Biomaterial-Enhanced Cell and Drug Delivery: Lessons Learned in the Cardiac Field and Future Perspectives

Cross Talk Between Cells and the Current Bioceramics in Bone Regeneration: A Comprehensive Review

The conventional approach for addressing bone defects and stubborn non-unions typically involves the use of autogenous bone grafts. Nevertheless, obtaining these grafts can be challenging, and the procedure can lead to significant morbidity. Three primary treatment strategies for managing bone defects and non-unions prove resistant to conventional treatments: synthetic bone graft substitutes (BGS), a combination of BGS with bioactive molecules, and the use of BGS in conjunction with stem cells. In the realm of synthetic BGS, a multitude of biomaterials have emerged for creating scaffolds in bone tissue engineering (TE). These materials encompass biometals like titanium, iron, magnesium, and zinc, as well as bioceramics such as hydroxyapatite (HA) and tricalcium phosphate (TCP). Bone TE scaffolds serve as temporary implants, fostering tissue ingrowth and the regeneration of new bone. They are meticulously designed to enhance bone healing by optimizing geometric, mechanical, and biological properties. These scaffolds undergo continual remodeling facilitated by bone cells like osteoblasts and osteoclasts. Through various signaling pathways, stem cells and bone cells work together to regulate bone regeneration when a portion of bone is damaged or deformed. By targeting signaling pathways, bone TE can improve bone defects through effective therapies. This review provided insights into the interplay between cells and the current state of bioceramics in the context of bone regeneration.

Extracellular Matrix/Glycopeptide Hybrid Hydrogel as an Immunomodulatory Niche for Endogenous Cardiac Repair after Myocardial Infarction

The treatment of myocardial infarction (MI) remains a substantial challenge due to excessive inflammation, massive cell death, and restricted regenerative potential, leading to maladaptive healing process and eventually heart failure. Current strategies of regulating inflammation or improving cardiac tissue regeneration have limited success. Herein, a hybrid hydrogel coassembled by acellular cardiac extracellular matrix (ECM) and immunomodulatory glycopeptide is developed for endogenous tissue regeneration after MI. The hydrogel constructs a niche recapitulating the architecture of native ECM for attracting host cell homing, controlling macrophage differentiation via glycopeptide unit, and promoting endotheliocyte proliferation by enhancing the macrophage-endotheliocyte crosstalk, which coordinate the innate healing mechanism for cardiac tissue regeneration. In a rodent MI model, the hybrid hydrogel successfully orchestrates a proreparative response indicated by enhanced M2 macrophage polarization, increased angiogenesis, and improved cardiomyocyte survival, which alleviates infarct size, improves wall thicknesses, and enhances cardiac contractility. Furthermore, the safety and effectiveness of the hydrogel are demonstrated in a porcine MI model, wherein proteomics verifies the regulation of immune response, proangiogenesis, and accelerated healing process. Collectively, the injectable composite hydrogel serving as an immunomodulatory niche for promoting cell homing and proliferation, inflammation modulation, tissue remodeling, and function restoration provides an effective strategy for endogenous cardiac repair.

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

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

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

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

Tissue engineered drug delivery vehicles: Methods to monitor and regulate the release behavior

Tissue engineering is a rapidly evolving, multidisciplinary field that aims at generating or regenerating 3D functional tissues for in vitro disease modeling and drug screening applications or for in vivo therapies. A variety of advanced biological and engineering methods are increasingly being used to further enhance and customize the functionality of tissue engineered scaffolds. To this end, tunable drug delivery and release mechanisms are incorporated into tissue engineering modalities to promote different therapeutic processes, thus, addressing challenges faced in the clinical applications. In this review, we elaborate the mechanisms and recent developments in different drug delivery vehicles, including the quantum dots, nano/micro particles, and molecular agents. Different loading strategies to incorporate the therapeutic reagents into the scaffolding structures are explored. Further, we discuss the main mechanisms to tune and monitor/quantify the release kinetics of embedded drugs from engineered scaffolds. We also survey the current trend of drug delivery using stimuli driven biopolymer scaffolds to enable precise spatiotemporal control of the release behavior. Recent advancements, challenges facing current scaffold-based drug delivery approaches, and areas of future research are discussed.

Conductive nanocomposite hydrogel and mesenchymal stem cells for the treatment of myocardial infarction and non-invasive monitoring via PET/CT

Background

Injectable hydrogels have great promise in the treatment of myocardial infarction (MI); however, the lack of electromechanical coupling of the hydrogel to the host myocardial tissue and the inability to monitor the implantation may compromise a successful treatment. The introduction of conductive biomaterials and mesenchymal stem cells (MSCs) may solve the problem of electromechanical coupling and they have been used to treat MI. In this study, we developed an injectable conductive nanocomposite hydrogel (GNR@SN/Gel) fabricated by gold nanorods (GNRs), synthetic silicate nanoplatelets (SNs), and poly(lactide-co-glycolide)-b-poly (ethylene glycol)-b-poly(lactide-co-glycolide) (PLGA-PEG-PLGA). The hydrogel was used to encapsulate MSCs and ⁶⁸Ga³⁺ cations, and was then injected into the myocardium of MI rats to monitor the initial hydrogel placement and to study the therapeutic effect via ¹⁸F-FDG myocardial PET imaging.

Results

Our data showed that SNs can act as a sterically stabilized protective shield for GNRs, and that mixing SNs with GNRs yields uniformly dispersed and stabilized GNR dispersions (GNR@SN) that meet the requirements of conductive nanofillers. We successfully constructed a thermosensitive conductive nanocomposite hydrogel by crosslinking GNR@SN with PLGA₂₀₀₀-PEG₃₄₀₀-PLGA₂₀₀₀, where SNs support the proliferation of MSCs. The cation-exchange capability of SNs was used to adsorb ⁶⁸Ga³⁺ to locate the implanted hydrogel in myocardium via PET/CT. The combination of MSCs and the conductive hydrogel had a protective effect on both myocardial viability and cardiac function in MI rats compared with controls, as revealed by ¹⁸F-FDG myocardial PET imaging in early and late stages and ultrasound; this was further validated by histopathological investigations.

Conclusions

The combination of MSCs and the GNR@SN/Gel conductive nanocomposite hydrogel offers a promising strategy for MI treatment.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01432-7.

Biomaterials to enhance stem cell transplantation

The successful transplantation of stem cells has the potential to transform regenerative medicine approaches and open promising avenues to repair, replace, and regenerate diseased, damaged, or aged tissues. However, pre-/post-transplantation issues of poor cell survival, retention, cell fate regulation, and insufficient integration with host tissues constitute significant challenges. The success of stem cell transplantation depends upon the coordinated sequence of stem cell renewal, specific lineage differentiation, assembly, and maintenance of long-term function. Advances in biomaterials can improve pre-/post-transplantation outcomes by integrating biophysiochemical cues and emulating tissue microenvironments. This review highlights leading biomaterials-based approaches for enhancing stem cell transplantation.

Organ-on-a-Chip: Design and Simulation of Various Microfluidic Channel Geometries for the Influence of Fluid Dynamic Parameters

Shear stress, pressure, and flow rate are fluid dynamic parameters that can lead to changes in the morphology, proliferation, function, and survival of many cell types and have a determinant impact on tissue function and viability. Microfluidic devices are promising tools to investigate these parameters and fluid behaviour within different microchannel geometries. This study discusses and analyses different designed microfluidic channel geometries regarding the influence of fluid dynamic parameters on their microenvironment at specified fluidic parameters. The results demonstrate that in the circular microchamber, the velocity and shear stress profiles assume a parabolic shape with a maximum velocity occurring in the centre of the chamber and a minimum velocity at the walls. The longitudinal microchannel shows a uniform velocity and shear stress profile throughout the microchannel. Simulation studies for the two geometries with three parallel microchannels showed that in proximity to the micropillars, the velocity and shear stress profiles decreased. Moreover, the pressure is inversely proportional to the width and directly proportional to the flow rate within the microfluidic channels. The simulations showed that the velocity and wall shear stress indicated different values at different flow rates. It was also found that the width and height of the microfluidic channels could affect both velocity and shear stress profiles, contributing to the control of shear stress. The study has demonstrated strategies to predict and control the effects of these forces and the potential as an alternative to conventional cell culture as well as to recapitulate the cell- and organ-specific microenvironment.

Engineering microparticles based on solidified stem cell secretome with an augmented pro-angiogenic factor portfolio for therapeutic angiogenesis

Tissue (re)vascularization strategies face various challenges, as therapeutic cells do not survive long enough in situ, while the administration of pro-angiogenic factors is hampered by fast clearance and insufficient ability to emulate complex spatiotemporal signaling. Here, we propose to address these limitations by engineering a functional biomaterial capable of capturing and concentrating the pro-angiogenic activities of mesenchymal stem cells (MSCs).

In particular, dextran sulfate, a high molecular weight sulfated glucose polymer, supplemented to MSC cultures, interacts with MSC-derived extracellular matrix (ECM) components and facilitates their co-assembly and accumulation in the pericellular space. Upon decellularization, the resulting dextran sulfate-ECM hybrid material can be processed into MIcroparticles of SOlidified Secretome (MIPSOS). The insoluble format of MIPSOS protects protein components from degradation, while facilitating their sustained release. Proteomic analysis demonstrates that MIPSOS are highly enriched in pro-angiogenic factors, resulting in an enhanced pro-angiogenic bioactivity when compared to naïve MSC-derived ECM (cECM). Consequently, intravital microscopy of full-thickness skin wounds treated with MIPSOS demonstrates accelerated revascularization and healing, far superior to the therapeutic potential of cECM. Hence, the microparticle-based solidified stem cell secretome provides a promising platform to address major limitations of current therapeutic angiogenesis approaches.

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Dextran sulfate assembles with mesenchymal stem cell secretome.

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As a result, microparticles of solidified stem cell secretome (MIPSOS) are formed.

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The insoluble MIPSOS format protects proteins from premature degradation.

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MIPSOS are enriched in pro-angiogenic factors and exhibit gradual release kinetics.

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MIPSOS demonstrate superior pro-angiogenic properties and thus therapeutic potential.

Chitosan as Functional Biomaterial for Designing Delivery Systems in Cardiac Therapies

Cardiovascular diseases are a leading cause of mortality across the globe, and transplant surgeries are not always successful since it is not always possible to replace most of the damaged heart tissues, for example in myocardial infarction. Chitosan, a natural polysaccharide, is an important biomaterial for many biomedical and pharmaceutical industries. Based on the origin, degree of deacetylation, structure, and biological functions, chitosan has emerged for vital tissue engineering applications. Recent studies reported that chitosan coupled with innovative technologies helped to load or deliver drugs or stem cells to repair the damaged heart tissue not just in a myocardial infarction but even in other cardiac therapies. Herein, we outlined the latest advances in cardiac tissue engineering mediated by chitosan overcoming the barriers in cardiac diseases. We reviewed in vitro and in vivo data reported dealing with drug delivery systems, scaffolds, or carriers fabricated using chitosan for stem cell therapy essential in cardiac tissue engineering. This comprehensive review also summarizes the properties of chitosan as a biomaterial substrate having sufficient mechanical stability that can stimulate the native collagen fibril structure for differentiating pluripotent stem cells and mesenchymal stem cells into cardiomyocytes for cardiac tissue engineering.

Research fronts of Chemical Biology

Over the past decades, researchers have witnessed substantially increasing and ever-growing interests and efforts in Chemical Biology studies, thanks to the development of genome and epi-genome sequencing (revealing potential drug targets), synthetic chemistry (producing new medicines), bioorthogonal chemistry (chemistry in living systems) and high-throughput screening technologies (in vitro cell systems, protein binding assays and phenotypic assays). This report presents literature search results for current research in Chemical Biology, to explore basic principles, summarize recent advances, identify key challenges, and provide suggestions for future research (with a focus on Chemical Biology in the context of human health and diseases). Chemical Biology research can positively contribute to delivering a better understanding of the molecular and cellular mechanisms that accompany pathology underlying diseases, as well as developing improved methods for diagnosis, drug discovery, and therapeutic delivery. While much progress has been made, as shown in this report, there are still further needs and opportunities. For instance, pressing challenges still exist in selecting appropriate targets in biological systems and adopting more rational design strategies for the development of innovative and sustainable diagnostic technologies and medical treatments. Therefore, more than ever, researchers from different disciplines need to collaborate to address the challenges in Chemical Biology.

The role of anti-inflammatory drugs and nanoparticle-based drug delivery models in the management of ischemia-induced heart failure

Ongoing advancements in the treatment of acute myocardial infarction (MI) have significantly decreased MI related mortality. Consequently, the number of patients experiencing post-MI heart failure (HF) has continued to rise. Infarction size and the extent of left ventricular (LV) remodeling are largely determined by the extent of ischemia at the time of myocardial injury. In the setting of MI or acute phase of post-MI LV remodeling, anti-inflammatory drugs including intravenous immunoglobulin (IVIG) and Pentoxifylline have shown potential efficacy in preventing post-MI remodeling in-vitro and in some clinical trials. However, systemic administration of anti-inflammatory drugs are not without their off-target side effects. Herein, we explore the clinical feasibility of targeted myocardial delivery of anti-inflammatory drugs via biodegradable polymers, liposomes, hydrogels, and nano-particle based drug delivery models (NDDM) based on existing pre-clinical and clinical models. We summarize the barriers to clinical application of targeted anti-inflammatory delivery post-MI, including challenges in achieving sufficient retention and distribution, as well as the potential need for multiple dosing. Collectively, we suggest that localized delivery of anti-inflammatory agents to the myocardium using NDDM is a promising approach for successful treatment of ischemic HF. Future studies will be instrumental in determining the most effective target and delivery modalities for orchestrating NDDM-mediated treatment of HF.

3D bioprinting in cardiac tissue engineering

Heart disease is the main cause of death worldwide. Because death of the myocardium is irreversible, it remains a significant clinical challenge to rescue myocardial deficiency. Cardiac tissue engineering (CTE) is a promising strategy for repairing heart defects and offers platforms for studying cardiac tissue. Numerous achievements have been made in CTE in the past decades based on various advanced engineering approaches. 3D bioprinting has attracted much attention due to its ability to integrate multiple cells within printed scaffolds with complex 3D structures, and many advancements in bioprinted CTE have been reported recently. Herein, we review the recent progress in 3D bioprinting for CTE. After a brief overview of CTE with conventional methods, the current 3D printing strategies are discussed. Bioink formulations based on various biomaterials are introduced, and strategies utilizing composite bioinks are further discussed. Moreover, several applications including heart patches, tissue-engineered cardiac muscle, and other bionic structures created via 3D bioprinting are summarized. Finally, we discuss several crucial challenges and present our perspective on 3D bioprinting techniques in the field of CTE.

A Stretchable Scaffold with Electrochemical Sensing for 3D Culture, Mechanical Loading, and Real-Time Monitoring of Cells

In the field of three-dimensional (3D) cell culture and tissue engineering, great advance focusing on functionalized materials and desirable culture systems has been made to mimic the natural environment of cells in vivo. Mechanical loading is one of the critical factors that affect cell/tissue behaviors and metabolic activities, but the reported models or detection methods offer little direct and real-time information about mechanically induced cell responses. Herein, for the first time, a stretchable and multifunctional platform integrating 3D cell culture, mechanical loading, and electrochemical sensing is developed by immobilization of biomimetic peptide linked gold nanotubes on porous and elastic polydimethylsiloxane. The 3D scaffold demonstrates very good compatibility, excellent stretchability, and stable electrochemical sensing performance. This allows mimicking the articular cartilage and investigating its mechanotransduction by 3D culture, mechanical stretching of chondrocytes, and synchronously real-time monitoring of stretch-induced signaling molecules. The results disclose a previously unclear mechanotransduction pathway in chondrocytes that mechanical loading can rapidly activate nitric oxide signaling within seconds. This indicates the promising potential of the stretchable 3D sensing in exploring the mechanotransduction in 3D cellular systems and engineered tissues.

Injection of hybrid 3D spheroids composed of podocytes, mesenchymal stem cells, and vascular endothelial cells into the renal cortex improves kidney function and replenishes glomerular podocytes

Podocytes are highly differentiated epithelial cells that are crucial for maintaining the glomerular filtration barrier in the kidney. Podocyte injury followed by depletion is the major cause of pathological progression of kidney diseases. Although cell therapy has been considered a promising alternative approach to kidney transplantation for the treatment of kidney injury, the resultant therapeutic efficacy in terms of improved renal function is limited, possibly owing to significant loss of engrafted cells. Herein, hybrid three-dimensional (3D) cell spheroids composed of podocytes, mesenchymal stem cells, and vascular endothelial cells were designed to mimic the glomerular microenvironment and as a cell delivery vehicle to replenish the podocyte population by cell transplantation. After creating a native glomerulus-like condition, the expression of multiple genes encoding growth factors and basement membrane factors that are strongly associated with podocyte maturation and functionality was significantly enhanced. Our in vivo results demonstrated that intrarenal transplantation of podocytes in the form of hybrid 3D cell spheroids improved engraftment efficiency and replenished glomerular podocytes. Moreover, the proteinuria of the experimental mice with hypertensive nephropathy was effectively reduced. These data clearly demonstrated the potential of hybrid 3D cell spheroids for repairing injured kidneys.

Towards the use of localised delivery strategies to counteract cancer therapy-induced cardiotoxicities

Cancer therapies have significantly improved cancer survival; however, these therapies can often result in undesired side effects to off target organs. Cardiac disease ranging from mild hypertension to heart failure can occur as a result of cancer therapies. This can warrant the discontinuation of cancer treatment in patients which can be detrimental, especially when the treatment is effective. There is an urgent need to mitigate cardiac disease that occurs as a result of cancer therapy. Delivery strategies such as the use of nanoparticles, hydrogels, and medical devices can be used to localise the treatment to the tumour and prevent off target side effects. This review summarises the advancements in localised delivery of anti-cancer therapies to tumours. It also examines the localised delivery of cardioprotectants to the heart for patients with systemic disease such as leukaemia where localised tumour delivery might not be an option.

3D Spheroids of Umbilical Cord Blood MSC-Derived Schwann Cells Promote Peripheral Nerve Regeneration

Schwann cells (SCs) are promising candidates for cell therapy due to their ability to promote peripheral nerve regeneration. However, SC-based therapies are hindered by the lack of a clinically renewable source of SCs. In this study, using a well-defined non-genetic approach, umbilical cord blood mesenchymal stem cells (cbMSCs), a clinically applicable cell type, were phenotypically, epigenetically, and functionally converted into SC-like cells (SCLCs) that stimulated effective sprouting of neuritic processes from neuronal cells. To further enhance their therapeutic capability, the cbMSC-derived SCLCs were assembled into three-dimensional (3D) cell spheroids by using a methylcellulose hydrogel system. The cell-cell and cell-extracellular matrix interactions were well-preserved within the formed 3D SCLC spheroids, and marked increases in neurotrophic, proangiogenic and anti-apoptotic factors were detected compared with cells that were harvested using conventional trypsin-based methods, demonstrating the superior advantage of SCLCs assembled into 3D spheroids. Transplantation of 3D SCLC spheroids into crush-injured rat sciatic nerves effectively promoted the recovery of motor function and enhanced nerve structure regeneration. In summary, by simply assembling cells into a 3D-spheroid conformation, the therapeutic potential of SCLCs derived from clinically available cbMSCs for promoting nerve regeneration was enhanced significantly. Thus, these cells hold great potential for translation to clinical applications for treating peripheral nerve injury.

A Reactive Oxygen Species Scavenging and O2 Generating Injectable Hydrogel for Myocardial Infarction Treatment In vivo

The excessive reactive oxygen species (ROS) and hypoxia deteriorate the inflammation-related diseases such as myocardial infarction (MI), and thereby deter the normal tissue repair and recovery and further lead to severe fibrosis and malfunction of tissues and organs. In particular, the MI has become one of the leading causes of death nowadays. In this study, a novel type of injectable hydrogel with dual functions of ROS scavenging and O₂ generating is fabricated for MI treatment in vivo. The hydrogel is formed within 3 s from the synthetic ROS-cleavable hyperbranched polymers and methacrylate hyaluronic acid (HA-MA) under UV-irradiation. Addition of biocompatible and applicable catalase in vivo enables the further transition of H₂ O₂ , a major type of ROS, to O₂ and H₂ O. Results of rat MI model demonstrate that this hydrogel can significantly remove excessive ROS, inhibit cell apoptosis, increase M2/M1 macrophage ratio, promote angiogenesis, reduce infarcted area, and improve cardiac functions. With the appropriate degradation rate, simple structure and composition without cell seeding, and very excellent MI therapeutic effect, this ROS scavenging and O₂ generating hydrogel has a great promise to be applied clinically.

Clinical Translation of Pluripotent Stem Cell Therapies: Challenges and Considerations

Although the clinical outcomes of cell therapy trials have not met initial expectations, emerging evidence suggests that injury-mediated tissue damage might benefit from the delivery of cells or their secreted products. Pluripotent stem cells (PSCs) are promising cell sources primarily because of their capacity to generate stage- and lineage-specific differentiated derivatives. However, they carry inherent challenges for safe and efficacious clinical translation. This Review describes completed or ongoing trials of PSCs, discusses their potential mechanisms of action, and considers how to address the challenges required for them to become a major therapy, using heart repair as a case study.

Biodegradable MRI Visible Drug Eluting Stent Reinforced by Metal Organic Frameworks

Metal-organic frameworks (MOFs) have applications in numerous fields. However, the development of MOF-based "theranostic" macroscale devices is not achieved. Here, heparin-coated biocompatible MOF/poly(ε-caprolactone) (PCL) "theranostic" stents are developed, where NH₂ -Materials of Institute Lavoisier (MIL)-101(Fe) encapsulates and releases rapamycin (an immunosuppressive drug). These stents also act as a remarkable source of contrast in ex vivo magnetic resonance imaging (MRI) compared to the invisible polymeric stent. The in vitro release patterns of heparin and rapamycin respectively can ensure a type of programmed model to prevent blood coagulation immediately after stent placement in the artery and stenosis over a longer term. Due to the presence of hydrolysable functionalities in MOFs, the stents are shown to be highly biodegradable in degradation tests under various conditions. Furthermore, there is no compromise of mechanical strength or flexibility with MOF compositing. The system described here promises many biomedical applications in macroscale theranostic devices. The use of MOF@PCL can render a medical device MRI-visible while simultaneously acting as a carrier for therapeutic agents.

Radio-metal cross-linking of alginate hydrogels for non-invasive in vivo imaging

Alginate hydrogels are cross-linked polymers with high water content, tuneable chemical and material properties, and a range of biomedical applications including drug delivery, tissue engineering, and cell therapy. However, their similarity to soft tissue often renders them undetectable within the body using conventional bio-medical imaging techniques. This leaves much unknown about their behaviour in vivo, posing a challenge to therapy development and validation. To address this, we report a novel, fast, and simple method of incorporating the nuclear imaging radio-metal 111In into the structure of alginate hydrogels by utilising its previously-undescribed capacity as an ionic cross-linking agent. This enabled non-invasive in vivo nuclear imaging of hydrogel delivery and retention across the whole body, over time, and across a range of model therapies including: nasal and oral drug delivery, stem cell transplantation, and cardiac tissue engineering. This information will facilitate the development of novel therapeutic hydrogel formulations, encompassing alginate, across disease categories.

Implantable Therapeutic Reservoir Systems for Diverse Clinical Applications in Large Animal Models

Regenerative medicine approaches, specifically stem cell technologies, have demonstrated significant potential to treat a diverse array of pathologies. However, such approaches have resulted in a modest clinical benefit, which may be attributed to poor cell retention/survival at the disease site. A delivery system that facilitates regional and repeated delivery to target tissues can provide enhanced clinical efficacy of cell therapies when localized delivery of high doses of cells is required. In this study, a new regenerative reservoir platform (Regenervoir) is described for use in large animal models, with relevance to cardiac, abdominal, and soft tissue pathologies. Regenervoir incorporates multiple novel design features essential for clinical translation, with a focus on scalability, mechanism of delivery, fixation to target tissue, and filling/refilling with a therapeutic cargo, and is demonstrated in an array of clinical applications that are easily translated to human studies. Regenervoir consists of a porous reservoir fabricated from a single material, a flexible thermoplastic polymer, capable of delivering cargo via fill lines to target tissues. A radiopaque shear thinning hydrogel can be delivered to the therapy reservoir and multiple fixation methods (laparoscopic tacks and cyanoacrylate bioadhesive) can be used to secure Regenervoir to target tissues through a minimally invasive approach.

Pre-culture of mesenchymal stem cells within RGD-modified hyaluronic acid hydrogel improves their resilience to ischaemic conditions

The incorporation of the RGD peptide (arginine-glycine-aspartate) into biomaterials has been proposed to promote cell adhesion to the matrix, which can influence and control cell behaviour and function. While many studies have utilised RGD modified biomaterials for cell delivery, few have examined its effect under the condition of reduced oxygen and nutrients, as found at ischaemic injury sites. Here, we systematically examine the effect of RGD on hMSCs in hyaluronic acid (HA) hydrogel under standard and ischaemic culture conditions, to elucidate under what conditions RGD has beneficial effects over unmodified HA and its effectiveness in improving cell viability. Results demonstrate that under standard culture conditions, RGD significantly increased hMSC spreading and the release of vascular endothelial factor-1 (VEGF) and monocyte chemoattractant factor-1 (MCP-1), compared to unmodified HA hydrogel. As adhesion is known to influence cell survival, we hypothesised that cells in RGD hydrogels would exhibit increased cell viability under ischaemic culture conditions. However, results demonstrate that cell viability and protein release was comparable in both RGD modified and unmodified HA hydrogels. Confocal imaging revealed cellular morphology indicative of weak cell adhesion. Subsequent investigations found that RGD was could exert positive effects on encapsulated cells under ischaemic conditions but only if hMSCs were pre-cultured under standard conditions to allow strong adhesion to RGD before exposure. Together, these results provide novel insight into the value of RGD introduction and suggest that the adhesion of hMSCs to RGD prior to delivery could improve survival and function at ischaemic injury sites. STATEMENT OF SIGNIFICANCE: The development of a biomaterial scaffold capable of maintaining cell viability while promoting cell function is a major research goal in the field of cardiac tissue engineering. This study confirms the suitability of a modified HA hydrogel whereby stem cells in the modified hydrogel showed significantly greater cell spreading and protein secretion compared to cells in the unmodified HA hydrogel. A pre-culture period allowing strong adhesion of the cells to the modified hydrogel was shown to improve cell survival under conditions that mimic the myocardium post-MI. This finding may have a significant impact on the use and timelines of modifications to improve stem cell survival in harsh environments like the injured heart.

Cardiac cell therapy: Current status, challenges and perspectives

Although the initial clinical trials of cardiac cell therapy have failed to demonstrate unequivocal clinical benefits, the accumulation of preclinical data gathered in parallel can now help us to understand the main causes of failures, while providing mechanistic insights that may be leveraged to improve the outcomes of subsequent clinical studies using cells or their secreted products. This review briefly describes the current status of clinical trials, discusses the potential mechanisms of action of the grafted cells, and the impact of this knowledge on the design of future studies, and finally draws some perspectives.

Inducing Endogenous Cardiac Regeneration: Can Biomaterials Connect the Dots?

Heart failure (HF) after myocardial infarction (MI) due to blockage of coronary arteries is a major public health issue. MI results in massive loss of cardiac muscle due to ischemia. Unfortunately, the adult mammalian myocardium presents a low regenerative potential, leading to two main responses to injury: fibrotic scar formation and hypertrophic remodeling. To date, complete heart transplantation remains the only clinical option to restore heart function. In the last two decades, tissue engineering has emerged as a promising approach to promote cardiac regeneration. Tissue engineering aims to target processes associated with MI, including cardiomyogenesis, modulation of extracellular matrix (ECM) remodeling, and fibrosis. Tissue engineering dogmas suggest the utilization and combination of two key components: bioactive molecules and biomaterials. This chapter will present current therapeutic applications of biomaterials in cardiac regeneration and the challenges still faced ahead. The following biomaterial-based approaches will be discussed: Nano-carriers for cardiac regeneration-inducing biomolecules; corresponding matrices for their controlled release; injectable hydrogels for cell delivery and cardiac patches. The concept of combining cardiac patches with controlled release matrices will be introduced, presenting a promising strategy to promote endogenous cardiac regeneration.

Heparan sulfate proteoglycan promotes fibroblast growth factor-2 function for ischemic heart repair

It is well known that the basic fibroblast growth factor (bFGF) promotes angiogenesis after myocardial infarction (MI), but its biological functions decrease in the event of diffusion, enzymolysis, and weak binding with co-receptors in vivo. Heparan sulfate proteoglycans (HSPG) are a major component of extracellular matrices and have been shown to regulate a wide range of cellular functions and bioprocesses by acting as a co-receptor for bFGF and affecting its bioactivities. However, the influence of HSPG on the function of bFGF after myocardial infarction is unknown. Here, exogenous HSPG along with bFGF was injected into the hearts of rats to deliver the angiogenic growth factor for ischemic heart repair following induced MI. The specific binding of HSPG with bFGF protein was demonstrated, which was about 6-fold stronger than the binding of bFGF with heparin. The biological mechanisms of HSPG binding with bFGF were further studied by cell adhesion assay, and assays of bFGF and matrix metalloproteinase 2 (MMP2) activities demonstrated that HSPG enhances cell adhesion, promotes the bioactivity of bFGF in angiogenesis, and protects bFGF from enzymolysis. Our results indicate that HSPG has potential clinical utility as a delivery agent for heparin-binding growth factors. Additionally, HSPG shows high binding affinities with different ECM proteins which also help to anchor bFGF to heart tissue. Therefore, extracellular proteins that mimic the bio-scaffold of the extracellular matrix could promote the activities of bFGF to facilitate ischemic heart repair.

[Pluripotent stem cells for the treatment of heart failure: current status, persisting issues and perspectives]

Although the first wave of cell therapy trials has not commonly yielded clinically meaningful improvements, some encouraging hints have emerged which suggest that stem cells or their secreted products could ultimately find a place within the armamentarium of therapies that can be offered to patients with heart failure. In this setting, pluripotent stem cells raise a particular interest because of their unique ability to generate lineage-specific cells which can be transplanted at the desired stage of differentiation. This review discusses the current status of research in this field, the persisting roadblocks that need to be overcome and the approaches which might hasten the clinical applications of this cell type.

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

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

Cell therapy trials for heart regeneration - lessons learned and future directions

The effects of cell therapy on heart regeneration in patients with chronic cardiomyopathy have been assessed in several clinical trials. These trials can be categorized as those using noncardiac stem cells, including mesenchymal stem cells, and those using cardiac-committed cells, including KIT⁺ cardiac stem cells, cardiosphere-derived cells, and cardiovascular progenitor cells derived from embryonic stem cells. Although the safety of cell therapies has been consistently reported, their efficacy remains more elusive. Nevertheless, several lessons have been learned that provide useful clues for future studies. This Review summarizes the main outcomes of these studies and draws some perspectives for future cell-based regenerative trials, which are largely based on the primary therapeutic target: remuscularization of chronic myocardial scars by exogenous cells or predominant use of these cells to activate host-associated repair pathways though paracrine signalling. In the first case, the study design should entail delivery of large numbers of cardiac-committed cells, supply of supportive noncardiac cells, and promotion of cell survival and appropriate coupling with endogenous cardiomyocytes. If the primary objective is to harness endogenous repair pathways, then the flexibility of cell type is greater. As the premise is that the transplanted cells need to engraft only transiently, the priority is to optimize their early retention and possibly to switch towards the sole administration of their secretome.

A comparison of two quasi-static computational models for assessment of intra-myocardial injection as a therapeutic strategy for heart failure

Myocardial infarction, or heart attack, is the leading cause of mortality globally. Although the treatment of myocardial infarct has improved significantly, scar tissue that persists can often lead to increased stress and adverse remodeling of surrounding tissue and ultimately to heart failure. Intra-myocardial injection of biomaterials represents a potential treatment to attenuate remodeling, mitigate degeneration, and reverse the disease process in the tissue. In vivo experiments on animal models have shown functional benefits of this therapeutic strategy. However, a poor understanding of the optimal injection pattern, volume, and material properties has acted as a barrier to its widespread clinical adoption. In this study, we developed two quasistatic finite element simulations of the left ventricle to investigate the mechanical effect of intra-myocardial injection. The first model employed an idealized left ventricular geometry with rule-based cardiomyocyte orientation. The second model employed a subject-specific left ventricular geometry with cardiomyocyte orientation from diffusion tensor magnetic resonance imaging. Both models predicted cardiac parameters including ejection fraction, systolic wall thickening, and ventricular twist that matched experimentally reported values. All injection simulations showed cardiomyocyte stress attenuation, offering an explanation for the mechanical reinforcement benefit associated with injection. The study also enabled a comparison of injection location and the corresponding effect on cardiac performance at different stages of the cardiac cycle. While the idealized model has lower fidelity, it predicts cardiac function and differentiates the effects of injection location. Both models represent versatile in silico tools to guide optimal strategy in terms of injection number, volume, site, and material properties.

Chemical Engineering of Cell Therapy for Heart Diseases

Cardiovascular disease (CVD) is a major health problem worldwide. Since adult cardiomyocytes irreversibly withdraw from the cell cycle soon after birth, it is hard for cardiac cells to proliferate and regenerate after myocardial injury, such as that caused myocardial infarction (MI). Live cell-based therapies, which we term as first generation of therapeutic strategies, have been widely used for the treatment of many diseases, including CVD. However, cellular approaches have the problems of poor retention of the transplanted cells and the significant entrapment of the cells in the lungs when delivered intravenously. Another big problem is the low storage/shipping stability of live cells, which limits the manufacturability of living cell products. The field of chemical engineering focuses on designing large-scale processes to convert chemicals, raw materials, living cells, microorganisms, and energy into useful forms and products. By definition, chemical engineers conceive and design processes to produce, transform, and transport materials. This matches the direction that cell therapies are heading toward: "produce", from live cells to synthetic artificial cells; "transform", from bare cells to cell/matrix/factor combinations; and "transport". from simple systemic injections to targeted delivery. Thus, we hereby introduce the "chemical engineering of cell therapies" as a concept. In this Account, we summarize our recent efforts to develop chemical engineering approaches to repair injured hearts. To address the limitations of poor cellular retention and integration, the first step was the artificial manipulation of stem cells before injections (we term this the second generation of therapeutic strategies). For example, we took advantage of the natural infarct-targeting ability of platelet membranes by fusing them onto the surface of cardiac stromal/stem cells (CSCs). By doing so, we improved the rate at which they were delivered through the vasculature to sites of MI. In addition to modifying natural CSCs, we described a bioengineering approach that involved the encapsulation of CSCs in a polymeric microneedle patch for myocardium regeneration. The painless microneedle patches were used as an in situ delivery device, which directly transported the loaded CSCs to the MI heart. In addition to low cell retention, there are some other barriers that need to be addressed before further clinical application is viable, including the storage/shipping stability of and the evident safety concerns about live cells. Therefore, we developed the third generation of therapeutic strategies, which utilize cell-free approaches for cardiac cell therapies. Numerous studies have indicated that paracrine mechanisms reasonably explain stem cell based heart repair. By imitating or adapting natural stem cells, as well as their secretions, and using them in conjunction with biocompatible materials, we can simulate the function of natural stem cells while avoiding the complications association with the first and second generation therapeutic options. Additionally, we can develop approaches to capture endogenous stem cells and directly transport them to the infarct site. Using these third generation therapeutic strategies, we can provide unprecedented opportunities for cardiac cell therapies. We hope that our designs will promote the use of chemical engineering approaches to transform, transport, and fabricate cell-free systems as novel cardiac cell therapeutic agents for clinical applications.

Current research trends and challenges in tissue engineering for mending broken hearts

Cardiovascular disease (CVD) is among the leading causes of mortality worldwide. The shortage of donor hearts to treat end-stage heart failure patients is a critical problem. An average of 3500 heart transplant surgeries are performed globally, half of these transplants are performed in the US alone. Stem cell therapy is growing rapidly as an alternative strategy to repair or replace the damaged heart tissue after a myocardial infarction (MI). Nevertheless, the relatively poor survival of the stem cells in the ischemic heart is a major challenge to the therapeutic efficacy of stem-cell transplantation. Recent advancements in tissue engineering offer novel biomaterials and innovative technologies to improve upon the survival of stem cells as well as to repair the damaged heart tissue following a myocardial infarction (MI). However, there are several limitations in tissue engineering technologies to develop a fully functional, beating cardiac tissue. Therefore, the main goal of this review article is to address the current advancements and barriers in cardiac tissue engineering to augment the survival and retention of stem cells in the ischemic heart.

3D printing approaches for cardiac tissue engineering and role of immune modulation in tissue regeneration

Conventional tissue engineering, cell therapy, and current medical approaches were shown to be successful in reducing mortality rate and complications caused by cardiovascular diseases (CVDs). But still they have many limitations to fully manage CVDs due to complex composition of native myocardium and microvascularization. Fabrication of fully functional construct to replace infarcted area or regeneration of progenitor cells is important to address CVDs burden. Three-dimensional (3D) printed scaffolds and 3D bioprinting technique have potential to develop fully functional heart construct that can integrate with native tissues rapidly. In this review, we presented an overview of 3D printed approaches for cardiac tissue engineering, and advances in 3D bioprinting of cardiac construct and models. We also discussed role of immune modulation to promote tissue regeneration.

Advanced Material Catheter (AMCath), a minimally invasive endocardial catheter for the delivery of fast-gelling covalently cross-linked hyaluronic acid hydrogels

Injectable hydrogels that aim to mechanically stabilise the weakened left ventricle wall to restore cardiac function or to deliver stem cells in cardiac regenerative therapy have shown promising data. However, the clinical translation of hydrogel-based therapies has been limited due to difficulties injecting them through catheters. We have engineered a novel catheter, Advanced Materials Catheter (AMCath), that overcomes translational hurdles associated with delivering fast-gelling covalently cross-linked hyaluronic acid hydrogels to the myocardium. We developed an experimental technique to measure the force required to inject such hydrogels and determined the mechanical/viscoelastic properties of the resulting hydrogels. The preliminary in vivo feasibility of delivering fast-gelling hydrogels through AMCath was demonstrated by accessing the porcine left ventricle and showing that the hydrogel was retained in the myocardium post-injection (three 200 μL injections delivered, 192, 204 and 183 μL measured). However, the mechanical properties of the hydrogels were reduced by passage through AMCath (≤20.62% reduction). We have also shown AMCath can be used to deliver cardiopoietic adipose-derived stem cell-loaded hydrogels without compromising the viability (80% viability) of the cells in vitro. Therefore, we show that hydrogel/catheter compatibility issues can be overcome as we have demonstrated the minimally invasive delivery of a fast-gelling covalently cross-linked hydrogel to the beating myocardium.

The protective effects of acupoint gel embedding on rats with myocardial ischemia-reperfusion injury

AIMS

Prevention and treatment of myocardial ischemia-reperfusion (I/R) injury has for many years been a hot topic in treating ischemic heart disease. As one of the most well-known methods of complementary and alternative medicine, acupuncture has attracted increasing interest in preventing myocardial I/R injury due to its remarkable effectiveness and minimal side effect. However, traditional acupuncture approaches are limited by cumbersome execution, high labor costs and inevitable pain caused by frequent stimulation. Therefore, in this work, we aimed to develop a novel acupoint gel embedding approach and investigated its role in protecting against myocardial I/R injury in rats.

MAIN METHODS

Gels were embedded at bilateral Neiguan (PC6) points of rats and their protective effects against myocardial I/R injury evaluated in terms of changes in histomorphology, myocardial enzymology, antioxidant capacity, anti-inflammatory response, and anti-apoptosis of cells.

KEY FINDINGS

We found that the approach of acupoint gel embedding could significantly reduce myocardial infarcted size, repair pathological changes, mitigate oxidative stress damage and inflammatory response, as well as inhibit apoptosis of cardiomyocytes. Such cardioprotective effects were found to be associated with Notch-1/Jagged-1 signaling pathway.

SIGNIFICANCE

The proposed approach of acupoint gel embedding has advantages in continuous acupoint stimulation, dosing controls, and no side effects in the course of treatment, as well as in reducing the pain caused by frequent acupuncture. It can form an alternative therapy to not only protect against myocardial I/R injury but also hold great potential in treating other diseases in the future.

A biodegradable hybrid inorganic nanoscaffold for advanced stem cell therapy

Stem cell transplantation, as a promising treatment for central nervous system (CNS) diseases, has been hampered by crucial issues such as a low cell survival rate, incomplete differentiation, and limited neurite outgrowth in vivo. Addressing these hurdles, scientists have designed bioscaffolds that mimic the natural tissue microenvironment to deliver physical and soluble cues. However, several significant obstacles including burst release of drugs, insufficient cellular adhesion support, and slow scaffold degradation rate remain to be overcome before the full potential of bioscaffold-based stem-cell therapies can be realized. To this end, we developed a biodegradable nanoscaffold-based method for enhanced stem cell transplantation, differentiation, and drug delivery. These findings collectively support the therapeutic potential of our biodegradable hybrid inorganic (BHI) nanoscaffolds for advanced stem cell transplantation and neural tissue engineering.

Folic Acid Derived Hydrogel Enhances the Survival and Promotes Therapeutic Efficacy of iPS Cells for Acute Myocardial Infarction

Stem cell therapy has obtained extensive consensus to be an effective method for post myocardial infarction (MI) intervention. Induced pluripotent stem (iPS) cells, which are able to differentiate into multiple cell types, have the potential to generate cardiovascular lineage cells for myocardial repair after ischemic damage, but their poor retention rate significantly hinders the therapeutic efficacy. In the present study, we developed a supramolecular hydrogel which is formed by the self-assembly of folic acid (FA)-modified peptide via a biocompatible method (glutathione reduction) and suitable for cell encapsulation and transplantation. The iPS cells labeled with CM-Dil were transplanted into the MI hearts of mice with or without FA hydrogel encapsulation. The results corroborated that the FA hydrogel significantly improved the retention and survival of iPS cells in MI hearts post injection, leading to augmentation of the therapeutic efficacy of iPS cells including better cardiac function and much less adverse heart remodeling, by subsequent differentiation toward cardiac cells and stimulation of neovascularization. This study reported a novel supramolecular hydrogel based on FA-peptides capable of improving the therapeutic capacity of iPS cells, which held big potential in the treatment of MI.

Electroactive polymers for tissue regeneration: Developments and perspectives

Human body motion can generate a biological electric field and a current, creating a voltage gradient of -10 to -90 mV across cell membranes. In turn, this gradient triggers cells to transmit signals that alter cell proliferation and differentiation. Several cell types, counting osteoblasts, neurons and cardiomyocytes, are relatively sensitive to electrical signal stimulation. Employment of electrical signals in modulating cell proliferation and differentiation inspires us to use the electroactive polymers to achieve electrical stimulation for repairing impaired tissues. Electroactive polymers have found numerous applications in biomedicine due to their capability in effectively delivering electrical signals to the seeded cells, such as biosensing, tissue regeneration, drug delivery, and biomedical implants. Here we will summarize the electrical characteristics of electroactive polymers, which enables them to electrically influence cellular function and behavior, including conducting polymers, piezoelectric polymers, and polyelectrolyte gels. We will also discuss the biological response to these electroactive polymers under electrical stimulation. In particular, we focus this review on their applications in regenerating different tissues, including bone, nerve, heart muscle, cartilage and skin. Additionally, we discuss the challenges in tissue regeneration applications of electroactive polymers. We conclude that electroactive polymers have a great potential as regenerative biomaterials, due to their ability to stimulate desirable outcomes in various electrically responsive cells.

Engineered modular biomaterial logic gates for environmentally triggered therapeutic delivery

The successful transport of drug- and cell-based therapeutics to diseased sites represents a major barrier in the development of clinical therapies. Targeted delivery can be mediated through degradable biomaterial vehicles that utilize disease biomarkers to trigger payload release. Here, we report a modular chemical framework for imparting hydrogels with precise degradative responsiveness by using multiple environmental cues to trigger reactions that operate user-programmable Boolean logic. By specifying the molecular architecture and connectivity of orthogonal stimuli-labile moieties within material cross-linkers, we show selective control over gel dissolution and therapeutic delivery. To illustrate the versatility of this methodology, we synthesized 17 distinct stimuli-responsive materials that collectively yielded all possible YES/OR/AND logic outputs from input combinations involving enzyme, reductant and light. Using these hydrogels we demonstrate the first sequential and environmentally stimulated release of multiple cell lines in well-defined combinations from a material. We expect these platforms will find utility in several diverse fields including drug delivery, diagnostics and regenerative medicine.

Agarose-based biomaterials for tissue engineering

Agarose is a natural polysaccharide polymer having unique characteristics that give reason to consider it for tissue engineering applications. Special characteristics of agarose such as its excellent biocompatibility, thermo-reversible gelation behavior and physiochemical features support its use as a biomaterial for cell growth and/or controlled/localized drug delivery. The resemblance of this natural carbohydrate polymer to the extracellular matrix results in attractive features that bring about a strong interest in its usage in the field. The scope of this review is to summarize the extensive researches addressing agarose-based biomaterials in order to provide an in-depth understanding of its tissue engineering-related applications.