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

Advanced Nanomedicine Approaches for Myocardial Infarction Treatment

Myocardial infarction, usually caused by the rupture of atherosclerotic plaque, leads to irreversible ischemic cardiomyocyte death within hours followed by impaired cardiac performance or even heart failure. Current interventional reperfusion strategies for myocardial infarction still face high mortality with the development of heart failure. Nanomaterial-based therapy has made great progress in reducing infarct size and promoting cardiac repair after MI, although most studies are preclinical trials. This review focuses primarily on recent progress (2016-now) in the development of various nanomedicines in the treatment of myocardial infarction. We summarize these applications with the strategy of mechanism including anti-cardiomyocyte death strategy, activation of neovascularization, antioxidants strategy, immunomodulation, anti-cardiac remodeling, and cardiac repair.

Hydrogels for Cardio and Vascular Tissue Repair and Regeneration

Cardiovascular disease (CVD), the leading cause of death globally, affects the heart and arteries with a variety of clinical manifestations, the most dramatic of which are myocardial infarction (MI), abdominal aortic aneurysm (AAA), and intracranial aneurysm (IA) rupture. In MI, necrosis of the myocardium, scar formation, and loss of cardiomyocytes result from insufficient blood supply due to coronary artery occlusion. Beyond stenosis, the arteries that are structurally and functionally connected to the cardiac tissue can undergo pathological dilation, i.e., aneurysmal dilation, with high risk of rupture. Aneurysms of the intracranial arteries (IAs) are more commonly seen in young adults, whereas those of the abdominal aorta (AAA) are predominantly seen in the elderly. IAs, unpredictably, can undergo rupture and cause life-threatening hemorrhage, while AAAs can result in rupture, internal bleeding and high mortality rate. In this clinical context, hydrogels, three-dimensional networks of water-seizing polymers, have emerged as promising biomaterials for cardiovascular tissue repair or protection due to their biocompatibility, tunable properties, and ability to encapsulate and release bioactive molecules. This review provides an overview of the current state of research on the use of hydrogels as an innovative platform to promote cardiovascular-specific tissue repair in MI and functional recovery or protection in aneurysmal dilation.

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.

Polysaccharide-based hydrogels for medical devices, implants and tissue engineering: A review

Hydrogels are highly biocompatible biomaterials composed of crosslinked three-dimensional networks of hydrophilic polymers. Owing to their natural origin, polysaccharide-based hydrogels (PBHs) possess low toxicity, high biocompatibility and demonstrate in vivo biodegradability, making them great candidates for use in various biomedical devices, implants, and tissue engineering. In addition, many polysaccharides also show additional biological activities such as antimicrobial, anticoagulant, antioxidant, immunomodulatory, hemostatic, and anti-inflammatory, which can provide additional therapeutic benefits. The porous nature of PBHs allows for the immobilization of antibodies, aptamers, enzymes and other molecules on their surface, or within their matrix, potentiating their use in biosensor devices. Specific polysaccharides can be used to produce transparent hydrogels, which have been used widely to fabricate ocular implants. The ability of PBHs to encapsulate drugs and other actives has been utilized for making neural implants and coatings for cardiovascular devices (stents, pacemakers and venous catheters) and urinary catheters. Their high water-absorption capacity has been exploited to make superabsorbent diapers and sanitary napkins. The barrier property and mechanical strength of PBHs has been used to develop gels and films as anti-adhesive formulations for the prevention of post-operative adhesion. Finally, by virtue of their ability to mimic various body tissues, they have been explored as scaffolds and bio-inks for tissue engineering of a wide variety of organs. These applications have been described in detail, in this review.

A Cardiac-Targeted Nanozyme Interrupts the Inflammation-Free Radical Cycle in Myocardial Infarction

Severe systemic inflammation following myocardial infarction (MI) is a major cause of patient mortality. MI-induced inflammation can trigger the production of free radicals, which in turn ultimately leads to increased inflammation in cardiac lesions (i.e., inflammation-free radicals cycle), resulting in heart failure and patient death. However, currently available anti-inflammatory drugs have limited efficacy due to their weak anti-inflammatory effect and poor accumulation at the cardiac site. Herein, a novel Fe-Cur@TA nanozyme is developed for targeted therapy of MI, which is generated by coordinating Fe3+ and anti-inflammatory drug curcumin (Cur) with further modification of tannic acid (TA). Such Fe-Cur@TA nanozyme exhibits excellent free radicals scavenging and anti-inflammatory properties by reducing immune cell infiltration, promoting macrophage polarization toward the M2-like phenotype, suppressing inflammatory cytokine secretion, and blocking the inflammatory free radicals cycle. Furthermore, due to the high affinity of TA for cardiac tissue, Fe-Cur@TA shows an almost tenfold greater in cardiac retention and uptake than Fe-Cur. In mouse and preclinical beagle dog MI models, Fe-Cur@TA nanozyme preserves cardiac function and reduces scar size, suggesting promising potential for clinical translation in cardiovascular disease.

A superior extracellular matrix binding motif to enhance the regenerative activity and safety of therapeutic proteins

Among therapeutic proteins, cytokines and growth factors have great potential for regenerative medicine applications. However, these molecules have encountered limited clinical success due to low effectiveness and major safety concerns, highlighting the need to develop better approaches that increase efficacy and safety. Promising approaches leverage how the extracellular matrix (ECM) controls the activity of these molecules during tissue healing. Using a protein motif screening strategy, we discovered that amphiregulin possesses an exceptionally strong binding motif for ECM components. We used this motif to confer the pro-regenerative therapeutics platelet-derived growth factor-BB (PDGF-BB) and interleukin-1 receptor antagonist (IL-1Ra) a very high affinity to the ECM. In mouse models, the approach considerably extended tissue retention of the engineered therapeutics and reduced leakage in the circulation. Prolonged retention and minimal systemic diffusion of engineered PDGF-BB abolished the tumour growth-promoting adverse effect that was observed with wild-type PDGF-BB. Moreover, engineered PDGF-BB was substantially more effective at promoting diabetic wound healing and regeneration after volumetric muscle loss, compared to wild-type PDGF-BB. Finally, while local or systemic delivery of wild-type IL-1Ra showed minor effects, intramyocardial delivery of engineered IL-1Ra enhanced cardiac repair after myocardial infarction by limiting cardiomyocyte death and fibrosis. This engineering strategy highlights the key importance of exploiting interactions between ECM and therapeutic proteins for developing effective and safer regenerative therapies.

An injectable conductive hydrogel restores electrical transmission at myocardial infarct site to preserve cardiac function and enhance repair

Myocardial infarction (MI) leads to massive cardiomyocyte death and deposition of collagen fibers. This fibrous tissue disrupts electrical signaling in the myocardium, leading to cardiac systolic and diastolic dysfunction, as well as arrhythmias. Conductive hydrogels are a promising therapeutic strategy for MI. Here, we prepared a highly water-soluble conductive material (GP) by grafting polypyrrole (PPy) onto non-conductive gelatin. This component was added to the gel system formed by the Schiff base reaction between oxidized xanthan gum (OXG) and gelatin to construct an injectable conductive hydrogel. The prepared self-healing OGGP3 (3 wt% GP) hydrogel had good biocompatibility, elastic modulus, and electrical conductivity that matched the natural heart. The prepared biomaterials were injected into the rat myocardial scar tissue 2 days after MI. We found that the cardiac function of the rats treated with OGGP3 was improved, making it more difficult to induce arrhythmias. The electrical resistivity of myocardial fibrous tissue was reduced, and the conduction velocity of myocardial tissue was increased. Histological analysis showed reduced infarct size, increased left ventricular wall thickness, increased vessel density, and decreased inflammatory response in the infarcted area. Our findings clearly demonstrate that the OGGP3 hydrogel attenuates ventricular remodeling and inhibits infarct dilation, thus showing its potential for the treatment of MI.

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An injectable self-healing conductive hydrogel was synthesized for the treatment of myocardial infarction (MI).

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The OGGP3 hydrogel had elastic modulus (20.77 kPa) and conductivity (5.52 × 10⁻⁴ S/cm) that matched the natural heart.

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The hydrogel could protect cardiac function, reduce arrhythmia susceptibility and the resistivity of cardiac scar tissue.

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The hydrogel could increase left ventricular wall thickness, reduce infarct size and cardiac fibrosis in the infarcted area.

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The hydrogel could promote the expression level of cardiac-specific markers, induce angiogenesis, and reduce inflammation.

Nanomaterial-Based Electrically Conductive Hydrogels for Cardiac Tissue Repair

Cardiovascular disease is one of major causes of deaths, and its incidence has gradually increased worldwide. For cardiovascular diseases, several therapeutic approaches, such as drugs, cell-based therapy, and heart transplantation, are currently employed; however, their therapeutic efficacy and/or practical availability are still limited. Recently, biomaterial-based tissue engineering approaches have been recognized as promising for regenerating cardiac function in patients with cardiovascular diseases, including myocardial infarction (MI). In particular, materials mimicking the characteristics of native cardiac tissues can potentially prevent pathological progression and promote cardiac repair of the heart tissues post-MI. The mechanical (softness) and electrical (conductivity) properties of biomaterials as non-biochemical cues can improve the cardiac functions of infarcted hearts by mitigating myocardial cell death and subsequent fibrosis, which often leads to cardiac tissue stiffening and high electrical resistance. Consequently, electrically conductive hydrogels that can provide mechanical strength and augment the electrical activity of the infarcted heart tissue are considered new functional materials capable of mitigating the pathological progression to heart failure and stimulating cardiac regeneration. In this review, we highlight nanomaterial-incorporated hydrogels that can induce cardiac repair after MI. Nanomaterials, including carbon-based nanomaterials and recently discovered two-dimensional nanomaterials, offer great opportunities for developing functional conductive hydrogels owing to their excellent electrical conductivity, large surface area, and ease of modification. We describe recent results using nanomaterial-incorporated conductive hydrogels as cardiac patches and injectable hydrogels for cardiac repair. While further evaluations are required to confirm the therapeutic efficacy and toxicity of these materials, they could potentially be used for the regeneration of other electrically active tissues, such as nerves and muscles.

Co-axial fibrous scaffolds integrating with carbon fiber promote cardiac tissue regeneration post myocardial infarction

Myocardium is an excitable tissue with electrical conductivity and mechanical strength. In this work, carbon fibers (CFs) and co-axial fibrous mesh were integrated which combined the high modulus and excellent electrical conductivity of CFs and the fibrous and porous structures of the electrospun fibers. The scaffold was fabricated by simply integrating coaxial electrospun fibers and carbon fibers through a freeze-drying procedure. It was shown that the integration of carbon fibers have the conductivity and Young's modulus of the fibrous mesh increased significantly, meanwhile, upregulated the expression of CX43, α-actinin, RhoA of the neonatal rat primary cardiomyocytes and primary human umbilical vein endothelial cells (HUVECs), and promoted the secretion of VEGF of HUVECs. Moreover, the cardiomyocytes grown on the scaffolds increased the ability of HUVECs migration. When implanted to the injury area post myocardial infraction, the scaffolds were able to effectively enhance the tissue regeneration and new vessel formation, which rescued the heart dysfunction induced by the myocardial infraction, evidenced by the results of echocardiography and histochemical analysis. In conclusion, the composite scaffolds could promote the myocardium regeneration and function's recovery by enhancing cardiomyocytes maturation and angiogenesis and establishing the crosstalk between the cardiomyocytes and the vascular endothelial cells.

Development of Innovative Biomaterials and Devices for the Treatment of Cardiovascular Diseases

Cardiovascular diseases have become the leading cause of death worldwide. The increasing burden of cardiovascular diseases has become a major public health problem and how to carry out efficient and reliable treatment of cardiovascular diseases has become an urgent global problem to be solved. Recently, implantable biomaterials and devices, especially minimally invasive interventional ones, such as vascular stents, artificial heart valves, bioprosthetic cardiac occluders, artificial graft cardiac patches, atrial shunts, and injectable hydrogels against heart failure, have become the most effective means in the treatment of cardiovascular diseases. Herein, an overview of the challenges and research frontier of innovative biomaterials and devices for the treatment of cardiovascular diseases is provided, and their future development directions are discussed.

Characterization of decellularized left and right ventricular myocardial matrix hydrogels and their effects on cardiac progenitor cells

Congenital heart defects are the leading cause of right heart failure in pediatric patients. Implantation of c-kit+ cardiac-derived progenitor cells (CPCs) is being clinically evaluated to treat the failing right ventricle (RV), but faces limitations due to reduced transplant cell survival, low engraftment rates, and low retention. These limitations have been exacerbated due to the nature of cell delivery (narrow needles) and the non-optimal recipient microenvironment (reactive oxygen species (ROS)). Extracellular matrix (ECM) hydrogels derived from porcine left ventricular (LV) myocardium have emerged as a potential therapy to treat the ischemic LV and have shown promise as a vehicle to deliver cells to injured myocardium. However, no studies have evaluated the combination of an injectable biomaterial, such as an ECM hydrogel, in combination with cell therapy for treating RV failure. In this study we characterized LV and RV myocardial matrix (MM) hydrogels and performed in vitro evaluations of their potential to enhance CPC delivery, including resistance to forces experienced during injection and exposure to ROS, as well as their potential to enhance angiogenic paracrine signaling. While physical properties of the two hydrogels are similar, the decellularized LV and RV have distinct protein signatures. Both materials were equally effective in protecting CPCs against needle forces and ROS. CPCs encapsulated in either the LV MM or RV MM exhibited similar enhanced potential for angiogenic paracrine signaling when compared to CPCs in collagen. The RV MM without cells, however, likewise improved tube formation, suggesting it should also be evaluated as a potential standalone treatment.

Sulfonated Thermoresponsive Injectable Gel for Sequential Release of Therapeutic Proteins to Protect Cardiac Function after Myocardial Infarction

Myocardial infarction causes cardiomyocyte death and persistent inflammatory responses, which generate adverse pathological remodeling. Delivering therapeutic proteins from injectable materials in a controlled-release manner may present an effective biomedical approach for treating this disease. A thermoresponsive injectable gel composed of chitosan, conjugated with poly(N-isopropylacrylamide) and sulfonate groups, was developed for spatiotemporal protein delivery to protect cardiac function after myocardial infarction. The thermoresponsive gel delivered vascular endothelial growth factor (VEGF), interleukin-10 (IL-10), and platelet-derived growth factor (PDGF) in a sequential and sustained manner in vitro. An acute myocardial infarction mouse model was used to evaluate polymer biocompatibility and to determine therapeutic effects from the delivery system on cardiac function. Immunohistochemistry showed biocompatibility of the hydrogel, while the controlled delivery of the proteins reduced macrophage infiltration and increased vascularization. Echocardiography showed an improvement in ejection fraction and fractional shortening after injecting the thermal gel and proteins. A factorial design of experimental study was implemented to optimize the delivery system for the best combination and doses of proteins for further increasing stable vascularization and reducing inflammation using a subcutaneous injection mouse model. The results showed that VEGF, IL-10, and FGF-2 demonstrated significant contributions toward promoting long-term vascularization, while PDGF's effect was minimal.

Injectable, Anti-Cancer Drug-Eluted Chitosan Microspheres against Osteosarcoma

The purpose of this study is to fabricate different anti-cancer drug-eluted chitosan microspheres for combination therapy of osteosarcoma. In this study, electrospray in combination with ground liquid nitrogen was utilized to manufacture the microspheres. The size of obtained chitosan microspheres was uniform, and the average diameter was 532 μm. The model drug release rate and biodegradation rate of chitosan microspheres could be controlled by the glutaraldehyde vapor crosslinking time. Then the 5-fluorouracil (5-FU), paclitaxel (PTX), and Cis-dichlorodiammine-platinum (CDDP) eluted chitosan microspheres were prepared, and two osteosarcoma cell lines, namely, HOS and MG-63, were selected as cell models for in vitro demonstration. We found the 5-FU microspheres, PTX microspheres, and CDDP microspheres could significantly inhibit the growth and migration of both HOS and MG-63 cells. The apoptosis of both cells treated with 5-FU microspheres, PTX microspheres, and CDDP microspheres was significantly increased compared to the counterparts of control and blank groups. The anti-cancer drug-eluted chitosan microspheres show great potential for the treatment of osteosarcoma.

Scalable Milk-Derived Whey Protein Hydrogel as an Implantable Biomaterial

There are limited naturally derived protein biomaterials for the available medical implants. High cost, low yield, and batch-to-batch inconsistency, as well as intrinsically differing bioactivity in some of the proteins, make them less beneficial as common implant materials compared to their synthetic counterparts. Here, we present a milk-derived whey protein isolate (WPI) as a new kind of natural protein-based biomaterial for medical implants. The WPI was methacrylated at 100 g bench scale, >95% conversion, and 90% yield to generate a photo-cross-linkable material. WPI-MA was further processed into injectable hydrogels, monodispersed microspheres, and patterned scaffolds with photo-cross-linking-based advanced processing methods including microfluidics and 3D printing. In vivo evaluation of the WPI-MA hydrogels showed promising biocompatibility and degradability. Intramyocardial implantation of injectable WPI-MA hydrogels in a model of myocardial infarction attenuated the pathological changes in the left ventricle. Our results indicate a possible therapeutic value of WPI-based biomaterials and give rise to a potential collaboration between the dairy industry and the production of medical therapeutics.

Progress in Bioengineering Strategies for Heart Regenerative Medicine

The human heart has the least regenerative capabilities among tissues and organs, and heart disease continues to be a leading cause of mortality in the industrialized world with insufficient therapeutic options and poor prognosis. Therefore, developing new therapeutic strategies for heart regeneration is a major goal in modern cardiac biology and medicine. Recent advances in stem cell biology and biotechnologies such as human pluripotent stem cells (hPSCs) and cardiac tissue engineering hold great promise for opening novel paths to heart regeneration and repair for heart disease, although these areas are still in their infancy. In this review, we summarize and discuss the recent progress in cardiac tissue engineering strategies, highlighting stem cell engineering and cardiomyocyte maturation, development of novel functional biomaterials and biofabrication tools, and their therapeutic applications involving drug discovery, disease modeling, and regenerative medicine for heart disease.

Lyotropic Liquid Crystals: A Biocompatible and Safe Material for Local Cardiac Application

The regeneration of cardiac tissue is a multidisciplinary research field aiming to improve the health condition of the post-heart attack patient. Indeed, myocardial tissue has a poor ability to self-regenerate after severe damage. The scientific efforts focused on the research of a biomaterial able to adapt to heart tissue, thus guaranteeing the in situ release of active substances or growth promoters. Many types of hydrogels were proposed for this purpose, showing several limitations. The aim of this study was to suggest a new usage for glyceryl monooleate-based lyotropic liquid crystals (LLCs) as a biocompatible and inert material for a myocardial application. The main advantages of LLCs are mainly related to their easy in situ injection as lamellar phase and their instant in situ transition in the cubic phase. In vivo studies proved the biocompatibility and the inertia of LLCs after their application on the myocardial tissue of mice. In detail, the cardiac activity was monitored through 28 days, and no significant alterations were recorded in the heart anatomy and functionality. Moreover, gross anatomy showed the ability of LLCs to be bio-degraded in a suitable time frame. Overall, these results permitted us to suppose a potential use of LLCs as materials for cardiac drug delivery.

An MMP-degradable and conductive hydrogel to stabilize HIF-1α for recovering cardiac functions

Rationale: Although a few injectable hydrogels have shown a reliable biosafety and a moderate promise in treating myocardial infarction (MI), the updated hydrogel systems with an on-demand biodegradation and multi-biofunctions to deliver therapeutic drug would achieve more prominent efficacy in the future applications. In this report, a conductive and injectable hydrogel crosslinked by matrix metalloproteinase-sensitive peptides (MMP-SP) was rationally constructed to stabilize hypoxia-inducible factor-1α (HIF-1α) to recover heart functions after MI.

Methods: Firstly, tetraaniline (TA) was incorporated into partially oxidized alginate (ALG-CHO) to endow the hydrogels with conductivity. The 1,4-dihydrophenonthrolin-4-one-3-carboxylic acid (DPCA) nanodrug was manufactured with high drug loading capacity and decorated with polymerized dopamine (PDA) to achieve a stable release of the drug. Both ALG-CHO and DPCA@PDA can be cross-linked by thiolated hyaluronic acid (HA-SH) and thiolated MMP-SP to construct a MMP-degradable and conductive hydrogel. After administration in the infarcted heart of rats, echocardiographic assessments, histological evaluation, and RT-PCR were used to evaluate therapeutic effects of hydrogels.

Results: The cell viability and the results of subcutaneous implantation verify a good cytocompatibility and biocompatibility of the resulting hydrogels. The hydrogel shows remarkable strength in decreasing the expression of inflammatory factors, maintaining a high level of HIF-1α to promote the vascularization, and promoting the expression of junctional protein connexin 43. Meanwhile, the multifunctional hydrogels greatly reduce the infarcted area (by 33.8%) and improve cardiac functions dramatically with ejection fraction (EF) and fractional shortening (FS) being increased by 31.3% and 19.0%, respectively.

Conclusion: The as-prepared hydrogels in this report achieve a favorable therapeutic effect, offering a promising therapeutic strategy for treating heart injury.

Evaluation of Therapeutic Collagen-Based Biomaterials in the Infarcted Mouse Heart by Extracellular Matrix Targeted MALDI Imaging Mass Spectrometry

The goal of this study was to develop strategies to localize human collagen-based hydrogels within an infarcted mouse heart, as well as analyze its impact on endogenous extracellular matrix (ECM) remodeling. Collagen is a natural polymer that is abundantly used in bioengineered hydrogels because of its biocompatibility, cell permeability, and biodegradability. However, without the use of tagging techniques, collagen peptides derived from hydrogels can be difficult to differentiate from the endogenous ECM within tissues. Imaging mass spectrometry is a robust tool capable of visualizing synthetic and natural polymeric molecular structures yet is largely underutilized in the field of biomaterials outside of surface characterization. In this study, our group leveraged a recently developed matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) technique to enzymatically target collagen and other ECM peptides within the tissue microenvironment that are both endogenous and hydrogel-derived. Using a multimodal approach of fluorescence microscopy and ECM-IMS techniques, we were able to visualize and relatively quantify significantly abundant collagen peptides in an infarcted mouse heart that were localized to regions of therapeutic hydrogel injection sites. On-tissue MALDI MS/MS was used to putatively identify sites of collagen peptide hydroxyproline site occupancy, a post-translational modification that is critical in collagen triple helical stability. Additionally, the technique could putatively identify over 35 endogenously expressed ECM peptides that were expressed in hydrogel-injected mouse hearts. Our findings show evidence for the use of MALDI-IMS in assessing the therapeutic application of collagen-based biomaterials.

The role of regional myocardial topography post-myocardial infarction on infarct extension

Infarct extension involves necrosis of healthy myocardium in the border zone (BZ), progressively enlarging the infarct zone (IZ) and recruiting the remote zone (RZ) into the BZ, eventually leading to heart failure. The mechanisms underlying infarct extension remain unclear, but myocyte stretching has been suggested as the most likely cause. Using human patient-specific left-ventricular (LV) numerical simulations established from cardiac magnetic resonance imaging (MRI) of myocardial infarction (MI) patients, the correlation between infarct extension and regional mechanics abnormality was investigated by analysing the fibre stress-strain loops (FSSLs). FSSL abnormality was characterised using the directional regional external work (DREW) index, which measures FSSL area and loop direction. Sensitivity studies were also performed to investigate the effect of infarct stiffness on regional myocardial mechanics and potential for infarct extension. We found that infarct extension was correlated to severely abnormal FSSL in the form of counter-clockwise loop at the RZ close to the infarct, as indicated by negative DREW values. In regions demonstrating negative DREW values, we observed substantial fibre stretching in the isovolumic relaxation (IVR) phase accompanied by a reduced rate of systolic shortening. Such stretching in IVR phase in part of the RZ was due to its inability to withstand the high LV pressure that was still present and possibly caused by regional myocardial stiffness inhomogeneity. Further analysis revealed that the occurrence of severely abnormal FSSL due to IVR fibre stretching near the RZ-BZ boundary was due to a large amount of surrounding infarcted tissue, or an excessively stiff IZ.

Oxygen-rich Environment Ameliorates Cell Therapy Outcomes of Cardiac Progenitor Cells for Myocardial Infarction

To some extent, cell therapy for myocardial infarction (MI) has supported the idea of cardiac repair; however, further optimizations are inevitable. Combined approaches that comprise suitable cell sources and supporting molecules considerably improved its effect. Here, we devised a strategy of simultaneous transplantation of human cardiac progenitor cells (CPCs) and an optimized oxygen generating microparticles (MPs) embedded in fibrin hydrogel, which was injected into a left anterior descending artery (LAD) ligating-based rat model of acute myocardial infarction (AMI). Functional parameters of the heart, particularly left ventricular systolic function, markedly improved and reached pre-AMI levels. This functional restoration was well correlated with substantially lower fibrotic tissue formation and greater vascular density in the infarct area. Our novel approach promoted CPCs retention and differentiation into cardiovascular lineages. We propose this novel co-transplantation strategy for more efficient cell therapy of AMI which may function by providing an oxygen-rich microenvironment, and thus regulate cell survival and differentiation.

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.

Mechanical Considerations of Electrospun Scaffolds for Myocardial Tissue and Regenerative Engineering

Biomaterials to facilitate the restoration of cardiac tissue is of emerging importance. While there are many aspects to consider in the design of biomaterials, mechanical properties can be of particular importance in this dynamically remodeling tissue. This review focuses on one specific processing method, electrospinning, that is employed to generate materials with a fibrous microstructure that can be combined with material properties to achieve the desired mechanical behavior. Current methods used to fabricate mechanically relevant micro-/nanofibrous scaffolds, in vivo studies using these scaffolds as therapeutics, and common techniques to characterize the mechanical properties of the scaffolds are covered. We also discuss the discrepancies in the reported elastic modulus for physiological and pathological myocardium in the literature, as well as the emerging area of in vitro mechanobiology studies to investigate the mechanical regulation in cardiac tissue engineering. Lastly, future perspectives and recommendations are offered in order to enhance the understanding of cardiac mechanobiology and foster therapeutic development in myocardial regenerative medicine.

Modulating nonlinear elastic behavior of biodegradable shape memory elastomer and small intestinal submucosa(SIS) composites for soft tissue repair

Structural repair of soft tissue for regenerative therapies can be advanced by developing biocompatible and bioresorbable materials with mechanical properties similar to the tissue targeted for therapy. Developing new materials modeling soft tissue mechanics can mitigate many limitations of material based therapies, specifically concerning the mechanical stress and deformation the material imposes on surrounding tissue structures. However, many elastomeric materials used in soft tissue repair lack the ability to be delivered through minimally invasive surgical (MIS) or transcatheter routes and require open surgical approaches for placement and application. We have developed a biocompatible and fully biodegradable shape memory elastomer, poly-(glycerol dodecanedioate) (PGD), which fulfills the requirements for hyperelasticity and exhibits shape memory behavior to serve as a novel substrate material for regenerative therapy in minimally invasive clinical procedures. Our previous work demonstrated control over the tangent modulus at 12.5% compressive strain between 1 and 3 MPa by increasing the crosslinking density in the polymer. In order to improve control over a broader range of mechanical properties, nonlinear behavior, and toughness, we 1) varied PGD physical crosslink density, 2) incorporated sheets of porcine small intestinal submucosa (SIS, Cook Biotech, Inc.) with varying thickness, and 3) mixed lyophilized SIS particulates into PGD at different weight percentages. Tensile testing (ASTM D412a) revealed PGD containing SIS sheets of were stiffer than controls (p < 0.01). Incorporating lyophilized SIS particulates into PGD increased the strain to failure (p < 0.001) compared to PGD controls. Test specimens with 1 ply sheets had greater tear strength (ASTM D624c) compared to PGD tear specimens prepared control specimens (p < 0.001). However, incorporating SIS particulates decreased tear strength of PGD-SIS 0.5 wt% particulate composites (p < 0.01) compared to PGD controls. Incorporating 2 ply and 4 ply sheets and 0.5 wt% particulates into PGD decreased the fixity and recovery of composite materials compared to controls (p < 0.01). Nonlinear modeling of stress strain curves under uniaxial tension demonstrated tunability of PGD-SIS composite materials to model various nonlinear soft tissues. These findings support the use of shape memory PGD-SIS composite materials towards the design of implantable devices for a variety of soft tissue regeneration applications by minimally invasive surgery.

In-silico study of the cardiac arrhythmogenic potential of biomaterial injection therapy

Biomaterial injection is a novel therapy to treat ischemic heart failure (HF) that has shown to reduce remodeling and restore cardiac function in recent preclinical studies. While the effect of biomaterial injection in reducing mechanical wall stress has been recently demonstrated, the influence of biomaterials on the electrical behavior of treated hearts has not been elucidated. In this work, we developed computational models of swine hearts to study the electrophysiological vulnerability associated with biomaterial injection therapy. The propagation of action potentials on realistic biventricular geometries was simulated by numerically solving the monodomain electrophysiology equations on anatomically-detailed models of normal, HF untreated, and HF treated hearts. Heart geometries were constructed from high-resolution magnetic resonance images (MRI) where the healthy, peri-infarcted, infarcted and gel regions were identified, and the orientation of cardiac fibers was informed from diffusion-tensor MRI. Regional restitution properties in each case were evaluated by constructing a probability density function of the action potential duration (APD) at different cycle lengths. A comparative analysis of the ventricular fibrillation (VF) dynamics for every heart was carried out by measuring the number of filaments formed after wave braking. Our results suggest that biomaterial injection therapy does not affect the regional dispersion of repolarization when comparing untreated and treated failing hearts. Further, we found that the treated failing heart is more prone to sustain VF than the normal heart, and is at least as susceptible to sustained VF as the untreated failing heart. Moreover, we show that the main features of VF dynamics in a treated failing heart are not affected by the level of electrical conductivity of the biogel injectates. This work represents a novel proof-of-concept study demonstrating the feasibility of computer simulations of the heart in understanding the arrhythmic behavior in novel therapies for HF.

Intra-myocardial alginate hydrogel injection acts as a left ventricular mid-wall constraint in swine

Despite positive initial outcomes emerging from preclinical and early clinical investigation of alginate hydrogel injection therapy as a treatment for heart failure, the lack of knowledge about the mechanism of action remains a major shortcoming that limits the efficacy of treatment design. To identify the mechanism of action, we examined previously unobtainable measurements of cardiac function from in vivo, ex vivo, and in silico states of clinically relevant heart failure (HF) in large animals. High-resolution ex vivo magnetic resonance imaging and histological data were used along with state-of-the-art subject-specific computational model simulations. Ex vivo data were incorporated in detailed geometric computational models for swine hearts in health (n = 5), ischemic HF (n = 5), and ischemic HF treated with alginate hydrogel injection therapy (n = 5). Hydrogel injection therapy mitigated elongation of sarcomere lengths (1.68 ± 0.10μm [treated] vs. 1.78 ± 0.15μm [untreated], p<0.001). Systolic contractility in treated animals improved substantially (ejection fraction = 43.9 ± 2.8% [treated] vs. 34.7 ± 2.7% [untreated], p<0.01). The in silico models realistically simulated in vivo function with >99% accuracy and predicted small myofiber strain in the vicinity of the solidified hydrogel that was sustained for up to 13 mm away from the implant. These findings suggest that the solidified alginate hydrogel material acts as an LV mid-wall constraint that significantly reduces adverse LV remodeling compared to untreated HF controls without causing negative secondary outcomes to cardiac function. STATEMENT OF SIGNIFICANCE: Heart failure is considered a growing epidemic and hence an important health problem in the US and worldwide. Its high prevalence (5.8 million and 23 million, respectively) is expected to increase by 25% in the US alone by 2030. Heart failure is associated with high morbidity and mortality, has a 5-year mortality rate of 50%, and contributes considerably to the overall cost of health care ($53.1 billion in the US by 2030). Despite positive initial outcomes emerging from preclinical and early clinical investigation of alginate hydrogel injection therapy as a treatment for heart failure, the lack of knowledge concerning the mechanism of action remains a major shortcoming that limits the efficacy of treatment design. To understand the mechanism of action, we combined high-resolution ex vivo magnetic resonance imaging and histological data in swine with state-of-the-art subject-specific computational model simulations. The in silico models realistically simulated in vivo function with >99% accuracy and predicted small myofiber strain in the vicinity of the solidified hydrogel that was sustained for up to 13 mm away from the implant. These findings suggest that the solidified alginate hydrogel material acts as a left ventricular mid-wall constraint that significantly reduces adverse LV remodeling compared to untreated heart failure controls without causing negative secondary outcomes to cardiac function. Moreover, if the hydrogel can be delivered percutaneously rather than via the currently used open-chest procedure, this therapy may become routine for heart failure treatment. A minimally invasive procedure would be in the best interest of this patient population; i.e., one that cannot tolerate general anesthesia and surgery, and it would be significantly more cost-effective than surgery.

Extracellular matrix-based biomaterials for cardiac regeneration and repair

The spectrum of ischemic heart diseases, encompassing acute myocardial infarction to heart failure, represents the leading cause of death worldwide. Although extensive progress in cardiovascular diagnoses and therapy has been made, the prevalence of the disease continues to increase. Cardiac regeneration has a promising perspective for the therapy of heart failure. Recently, extracellular matrix (ECM) has been shown to play an important role in cardiac regeneration and repair after cardiac injury. There is also evidence that the ECM could be directly used as a drug to promote cardiomyocyte proliferation and cardiac regeneration. Increasing evidence supports that applying ECM biomaterials to maintain heart function recovery is an important approach to apply the concept of cardiac regenerative medicine to clinical practice in the future. Here, we will introduce the essential role of cardiac ECM in cardiac regeneration and summarize the approaches of delivering ECM biomaterials to promote cardiac repair in this review.

Promoting Cardiac Regeneration and Repair Using Acellular Biomaterials

Ischemic heart disease is a common cause of end-stage heart failure and has persisted as one of the main causes of end stage heart failure requiring transplantation. Maladaptive myocardial remodeling due to ischemic injury involves multiple cell types and physiologic mechanisms. Pathogenic post-infarct remodeling involves collagen deposition, chamber dilatation and ventricular dysfunction. There have been significant improvements in medication and revascularization strategies. However, despite medical optimization and opportunities to restore blood flow, physicians lack therapies that directly access and manipulate the heart to promote healthy post-infarct myocardial remodeling. Strategies are now arising that use bioactive materials to promote cardiac regeneration by promoting angiogenesis and inhibiting cardiac fibrosis; and many of these strategies leverage the unique advantage of cardiac surgery to directly visualize and manipulate the heart. Although cellular-based strategies are emerging, multiple barriers exist for clinical translation. Acellular materials have also demonstrated preclinical therapeutic potential to promote angiogenesis and attenuate fibrosis and may be able to surmount these translational barriers. Within this review we outline various acellular biomaterials and we define epicardial infarct repair and intramyocardial injection, which focus on administering bioactive materials to the cardiac epicardium and myocardium respectively to promote cardiac regeneration. In conjunction with optimized medical therapy and revascularization, these techniques show promise to upregulate pathways of cardiac regeneration to preserve heart function.

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.

Degradation properties of a biodegradable shape memory elastomer, poly(glycerol dodecanoate), for soft tissue repair

Development of biodegradable shape memory elastomers (SMEs) is driven by the growing need for materials to address soft tissue pathology using a minimally invasive surgical approach. Composition, chain length and crosslinking of biocompatible polymers like PCL and PLA have been investigated to control mechanical properties, shape recovery and degradation rates. Depending on the primary mechanism of degradation, many of these polymers become considerably stiffer or softer resulting in mechanical properties that are inappropriate to support the regeneration of surrounding soft tissues. Additionally, concerns regarding degradation byproducts or residual organic solvents during synthesis accelerated interest in development of materials from bioavailable monomers. We previously developed a biodegradable SME, poly(glycerol dodecanoate) (PGD), using biologically relevant metabolites and controlled synthesis conditions to tune mechanical properties for soft tissue repair. In this study, we investigate the influence of crosslinking density on the mechanical and thermal properties of PGD during in vitro and in vivo degradation. Results suggest polymer degradation in vivo is predominantly driven by surface erosion, with no significant effects of initial crosslinking density on degradation time under the conditions investigated. Importantly, mechanical integrity is maintained during degradation. Additionally, shifts in melt transitions on thermograms indicate a potential shift in shape memory transition temperatures as the polymers degrade. These findings support the use of PGD for soft tissue repair and warrant further investigation towards tuning the molecular and macromolecular properties of the polymer to tailor degradation rates for specific clinical applications.

Intra-myocardial Delivery of a Novel Thermosensitive Hydrogel Inhibits Post-infarct Heart Failure After Degradation in Rat

Whether intra-myocardial delivery of hydrogel can prevent post-infarct heart failure (HF) in a long follow-up period, especially after it is degraded, remains unclear. In this study, Dex-PCL-HEMA/PNIPAAm (DPHP) hydrogel was delivered into peri-infarct myocardium of rat when coronary artery was ligated, while PBS was employed as control. Twelve weeks later, compared with control, left ventricle remodeling was attenuated and cardiac function was preserved; serum brain natriuretic peptide, cardiac aldosterone, and pulmonary congestion were suppressed in hydrogel group. Pro-fibrogenic mRNA increased in infarct area while decreased in remote zone, as well as hypertrophic mRNA. These data proves DPHP hydrogel suppresses ventricular remodeling and HF by promoting fibrotic healing in infarct area and inhibiting reactive fibrosis and hypertrophy in remote zone. Timely intra-myocardial hydrogel implantation is an effective strategy to inhibit post-infarct cardiac remodeling and have a long-term beneficial effect even after it has been biodegraded.

Coadministration of an Adhesive Conductive Hydrogel Patch and an Injectable Hydrogel to Treat Myocardial Infarction

Over the past decade, tissue-engineering strategies, mainly involving injectable hydrogels and epicardial biomaterial patches, have been pursued to treat myocardial infarction. However, only limited therapeutic efficacy is achieved with a single means. Here, a combined therapy approach is proposed, that is, the coadministration of a conductive hydrogel patch and injectable hydrogel to the infarcted myocardium. The self-adhesive conductive hydrogel patch is fabricated based on Fe³⁺-induced ionic coordination between dopamine-gelatin (GelDA) conjugates and dopamine-functionalized polypyrrole (DA-PPy), which form a homogeneous network. The injectable and cleavable hydrogel is formed in situ via a Schiff base reaction between oxidized sodium hyaluronic acid (HA-CHO) and hydrazided hyaluronic acid (HHA). Compared with a single-mode system, injecting the HA-CHO/HHA hydrogel intramyocardially followed by painting a conductive GelDA/DA-PPy hydrogel patch on the heart surface results in a more pronounced improvement of the cardiac function in terms of echocardiographical, histological, and angiogenic outcomes.

Injectable Shear-Thinning Hydrogels Prevent Ischemic Mitral Regurgitation and Normalize Ventricular Flow Dynamics

Injectable hydrogels are known to attenuate left-ventricular (LV) remodeling following myocardial infarction (MI), dependent on material mechanical properties. The effect of hydrogel injection on ischemic mitral regurgitation (IMR) resultant from LV remodeling remains relatively unexplored. This study uses multiple imaging methods to evaluate the efficacy of injectable hydrogels with tunable modulus to prevent post-MI development of IMR. Posterolateral MI was induced in 20 sheep with subsequent epicardial injection of saline (control (MI); n = 7), soft hydrogel (guest-host crosslinking, modulus <1 kPa, n = 7), or stiff hydrogel (dual-crosslinking, modulus = 41.4 ± 4.3 kPa, n = 6) within the infarct region and 8-week follow-up. IMR and valve geometry were assessed by echocardiography. LV geometry (long-axis dimension, posterior chordae length) and ventricular flow dynamics were assessed by magnetic resonance imaging. IMR developed in MI controls at 8 weeks and was attenuated with hydrogel treatment (IMR grade for MI: 1.86 ± 0.69; guest-host crosslinking: 1.29 ± 1.11; dual-crosslinking: 0.50 ± 0.55, P = 0.02 vs MI). Tethering of the posterior leaflet increased in MI controls, but not with stiff hydrogel treatment. Across cohorts, IMR was correlated with changes in the long-axis dimension (Spearman R = 0.77) and posterior chordae length (Spearman R = 0.64). Intraventricular flow dynamics were highly disturbed in MI controls, but stiff hydrogel treatment normalized flow patterns and reduced the prevalence of large (≥2+ MR, >5 mL) regurgitant volumes. Injectable hydrogels attenuated subvalvular remodeling and leaflet tethering, preventing IMR development and normalizing LV flow dynamics. Hydrogels with a supraphysiological modulus yielded best outcomes.

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.

Injectable Click-Crosslinked Hyaluronic Acid Depot To Prolong Therapeutic Activity in Articular Joints Affected by Rheumatoid Arthritis

The aim of this study was to design a click-crosslinked hyaluronic acid (HA) (Cx-HA) depot via a click crosslinking reaction between tetrazine-modified HA and trans-cyclooctene-modified HA for direct intra-articular injection into joints affected by rheumatoid arthritis (RA). The Cx-HA depot had significantly more hydrogel-like features and a longer in vivo residence time than the HA depot. Methotrexate (MTX)-loaded Cx-HA (MTX-Cx-HA)-easily prepared as an injectable formulation-quickly formed an MTX-Cx-HA depot that persisted at the injection site for an extended period. In vivo MTX biodistribution in MTX-Cx-HA depots showed that a high concentration of MTX persisted at the intra-articular injection site for an extended period, with little distribution of MTX to normal tissues. In contrast, direct intra-articular injection of MTX alone or MTX-HA resulted in rapid clearance from the injection site. After intra-articular injection of MTX-Cx-HA into rats with RA, we noted the most significant RA reversal, measured by an articular index score, increased cartilage thickness, extensive generation of chondrocytes and glycosaminoglycan deposits, extensive new bone formation in the RA region, and suppression of tumor necrosis factor-α or interleukin-6 expression. Therefore, MTX-Cx-HA injected intra-articularly persists at the joint site in therapeutic MTX concentrations for an extended period, thus increasing the duration of RA treatment, resulting in an improved relief of RA.

Current and Future Considerations in the Use of Mechanical Circulatory Support Devices: An Update, 2008–2018

Our review in the 2008 volume of this journal detailed the use of mechanical circulatory support (MCS) for treatment of heart failure (HF). MCS initially utilized bladder-based blood pumps generating pulsatile flow; these pulsatile flow pumps have been supplanted by rotary blood pumps, in which cardiac support is generated via the high-speed rotation of computationally designed blading. Different rotary pump designs have been evaluated for their safety, performance, and efficacy in clinical trials both in the United States and internationally. The reduced size of the rotary pump designs has prompted research and development toward the design of MCS suitable for infants and children. The past decade has witnessed efforts focused on tissue engineering–based therapies for the treatment of HF. This review explores the current state and future opportunities of cardiac support therapies within our larger understanding of the treatment options for HF.

Uncertainty in cardiac myofiber orientation and stiffnesses dominate the variability of left ventricle deformation response

Computational cardiac modelling is a mature area of biomedical computing and is currently evolving from a pure research tool to aiding in clinical decision making. Assessing the reliability of computational model predictions is a key factor for clinical use, and uncertainty quantification (UQ) and sensitivity analysis are important parts of such an assessment. In this study, we apply UQ in computational heart mechanics to study uncertainty both in material parameters characterizing global myocardial stiffness and in the local muscle fiber orientation that governs tissue anisotropy. The uncertainty analysis is performed using the polynomial chaos expansion (PCE) method, which is a nonintrusive meta-modeling technique that surrogates the original computational model with a series of orthonormal polynomials over the random input parameter space. In addition, in order to study variability in the muscle fiber architecture, we model the uncertainty in orientation of the fiber field as an approximated random field using a truncated Karhunen-Loéve expansion. The results from the UQ and sensitivity analysis identify clear differences in the impact of various material parameters on global output quantities. Furthermore, our analysis of random field variations in the fiber architecture demonstrate a substantial impact of fiber angle variations on the selected outputs, highlighting the need for accurate assignment of fiber orientation in computational heart mechanics models.

Hang on tight: reprogramming the cell with microstructural cues

Cells interact intimately with complex microdomains in their extracellular matrix (ECM) and maintain a delicate balance of mechanical forces through mechanosensitive cellular components. Tissue injury results in acute degradation of the ECM and disruption of cell-ECM contacts, manifesting in loss of cytoskeletal tension, leading to pathological cell transformation and the onset of disease. Recently, microscale hydrogel constructs have been developed to provide cells with microdomains to form focal adhesion binding sites, which enable restoration of cytoskeletal tension. These synthetic anchors can recapitulate the complex 3D architecture of the native ECM to provide microtopographical cues. The mechanical deformation of proteins at the cell surface can activate signaling cascades to modulate downstream gene-level transcription, making this a unique materials-based approach for reprogramming cell behavior. An overview of the mechanisms underlying these mechanosensitive interactions in fibroblasts, stem and other cell types is provided to review their effects on cellular reprogramming. Recent investigations on the fabrication, functionalization and implementation of these materials and microtopographical features for drug testing and therapeutic applications are discussed.

Functionalization of soft materials for cardiac repair and regeneration

Coronary artery disease is a leading cause of death in developed nations. As the disease progresses, myocardial infarction can occur leaving areas of dead tissue in the heart. To compensate, the body initiates its own repair/regenerative response in an attempt to restore function to the heart. These efforts serve as inspiration to researchers who attempt to capitalize on the natural regenerative processes to further augment repair. Thus far, researchers are exploiting these repair mechanisms in the functionalization of soft materials using a variety of growth factor-, ligand- and peptide-incorporating approaches. The goal of functionalizing soft materials is to best promote and direct the regenerative responses that are needed to restore the heart. This review summarizes the opportunities for the use of functionalized soft materials for cardiac repair and regeneration, and some of the different strategies being developed.

Rebuilding Postinfarcted Cardiac Functions by Injecting TIIA@PDA Nanoparticle-Cross-linked ROS-Sensitive Hydrogels

Drug-loaded injectable hydrogels have been proven to possess huge potential for applications in tissue engineering. However, increasing the drug loading capacity and regulating the release system to adapt to the microenvironment after myocardial infarction face a huge challenge. In this research, an ROS-sensitive injectable hydrogel strengthened by self-nanodrugs was constructed. A hyperbranched ROS-sensitive macromer (HB-PBAE) with multiacrylate end groups was synthesized through dynamic controlled Michael addition. Meanwhile, a simple protocol based on dopamine polymerization was employed to generate a polydopamine (PDA) layer deposited on the tanshinone IIA (TIIA) nanoparticles (NPs) formed from spontaneous hydrophobic self-assembly. The HB-PBAE reacted with thiolate-modified hyaluronic acid (HA-SH) to form an in situ hydrogel, where TIIA@PDA NPs can be conveniently entrapped through the chemical cross-link between thiolate and quinone groups on PDA, which doubles the modulus of hydrogels. The in vivo degradation behavior of the hydrogels was characterized by MRI, exhibiting a much slower degradation behavior that is markedly different from that of in vitro. Importantly, a significant improvement of cardiac functions was achieved after hydrogel injection in terms of increased ejection fraction and decreased infarction size, accompanied by inhibition of the expression of inflammation factors, such as IL-1β, IL-6, and TNF-α.

Optimizing Epicardial Restraint and Reinforcement Following Myocardial Infarction: Moving Towards Localized, Biomimetic, and Multitherapeutic Options

The mechanical reinforcement of the ventricular wall after a myocardial infarction has been shown to modulate and attenuate negative remodeling that can lead to heart failure. Strategies include wraps, meshes, cardiac patches, or fluid-filled bladders. Here, we review the literature describing these strategies in the two broad categories of global restraint and local reinforcement. We further subdivide the global restraint category into biventricular and univentricular support. We discuss efforts to optimize devices in each of these categories, particularly in the last five years. These include adding functionality, biomimicry, and adjustability. We also discuss computational models of these strategies, and how they can be used to predict the reduction of stresses in the heart muscle wall. We discuss the range of timing of intervention that has been reported. Finally, we give a perspective on how novel fabrication technologies, imaging techniques, and computational models could potentially enhance these therapeutic strategies.

An injectable sulfonated reversible thermal gel for therapeutic angiogenesis to protect cardiac function after a myocardial infarction

BACKGROUND

Cardiovascular disease and myocardial infarction are associated with high mortality and morbidity and a more effective treatment remains a major clinical need. The intramyocardial injection of biomaterials has been investigated as a potential treatment for heart failure by providing mechanical support to the myocardium and reducing stress on cardiomyocytes. Another treatment approach that has been explored is therapeutic angiogenesis that requires careful spatiotemporal control of angiogenic drug delivery. An injectable sulfonated reversible thermal gel composed of a polyurea conjugated with poly(N-isopropylacrylamide) and sulfonate groups has been developed for intramyocardial injection with angiogenic factors for the protection of cardiac function after a myocardial infarction.

RESULTS

The thermal gel allowed for the sustained, localized release of VEGF in vivo with intramyocardial injection after two weeks. A myocardial infarction reperfusion injury model was used to evaluate therapeutic benefits to cardiac function and vascularization. Echocardiography presented improved cardiac function, infarct size and ventricular wall thinning were reduced, and immunohistochemistry showed improved vascularization with thermal gel injections. The thermal gel alone showed cardioprotective and vascularization properties, and slightly improved further with the additional delivery of VEGF. An inflammatory response evaluation demonstrated the infiltration of macrophages due to the myocardial infarction was more significant compared to the foreign body inflammatory response to the thermal gel. Detecting DNA fragments of apoptotic cells also demonstrated potential anti-apoptotic effects of the thermal gel.

CONCLUSION

The intramyocardial injection of the sulfonated reversible thermal gel has cardioprotective and vascularization properties for the treatment of myocardial infarction.

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.

Minimally Invasive and Regenerative Therapeutics

Advances in biomaterial synthesis and fabrication, stem cell biology, bioimaging, microsurgery procedures, and microscale technologies have made minimally invasive therapeutics a viable tool in regenerative medicine. Therapeutics, herein defined as cells, biomaterials, biomolecules, and their combinations, can be delivered in a minimally invasive way to regenerate different tissues in the body, such as bone, cartilage, pancreas, cardiac, skeletal muscle, liver, skin, and neural tissues. Sophisticated methods of tracking, sensing, and stimulation of therapeutics in vivo using nano-biomaterials and soft bioelectronic devices provide great opportunities to further develop minimally invasive and regenerative therapeutics (MIRET). In general, minimally invasive delivery methods offer high yield with low risk of complications and reduced costs compared to conventional delivery methods. Here, minimally invasive approaches for delivering regenerative therapeutics into the body are reviewed. The use of MIRET to treat different tissues and organs is described. Although some clinical trials have been performed using MIRET, it is hoped that such therapeutics find wider applications to treat patients. Finally, some future perspective and challenges for this emerging field are highlighted.

Effects of hydrogel injection on borderzone contractility post-myocardial infarction

Injectable hydrogels are a potential therapy for mitigating adverse left ventricular (LV) remodeling after myocardial infarction (MI). Previous studies using magnetic resonance imaging (MRI) have shown that hydrogel treatment improves systolic strain in the borderzone (BZ) region surrounding the infarct. However, the corresponding contractile properties of the BZ myocardium are still unknown. The goal of the current study was to quantify the in vivo contractile properties of the BZ myocardium post-MI in an ovine model treated with an injectable hydrogel. Contractile properties were determined 8 weeks following posterolateral MI by minimizing the difference between in vivo strains and volume calculated from MRI and finite element model predicted strains and volume. This was accomplished by using a combination of MRI, catheterization, finite element modeling, and numerical optimization. Results show contractility in the BZ of animals treated with hydrogel injection was significantly higher than untreated controls. End-systolic (ES) fiber stress was also greatly reduced in the BZ of treated animals. The passive stiffness of the treated infarct region was found to be greater than the untreated control. Additionally, the wall thickness in the infarct and BZ regions was found to be significantly higher in the treated animals. Treatment with hydrogel injection significantly improved BZ function and reduced LV remodeling, via altered MI properties. These changes are linked to a reduction in the ES fiber stress in the BZ myocardium surrounding the infarct. The current results imply that injectable hydrogels could be a viable therapy for maintaining LV function post-MI.

In situ cardiac regeneration by using neuropeptide substance P and IGF-1C peptide eluting heart patches

Cardiovascular diseases cause huge socio-economic burden worldwide. Although a mammalian myocardium has its own limited healing capability, scaffold materials capable of releasing stem cell recruiting/engrafting factors may facilitate the regeneration of the infarcted myocardium. The aim of this research was to develop cardiac patches capable of simultaneously eluting substance P (SP) and insulin-like growth factor-1C (IGF-1C) peptide. Polycaprolactone/collagen type 1-based patches with or without SP and IGF-1C peptide were fabricated by co-electrospinning, which exhibited nanofibrous morphology. SP and IGF-1C/SP patches recruited significantly higher numbers of bone marrow-mesenchymal stem cells than that of the negative control and patch-only groups in vitro. The developed patches were transplanted in an infarcted myocardium for up to 14 days. Mice underwent left anterior descending artery ligation and received one of the following treatments: (i) sham, (ii) saline, (iii) patch-only, (iv) IGF-1C patch, (v) SP patch and (vi) IGF-1C/SP patch. SP and IGF-1C/SP patch-treated groups exhibited better heart function and attenuated adverse cardiac remodeling than that of the saline, patch-only and individual peptide containing cardiac patches. SP patch and IGF-1C/SP patch-treated groups also showed higher numbers of CD31-positive vessels and isolectin B4-positive capillaries than that of other groups. IGF-1C/SP-treated group also showed thicker left ventricular wall in comparison to the saline and patch-only groups. Moreover, IGF-1C/SP patches recruited significantly higher numbers of CD29-positive cells and showed less numbers of Tunel-positive cells compared with the other groups. These data suggest that SP and IGF-1C peptides may act synergistically for in situ tissue repair.