time, cardiovascular clinicians have focused their research on coronary atherosclerotic cardiovascular disease and acute myocardial infarction due to their high morbidity, high mortality, high disability rate, and limited treatment options. Despite the continuous optimization of the therapeutic methods and pharmacological therapies for myocardial ischemia-reperfusion, the incidence rate of heart failure continues to increase year by year. This situation is speculated to be caused by the current therapies, such as reperfusion therapy after ischemic injury, drugs, rehabilitation, and other traditional treatments, that do not directly target the infarcted myocardium. Consequently, these therapies cannot fundamentally solve the problems of myocardial pathological remodeling and the reduction of cardiac function after myocardial infarction, allowing for the progression of heart failure after myocardial infarction. Coupled with the decline in mortality caused by acute myocardial infarction in recent years, this combination leads to an increase in the incidence of heart failure. As a new promising therapy rising at the beginning of the twenty-first century, cardiac regenerative medicine provides a new choice and hope for the recovery of cardiac function and the prevention and treatment of heart failure after myocardial infarction. In the past two decades, regeneration engineering researchers have explored and summarized the elements, such as cells, scaffolds, and cytokines, required for myocardial regeneration from all aspects and various levels day and night, paving the way for our later scholars to carry out relevant research and also putting forward the current problems and directions for us. Here, we describe the advantages and challenges of cardiac tissue engineering, a contemporary innovative therapy after myocardial infarction, to provide a reference for clinical treatment.

Therapeutic angiogenesis based on injectable hydrogel for protein delivery in ischemic heart disease

Ischemic heart disease (IHD) remains the leading cause of death and disability worldwide and leads to myocardial necrosis and negative myocardial remodeling, ultimately leading to heart failure. Current treatments include drug therapy, interventional therapy, and surgery. However, some patients with severe diffuse coronary artery disease, complex coronary artery anatomy, and other reasons are unsuitable for these treatments. Therapeutic angiogenesis stimulates the growth of the original blood vessels by using exogenous growth factors to generate more new blood vessels, which provides a new treatment for IHD. However, direct injection of these growth factors can cause a short half-life and serious side effects owing to systemic spread. Therefore, to overcome this problem, hydrogels have been developed for temporally and spatially controlled delivery of single or multiple growth factors to mimic the process of angiogenesis in vivo. This paper reviews the mechanism of angiogenesis, some important bioactive molecules, and natural and synthetic hydrogels currently being applied for bioactive molecule delivery to treat IHD. Furthermore, the current challenges of therapeutic angiogenesis in IHD and its potential solutions are discussed to facilitate real translation into clinical applications in the future.

Progress in Stimuli-Responsive Biomaterials for Treating Cardiovascular and Cerebrovascular Diseases

Cardiovascular and cerebrovascular diseases (CCVDs) describe abnormal vascular system conditions affecting the brain and heart. Among these, ischemic heart disease and ischemic stroke are the leading causes of death worldwide, resulting in 16% and 11% of deaths globally. Although several therapeutic approaches are presented over the years, the continuously increasing mortality rates suggest the need for more advanced strategies for their treatment. One of these strategies lies in the use of stimuli-responsive biomaterials. These "smart" biomaterials can specifically target the diseased tissue, and after "reading" the altered environmental cues, they can respond by altering their physicochemical properties and/or their morphology. In this review, the progress in the field of stimuli-responsive biomaterials for CCVDs in the last five years, aiming at highlighting their potential as early-stage therapeutics in the preclinical scenery, is described.

Injectable selenium-containing polymeric hydrogel formulation for effective treatment of myocardial infarction

Myocardial infarction (MI) is a serious threat to people’s life and health, which is significantly hindered by effective treatment formulations. Interestingly, our recent endeavour of designing selenium-containing polymeric hydrogel has been experimentally proved to be helpful in combating inflammatory responses and treating MI. The design was inspired by selenium with anti-inflammatory and anti-fibrosis activities, and the formulation could also serve as a support of myocardial tissue upon the failure of this function. In details, an injectable selenium-containing polymeric hydrogel, namely, poly[di-(1-hydroxylyndecyl) selenide/polypropylene glycol/polyethylene glycol urethane] [poly(DH-SE/PEG/PPG urethane)], was synthesised by combining a thermosensitive PPG block, DH-Se (which has oxidation-reduction properties), and hydrophilic PEG segments. Based on the established mouse model of MI, this formulation was experimentally validated to effectively promote the recovery of cardiac function. At the same time, we confirmed by enzyme-linked immunosorbent assay, Masson staining and Western blotting that this formulation could inhibit inflammation and fibrosis, so as to significantly improve left ventricular remodelling. In summary, a selenium-containing polymeric hydrogel formulation analysed in the current study could be a promising therapeutic formulation, which can provide new strategies towards the effective treatment of myocardial infarction or even other inflammatory diseases.

Targeting Myocardial Fibrosis—A Magic Pill in Cardiovascular Medicine?

Fibrosis, characterized by an excessive accumulation of extracellular matrix, has long been seen as an adaptive process that contributes to tissue healing and regeneration. More recently, however, cardiac fibrosis has been shown to be a central element in many cardiovascular diseases (CVDs), contributing to the alteration of cardiac electrical and mechanical functions in a wide range of clinical settings. This paper aims to provide a comprehensive review of cardiac fibrosis, with a focus on the main pathophysiological pathways involved in its onset and progression, its role in various cardiovascular conditions, and on the potential of currently available and emerging therapeutic strategies to counteract the development and/or progression of fibrosis in CVDs. We also emphasize a number of questions that remain to be answered, and we identify hotspots for future research.

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.

Adipose-derived stem cell sheet under an elastic patch improves cardiac function in rats after myocardial infarction

OBJECTIVES

Although adipose-derived stem cells (ADSCs) have shown promise in cardiac regeneration, stable engraftment is still challenging. Acellular bioengineered cardiac patches have shown promise in positively altering ventricular remodeling in ischemic cardiomyopathy. We hypothesized that combining an ADSC sheet approach with a bioengineered patch would enhance ADSC engraftment and positively promote cardiac function compared with either therapy alone in a rat ischemic cardiomyopathy model.

METHODS

Cardiac patches were generated from poly(ester carbonate urethane) urea and porcine decellularized cardiac extracellular matrix. ADSCs constitutively expressing green fluorescent protein were established from F344 rats and transplanted as a cell sheet over the left ventricle 3 days after left anterior descending artery ligation with or without an overlying cardiac patch. Cardiac function was serially evaluated using echocardiography for 8 weeks, comparing groups with combined cells and patch (group C, n = 9), ADSCs alone (group A, n = 7), patch alone (group P, n = 6) or sham groups (n = 7).

RESULTS

Much greater numbers of ADSCs survived in the C versus A groups (P < .01). At 8 weeks posttransplant, the percentage fibrotic area was lower (P < .01) in groups C and P compared with the other groups and vasculature in the peri-infarct zone was greater in group C versus other groups (P < .01), and hepatocyte growth factor expression was higher in group C than in other groups (P < .05). Left ventricular ejection fraction was higher in group C versus other groups.

CONCLUSIONS

A biodegradable cardiac patch enhanced ADSC engraftment, which was associated with greater cardiac function and neovascularization in the peri-infarct zone following subacute myocardial infarction.

Platelet-rich plasma exhibits anti-inflammatory effect and attenuates cardiomyocyte damage by reducing NF-κB and enhancing VEGF expression in isoproterenol induced cardiotoxicity model

The present study investigated the cardioprotective effects of activated platelet-rich plasma (PRP) on high dose isoproterenol (ISO) induced cardiotoxicity. ISO was injected at a dose of 85 mg/kg/day, s.c. for 2 days. Cardiac function parameters including dp/dt max/min, left ventricular end diastolic pressure (LVEDP), relaxation constant (tau) and electrocardiogram (ECG) changes, anti-oxidant and membrane bound enzymes assays, pro-inflammatory cytokine levels, collagen content, immunohistochemical staining/gene expression of vascular endothelial growth factor (VEGF), cTnI (cardiac troponin I), NF-κB (nuclear factor kappa B), Smad-2/3, TGF-β (transforming growth factor), collagen-1/3 proteins were evaluated. PRP and platelet-poor plasma (PPP) were injected intramyocardially (200 μl in each ventricle region) 3 h after first dose of ISO under anesthesia. ISO injection induced cardiac dysfunction, hypertrophy, fibrosis, necrosis due to decline in anti-oxidant capacity, enhanced NF-κB and reduced cTnI immunostaining. However, the PRP injection attenuated these cardiac pathological changes by exerting anti-inflammatory properties and promoting cardiomyocyte repair.

From dissection of fibrotic pathways to assessment of drug interactions to reduce cardiac fibrosis and heart failure

Cardiac fibrosis is characterized by extracellular matrix deposition in the cardiac interstitium, and this contributes to cardiac contractile dysfunction and progression of heart failure. The main players involved in this process are the cardiac fibroblasts, which, in the presence of pro-inflammatory/pro-fibrotic stimuli, undergo a complete transformation acquiring a more proliferative, a pro-inflammatory and a secretory phenotype. This review discusses the cellular effectors and molecular pathways implicated in the pathogenesis of cardiac fibrosis and suggests potential strategies to monitor the effects of specific drugs designed to slow down the progression of this disease by specifically targeting the fibroblasts.

Ischemic Microenvironment-Responsive Therapeutics for Cardiovascular Diseases

Cardiovascular diseases caused by ischemia are attracting considerable attention owing to its high morbidity and mortality worldwide. Although numerous agents with cardioprotective benefits have been identified, their clinical outcomes are hampered by their low bioavailability, poor drug solubility, and systemic adverse effects. Advances in nanoscience and nanotechnology provide a new opportunity to effectively deliver drugs for treating ischemia-related diseases. In particular, cardiac ischemia leads to a characteristic pathological environment called an ischemic microenvironment (IME), significantly different from typical cardiac regions. These remarkable differences between ischemic sites and normal tissues have inspired the development of stimuli-responsive systems for the targeted delivery of therapeutic drugs to damaged cardiomyocytes. Recently, many biomaterials with intelligent properties have been developed to enhance the therapeutic benefits of drugs for the treatment of myocardial ischemia. Strategies for stimuli-responsive drug delivery and release based on IME include reactive oxygen species, pH-, hypoxia-, matrix metalloproteinase-, and platelet-inspired targeting strategies. In this review, state-of-the-art IME-responsive biomaterials for the treatment of myocardial ischemia are summarized. Perspectives, limitations, and challenges are also discussed for the further development of innovative and effective approaches to treat ischemic diseases with high effectiveness and biocompatibility.

Cardiac Tissue Engineering for the Treatment of Myocardial Infarction

Poor cell engraftment rate is one of the primary factors limiting the effectiveness of cell transfer therapy for cardiac repair. Recent studies have shown that the combination of cell-based therapy and tissue engineering technology can improve stem cell engraftment and promote the therapeutic effects of the treatment for myocardial infarction. This mini-review summarizes the recent progress in cardiac tissue engineering of cardiovascular cells from differentiated human pluripotent stem cells (PSCs), highlights their therapeutic applications for the treatment of myocardial infarction, and discusses the present challenges of cardiac tissue engineering and possible future directions from a clinical perspective.

Innovations in Disease State Responsive Soft Materials for Targeting Extracellular Stimuli Associated with Cancer, Cardiovascular Disease, Diabetes, and Beyond

Recent advances in polymer chemistry, materials sciences, and biotechnology have allowed the preclinical development of sophisticated programmable nanomedicines and materials that are able to precisely respond to specific disease-associated triggers and microenvironments. These stimuli, endogenous to the targeted diseases, include pH, redox-state, small molecules, and protein upregulation. Herein, recent advances and innovative approaches in programmable soft materials capable of sensing the aforementioned disease-associated stimuli and responding via a range of dynamic processes including morphological and size transitions, changes in mobility and retention, as well as disassembly are described. In this field generally, the majority of ongoing and past research effort has focused on oncology. Given this interest, examples of the latest innovative approaches to chemo- and immunotherapy treatment strategies for cancer are presented. Moreover, as the field broadens its attention, applications of programmable materials in other diseases are highlighted, with a special focus on cardiovascular disease and diabetes mellitus, where limited attention is paid by the field, but where many promising avenues exist with high potential impact.

Can a Biohybrid Patch Salvage Ventricular Function at a Late Time Point in the Post-Infarction Remodeling Process?

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A simple, biohybrid patch made of polymer (PECUU) and ECM, without cellular components, was able to induce positive remodeling features when applied over chronic infarcts with severely dilated hearts and high cardiac function impairment in rats.

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The remodeling benefit was particularly notable in a subgroup of the sickest rats with very low initial ejection fraction in which the echocardiographic endpoints were found to improve after treatment.

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This technological approach may hold promise for future translation to patients in a chronic scenario.

A biohybrid patch without cellular components was implanted over large infarcted areas in severely dilated hearts. Nonpatched animals were assigned to control or losartan therapy. Patch-implanted animals responded with better morphological and functional echocardiographic endpoints, which were more evident in a subgroup of animals with very low pre-treatment ejection fraction (<35%). Patched animals also had smaller infarcts than both nonpatched groups. This simple approach could hold promise for clinical translation and be applied using minimally invasive procedures over the epicardium in a large set of patients to induce better ventricular remodeling, especially among those who are especially frail.

Influence of sodium ferulate on miR-133a and left ventricle remodeling in rats with myocardial infarction

To explore the influence of sodium ferulate (SF) on miR-133a and left ventricle remodeling (LVR) in rats with myocardial infarction (MI). The left coronary artery was ligated to create 36 ischemia-reperfusion (IR) rat models that were randomly divided into mock surgical group (MSG) (not ligated), model group (MG), and sodium ferulate group (SFG). After the successful modeling, SFG was intravenously injected with SF at the dose of 10 mg/kg, and the other two groups were injected with the same volume of normal saline. After 28 days, cardiac hemodynamic indices of all groups were measured; the myocardial infarction size (MIS), left ventricular mass index (LVMI), and collagen volume fraction (CVF) were calculated, the content of serum malondialdehyde (MDA) and activities of catalase (CAT), superoxide dismutase (SOD) and glutathione catalase (GSH-px) were detected by ELISA, and miR-133a expression in myocardial tissues of the left ventricle (LV) was detected by RT-qPCR. SF improved the cardiac hemodynamic indices of rat model and reduced the MIS, LVMI and CVF. SF decreased the serum MDA level and increased the serum CAT, SOD and GSH-px levels in rat model. SF increased the expression of miR-133a in myocardial tissue of rat model. Therefore, SF could effectively reduce the myocardial injury of IR rats and improve the LVR. Its mechanism may be related to the antioxygenation and upregulation of miR-133a.

Scaffolds and Extracellular Vesicles as a Promising Approach for Cardiac Regeneration after Myocardial Infarction

Clinical studies have demonstrated the regenerative potential of stem cells for cardiac repair over the past decades, but their widespread use is limited by the poor tissue integration and survival obtained. Natural or synthetic hydrogels or microcarriers, used as cell carriers, contribute to resolving, in part, the problems encountered by providing mechanical support for the cells allowing cell retention, survival and tissue integration. Moreover, hydrogels alone also possess mechanical protective properties for the ischemic heart. The combined effect of growth factors with cells and an appropriate scaffold allow a therapeutic effect on myocardial repair. Despite this, the effects obtained with cell therapy remain limited and seem to be equivalent to the effects obtained with extracellular vesicles, key actors in intercellular communication. Extracellular vesicles have cardioprotective effects which, when combined proangiogenic properties with antiapoptotic and anti-inflammatory actions, make it possible to act on all the damages caused by ischemia. The evolution of biomaterial engineering allows us to envisage their association with new major players in cardiac therapy, extracellular vesicles, in order to limit undesirable effects and to envisage a transfer to the clinic. This new therapeutic approach could be associated with the release of growth factors to potentialized the beneficial effect obtained.

Injectable Drug-Releasing Microporous Annealed Particle Scaffolds for Treating Myocardial Infarction

Intramyocardial injection of hydrogels offers great potential for treating myocardial infarction (MI) in a minimally invasive manner. However, traditional bulk hydrogels generally lack microporous structures to support rapid tissue ingrowth and biochemical signals to prevent fibrotic remodeling toward heart failure. To address such challenges, a novel drug-releasing microporous annealed particle (drugMAP) system is developed by encapsulating hydrophobic drug-loaded nanoparticles into microgel building blocks via microfluidic manufacturing. By modulating nanoparticle hydrophilicity and pregel solution viscosity, drugMAP building blocks are generated with consistent and homogeneous encapsulation of nanoparticles. In addition, the complementary effects of forskolin (F) and Repsox (R) on the functional modulations of cardiomyocytes, fibroblasts, and endothelial cells in vitro are demonstrated. After that, both hydrophobic drugs (F and R) are loaded into drugMAP to generate FR/drugMAP for MI therapy in a rat model. The intramyocardial injection of MAP gel improves left ventricular functions, which are further enhanced by FR/drugMAP treatment with increased angiogenesis and reduced fibrosis and inflammatory response. This drugMAP platform represents a new generation of microgel particles for MI therapy and will have broad applications in regenerative medicine and disease therapy.

Cardiac Stem Cell-Loaded Delivery Systems: A New Challenge for Myocardial Tissue Regeneration

Cardiovascular disease (CVD) remains the leading cause of death in Western countries. Post-myocardial infarction heart failure can be considered a degenerative disease where myocyte loss outweighs any regenerative potential. In this scenario, regenerative biology and tissue engineering can provide effective solutions to repair the infarcted failing heart. The main strategies involve the use of stem and progenitor cells to regenerate/repair lost and dysfunctional tissue, administrated as a suspension or encapsulated in specific delivery systems. Several studies demonstrated that effectiveness of direct injection of cardiac stem cells (CSCs) is limited in humans by the hostile cardiac microenvironment and poor cell engraftment; therefore, the use of injectable hydrogel or pre-formed patches have been strongly advocated to obtain a better integration between delivered stem cells and host myocardial tissue. Several approaches were used to refine these types of constructs, trying to obtain an optimized functional scaffold. Despite the promising features of these stem cells’ delivery systems, few have reached the clinical practice. In this review, we summarize the advantages, and the novelty but also the current limitations of engineered patches and injectable hydrogels for tissue regenerative purposes, offering a perspective of how we believe tissue engineering should evolve to obtain the optimal delivery system applicable to the everyday clinical scenario.

Delivering More of an Injectable Human Recombinant Collagen III Hydrogel Does Not Improve Its Therapeutic Efficacy for Treating Myocardial Infarction

Injectable hydrogels are a promising method to enhance repair in the heart after myocardial infarction (MI). However, few studies have compared different strategies for the application of biomaterial treatments. In this study, we use a clinically relevant mouse MI model to assess the therapeutic efficacy of different treatment protocols for intramyocardial injection of a recombinant human collagen III (rHCIII) thermoresponsive hydrogel. Comparing a single hydrogel injection at an early time point (3 h) versus injections at multiple time points (3 h, 1 week, and 2 weeks) post-MI revealed that the single injection group led to superior cardiac function, reduced scar size and inflammation, and increased vascularization. Omitting the 3 h time point and delivering the hydrogel at 1 and 2 weeks post-MI led to poorer cardiac function. The positive effects of the single time point injection (3 h) on scar size and vascular density were lost when the hydrogel's collagen concentration was increased from 1% to 2%, and it did not confer any additional functional improvement. This study shows that early treatment with a rHCIII hydrogel can improve cardiac function post-MI but that injecting more rHCIII (by increased concentration or more over time) can reduce its efficacy, thus highlighting the importance of investigating optimal treatment strategies of biomaterial therapy for MI.

Biodegradable nanofibrous temperature-responsive gelling microspheres for heart regeneration

Myocardial infarction (heart attack) is the number one killer of heart patients. Existing treatments for heart attack do not address the underlying problem of cardiomyocyte (CM) loss and cannot regenerate the myocardium. Introducing exogenous cardiac cells is required for heart regeneration due to the lack of resident progenitor cells and very limited proliferative potential of adult CMs. Poor retention of transplanted cells is the critical bottleneck of heart regeneration. Here, we report the invention of a poly(l-lactic acid)-b-poly(ethylene glycol)-b-poly(N-Isopropylacrylamide) copolymer and its self-assembly into nanofibrous gelling microspheres (NF-GMS). The NF-GMS undergo thermally responsive transition to form not only a 3D hydrogel after injection in vivo, but also exhibit architectural and structural characteristics mimicking the native extracellular matrix (ECM) of nanofibrous proteins and gelling proteoglycans or polysaccharides. By integrating the ECM-mimicking features, injectable form, and the capability of maintaining 3D geometry after injection, the transplantation of hESC-derived CMs carried by NF-GMS led to a striking 10-fold graft size increase over direct CM injection in an infarcted rat model, which is the highest reported engraftment to date. Furthermore, NF-GMS carried CM transplantation dramatically reduced infarct size, enhanced integration of transplanted CMs, stimulated vascularization in the infarct zone, and led to a substantial recovery of cardiac function. The NF-GMS may also serve as advanced injectable and integrative biomaterials for cell/biomolecule delivery in a variety of biomedical applications.

Biodegradable nanofibrous temperature-responsive gelling microspheres for heart regeneration

Myocardial infarction (heart attack) is the number one killer of heart patients. Existing treatments for heart attack do not address the underlying problem of cardiomyocyte (CM) loss and cannot regenerate the myocardium. Introducing exogenous cardiac cells is required for heart regeneration due to the lack of resident progenitor cells and very limited proliferative potential of adult CMs. Poor retention of transplanted cells is the critical bottleneck of heart regeneration. Here, we report the invention of a poly(l-lactic acid)-b-poly(ethylene glycol)-b-poly(N-Isopropylacrylamide) copolymer and its self-assembly into nanofibrous gelling microspheres (NF-GMS). The NF-GMS undergo thermally responsive transition to form not only a 3D hydrogel after injection in vivo, but also exhibit architectural and structural characteristics mimicking the native extracellular matrix (ECM) of nanofibrous proteins and gelling proteoglycans or polysaccharides. By integrating the ECM-mimicking features, injectable form, and the capability of maintaining 3D geometry after injection, the transplantation of hESC-derived CMs carried by NF-GMS led to a striking 10-fold graft size increase over direct CM injection in an infarcted rat model, which is the highest reported engraftment to date. Furthermore, NF-GMS carried CM transplantation dramatically reduced infarct size, enhanced integration of transplanted CMs, stimulated vascularization in the infarct zone, and led to a substantial recovery of cardiac function. The NF-GMS may also serve as advanced injectable and integrative biomaterials for cell/biomolecule delivery in a variety of biomedical applications.

Biomechanics of infarcted left Ventricle-A review of experiments

Myocardial infarction (MI) is one of leading diseases to contribute to annual death rate of 5% in the world. In the past decades, significant work has been devoted to this subject. Biomechanics of infarcted left ventricle (LV) is associated with MI diagnosis, understanding of remodelling, MI micro-structure and biomechanical property characterizations as well as MI therapy design and optimization, but the subject has not been reviewed presently. In the article, biomechanics of infarcted LV was reviewed in terms of experiments achieved in the subject so far. The concerned content includes experimental remodelling, kinematics and kinetics of infarcted LVs. A few important issues were discussed and several essential topics that need to be investigated further were summarized. Microstructure of MI tissue should be observed even carefully and compared between different methods for producing MI scar in the same animal model, and eventually correlated to passive biomechanical property by establishing innovative constitutive laws. More uniaxial or biaxial tensile tests are desirable on MI, border and remote tissues, and viscoelastic property identification should be performed in various time scales. Active contraction experiments on LV wall with MI should be conducted to clarify impaired LV pumping function and supply necessary data to the function modelling. Pressure-volume curves of LV with MI during diastole and systole for the human are also desirable to propose and validate constitutive laws for LV walls with MI.

Human mesenchymal stem cells encapsulated-coacervated photoluminescent nanodots layered bioactive chitosan/collagen hydrogel matrices to indorse cardiac healing after acute myocardial infarction

Acute Myocardial Infarction (MI) is one of the foremost causes of human death worldwide and it leads to mass death of cardiomyocytes, interchanges of unfavorable biological environment and affecting electrical communications by fibrosis scar formations, and specifically deficiency of blood supply to heart which leads to heart damage and heart failure. Recently, numerous appropriate strategies have been applied to base on solve these problems wound be provide prominent therapeutic potential to cardiac regeneration after acute MI. In the present study, a combined biopolymeric conductive hydrogel was fabricated with conductive ultra-small graphene quantum dots as a soft injectable hydrogel for cardiac regenerations. The resultant hydrogel was combined with human Mesenchymal stem cells (hMSCs) to improved angiogenesis in cardiovascular tissues and decreasing cardiomyocyte necrosis of hydrogel treated acute-infarcted region has been greatly associated with the development of cardiac functions in MI models. The prepared graphene quantum dots and hydrogel groups was physico-chemically analyzed and confirmed the suitability of the materials for cardiac regeneration applications. The in vitro analyzes of hydrogels with hMSCs have established that enhanced cell survival rate, increased expressions of pro-inflammatory factors, pro-angiogenic factors and early cardiogenic markers. The results of in vivo myocardial observations and electrocardiography data demonstrated a favorable outcome of ejection fraction, fibrosis area, vessel density with reduced infarction size, implying that significant development of heart regenerative function after MI. This novel strategy of injectable hydrogel with hMSCs could be appropriate for the effective treatment of cardiac therapies after acute MI.

An injectable thermosensitive hydrogel loaded with an ancient natural drug colchicine for myocardial repair after infarction

Localized administration of anti-inflammatory agents benefits patients after myocardial infarction (MI) by repressing/modulating inflammatory response of the MI region and thus accelerating repair of the impaired tissues. Colchicine (Col), an ancient natural drug, has excellent anti-inflammatory effects; however, its utilization is strictly limited due to its severe systemic toxicity and narrow therapeutic window. In this study, we developed an intramyocardial delivery system of Col using an injectable, thermosensitive poly(lactide-co-glycolide)-poly(ethylene glycol)-poly(lactide-co-glycolide) (PLGA-PEG-PLGA) polymer hydrogel as the vehicle for the treatment of MI while minimizing its systemic toxicity. The aqueous PLGA-PEG-PLGA solution loaded with Col (Col@Gel) underwent a sol-gel transition at 35 °C and maintained a gel state at body temperature. Col was released from the Col@Gel in an initial burst followed by a sustained release manner for over 8 days. The in vitro cell tests showed that the Col@Gel system significantly inhibited macrophage proliferation and migration. In a mouse model of MI, a single intramyocardial administration of the Col@Gel effectively alleviated cardiac inflammation, inhibited myocardial apoptosis and fibrosis, improved cardiac function and structure, and increased mouse survival without inducing severe systemic toxicity, which was observed following intraperitoneal administration of Col solution. These results suggested that the Col@Gel system is a reliable drug delivery system for the sustained local release of Col and has great potential as an anti-inflammatory therapy for the treat of MI.

Development of Injectable Amniotic Membrane Matrix for Postmyocardial Infarction Tissue Repair

Ischemic heart disease represents the leading cause of death worldwide. Heart failure following myocardial infarction (MI) is associated with severe fibrosis formation and cardiac remodeling. Recently, injectable hydrogels have emerged as a promising approach to repair the infarcted heart and improve heart function through minimally invasive administration. Here, a novel injectable human amniotic membrane (hAM) matrix is developed to enhance cardiac regeneration following MI. Human amniotic membrane is isolated from human placenta and engineered to be a thermoresponsive, injectable gel around body temperature. Ultrasound-guided injection of hAM matrix into rat MI hearts significantly improves cardiac contractility, as measured by ejection fraction (EF), and decrease fibrosis. The results of this study demonstrate the feasibility of engineering as an injectable hAM matrix and its efficacy in attenuating degenerative changes in cardiac function following MI, which may have broad applications in tissue regeneration.

Myocardial-Infarction-Responsive Smart Hydrogels Targeting Matrix Metalloproteinase for On-Demand Growth Factor Delivery

Although in situ restoration of blood supply to the infarction region and attenuating pre-existing extracellular matrix degradation remain potential therapeutic approaches for myocardial infarction (MI), local delivery of therapeutics has been limited by low accumulation (inefficacy) and unnecessary diffusion (toxicity). Here, a dual functional MI-responsive hydrogel is fabricated for on-demand drug delivery to promote angiogenesis and inhibit cardiac remodeling by targeting upregulated matrix metalloproteinase-2/9 (MMP-2/9) after MI. A glutathione (GSH)-modified collagen hydrogel (collagen-GSH) is prepared by conjugating collagen amine groups with GSH sulfhydryl groups and the recombinant protein GST-TIMP-bFGF (bFGF: basic fibroblast growth factor) by fusing bFGF with glutathione-S-transferase (GST) and MMP-2/9 cleavable peptide PLGLAG (TIMP). Specific binding between GST and GSH significantly improves the amount of GST-TIMP-bFGF loaded in collagen-GSH hydrogel. The TIMP peptide enclosed between GST and bFGF responds to MMPs for on-demand release during MI. Additionally, the TIMP peptide is a competitive substrate of MMPs that inhibits the excessive degradation of cardiac matrix by MMPs after MI. GST-TIMP-bFGF/collagen-GSH hydrogels promote the recovery of MI rats by enhancing vascularization and ameliorating myocardium remodeling. The results suggest that on-demand growth factor delivery by synchronously controlling binding and responsive release to promote angiogenesis and attenuate cardiac remodeling might be promising for the treatment of ischemic heart disease.

Spatiotemporal delivery of basic fibroblast growth factor to directly and simultaneously attenuate cardiac fibrosis and promote cardiac tissue vascularization following myocardial infarction

Following myocardial infarction (MI), the destruction of vasculature in the infarcted heart muscle and progression of cardiac fibrosis lead to cardiac function deterioration. Vascularization of the damaged tissue and prevention of cardiac fibrosis represent promising strategies to improve cardiac function. Herein we have developed a bFGF release system with suitable release kinetics to simultaneously achieve the two goals. The release system was based on an injectable, thermosensitive, and fast gelation hydrogel and bFGF. The hydrogel had gelation time <7 s. It can quickly solidify upon injection into tissue so as to increase drug retention in the tissue. Hydrogel complex modulus can be tuned by hydrogel solution concentration. The complex modulus of 176.6 Pa and lower allowed cardiac fibroblast to maintain its phenotype. Bioactive bFGF was able to gradually release from the hydrogel for 4 weeks. The released bFGF promoted cardiac fibroblast survival under ischemic conditions mimicking those of the infarcted hearts. It also attenuated cardiac fibroblasts from differentiating into myofibroblasts in the presence of TGFβ when tested in 3D collagen model mimicking the scenario when the bFGF release system was injected into hearts. Furthermore, the released bFGF stimulated human umbilical endothelial cells to form endothelial lumen. After 4 weeks of implantation into infarcted hearts, the bFGF release system significantly increased blood vessel density, decreased myofibroblast density and collagen content, augmented cardiac cell survival/proliferation, and reduced macrophage density. In addition, the bFGF release system significantly increased cardiac function. These results demonstrate that delivery of bFGF with appropriate release kinetics alone may represent an efficient approach to control cardiac remodeling after MI.

Elastic 3D-Printed Hybrid Polymeric Scaffold Improves Cardiac Remodeling after Myocardial Infarction

Myocardial remodeling, including ventricular dilation and wall thinning, is an important pathological process caused by myocardial infarction (MI). To intervene in this pathological process, a new type of cardiac scaffold composed of a thermoset (poly-[glycerol sebacate], PGS) and a thermoplastic (poly-[ε-caprolactone], PCL) is directly printed by employing fused deposition modeling 3D-printing technology. The PGS-PCL scaffold possesses stacked construction with regular crisscrossed filaments and interconnected micropores and exhibits superior mechanical properties. In vitro studies demonstrate favorable biodegradability and biocompatibility of the PGS-PCL scaffold. When implanted onto the infarcted myocardium, this scaffold improves and preserves heart function. Furthermore, the scaffold improves several vital aspects of myocardial remodeling. On the morphological level, the scaffold reduces ventricular wall thinning and attenuated infarct size, and on the cellular level, it enhances vascular density and increases M2 macrophage infiltration, which might further contribute to the mitigated myocardial apoptosis rate. Moreover, the flexible PGS-PCL scaffold can be tailored to any desired shape, showing promise for annular-shaped restraint device application and meeting the demands for minimal invasive operation. Overall, this study demonstrates the therapeutic effects and versatile applications of a novel 3D-printed, biodegradable and biocompatible cardiac scaffold, which represents a promising strategy for improving myocardial remodeling after MI.

Hyaluronic Acid Oligosaccharides Improve Myocardial Function Reconstruction and Angiogenesis against Myocardial Infarction by Regulation of Macrophages

Myocardial infarction (MI) is identified as one of the major causes of mortality and disability worldwide. For severe myocardial infarction, even advanced forms of clinical intervention often lead to unsatisfactory therapeutic results. Thus, alternative strategies for MI treatment are still desirable. Previously studies reported the capacity of degradative fragment of h-HA (high molecular weight hyaluronic acid), hyaluronan oligosaccharides (<10 disaccharides units, o-HA), for wound healing by influence on angiogenesis, inspiring us to study its potential for myocardial functional recovery against MI. However, there are few reports about o-HA in MI therapy.

Methods: In our study, we synthesized o-HA with 6~10 disaccharides (4-5 kDa) by enzymatic degradation and investigated its therapeutic effects on MI.

Results: We found that o-HA could reduce infarct size and apoptosis in MI region, also promote myocardial angiogenesis and myocardial function reconstruction in MI mouse model. Furthermore, our results also indicated that o-HA in cardiac improved polarization of M2 type macrophage, removed the inflammatory response caused by neutrophil for accelerating myocardial function reconstruction in vivo. The transcriptomic analyses revealed that o-HA could activate expression of chemokines Ccl2 and Cxcl5 for promoting macrophage polarization and stimulate MAPK and JAK/STAT signaling pathway for compensatory response of myocardial function.

Conclusion: Collectively, our results suggested o-HA with 6~10 disaccharides might be a potential agent for reconstruction of cardiac function against MI.

Biodegradation of injectable silk fibroin hydrogel prevents negative left ventricular remodeling after myocardial infarction

Random collagen fiber networks formed by a slowly degrading silk fibroin hydrogel injection prevented left ventricular enlargement after myocardial infarction.

Retracted Article: Development of functional hydrogels for heart failure

Hydrogel-based approaches were reviewed for cardiac tissue engineering and myocardial regeneration in ischemia-induced heart failure, with an emphasis on functional studies, translational status, and clinical advancements.

Fabrication of Nanosuspension Directly Loaded Fast-Dissolving Films for Enhanced Oral Bioavailability of Olmesartan Medoxomil: In Vitro Characterization and Pharmacokinetic Evaluation in Healthy Human Volunteers

Olmesartan medoxomil (OM) is an antihypertensive drug with poor water solubility and low oral bioavailability (28.6%). Accordingly, this study aimed to formulate and evaluate OM nanosuspension incorporated into oral fast-dissolving films (FDFs) for bioavailability enhancement. OM nanosuspension was prepared by antisolvent-precipitation-ultrasonication method and characterized regarding particle size (122.67 ± 5.03 nm), span value (1.40 ± 0.51), and zeta potential (- 46.56 ± 1.20 mV). Transmission electron microscopy (TEM) of the nanosuspension showed spherical non-aggregating nanoparticles. The nanosuspension was then directly loaded into FDFs by solvent casting technique. A full factorial design (2² × 3¹) was implemented for optimization of the FDFs using Design-Expert® software. Physical and mechanical characteristics in addition to dissolution profiles of the FDFs were investigated. The optimum formula (FDF1) showed 0.43 ± 0.02 kg/mm² tensile strength, 20.50 ± 2.12 s disintegration time, and 87.53 ± 2.50 and 95.99 ± 0.25% OM dissolved after 6 and 10 min, respectively. Accelerated and long-term shelf stability studies confirmed the stability of FDF1. More than 75% OM was dissolved within 10 min from FDF1 compared with 9.80 and 47.80% for films prepared using coarse drug powder and market tablet, respectively. Relative bioavailability of FDF1 compared to market tablet was assessed in healthy human volunteers. The C_max value increased significantly from 66.62 ± 14.95 to 179.28 ± 23.96 ng/mL for market tablet and FDF1, respectively. Similarly, the AUC_0-72 value significantly increased from 498.36 ± 217.46 to 1083.67 ± 246.32 ng h/mL for market tablet and FDF1, respectively. Relative bioavailability of FDF1 was 209.28%. The highlighted results verified the effectiveness of OM nanosuspension-loaded FDFs in improving OM bioavailability.

Injectable, porous, biohybrid hydrogels incorporating decellularized tissue components for soft tissue applications

Biodegradable injectable hydrogels have been extensively studied and evaluated in various medical applications such as for bulking agents, drug delivery reservoirs, temporary barriers, adhesives, and cell delivery matrices. Where injectable hydrogels are intended to facilitate a healing response, it may be desirable to encourage rapid cellular infiltration into the hydrogel volume from the tissue surrounding the injection site. In this study, we developed a platform technique to rapidly form pores in a thermally responsive injectable hydrogel, poly(NIPAAm-co-VP-co-MAPLA) by using mannitol particles as porogens. In a rat hindlimb muscle injection model, hydrogels incorporating porosity had significantly accelerated cellular infiltration. To influence the inflammatory response to the injected hydrogel, enzymatically digested urinary bladder matrix (UBM) was mixed with the solubilized hydrogel. The presence of UBM was associated with greater polarization of the recruited macrophage population to the M2 phenotype, indicating a more constructive foreign body response. The hybrid hydrogel positively affected the wound healing outcomes of defects in rabbit adipose tissue with negligible inflammation and fibrosis, whereas scar formation and chronic inflammation were observed with autotransplantation and in saline injected groups. These results demonstrate the value of combining the effects of promoting cell infiltration and mediating the foreign body response for improved biomaterials options soft tissue defect filling applications.

STATEMENT OF SIGNIFICANCE

Our objective was to develop a fabrication process to create porous injectable hydrogels incorporating decellularized tissue digest material. This new hydrogel material was expected to exhibit faster cellular infiltration and a greater extent of pro-M2 macrophage polarization compared to control groups not incorporating each of the functional components. Poly(NIPAAm-co-VP-co-MAPLA) was chosen as the representative thermoresponsive hydrogel, and mannitol particles and digested urinary bladder matrix (UBM) were selected as the porogen and the bioactive decellularized material components respectively. In rat hindlimb intramuscular injection models, this new hydrogel material induced more rapid cellular infiltration and a greater extent of M2 macrophage polarization compared to control groups not incorporating all of the functional components. The hybrid hydrogel positively affected the wound healing outcomes of defects in rabbit adipose tissue with negligible inflammation and fibrosis, whereas scar formation and chronic inflammation were observed with autotransplantation and in saline injected groups. The methodology of this report provides a straightforward and convenient mechanism to promote cell infiltration and mediate foreign body response in injectable hydrogels for soft tissue applications. We believe that the readership of Acta Biomaterialia will find the work of interest both for its specific results and general translatability of the findings.

Study on the morphological and biocompatible properties of chitosan grafted silk fibre reinforced PVA films for tissue engineering applications

The current study delineates the preparation of novel chitosan grafted silk fibre reinforced Poly (vinyl alcohol) (PVA) composite films with desirable properties. Although silk fibroin has been extensively used for various biomedical applications, its properties could be further re-tailored for its suitability in the field of regenerative medicine. Chitosan was successfully grafted over silk, via acylation with succinic anhydride and thereby the fibres were incised and used for the preparation of the films. The grafted silk fibre reinforced PVA films were subjected to FTIR studies, microscopic analysis by atomic force microscopy (AFM) and optical microscopy techniques, X-ray diffraction (XRD) analysis and further evaluated for in vitro biocompatibility studies. The composite films demonstrated improved surface roughness with increasing concentration of the fibre and its dispersion in the polymer matrix was observed. Furthermore, in vitro biocompatibility and cellular behaviour such as adhesion and proliferation of mouse fibroblasts as well as astrocyte cells was studied and the results showed improved proliferative activity, when compared to the pristine PVA films. These results were further supported by the results confirmed by MTT assay demonstrating the films to be non-toxic. The efficiency and feasibility of the films to be used for tissue engineering, was further evaluated by haemocompatibility studies using human erythrocytes, thus making them a potential material to be used for biomedical applications.

Injectable Granular Hydrogels with Multifunctional Properties for Biomedical Applications

Injectable hydrogels are useful for numerous biomedical applications, such as to introduce therapeutics into tissues or for 3D printing. To expand the complexity of available injectable hydrogels, shear-thinning and self-healing granular hydrogels are developed from microgels that interact via guest-host chemistry. The microgel properties (e.g., degradation, molecule release) are tailored through their crosslinking chemistry, including degradation in response to proteases. When microgels of varied formulations are mixed, complex release and degradation behaviors are observed, including after injection to permit cellular invasion.

An Injectable Oxygen Release System to Augment Cell Survival and Promote Cardiac Repair Following Myocardial Infarction

Oxygen deficiency after myocardial infarction (MI) leads to massive cardiac cell death. Protection of cardiac cells and promotion of cardiac repair are key therapeutic goals. These goals may be achieved by re-introducing oxygen into the infarcted area. Yet current systemic oxygen delivery approaches cannot efficiently diffuse oxygen into the infarcted area that has extremely low blood flow. In this work, we developed a new oxygen delivery system that can be delivered specifically to the infarcted tissue, and continuously release oxygen to protect the cardiac cells. The system was based on a thermosensitive, injectable and fast gelation hydrogel, and oxygen releasing microspheres. The fast gelation hydrogel was used to increase microsphere retention in the heart tissue. The system was able to continuously release oxygen for 4 weeks. The released oxygen significantly increased survival of cardiac cells under the hypoxic condition (1% O₂) mimicking that of the infarcted hearts. It also reduced myofibroblast formation under hypoxic condition (1% O₂). After implanting into infarcted hearts for 4 weeks, the released oxygen significantly augmented cell survival, decreased macrophage density, reduced collagen deposition and myofibroblast density, and stimulated tissue angiogenesis, leading to a significant increase in cardiac function.

Injectable Shear-Thinning Hydrogels for Minimally Invasive Delivery to Infarcted Myocardium to Limit Left Ventricular Remodeling

BACKGROUND

Injectable, acellular biomaterials hold promise to limit left ventricular remodeling and heart failure precipitated by infarction through bulking or stiffening the infarct region. A material with tunable properties (eg, mechanics, degradation) that can be delivered percutaneously has not yet been demonstrated. Catheter-deliverable soft hydrogels with in vivo stiffening to enhance therapeutic efficacy achieve these requirements.

METHODS AND RESULTS

We developed a hyaluronic acid hydrogel that uses a tandem crosslinking approach, where the first crosslinking (guest-host) enabled injection and localized retention of a soft (<1 kPa) hydrogel. A second crosslinking reaction (dual-crosslinking) stiffened the hydrogel (41.4±4.3 kPa) after injection. Posterolateral infarcts were investigated in an ovine model (n≥6 per group), with injection of saline (myocardial infarction control), guest-host hydrogels, or dual-crosslinking hydrogels. Computational (day 1), histological (1 day, 8 weeks), morphological, and functional (0, 2, and 8 weeks) outcomes were evaluated. Finite-element modeling projected myofiber stress reduction (>50%; P<0.001) with dual-crosslinking but not guest-host injection. Remodeling, assessed by infarct thickness and left ventricular volume, was mitigated by hydrogel treatment. Ejection fraction was improved, relative to myocardial infarction at 8 weeks, with dual-crosslinking (37% improvement; P=0.014) and guest-host (15% improvement; P=0.058) treatments. Percutaneous delivery via endocardial injection was investigated with fluoroscopic and echocardiographic guidance, with delivery visualized by magnetic resonance imaging.

CONCLUSIONS

A percutaneous delivered hydrogel system was developed, and hydrogels with increased stiffness were found to be most effective in ameliorating left ventricular remodeling and preserving function. Ultimately, engineered systems such as these have the potential to provide effective clinical options to limit remodeling in patients after infarction.

Toward the development of biomimetic injectable and macroporous biohydrogels for regenerative medicine

Repairing or replacing damaged human tissues has been the ambitious goal of regenerative medicine for over 25years. One promising approach is the use of hydrated three-dimensional scaffolds, known as hydrogels, which have had good results repairing tissues in pre-clinical trials. Benefiting from breakthrough advances in the field of biology, and more particularly regarding cell/matrix interactions, these hydrogels are now designed to recapitulate some of the fundamental cues of native environments to drive the local tissue regeneration. We highlight the key parameters that are required for the development of smart and biomimetic hydrogels. We also review the wide variety of polymers, crosslinking methods, and manufacturing processes that have been developed over the years. Of particular interest is the emergence of supramolecular chemistries, allowing for the development of highly functional and reversible biohydrogels. Moreover, advances in computer assisted design and three-dimensional printing have revolutionized the production of macroporous hydrogels and allowed for more complex designs than ever before with the opportunity to develop fully reconstituted organs. Today, the field of biohydrogels for regenerative medicine is a prolific area of research with applications for most bodily tissues. On top of these applications, injectable hydrogels and macroporous hydrogels (foams) were found to be the most successful. While commonly associated with cells or biologics as drug delivery systems to increase therapeutic outcomes, they are steadily being used in the emerging fields of organs-on-chip and hydrogel-assisted cell therapy. To highlight these advances, we review some of the recent developments that have been achieved for the regeneration of tissues, focusing on the articular cartilage, bone, cardiac, and neural tissues. These biohydrogels are associated with improved cartilage and bone defects regeneration, reduced left ventricular dilation upon myocardial infarction and display promising results repairing neural lesions. Combining the benefits from each of these areas reviewed above, we envision that an injectable biohydrogel foam loaded with either stem cells or their secretome is the most promising hydrogel solution to trigger tissue regeneration. A paradigm shift is occurring where the combined efforts of fundamental and applied sciences head toward the development of hydrogels restoring tissue functions, serving as drug screening platforms or recreating complex organs.

Sustained Release of a Peptide-Based Matrix Metalloproteinase-2 Inhibitor to Attenuate Adverse Cardiac Remodeling and Improve Cardiac Function Following Myocardial Infarction

Following myocardial infarction (MI), degradation of extracellular matrix (ECM) by upregulated matrix metalloproteinases (MMPs) especially MMP-2 decreases tissue mechanical properties, leading to cardiac function deterioration. Attenuation of cardiac ECM degradation at the early stage of MI has the potential to preserve tissue mechanical properties, resulting in cardiac function increase. Yet the strategy for efficiently preventing cardiac ECM degradation remains to be established. Current preclinical approaches have shown limited efficacy because of low drug dosage allocated to the heart tissue, dose-limiting side effects, and cardiac fibrosis. To address these limitations, we have developed a MMP-2 inhibitor delivery system that can be specifically delivered into infarcted hearts at early stage of MI to efficiently prevent MMP-2-mediated ECM degradation. The system was based on an injectable, degradable, fast gelation, and thermosensitive hydrogel, and a MMP-2 specific inhibitor, peptide CTTHWGFTLC (CTT). The use of fast gelation hydrogel allowed to completely retain CTT in the heart tissue. The system was able to release low molecular weight CTT over 4 weeks possibly due to the strong hydrogen bonding between the hydrogel and CTT. The release kinetics was modulated by amount of CTT loaded into the hydrogel, and using chondroitin sulfate and heparin that can interact with CTT and the hydrogel. Both glycosaminoglycans augmented CTT release, while heparin more greatly accelerated the release. After it was injected into the infarcted hearts for 4 weeks, the released CTT efficiently prevented cardiac ECM degradation as it not only increased tissue thickness but also preserved collagen composition similar to that in the normal heart tissue. In addition, the delivery system significantly improved cardiac function. Importantly, the delivery system did not induce cardiac fibrosis. These results demonstrate that the developed MMP-2 inhibitor delivery system has potential to efficiently reduce adverse myocardial remodeling and improve cardiac function.

Spatiotemporal delivery of nanoformulated liraglutide for cardiac regeneration after myocardial infarction

The local, intramyocardial injection of proteins into the infarcted heart is an attractive option to initiate cardiac regeneration after myocardial infarction (MI). Liraglutide, which was developed as a treatment for type 2 diabetes, has been implicated as one of the most promising protein candidates in cardiac regeneration. A significant challenge to the therapeutic use of this protein is its short half-life in vivo. In this study, we evaluated the therapeutic effects and long-term retention of liraglutide loaded in poly(lactic-co-glycolic acid)-poly(ethylene glycol) (PLGA-PEG) nanoparticles (NP-liraglutide) on experimental MI. PLGA-PEG nanoparticles (NPs) have been shown to efficiently load liraglutide and release bioactive liraglutide in a sustained manner. For in vitro test, the released liraglutide retained bioactivity, as measured by its ability to activate liraglutide signaling pathways. Next, we compared the effects of an intramyocardial injection of saline, empty NPs, free liraglutide and NP-liraglutide in a rat model of MI. NPs were detected in the myocardium for up to 4 weeks. More importantly, an intramyocardial injection of NP-liraglutide was sufficient to improve cardiac function (P<0.05), attenuate the infarct size (P<0.05), preserve wall thickness (P<0.05), promote angiogenesis (P<0.05) and prevent cardiomyocyte apoptosis (P<0.05) at 4 weeks after injection without affecting glucose levels. The local, controlled, intramyocardial delivery of NP-liraglutide represents an effective and promising strategy for the treatment of MI.

Ventricular wall biomaterial injection therapy after myocardial infarction: Advances in material design, mechanistic insight and early clinical experiences

Intramyocardial biomaterial injection therapy for myocardial infarction has made significant progress since concept initiation more than 10 years ago. The interim successes and progress in the first 5 years have been extensively reviewed. During the last 5 years, two phase II clinical trials have reported their long term follow up results and many additional biomaterial candidates have reached preclinical and clinical testing. Also in recent years deeper investigations into the mechanisms behind the beneficial effects associated with biomaterial injection therapy have been pursued, and a variety of process and material parameters have been evaluated for their impact on therapeutic outcomes. This review explores the advances made in this biomaterial-centered approach to ischemic cardiomyopathy and discusses potential future research directions as this therapy seeks to positively impact patients suffering from one of the world's most common sources of mortality.