Therapeutic cell delivery and fate control in hydrogels and hydrogel hybrids

Bioelectronics hydrogels for implantable cardiac and brain disease medical treatment application

Hydrogel-based bioelectronic systems offer significant benefits for point-of-care diagnosis, treatment of cardiac and cerebral disease, surgical procedures, and other medical applications, ushering in a new era of advancements in medical technology. Progress in hydrogel-based bioelectronics has advanced from basic instrument and sensing capabilities to sophisticated multimodal perceptions and feedback systems. Addressing challenges related to immune responses and inflammation regulation after implantation, physiological dynamic mechanism, biological toxicology as well as device size, power consumption, stability, and signal conversion is crucial for the practical implementation of hydrogel-based bioelectronics in medical implants. Therefore, further exploration of hydrogel-based bioelectronics is imperative, and a comprehensive review is necessary to steer the development of these technologies for use in implantable therapies for cardiac and brain/neural conditions. In this review, a concise overview is provided on the fundamental principles underlying ionic electronic and ionic bioelectronic mechanisms. Additionally, a comprehensive examination is conducted on various bioelectronic materials integrated within hydrogels for applications in implantable medical treatments. The analysis encompasses a detailed discussion on the representative structures and physical attributes of hydrogels. This includes an exploration of their intrinsic properties such as mechanical strength, dynamic capabilities, shape-memory features, stability, stretchability, and water retention characteristics. Moreover, the discussion extends to properties related to interactions with tissues or the environment, such as adhesiveness, responsiveness, and degradability. The intricate relationships between the structure and properties of hydrogels are thoroughly examined, along with an elucidation of how these properties influence their applications in implantable medical treatments. The review also delves into the processing techniques and characterization methods employed for hydrogels. Furthermore, recent breakthroughs in the applications of hydrogels are logically explored, covering aspects such as materials, structure, properties, functions, fabrication procedures, and hybridization with other materials. Finally, the review concludes by outlining the future prospects and challenges associated with hydrogels-based bioelectronics systems.

Biocompatible DNA hydrogel composed of minimized Takumi-shaped DNA nanostructure exhibits sustained retention after in vivo administration

Our previous studies showed that DNA hydrogels containing unmethylated CpG motifs effectively induced antigen-specific immune responses when combined with the appropriate antigens. A potential drawback of existing DNA hydrogels for further applications is the need for many oligodeoxynucleotide (ODN) types. Therefore, in this study, we attempted to optimize and minimize the nanostructured DNA units for DNA hydrogels to reduce the preparation cost, design difficulty, and possible risk of sequence-dependent off-target effects, and prepare DNA hydrogels with sustained retention ability. A Takumi-shaped unit with a stem and four flanking cohesive parts was constructed using one type of ODN with a palindromic sequence. A DNA hydrogel was prepared by mixing two Takumi-shaped units with complementary cohesive parts. The required length of the cohesive part was first examined using ODNs with 14 or 18 bases of stem length. Electrophoresis, melting temperature measurements, and viscoelastic analysis showed that the properties of the cohesive part determined the hydrogel properties. ODNs with a cohesive part consisting of GC-rich 5'-ccgcaagacg-3' efficiently formed a hydrogel with sustained retention in mice after administration. Several ODNs with optimized cohesive sequences and different stem lengths and sequences were designed. Analyses showed that a stem of 10 bases or longer was required for efficient hydrogel formation, and ODNs with a 12-base stem part exhibited the most prolonged retention after subcutaneous injection into mice. Thus, the present study demonstrated the requirements of minimal DNA units for preparing DNA hydrogels with sustained retention ability.

Regenerative Medicine and Nanotechnology Approaches against Cardiovascular Diseases: Recent Advances and Future Prospective

Regenerative medicine refers to medical research focusing on repairing, replacing, or regenerating damaged or diseased tissues or organs. Cardiovascular disease (CVDs) is a significant health issue globally and is the leading cause of death in many countries. According to the Centers for Disease Control and Prevention (CDC), one person dies every 34 seconds in the United States from cardiovascular diseases, and according to a World Health Organization (WHO) report, cardiovascular diseases are the leading cause of death globally, taking an estimated 17.9 million lives each year. Many conventional treatments are available using different drugs for cardiovascular diseases, but these treatments are inadequate. Stem cells and nanotechnology are promising research areas for regenerative medicine treating CVDs. Regenerative medicines are a revolutionary strategy for advancing and successfully treating various diseases, intending to control cardiovascular disorders. This review is a comprehensive study of different treatment methods for cardiovascular diseases using different types of biomaterials as regenerative medicines, the importance of different stem cells in therapeutics, the expanded role of nanotechnology in treatment, the administration of several types of stem cells, their tracking, imaging, and the final observation of clinical trials on many different levels as well as it aims to keep readers up to pace on emerging therapeutic applications of some specific organs and disorders that may improve from regenerative medicine shortly.

Endothelial progenitor cells for fabrication of engineered vascular units and angiogenesis induction

The promotion of vascularization and angiogenesis in the grafts is a crucial phenomenon in the healing process and tissue engineering. It has been shown that stem cells, especially endothelial progenitor cells (EPCs), can stimulate blood vessel formation inside the engineered hydrogels after being transplanted into the target sites. The incorporation of EPCs into the hydrogel can last the retention time, long-term survival, on-target delivery effects, migration and differentiation into mature endothelial cells. Despite these advantages, further modifications are mandatory to increase the dynamic growth and angiogenesis potential of EPCs in in vitro and in vivo conditions. Chemical modifications of distinct composites with distinct physical properties can yield better regenerative potential and angiogenesis during several pathologies. Here, we aimed to collect recent findings related to the application of EPCs in engineered vascular grafts and/or hydrogels for improving vascularization in the grafts. Data from the present article can help us in the application of EPCs as valid cell sources in the tissue engineering of several ischemic tissues.

Improved Composite Hydrogel for Bioengineered Tracheal Graft Demonstrates Effective Early Angiogenesis

Background/Objectives: Collagen-agarose hydrogel blends currently used in tracheal graft bioengineering contain relatively high concentrations of collagen to withstand mechanical stresses associated with native trachea function (e.g., breathing). Unfortunately, the high collagen content restricts effective cell infiltration into the hydrogel. In this study, we created an improved hydrogel blend with lower concentrations of collagen (<5 mg/mL) and characterized its capacity for fibroblast invasion and angiogenesis. Methods: Four collagen-agarose hydrogel blends were created: 1 mg/mL type 1 collagen (T1C) and 0.25% agarose, 1 mg/mL T1C and 0.125% agarose, 2 mg/mL T1C and 0.25% agarose, and 2 mg/mL T1C and 0.125% agarose. The hydrogel surface was seeded with fibroblasts, while both endothelial cells and fibroblasts (3:1 ratio) were mixed within the hydrogel matrix. We assessed early angiogenesis by observing fibroblast migration and endothelial cell morphology (elongation and branching) at 7 days. In addition, we performed immunostaining for alpha-smooth muscle actin (aSMA) and explored the gene expression of various angiogenic markers (including vascular endothelial growth factor; VEGF). Results: Gels with lower agarose concentrations (0.125%) with 1 or 2 mg/mL T1C were more effective in allowing early attachment and migration of surface-applied fibroblasts compared to gels with higher (0.25%) agarose concentrations. The low-agarose gels also allowed cells to quickly adopt a spread morphology and self-assemble into elongated structures indicative of early angiogenesis, while demonstrating positive immunostaining for aSMA and increased gene expression of VEGF by day 7. Conclusions: Hydrogel blends with collagen and low agarose concentrations may be effective in allowing early cellular infiltration and angiogenesis, making such gels a suitable cell substrate for use in the development of composite bioengineered tracheal grafts. The collagen-agarose hydrogel blend is meant to be cast around a three-dimensional (3D) printed polycaprolactone support structure and wrapped in porcine small intestine submucosa ECM to create an off-the-shelf bioengineered tracheal implant.

Approaches to scarless burn wound healing: application of 3D printed skin substitutes with dual properties of anti-infection and balancing wound hydration levels

BACKGROUND

Severe burn wounds face two primary challenges: dysregulated cellular impairment functions following infection and an unbalanced wound hydration microenvironment leading to excessive inflammation and collagen deposition. These results in hypertrophic scar contraction, causing significant deformity and disability in survivors.

METHODS

A three-dimensional (3D) printed double-layer hydrogel (DLH) was designed and fabricated to address the problem of scar formation after burn injury. DLH was developed using methacrylated silk fibroin (SFMA) and gelatin methacryloyl (GelMA) for the upper layer, and GelMA and hyaluronic acid methacryloyl (HAMA) for the lower layer. To combat infection, copper-epigallocatechin gallate (Cu-EGCG) was incorporated into the lower layer bioink, collectively referred to as DLS. To balance wound hydration levels, HaCaT cells were additionally encapsulated in the upper layer, designed as DLS/c.

FINDINGS

DLH demonstrated suitable porosity, appropriate mechanical properties, and excellent biocompatibility. DLS exhibited potent antimicrobial properties, exerted anti-inflammatory effects by regulating macrophage polarisation, and may enhance angiogenesis through the HIF-1α/VEGF pathway. In the DLS/c group, animal studies showed significant improvements in epidermal formation, barrier function, and epidermal hydration, accompanied by reduced inflammation. In addition, Masson's trichrome and Sirius red staining revealed that the structure and ratio of dermal collagen in DLS/c resembled that of normal skin, indicating considerable potential for scarless wound healing.

INTERPRETATION

This biomimetic matrix shows promise in addressing the challenges of burn wounds and aiming for scarless repair, with benefits such as anti-infection, epidermal hydration, biological induction, and optimised topological properties.

FUNDING

Shown in Acknowledgements.

A novel injectable sericin hydrogel with strong fluorescence for tracing

Hydrogel systems with strong fluorescence, as convenient tracers or bio-probes, have attracted much attention in biomedical engineering. Currently, most hydrogels endowed fluorescent properties due to modifying additional fluorophores. However, these fluorophores owing to photobleaching and toxicity limit the practical applications of hydrogels. Herein, we prepared a novel self-luminescence hydrogel through double crosslinking glutaraldehyde and hydrogen peroxide/horseradish peroxidase (H2O2/HRP) with sericin protein. The double cross-linked sericin hydrogel exhibits strong green and red intrinsic fluorescence which can be excited over a wide range of wavelengths. Moreover, this hydrogel with strong intrinsic fluorescence could penetrate thick pigskin tissue, which has potential application in implantable bio-tracer areas. In addition to the above unique properties, this sericin hydrogel possesses two types of micropore structures with high porosity, swelling properties, pH-responsive degradability, super elasticity, injectability, viscosity, and excellent biocompatibility. The investigation could significantly expand the scope of protein hydrogels in biomedical applications.

Suitability of Ex Vivo-Expanded Microtic Perichondrocytes for Auricular Reconstruction

Tissue engineering (TE) techniques offer solutions for tissue regeneration but require large quantities of cells. For microtia patients, TE methods represent a unique opportunity for therapies with low donor-site morbidity and reliance on the surgeon's individual expertise. Microtia-derived chondrocytes and perichondrocytes are considered a valuable cell source for autologous reconstruction of the pinna. The aim of this study was to investigate the suitability of perichondrocytes from microtia patients for autologous reconstruction in comparison to healthy perichondrocytes and microtia chondrocytes. Perichondrocytes were isolated via two different methods: explant culture and enzymatic digestion. The isolated cells were analyzed in vitro for their chondrogenic cell properties. We examined migration activity, colony-forming ability, expression of mesenchymal stem cell markers, and gene expression profile. We found that microtic perichondrocytes exhibit similar chondrogenic properties compared to chondrocytes in vitro. We investigated the behavior in three-dimensional cell cultures (spheroids and scaffold-based 3D cell cultures) and assessed the expression of cartilage-specific proteins via immunohistochemistry, e.g., collagen II, which was detected in all samples. Our results show that perichondrocytes from microtia patients are comparable to healthy perichondrocytes and chondrocytes in terms of chondrogenic cell properties and could therefore be a promising cell source for auricular reconstruction.

ECM-Like Adhesive Hydrogel for the Regeneration of Large Corneal Stromal Defects

The repair of large-diameter corneal stroma defects is a major clinical problem. Although some studies have attempted to use hydrogels to repair corneal damage, most of these hydrogels can only be used for focal stromal defects that are ≤3.5 mm in diameter due to poor hydrogel adhesion. Here, a photocurable adhesive hydrogel that mimics the extracellular matrix (ECM) with regard to composition for repairing 6 mm-diameter corneal stromal defects in rabbits is investigated. This ECM-like adhesive can be rapidly cured after light exposure, with high light transmittance and good mechanical properties. More importantly, this hydrogel maintains the viability and adhesion of cornea-derived cells and promotes their migration in vitro in 2D and 3D culture environments. Proteomics analysis confirms that the hydrogel promotes cell proliferation and ECM synthesis. Furthermore, in rabbit corneal stromal defect repair experiments, it is proven by histological and proteomic analysis that this hydrogel can effectively promote corneal stroma repair, reduce scar formation, and increase corneal stromal-neural regeneration at the six months follow-up. This work demonstrates the great application of ECM-like adhesive hydrogels for the regeneration of large-diameter corneal defects.

Visible light-crosslinkable tyramine-conjugated alginate-based microgel bioink for multiple cell-laden 3D artificial organ

While the natural carbohydrate alginate has enabled effective three-dimensional (3D) extrusion bioprinting, it still suffers from some issues such as low printability and resolution and limited cellular function due to ionic crosslinking dependency. Here, we prepared a harmless visible light-based photocrosslinkable alginate by chemically bonding tyrosine-like residues onto alginate chains to propose a new microgel manufacturing system for the development of 3D-printed bioinks. The photocrosslinkable tyramine-conjugated alginate microgel achieved both higher cell viability and printing resolution compared to the bulk gel form. This alginate-based jammed granular microgel bioink showed excellent 3D bioprinting ability with maintained structural stability. As a biocompatible material, the developed multiple cell-loaded photocrosslinkable alginate-based microgel bioink provided excellent proliferation and migration abilities of laden living cells, providing an effective strategy to construct implantable functional artificial organ structures for 3D bioprinting-based tissue engineering.

Silk fibroin microgels as a platform for cell microencapsulation

Cell microencapsulation has been utilized for years as a means of cell shielding from the external environment while facilitating the transport of gases, general metabolites, and secretory bioactive molecules at once. In this light, hydrogels may support the structural integrity and functionality of encapsulated biologics whereas ensuring cell viability and function and releasing potential therapeutic factors once in situ. In this work, we describe a straightforward strategy to fabricate silk fibroin (SF) microgels (µgels) and encapsulate cells into them. SF µgels (size ≈ 200 µm) were obtained through ultrasonication-induced gelation of SF in a water-oil emulsion phase. A thorough physicochemical (SEM analysis, and FT-IR) and mechanical (microindentation tests) characterization of SF µgels were carried out to assess their nanostructure, porosity, and stiffness. SF µgels were used to encapsulate and culture L929 and primary myoblasts. Interestingly, SF µgels showed a selective release of relatively small proteins (e.g., VEGF, molecular weight, M_W = 40 kDa) by the encapsulated primary myoblasts, while bigger (macro)molecules (M_W = 160 kDa) were hampered to diffusing through the µgels. This article provided the groundwork to expand the use of SF hydrogels into a versatile platform for encapsulating relevant cells able to release paracrine factors potentially regulating tissue and/or organ functions, thus promoting their regeneration.

Polysaccharide-based hydrogels for drug delivery and wound management: a review

INTRODUCTION

Polysaccharide-based hydrogels (PBHs) offer several advantages over their synthetic counterparts. Their natural origin contributes to their nontoxicity, high biocompatibility, and in vivo biodegradability. Their properties can be tuned finely to obtain hydrogels with desired mechanical, structural, and chemical properties.

AREAS COVERED

Such versatile characteristics have potentiated the use of PBHs for the delivery of drugs, vaccines, protein and peptide therapeutics, genes, cells, probiotics, bacteriophages, and other therapeutic agents. Recent advances in hydrogel-based formulations such as nanogels, microgels, microneedles, hydrogel beads, nanocarrier-loaded hydrogels, and complexation hydrogels have enabled the precise delivery of a wide range of therapeutics. This review aims to give a holistic overview of hydrogels in the delivery of a variety of therapeutics through different routes.

EXPERT OPINION

PBHs have been used to enable the oral delivery of vaccines and other biologicals, thereby allowing self-administration of life-saving vaccines during public health emergencies. There is a lack of commercialized wound dressings for the treatment of chronic wounds. PBH-based wound dressings, especially those based on chitosan and loaded with actives and growth factors, have the potential to help in the long-term treatment of such wounds. Recent developments in the 3D printing of hydrogels can enable the quick and large-scale production of drug-loaded hydrogels.

Dynamic gelatin-based hydrogels promote the proliferation and self-renewal of embryonic stem cells in long-term 3D culture

Long-term maintenance of embryonic stem cells (ESCs) in the undifferentiated state is still challenging. Compared with traditional 2D culture methods, 3D culture in biomaterials such as hydrogels is expected to better support the long-term self-renewal of ESCs by emulating the biophysical and biochemical properties of the extracellular matrix (ECM). Although prior studies showed that soft and degradable hydrogels favor the 3D growth of ESCs, few studies have examined the impact of the structural dynamics of the hydrogel matrix on ESC behaviors. Herein, we report a gelatin-based structurally dynamic hydrogel (GelCD hydrogel) that emulates the intrinsic structural dynamics of the ECM. Compared with covalently crosslinked gelatin hydrogels (GelMA hydrogels) with similar stiffness and biodegradability, GelCD hydrogels significantly promote the clonal expansion and viability of encapsulated mouse ESCs (mESCs) independent of MMP-mediated hydrogel degradation. Furthermore, GelCD hydrogels better maintain the pluripotency of encapsulated mESCs than do traditional 2D culture methods that use MEF feeder cells or medium supplementation with GSK3β and MEK 1/2 inhibitors (2i). When cultured in GelCD hydrogels for an extended period (over 2 months) with cell passaging every 7 days, mESCs preserve their normal morphology and maintain their pluripotency and full differentiation capability. Our findings highlight the critical role of the structural dynamics of the hydrogel matrix in accommodating the volume expansion that occurs during clonal ESC growth, and we believe that our dynamic hydrogels represent a valuable tool to support the long-term 3D culture of ESCs.

Ultrasound-Induced Drug Release from Stimuli-Responsive Hydrogels

Stimuli-responsive hydrogel drug delivery systems are designed to release a payload when prompted by an external stimulus. These platforms have become prominent in the field of drug delivery due to their ability to provide spatial and temporal control for drug release. Among the different external triggers that have been used, ultrasound possesses several advantages: it is non-invasive, has deep tissue penetration, and can safely transmit acoustic energy to a localized area. This review summarizes the current state of understanding about ultrasound-responsive hydrogels used for drug delivery. The mechanisms of inducing payload release and activation using ultrasound are examined, along with the latest innovative formulations and hydrogel design strategies. We also report on the most recent applications leveraging ultrasound activation for both cancer treatment and tissue engineering. Finally, the future perspectives offered by ultrasound-sensitive hydrogels are discussed.

Bilayer Hydrogels for Wound Dressing and Tissue Engineering

A large number of different skin diseases such as hits, acute, and chronic wounds dictate the search for alternative and effective treatment options. The wound healing process requires a complex approach, the key step of which is the choice of a dressing with controlled properties. Hydrogel-based scaffolds can serve as a unique class of wound dressings. Presented on the commercial market, hydrogel wound dressings are not found among proposals for specific cases and have a number of disadvantages—toxicity, allergenicity, and mechanical instability. Bilayer dressings are attracting great attention, which can be combined with multifunctional properties, high criteria for an ideal wound dressing (antimicrobial properties, adhesion and hemostasis, anti-inflammatory and antioxidant effects), drug delivery, self-healing, stimulus manifestation, and conductivity, depending on the preparation and purpose. In addition, advances in stem cell biology and biomaterials have enabled the design of hydrogel materials for skin tissue engineering. To improve the heterogeneity of the cell environment, it is possible to use two-layer functional gradient hydrogels. This review summarizes the methods and application advantages of bilayer dressings in wound treatment and skin tissue regeneration. Bilayered hydrogels based on natural as well as synthetic polymers are presented. The results of the in vitro and in vivo experiments and drug release are also discussed.

Topical Polydeoxyribonucleotide Loaded in Hydrogel Formulation for Wound Healing in Diabetic Rats

Patients with diabetes mellitus experience delayed wound healing because of the uncontrolled glucose level leads to impaired cell proliferative function, poor circulation, decreased production and repair of new blood vessels. Polydeoxyribonucleotide (PDRN) is used in wound healing as a substance that stimulates tissue repair. A hydrogel is a reticular substance generally used as a dressing formulation to accelerate wound healing, and also used as a bio-applicable scaffold or vehicle. The aim of study is to investigate the effects of PDRN loaded in hydrogel on wound healing, in combination and separately, in an animal diabetic wound model. Methods: We studied the effects of PDRN in diabetes-related healing defect using an incisional skin-wound model produced on the back of male diabetic rats. A total of 36 wounds, were classified into 3 groups: a control group, a hydrogel-only group, a PDRN loaded in hydrogel combined-treatment group. All rats were assessed for changes in wound size and photographed on scheduled dates. The skin specimen sample of diabetic rat wound model were observed on 3, 7, 14 and 21 days after skin injury to measure tissue remodeling through histological evaluation of fibroblasts proliferation, and collagen production, also the number of blood vessels was measured in all specimens. Results: Differences in the decrease and change in wound size in the PDRN loaded in hydrogel group were more significant than those in the control and hydrogel single-treatment groups. Analysis of the fibroblasts proliferation, collagen production and number of blood vessels through histological examination showed a pattern of increase over time that occurred in PDRN loaded in hydrogel combined-treatment group. Conclusion: This experiment demonstrated improved wound healing using a PDRN loaded in hydrogel combined treatment compared to either two groups, resulting in a decrease in diabetic wound size and a shortening of the healing period

Restoring Carboxylates on Highly Modified Alginates Improves Gelation, Tissue Retention and Systemic Capture

Alginate hydrogels are gaining traction for use in drug delivery, regenerative medicine, and as tissue engineered scaffolds due to their physiological gelation conditions, high tissue biocompatibility, and wide chemical versatility. Traditionally, alginate is decorated at the carboxyl group to carry drug payloads, peptides, or proteins. While low degrees of substitution do not cause noticeable mechanical changes, high degrees of substitution can cause significant losses to alginate properties including complete loss of calcium cross-linking. While most modifications used to decorate alginate deplete the carboxyl groups, we propose that alginate modifications that replenish the carboxyl groups could overcome the loss in gel integrity and mechanics. In this report, we demonstrate that restoring carboxyl groups during functionalization maintains calcium cross-links as well as hydrogel shear-thinning and self-healing properties. In addition, we demonstrate that alginate hydrogels modified to a high degree with azide modifications that restore the carboxyl groups have improved tissue retention at intramuscular injection sites and capture blood-circulating cyclooctynes better than alginate hydrogels modified with azide modifications that deplete the carboxyl groups. Taken together, alginate modifications that restore carboxyl groups could significantly improve alginate hydrogel mechanics for clinical applications. STATEMENT OF SIGNIFICANCE: Chemical modification of hydrogels provides a powerful tool to regulate cellular adhesion, immune response, and biocompatibility with local tissues. Alginate, due to its biocompatibility and easy chemical modification, is being explored for tissue engineering and drug delivery. Unfortunately, modifying alginate to a high degree of substitution consumes carboxyl group, which are necessary for ionic gelation, leading to poor hydrogel crosslinking. We introduce alginate modifications that restore the alginate's carboxyl groups. We demonstrate that modifications that reintroduce carboxyl groups restore gelation and improve gel mechanics and tissue retention. In addition to contributing to a basic science understanding of hydrogel properties, we anticipate our approach will be useful to create tissue engineered scaffolds and drug delivery platforms.

Identification of Key Genes Associated with Endothelial Cell Dysfunction in Atherosclerosis Using Multiple Bioinformatics Tools

Atherosclerosis is the most notable cardiovascular disease, the latter being the main cause of death globally. Endothelial cell dysfunction plays a major role in the pathogenesis of atherosclerosis. However, it is currently unclear which genes are involved between endothelial cell dysfunction and atherosclerosis. This study was aimed at identifying these genes. Based on the GSE83500 dataset, the quantification of endothelial cell function was conducted using single-sample gene set enrichment analysis; the coexpression modules were conducted using weighted correlation network analysis. After building module-trait relationships, tan and yellow modules were regarded as hub modules. 10 hub genes from each hub module were identified by the protein-protein interaction network analysis. The key genes (RAB5A, CTTN, ITGB1, and MMP9) were obtained by comparing the expression differences of the hub gene between atherosclerotic and normal groups from the GSE28829 and GSE43292 datasets, respectively. ROC analysis showed the diagnostic value of key genes. Moreover, the differential expression of key genes in normal and atherosclerotic aortic walls was verified. In vitro, we establish a model of ox-LDL-injured endothelial cells and transfect RAB5A overexpression and shRNA plasmids. The results showed that overexpression of RAB5A ameliorates the proliferation and migration function of ox-LDL-injured endothelial cells, including the ability of tubule formation. It was speculated that the interferon response, Notch signaling pathways, etc. were involved in this function of RAB5A by using gene set variation analysis. With the multiple bioinformatics analysis methods, we detected that yellow and tan modules are related to the abnormal proliferation and migration of endothelial cells associated with atherosclerosis. RAB5A, CTTN, ITGB1, and MMP9 can be used as potential targets for therapy and diagnostic markers. In vitro, overexpression of RAB5A can ameliorate the proliferation and migration function of ox-LDL-injured endothelial cells, and the possible molecules involved in this process were speculated.

Poly (l-lactic acid) membrane crosslinked with Genipin for guided bone regeneration

In this study, we chemically modified poly(L-lactic acid) (PLLA) with functional amine groups and fabricated a PLLA membrane crosslinked with genipin as a biomembrane for inducing guided bone regeneration (GBR). The mechanical strength of the PLLA-amine membrane was improved by crosslinking with genipin compared to pure PLLA membrane. The surface of the PLLA-amine membrane crosslinked with genipin had many more uniform pores. Attachment and proliferation of MC3T3-E1 cells were increased and improved on the PLLA-amine membrane crosslinked with genipin. In an in vitro osteogenesis study, MC3T3-E1 cells on the PLLA membrane showed higher alkaline phosphatase (ALP) activity and calcification ability evaluated by alizarin red S staining than those on the pure PLLA membrane. When a skull defect hole of a rat was covered with the PLLA-amine membrane crosslinked with genipin, vigorous new bone regeneration determined by computed tomography at 8 weeks post operation was superior to that when the skull defect was covered with the pure PLLA membrane. Taken together, these results demonstrate that the PLLA-amine membrane crosslinked with genipin has a promising therapeutic application to GBR as a barrier membrane for covering the defect site.

Engineering Bioactive Scaffolds for Skin Regeneration

Large skin wounds pose a major clinical challenge. Scarcity of donor site and postsurgical scarring contribute to the incomplete or partial loss of function and aesthetic concerns in skin wound patients. Currently, a wide variety of skin grafts are being applied in clinical settings. Scaffolds are used to overcome the issues related to the misaligned architecture of the repaired skin tissues. The current review summarizes the contribution of biomaterials to wound healing and skin regeneration and addresses the existing limitations in skin grafting. Then, the clinically approved biologic and synthetic skin substitutes are extensively reviewed. Next, the techniques for modification of skin grafts aiming for enhanced tissue regeneration are outlined, and a summary of different growth factor delivery systems using biomaterials is presented. Considering the significant progress in biomaterial science and manufacturing technologies, the idea of biomaterial-based skin grafts with the ability for scarless wound healing and reconstructing full skin organ is more achievable than ever.

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

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

Injectable Nanocomposite Hydrogels for Cancer Therapy

Hydrogel is a kind of 3D polymer network with strong swelling ability in water and appropriate mechanical and biological properties, which make it feasible to maintain bioactive substances and has promising applications in the fields of biomaterials, soft machines, and artificial tissues. Unfortunately, traditional hydrogels prepared by chemical crosslinking have poor mechanical properties and limited functions, which limit their further application. In recent years, with the continuous development of nanoparticle research, more and more studies have combined nanoparticles with hydrogels to make up for the shortcomings of traditional hydrogels. In this article, the types and functions of hydrogels and nanomaterials are introduced first, as well as the functions and applications of injectable nanocomposite hydrogels (INHs), then the latest progress of INHs for cancer treatment is reviewed, some existing problems are summarized, and the application prospect of NHs is prospected.

Advances in Extracellular Matrix-Mimetic Hydrogels to Guide Stem Cell Fate

In the fields of regenerative medicine and tissue engineering, stem cells offer vast potential for treating or replacing diseased and damaged tissue. Much progress has been made in understanding stem cell biology, yielding protocols for directing stem cell differentiation toward the cell type of interest for a specific application. One particularly interesting and powerful signaling cue is the extracellular matrix (ECM) surrounding stem cells, a network of biopolymers that, along with cells, makes up what we define as a tissue. The composition, structure, biochemical features, and mechanical properties of the ECM are varied in different tissues and developmental stages, and serve to instruct stem cells toward a specific lineage. By understanding and recapitulating some of these ECM signaling cues through engineered ECM-mimicking hydrogels, stem cell fate can be directed in vitro. In this review, we will summarize recent advances in material systems to guide stem cell fate, highlighting innovative methods to capture ECM functionalities and how these material systems can be used to provide basic insight into stem cell biology or make progress toward therapeutic objectives.

Feasibility and safety of calcium alginate hydrogel sealant for the treatment of cryptoglandular fistula-in-ano: phase I/IIa clinical trial

AIM

Complex perianal fistulas pose a challenge to the surgeon since the fistulous tract must be eliminated without impairing continence. Although without strong scientific evidence, some bibliography has demonstrated the efficacy of some sealants in the treatment of anal fistulas. We aimed to assess the feasibility and safety of calcium alginate hydrogel injections into the fistulous tract as treatment for trans-sphincteric cryptoglandular fistulas.

METHODS

A prospective, single-centre, case series of this novel technique was conducted in a level 3 Spanish hospital, including patients diagnosed with trans-sphincteric perianal fistulas and treated with a calcium alginate hydrogel sealant. A strict follow-up was performed by an independent surgeon at 1, 3, 6 and 12 months. The main outcome measures were feasibility, safety (number of adverse events) and efficacy of the treatment.

RESULTS

Twenty patients were treated. The treatment was performed for all patients. Seven adverse events related to the injection product or the surgical procedure were identified. After a 12-month follow-up, 12 patients were completely cured and eight were not cured, with a greater response in the first 6 months. These findings were confirmed by endoanal ultrasound, with a Cohen's kappa concordance rate of 0.89. No statistically significant differences were observed in pain measured using the visual analogue scale, faecal incontinence measured using the Wexner scoring system, and quality of life analysed by the SF-36 Health Survey.

CONCLUSION

The treatment was feasible, safe and with discrete satisfactory healing results. It also demonstrated an acceptable safety profile, without worsening of faecal incontinence, quality of life and pain following treatment.

Biomaterial-based approaches to engineering immune tolerance

The development of biomaterial-based therapeutics to induce immune tolerance holds great promise for the treatment of autoimmune diseases, allergy, and graft rejection in transplantation. Historical approaches to treat these immunological challenges have primarily relied on systemic delivery of broadly-acting immunosuppressive agents that confer undesirable, off-target effects. The evolution and expansion of biomaterial platforms has proven to be a powerful tool in engineering immunotherapeutics and enabled a great diversity of novel and targeted approaches in engineering immune tolerance, with the potential to eliminate side effects associated with systemic, non-specific immunosuppressive approaches. In this review, we summarize the technological advances within three broad biomaterials-based strategies to engineering immune tolerance: nonspecific tolerogenic agent delivery, antigen-specific tolerogenic therapy, and the emergent area of tolerogenic cell therapy.

Injectable hydrogel for co-delivery of 5-azacytidine in zein protein nanoparticles with stem cells for cardiac function restoration

Heart failure is major cause of mortality associated with mostly Myocardial infarction (MI). Transplanting mesenchymal stem cells (MSC) have exhibited potential role in myocardial regeneration. Secretion of immune-modulatory cytokines and various growth factors after transplantation plays significant role in remodelling process of MI region. However, low retention, higher shear stress during administration and rejection at host infarct environment hinders therapeutic efficacy. Myocardial regeneration demands for accurate spatio-temporal delivery of MSCs with supportive vascular network that leads to improvement of cardiac function. In this study, injectable alginate based microporous hydrogel has been used to deliver 5-Azacytidine (5-Aza) in zein protein nanoparticle with MSCs for attenuating adverse cardiac remodelling after MI. Zein nanoparticles loaded with 5-Aza were prepared by liquid-liquid dispersion, and it was found that 35% of drug was released in 7 days supported with mathematical modelling. The presence of 5-Aza and zein in developed hydrogel supported in vitro MSC proliferation, migration and angiogenesis. Significant increased expression of cardiac specific markers, GATA4, MEF2C, MLC, SERCA and NKX2.5 was observed in vitro. 5-Aza loaded protein nanoparticle with MSCs encapsulated hydrogels in rat MI model also exhibited substantial improvement of functional cardiac parameters such as cardiac output and ejection fraction. Histopathological analysis showed reduced fibrosis, attenuated infarct expansion and cardiac tissue restoration and angiogenesis. In brief, we developed nanocarrier-hydrogel system a promising strategy for co-delivering 5-Aza as cardiac differentiation cue with MSCs to achieve higher cell retention and enhanced improvement in myocardial regeneration after MI.

Biodegradable Hydrogels Loaded with Magnetically Responsive Microspheres as 2D and 3D Scaffolds

Scaffolds play an essential role in the success of tissue engineering approaches. Their intrinsic properties are known to influence cellular processes such as adhesion, proliferation and differentiation. Hydrogel-based matrices are attractive scaffolds due to their high-water content resembling the native extracellular matrix. In addition, polymer-based magnetoelectric materials have demonstrated suitable bioactivity, allowing to provide magnetically and mechanically activated biophysical electrical stimuli capable of improving cellular processes. The present work reports on a responsive scaffold based on poly (L-lactic acid) (PLLA) microspheres and magnetic microsphere nanocomposites composed of PLLA and magnetostrictive cobalt ferrites (CoFe2O4), combined with a hydrogel matrix, which mimics the tissue's hydrated environment and acts as a support matrix. For cell proliferation evaluation, two different cell culture conditions (2D and 3D matrices) and two different strategies, static and dynamic culture, were applied in order to evaluate the influence of extracellular matrix-like confinement and the magnetoelectric/magneto-mechanical effect on cellular behavior. MC3T3-E1 proliferation rate is increased under dynamic conditions, indicating the potential use of hydrogel matrices with remotely stimulated magnetostrictive biomaterials for bone tissue engineering.

Fabrication of protease XIV-loaded microspheres for cell spreading in silk fibroin hydrogels

Due to their excellent mechanical strength and biocompatibility, silk fibroin(SF) hydrogels can serve as ideal scaffolds. However, their slow rate of natural degradation limits the space available for cell proliferation, which hinders their application. In this study, litchi-like calcium carbonate@hydroxyapatite (CaCO₃@HA) porous microspheres loaded with proteases from Streptomyces griseus (XIV) were used as drug carriers to regulate the biodegradation rate of SF hydrogels. The results showed that litchi-like CaCO₃@HA microspheres with different phase compositions could be prepared by changing the hydrothermal reaction time. The CaCO₃@HA microspheres controlled the release of Ca ions, which was beneficial for the osteogenic differentiation of mesenchymal stem cells (MSCs). The adsorption and release of protease XIV from the CaCO₃@HA microcarriers indicated that the loading and release amount can be controlled with the initial drug concentration. The weight loss test and SEM observation showed that the degradation of the fibroin hydrogel could be controlled by altering the amount of protease XIV-loaded CaCO₃@HA microspheres. A three-dimensional (3D) cell encapsulation experiment proved that incorporation of the SF hydrogel with protease XIV-loaded microspheres promoted cell dispersal and spreading, suggesting that the controlled release of protease XIV can regulate hydrogel degradation. SF hydrogels incorporated with protease XIV-loaded microspheres are suitable for cell growth and proliferation and are expected to serve as excellent bone tissue engineering scaffolds.

Controlled Delivery of Insulin-like Growth Factor-1 from Bioactive Glass-Incorporated Alginate-Poloxamer/Silk Fibroin Hydrogels

Thermosensitive alginate–poloxamer (ALG–POL) copolymer with an optimal POL content was synthesized, and it was used to combine with silk fibroin (SF) for building ALG–POL/SF hydrogels with dual network structure. Mesoporous bioactive glass (BG) nanoparticles (NPs) with a high level of mesoporosity and large pore size were prepared and they were employed as a vehicle for loading insulin-like growth factor-1 (IGF-1). IGF-1-loaded BG NPs were embedded into ALG–POL/SF hydrogels to achieve the controlled delivery of IGF-1. The resulting IGF-1-loaded BG/ALG–POL/SF gels were found to be injectable with their sol-gel transition near physiological temperature and pH. Rheological measurements showed that BG/ALG–POL/SF gels had their elastic modulus higher than 5kPa with large ratio of elastic modulus to viscous modulus, indicative of their mechanically strong features. The dry BG/ALG–POL/SF gels were seen to be highly porous with well-interconnected pore characteristics. The gels loaded with varied amounts of IGF-1 showed abilities to administer IGF-1 release in approximately linear manners for a few weeks while effectively preserving the bioactivity of encapsulated IGF-1. Results suggest that such constructed BG/ALG–POL/SF gels can function as a promising injectable biomaterial for bone tissue engineering applications.

Hybrid Sponge-Like Scaffolds Based on Ulvan and Gelatin: Design, Characterization and Evaluation of Their Potential Use in Bone Tissue Engineering

Ulvan, a bioactive natural sulfated polysaccharide, and gelatin, a collagen-derived biopolymer, have attracted interest for the preparation of biomaterials for different biomedical applications, due to their demonstrated compatibility for cell attachment and proliferation. Both ulvan and gelatin have exhibited osteoinductive potential, either alone or in combination with other materials. In the current work, a series of novel hybrid scaffolds based on crosslinked ulvan and gelatin was designed, prepared and characterized. Their mechanical performance, thermal stability, porosity, water-uptake and in vitro degradation ability were assessed, while their morphology was analyzed through scanning electron microscopy. The prepared hybrid ulvan/gelatin scaffolds were characterized by a highly porous and interconnected structure. Human adipose-derived mesenchymal stem cells (hADMSCs) were seeded in selected ulvan/gelatin hybrid scaffolds and their adhesion, survival, proliferation, and osteogenic differentiation efficiency was evaluated. Overall, it was found that the prepared hybrid sponge-like scaffolds could efficiently support mesenchymal stem cells' adhesion and proliferation, suggesting that such scaffolds could have potential uses in bone tissue engineering.

Inclusion of Cross-Linked Elastin in Gelatin/PEG Hydrogels Favourably Influences Fibroblast Phenotype

The capacity of a biomaterial to innately modulate cell behavior while meeting the mechanical property requirements of the implant is a much sought-after goal within bioengineering. Here we covalently incorporate soluble elastin into a gelatin–poly (ethylene glycol) (PEG) hydrogel for three-dimensional (3D) cell encapsulation to achieve these properties. The inclusion of elastin into a previously optimized gelatin–PEG hydrogel was then evaluated for effects on entrapped fibroblasts, with the aim to assess the hydrogel as an extracellular matrix (ECM)-mimicking 3D microenvironment for cellular guidance. Soluble elastin was incorporated both physically and covalently into novel gelatin/elastin hybrid PEG hydrogels with the aim to harness the cellular interactivity and mechanical tunability of both elastin and gelatin. This design allowed us to assess the benefits of elastin-containing hydrogels in guiding fibroblast activity for evaluation as a potential dermal replacement. It was found that a gelatin–PEG hydrogel with covalently conjugated elastin, supported neonatal fibroblast viability, promoted their proliferation from 7.3% to 13.5% and guided their behavior. The expression of collagen alpha-1(COL1A1) and elastin in gelatin/elastin hybrid gels increased 16-fold and 6-fold compared to control sample at day 9, respectively. Moreover, cells can be loaded into the hydrogel precursor solution, deposited, and the matrix cross-linked without affecting the incorporated cells adversely, thus enabling a potential injectable system for dermal wound healing.

Biopolymer-Based Microcarriers for Three-Dimensional Cell Culture and Engineered Tissue Formation

The concept of three-dimensional (3D) cell culture has been proposed to maintain cellular morphology and function as in vivo. Among different approaches for 3D cell culture, microcarrier technology provides a promising tool for cell adhesion, proliferation, and cellular interactions in 3D space mimicking the in vivo microenvironment. In particular, microcarriers based on biopolymers have been widely investigated because of their superior biocompatibility and biodegradability. Moreover, through bottom-up assembly, microcarriers have opened a bright door for fabricating engineered tissues, which is one of the cutting-edge topics in tissue engineering and regeneration medicine. This review takes an in-depth look into the recent advancements of microcarriers based on biopolymers-especially polysaccharides such as chitosan, chitin, cellulose, hyaluronic acid, alginate, and laminarin-for 3D cell culture and the fabrication of engineered tissues based on them. The current limitations and potential strategies were also discussed to shed some light on future directions.

Interplay between degradability and integrin signaling on mesenchymal stem cell function within poly(ethylene glycol) based microporous annealed particle hydrogels

Microporous annealed particle (MAP) hydrogels are promising materials for delivering therapeutic cells. It has previously been shown that spreading and mechanosensing activation of human mesenchymal stem cells (hMSCs) incorporated in these materials can be modulated by tuning the modulus of the microgel particle building blocks. However, the effects of degradability and functionalization with different integrin-binding peptides on cellular responses has not been explored. In this work, RGDS functionalized and enzymatically degradable poly(ethylene glycol) (PEG) microgels were annealed into MAP hydrogels via thiol-ene click chemistry and photopolymerization. During cell-mediated degradation, the microgel surfaces were remodeled to wrinkles or ridges, but the scaffold integrity was maintained. Moreover, cell spreading, proliferation, and secretion of extracellular matrix proteins were significantly enhanced in faster matrix metalloproteinase degrading (KCGPQGIWGQCK) MAP hydrogels compared to non-degradable controls after 8 days of culture. We subsequently evaluated paracrine activity by hMSCs seeded in the MAP hydrogels functionalized with either RGDS or c(RRETAWA), which is specific for α5β1 integrins, and evaluated the interplay between degradability and integrin-mediated signaling. Importantly, c(RRETAWA) functionalization upregulated secretion of bone morphogenetic protein-2 overall and on a per cell basis, but this effect was critically dependent on microgel degradability. In contrast, RGDS functionalization led to higher overall vascular endothelial growth factor secretion in degradable scaffolds due to the high cell number. These results demonstrate that integrin-binding peptides can modulate hMSC behavior in PEG-based MAP hydrogels, but the results strongly depend on the susceptibility of the microgel building blocks to cell-mediated matrix remodeling. This relationship should be considered in future studies aiming to further develop these materials for stem cell delivery and tissue engineering applications. STATEMENT OF SIGNIFICANCE: Microporous annealed particle (MAP) hydrogels are attracting increasing interest for tissue repair and regeneration and have shown superior results compared to conventional hydrogels in multiple applications. Here, we studied the impact of MAP hydrogel degradability and functionalization with different integrin-binding peptides on human mesenchymal stem cells (hMSCs) that were incorporated during particle annealing. Degradability was found to improve cell growth, spreading, and extracellular matrix production regardless of the integrin-binding peptide. Moreover, in degradable MAP hydrogels the integrin-binding peptide c(RRETAWA) was found to increase osteogenic protein expression by hMSCs compared to RGDS-functionalized MAP hydrogels. These results have important implications for the development of a MAP hydrogel-based hMSC delivery system for bone tissue engineering.

Hydrogel microparticles for biomedical applications

Hydrogel microparticles (HMPs) are promising for biomedical applications, ranging from the therapeutic delivery of cells and drugs to the production of scaffolds for tissue repair and bioinks for 3D printing. Biologics (cells and drugs) can be encapsulated into HMPs of predefined shapes and sizes using a variety of fabrication techniques (batch emulsion, microfluidics, lithography, electrohydrodynamic (EHD) spraying and mechanical fragmentation). HMPs can be formulated in suspensions to deliver therapeutics, as aggregates of particles (granular hydrogels) to form microporous scaffolds that promote cell infiltration or embedded within a bulk hydrogel to obtain multiscale behaviours. HMP suspensions and granular hydrogels can be injected for minimally invasive delivery of biologics, and they exhibit modular properties when comprised of mixtures of distinct HMP populations. In this Review, we discuss the fabrication techniques that are available for fabricating HMPs, as well as the multiscale behaviours of HMP systems and their functional properties, highlighting their advantages over traditional bulk hydrogels. Furthermore, we discuss applications of HMPs in the fields of cell delivery, drug delivery, scaffold design and biofabrication.

A novel cell encapsulatable cryogel (CECG) with macro-porous structures and high permeability: a three-dimensional cell culture scaffold for enhanced cell adhesion and proliferation

Hydrogel scaffold is a popular cell delivery vehicle in tissue engineering and regenerative medicine due to its capability to encapsulate cells as well as its modifiable properties. However, the inherent submicron- or nano-sized polymer networks of conventional hydrogel will produce spatial constraints on cellular activities of encapsulated cells. In this study, we endeavor to develop an innovative cell encapsulatable cryogel (CECG) platform with interconnected macro-pores, by combining cell cryopreservation technique with cryogel preparation process. The hyaluronan (HA) CECG constructs are fabricated under the freezing conditions via UV photo-crosslinking of the HA methacrylate (HA-MA) that are dissolved in the 'freezing solvent', namely the phosphate buffered saline supplemented with dimethyl sulphoxide and fetal bovine serum. Two model cell types, chondrocytes and human mesenchymal stem cells (hMSCs), can be uniformly three-dimensionally encapsulated into HA CECG constructs with high cell viability, respectively. The macro-porous structures, generated from phase separation under freezing, endow HA CECG constructs with higher permeability and more living space for cell growth. The chondrocytes encapsulated in HA CECG possess enhanced proliferation and extracellular matrix secretion than those in conventional HA hydrogels. In addition, the HA-Gel CECG constructs, fabricated with HA-MA and gelatin methacrylate precursors, provide cell-adhesive interfaces to facilitate hMSCs attachment and proliferation. The results of this work may lay the foundation for us to explore the applications of the CECG-based scaffolds in the field of tissue engineering and regenerative medicine.

Recent advances in three-dimensional bioprinting of stem cells

In spite of being a new field, three-dimensional (3D) bioprinting has undergone rapid growth in the recent years. Bioprinting methods offer a unique opportunity for stem cell distribution, positioning, and differentiation at the microscale to make the differentiated architecture of any tissue while maintaining precision and control over the cellular microenvironment. Bioprinting introduces a wide array of approaches to modify stem cell fate. This review discusses these methodologies of 3D bioprinting stem cells. Fabricating a fully operational tissue or organ construct with a long life will be the most significant challenge of 3D bioprinting. Once this is achieved, a whole human organ can be fabricated for the defect place at the site of surgery.

ESC Working Group on Cellular Biology of the Heart: position paper for Cardiovascular Research: tissue engineering strategies combined with cell therapies for cardiac repair in ischaemic heart disease and heart failure

Morbidity and mortality from ischaemic heart disease (IHD) and heart failure (HF) remain significant in Europe and are increasing worldwide. Patients with IHD or HF might benefit from novel therapeutic strategies, such as cell-based therapies. We recently discussed the therapeutic potential of cell-based therapies and provided recommendations on how to improve the therapeutic translation of these novel strategies for effective cardiac regeneration and repair. Despite major advances in optimizing these strategies with respect to cell source and delivery method, the clinical outcome of cell-based therapy remains unsatisfactory. Major obstacles are the low engraftment and survival rate of transplanted cells in the harmful microenvironment of the host tissue, and the paucity or even lack of endogenous cells with repair capacity. Therefore, new ways of delivering cells and their derivatives are required in order to empower cell-based cardiac repair and regeneration in patients with IHD or HF. Strategies using tissue engineering (TE) combine cells with matrix materials to enhance cell retention or cell delivery in the transplanted area, and have recently received much attention for this purpose. Here, we summarize knowledge on novel approaches emerging from the TE scenario. In particular, we will discuss how combinations of cell/bio-materials (e.g. hydrogels, cell sheets, prefabricated matrices, microspheres, and injectable matrices) combinations might enhance cell retention or cell delivery in the transplantation areas, thereby increase the success rate of cell therapies for IHD and HF. We will not focus on the use of classical engineering approaches, employing fully synthetic materials, because of their unsatisfactory material properties which render them not clinically applicable. The overall aim of this Position Paper from the ESC Working Group Cellular Biology of the Heart is to provide recommendations on how to proceed in research with these novel TE strategies combined with cell-based therapies to boost cardiac repair in the clinical settings of IHD and HF.

Enhancement of human adipose-derived stem cell spheroid differentiation in an in situ enzyme-crosslinked gelatin hydrogel

Standardized human adipose-derived stem cell spheroids can be harvested abundantly and the differentiation capability of cell spheroids performed well in the enzyme-crosslinked gelatin hydrogel.