Cellular therapy for myocardial ischemia using a temperature-responsive biodegradable injectable polymer system with adipose-derived stem cells

Hydrogel-based cardiac repair and regeneration function in the treatment of myocardial infarction

A life-threatening illness that poses a serious threat to human health is myocardial infarction. It may result in a significant number of myocardial cells dying, dilated left ventricles, dysfunctional heart function, and ultimately cardiac failure. Based on the development of emerging biomaterials and the lack of clinical treatment methods and cardiac donors for myocardial infarction, hydrogels with good compatibility have been gradually applied to the treatment of myocardial infarction. Specifically, based on the three processes of pathophysiology of myocardial infarction, we summarized various types of hydrogels designed for myocardial tissue engineering in recent years, including natural hydrogels, intelligent hydrogels, growth factors, stem cells, and microRNA-loaded hydrogels. In addition, we also describe the heart patch and preparation techniques that promote the repair of MI heart function. Although most of these hydrogels are still in the preclinical research stage and lack of clinical trials, they have great potential for further application in the future. It is expected that this review will improve our knowledge of and offer fresh approaches to treating myocardial infarction.

Adipose tissue-derived stem cells, in vivo and in vitro models for metabolic diseases

The primary role of adipose tissue stem cells (ADSCs) is to support the function and homeostasis of adipose tissue in physiological and pathophysiological conditions. However, when ADSCs become dysfunctional in diseases such as obesity and cancer, they become impaired, undergo signalling changes, and their epigenome is altered, which can have a dramatic effect on human health. In more recent years, the therapeutic potential of ADSCs in regenerative medicine, wound healing, and for treating conditions such as cancer and metabolic diseases has been extensively investigated with very promising results. ADSCs have also been used to generate two-dimensional (2D) and three-dimensional (3D) cellular and in vivo models to study adipose tissue biology and function as well as intracellular communication. Characterising the biology and function of ADSCs, how it is altered in health and disease, and its therapeutic potential and uses in cellular models is key for designing intervention strategies for complex metabolic diseases and cancer.

Development of immune cell delivery system using biodegradable injectable polymers for cancer immunotherapy

Immune cell delivery using injectable hydrogel attracts much attention for improving its therapeutic effect. Specifically, dendritic cells (DCs) are the trigger cells for immune responses, and DC vaccines are studied for improving cancer immunotherapy. Hydrogel-assisted cell delivery is expected to enhance the viability of the implanted cells. We recently reported temperature-responsive biodegradable injectable polymer (IP) formulation utilizing poly(ε-caprolactone-co-glycolide)-b-poly(ethylene glycol)(PEG)-b-poly(ε-caprolactone-co-glycolide) (tri-PCG). Tri-PCG-based IP was reported to exhibit immediate sol-to-gel transition in response to temperature increase, in vivo biodegradability, and excellent biocompatibility. In this study, tri-PCG-based IP was applied to DC delivery. IP encapsulated live DCs, and the DCs incorporated ovalbumin (OVA) as a model antigen and CpG-DNA (oligo DNA with adjuvant effect) in IP hydrogel. Results suggested that DCs encapsulated in IP hydrogel internalized OVA and CpG-DNA and DCs were maturated to present antigens to T cells. Moreover, subcutaneously injected tri-PCG-based IP prolonged the retention period of cell accumulation at injected sites. Tri-PCG IP hydrogel could release matured DCs as the degradation of the hydrogel progressed. Tri-PCG IP formulation improved treatment efficacy of OVA transfected mouse lymphoma (E.G7-OVA) tumor. Hence, tri-PCG IP is a promising platform for immune cell delivery.

Gelation upon the Mixing of Amphiphilic Graft and Triblock Copolymers Containing Enantiomeric Polylactide Segments through Stereocomplex Formation

Biodegradable injectable polymer (IP) systems that form hydrogels in situ when injected into the body have considerable potential as medical materials. In this paper, we report a new two-solution mixed biodegradable IP system that utilizes the stereocomplex (SC) formation of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA). We synthesized triblock copolymers of PLLA and poly(ethylene glycol), PLLA-b-PEG-b-PLLA (tri-L), and a graft copolymer of dextran (Dex) attached to a PDLA-b-PEG diblock copolymer, Dex-g-(PDLA-b-PEG) (gb-D). We found that a hydrogel can be obtained by mixing gb-D solution and tri-L solution via SC formation. Although it is already known that graft copolymers attached to enantiomeric PLLA and PDLA chains can form an SC hydrogel upon mixing, we revealed that hydrogels can also be formed by a combination of graft and triblock copolymers. In this system (graft vs. triblock), the gelation time was shorter, within 1 min, and the physical strength of the resulting hydrogel (G' > 100 Pa) was higher than when graft copolymers were mixed. Triblock copolymers form micelles (16 nm in diameter) in aqueous solutions and hydrophobic drugs can be easily encapsulated in micelles. In contrast, graft copolymers have the advantage that their molecular weight can be set high, contributing to improved mechanical strength of the obtained hydrogel. Various biologically active polymers can be used as the main chains of graft copolymers, and chemical modification using the remaining functional side chain groups is also easy. Therefore, the developed mixing system with a graft vs. triblock combination can be applied to medical materials as a highly convenient, physically cross-linked IP system.

Application of adipose-derived stem cells in ischemic heart disease: theory, potency, and advantage

Adipose-derived mesenchymal stem cells (ASCs) represent an innovative candidate to treat ischemic heart disease (IHD) due to their abundance, renewable sources, minor invasiveness to obtain, and no ethical limitations. Compared with other mesenchymal stem cells, ASCs have demonstrated great advantages, especially in the commercialization of stem cell-based therapy. Mechanistically, ASCs exert a cardioprotective effect not only through differentiation into functional cells but also via robust paracrine of various bioactive factors that promote angiogenesis and immunomodulation. Exosomes from ASCs also play an indispensable role in this process. However, due to the distinct biological functions of ASCs from different origins or donors with varing health statuses (such as aging, diabetes, or atherosclerosis), the heterogeneity of ASCs deserves more attention. This prompts scientists to select optimal donors for clinical applications. In addition, to overcome the primary obstacle of poor retention and low survival after transplantation, a variety of studies have been dedicated to the engineering of ASCs with biomaterials. Besides, clinical trials have confirmed the safety and efficacy of ASCs therapy in the context of heart failure or myocardial infarction. This article reviews the theory, efficacy, and advantages of ASCs-based therapy, the factors affecting ASCs function, heterogeneity, engineering strategies and clinical application of ASCs.

Overview of Injectable Hydrogels for the Treatment of Myocardial Infarction

Myocardial infarction (MI) triggers adverse remodeling mechanisms, thus leading to heart failure. Since the application of biomaterial-based scaffolds emerged as a viable approach for providing mechanical support and promoting cell growth, injectable hydrogels have garnered substantial attention in MI treatment because of their minimally invasive administration through injection and diminished risk of infection. To fully understand the interplay between injectable hydrogels and infarcted myocardium repair, this review provides an overview of recent advances in injectable hydrogel-mediated MI therapy, including: I) material designs for repairing the infarcted myocardium, considering the pathophysiological mechanism of MI and design principles for biomaterials in MI treatment; II) the development of injectable functional hydrogels for MI treatment, including conductive, self-healing, drug-loaded, and stimulus-responsive hydrogels; and III) research progress in using injectable hydrogels to restore cardiac function in infarcted myocardium by promoting neovascularization, enhancing cardiomyocyte proliferation, decreasing myocardial fibrosis, and inhibiting excessive inflammation. Overall, this review presents the current state of injectable hydrogel research in MI treatment, offering valuable information to facilitate interdisciplinary knowledge transfer and enable the development of prognostic markers for suitable injectable materials.

Cardiac tissue engineering for myocardial infarction treatment

Myocardial infarction is one of the major causes of morbidity and mortality worldwide. Current treatments can relieve the symptoms of myocardial ischemia but cannot repair the necrotic myocardial tissue. Novel therapeutic strategies based on cellular therapy, extracellular vesicles, non-coding RNAs and growth factors have been designed to restore cardiac function while inducing cardiomyocyte cycle re-entry, ensuring angiogenesis and cardioprotection, and preventing ventricular remodeling. However, they face low stability, cell engraftment issues or enzymatic degradation in vivo, and it is thus essential to combine them with biomaterial-based delivery systems. Microcarriers, nanocarriers, cardiac patches and injectable hydrogels have yielded promising results in preclinical studies, some of which are currently being tested in clinical trials. In this review, we cover the recent advances made in cellular and acellular therapies used for cardiac repair after MI. We present current trends in cardiac tissue engineering related to the use of microcarriers, nanocarriers, cardiac patches and injectable hydrogels as biomaterial-based delivery systems for biologics. Finally, we discuss some of the most crucial aspects that should be addressed in order to advance towards the clinical translation of cardiac tissue engineering approaches.

Injectable Hydrogels Encapsulating Dual-Functional Au@Pt Core-Shell Nanoparticles Regulate Infarcted Microenvironments and Enhance the Therapeutic Efficacy of Stem Cells through Antioxidant and Electrical Integration

Injectable functional biomaterials have made significant progress in cardiac regenerative. In addition, how to adjust the abominable infarction microenvironment and introduce therapeutic stem cells to improve the healing effect has become a hotspot. Herein, injectable stem cell vector is prepared by combining natural alginate hydrogel and Au@Pt nanoparticles (Au@Pt/Alg hydrogel) to encapsulate brown adipose stem cells (BASCs). Au@Pt nanoparticles with both antioxidative and conductive properties could effectively eliminate reactive oxygen species, enhance the frequency of action potential release of cardiomyocytes, and further reduce the inflammatory factors of macrophage in vitro. The Au@Pt/Alg hydrogel enhances the antioxidant, differentiation, and paracrine capability of BASCs. The effect of BASCs loaded Au@Pt/Alg hydrogel is evaluated in a rat myocardial infarction (MI) model. The antioxidant, anti-inflammatory, and heart electrical integration are showed in the MI model. More interestingly, Au@Pt/Alg hydrogel can effectively maintain the paracrine efficiency and pro-angiogenesis effects of BASCs in the infarcted area. This study led us to recognize the great value of Au@Pt/Alg hydrogels for their ability to actively regulate the microenvironment and carry stem cells for MI treatment.

The Role of Hydrogel in Cardiac Repair and Regeneration for Myocardial Infarction: Recent Advances and Future Perspectives

A myocardial infarction (MI) is the leading cause of morbidity and mortality, seriously threatens human health, and becomes a major health burden of our society. It is urgent to pursue effective therapeutic strategies for the regeneration and restore myocardial function after MI. This review discusses the role of hydrogel in cardiac repair and regeneration for MI. Hydrogel-based cardiac patches and injectable hydrogels are the most commonly used applications in cardiac regeneration medicine. With injectable hydrogels, bioactive compounds and cells can be delivered in situ, promoting in situ repair and regeneration, while hydrogel-based cardiac patches reduce myocardial wall stress, which passively inhibits ventricular expansion. Hydrogel-based cardiac patches work as mechanically supportive biomaterials. In cardiac regeneration medicine, clinical trials and commercial products are limited. Biomaterials, biochemistry, and biological actives, such as intelligent hydrogels and hydrogel-based exosome patches, which may serve as an effective treatment for MI in the future, are still under development. Further investigation of clinical feasibility is warranted. We can anticipate hydrogels having immense translational potential for cardiac regeneration in the near future.

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

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

A systematic study on the effects of the structure of block copolymers of PEG and poly(ε-caprolactone-co-glycolic acid) on their temperature-responsive sol-to-gel transition behavior

The effects of the molecular structure on the temperature-responsive sol-to-gel transition behavior and neat morphology of the block copolymers of poly(ethylene glycol) and poly(ε-caprolactone-co-glycolic acid) were systematically investigated.

Loss of multipotency in adipose-derived stem cells after culture in temperature-responsive injectable polymer hydrogels

Adipose-derived stem cells (AdSCs), a type of mesenchymal stem cell, are expected to be applicable to regenerative medicine and cellular delivery systems. The maintenance of cell multipotency and control of the differentiation direction are important for these applications. However, the differentiation direction of these cells is widely believed to depend on the physical properties of their scaffold. In this study, we explored whether the multipotency of AdSCs, that is, their ability to differentiate into multiple cells, is maintained when they are removed from injectable polymer (IP) hydrogels with various degrees of cross-linking and induced to differentiate into osteoblasts and adipocytes. We confirmed that AdSCs cultured in IP hydrogels maintained an undifferentiated state. However, their differentiation into osteoblasts and adipocytes cannot be ensured; specifically, the multipotency of AdSCs may decrease when they are cultured in IP hydrogels. When cultured in an IP hydrogel with extreme softness and poor cell adhesion properties, the AdSCs remained in an undifferentiated state, but their multipotency was reduced. These results provide important insights into stem cell delivery systems using IP hydrogels.

Phospholipid polymer hydrogels with rapid dissociation for reversible cell immobilization

A reversible and cytocompatible cell immobilization polymer matrix with a rapid dissociation rate was prepared using a zwitterionic phospholipid polymer bearing phenylboronic acid and poly(vinyl alcohol) (PVA). A reversible and spontaneously forming phospholipid polymer hydrogel is reported for use as a cell immobilization matrix which caused no invasive damage to the cells. To improve the possibility of applying the hydrogels as a reversible cell immobilization matrix, the stimuli-responsive dissociation rate of polymer hydrogels was designed to have a more rapid rate to ease the recovery of the immobilized cells. In this study, a phospholipid polymer containing 3-methacrylamide phenylboronic acid (MAPBA) as the phenylboronic acid unit was synthesized. The water-soluble phospholipid polymer (PMB-MAPBA) can spontaneously form polymer hydrogels after mixing with PVA solution under normal pressure, room temperature, and neutral pH conditions. Also, the dissociation of the hydrogels after the addition of D-sorbitol completely occurred within 10 minutes. The cells were easily immobilized on the hydrogels during the preparation process. Also, the recovery ratio of the immobilized cells was improved due to the rapid dissociation of the hydrogels. The reversible and spontaneously formed phospholipid polymer hydrogels are promising for use as soft materials for platforms for cell engineering.