An elastomeric patch derived from poly(glycerol sebacate) for delivery of embryonic stem cells to the heart

Bioactive Glass Fiber-Reinforced PGS Matrix Composites for Cartilage Regeneration

Poly(glycerol sebacate) (PGS) is an elastomeric polymer which is attracting increasing interest for biomedical applications, including cartilage regeneration. However, its limited mechanical properties and possible negative effects of its degradation byproducts restrict PGS for in vivo application. In this study, a novel PGS–bioactive glass fiber (F18)-reinforced composite was developed and characterized. PGS-based reinforced scaffolds were fabricated via salt leaching and characterized regarding their mechanical properties, degradation, and bioactivity in contact with simulated body fluid. Results indicated that the incorporation of silicate-based bioactive glass fibers could double the composite tensile strength, tailor the polymer degradability, and improve the scaffold bioactivity.

Norbornene-modified poly(glycerol sebacate) as a photocurable and biodegradable elastomer

Photocurable norbornene-functionalized poly(glycerol sebacate) (Nor-PGS) has been developed to fabricate cytocompatible, biodegradable and elastomeric scaffolds for tissue engineering applications.

Tailoring degree of esterification and branching of poly(glycerol sebacate) by energy efficient microwave irradiation

A branched poly(glycerol sebacate) prepolymer has been successfully synthesised via single mode microwave irradiation with an improved reaction rate and controllable properties.

Tissue Engineering Strategies for Myocardial Regeneration: Acellular Versus Cellular Scaffolds?

Heart disease remains one of the leading causes of death in industrialized nations with myocardial infarction (MI) contributing to at least one fifth of the reported deaths. The hypoxic environment eventually leads to cellular death and scar tissue formation. The scar tissue that forms is not mechanically functional and often leads to myocardial remodeling and eventual heart failure. Tissue engineering and regenerative medicine principles provide an alternative approach to restoring myocardial function by designing constructs that will restore the mechanical function of the heart. In this review, we will describe the cellular events that take place after an MI and describe current treatments. We will also describe how biomaterials, alone or in combination with a cellular component, have been used to engineer suitable myocardium replacement constructs and how new advanced culture systems will be required to achieve clinical success.

3D printing of photocurable poly(glycerol sebacate) elastomers

Three-dimensional (3D) printed scaffolds have great potential in biomedicine; however, it is important that we are able to design such scaffolds with a range of diverse properties towards specific applications. Here, we report the extrusion-based 3D printing of biodegradable and photocurable acrylated polyglycerol sebacate (Acr-PGS) to fabricate scaffolds with elastic properties. Two Acr-PGS macromers were synthesized with varied molecular weights and viscosity, which were then blended to obtain photocurable macromer inks with a range of viscosities. The quality of extruded and photocured scaffolds was dependent on the initial ink viscosity, with flow of printed material resulting in a loss of structural resolution or sample breaking observed with too low or too high viscosity inks, respectively. However, scaffolds with high print resolution and up to ten layers were fabricated with an optimal ink viscosity. The mechanical properties of printed scaffolds were dependent on printing density, where the scaffolds with lower printing density possessed lower moduli and failure properties than higher density scaffolds. The 3D printed scaffolds supported the culture of 3T3 fibroblasts and both spreading and proliferation were observed, indicating that 3D printed Acr-PGS scaffolds are cytocompatible. These results demonstrate that Acr-PGS is a promising material for the fabrication of elastomeric scaffolds for biomedical applications.

Elastomers in vascular tissue engineering

Elastomers are popular in vascular engineering applications, as they offer the ability to design implants that match the compliance of native tissue. By mimicking the natural tissue environment, elastic materials are able to integrate within the body to promote repair and avoid the adverse physiological responses seen in rigid alternatives that often disrupt tissue function. The design of elastomers has continued to evolve, moving from a focus on long term implants to temporary resorbable implants that support tissue regeneration. This has been achieved through designing chemistries and processing methodologies that control material behavior and bioactivity, while maintaining biocompatibility in vivo. Here we review the latest developments in synthetic and natural elastomers and their application in cardiovascular treatments.

Poly(Limonene Thioether) Scaffold for Tissue Engineering

A photocurable thiol-ene network polymer, poly(limonene thioether) (PLT32o), is synthesized, characterized, fabricated into tissue engineering scaffolds, and demonstrated in vitro and in vivo. Micromolded PLT32o grids exhibit compliant, elastomeric mechanical behavior similar to grids made of poly(glycerol sebacate) (PGS), an established biomaterial. Multilayered PL32o scaffolds with regular, geometrically defined pore architectures support heart cell seeding and culture in a manner similar to multilayered PGS scaffolds. Subcutaneous implantation of multilayered PLT32o scaffolds with cultured heart cells provides long-term 3D structural support and retains the exogenous cells, whereas PGS scaffolds lose both their structural integrity and the exogenous cells over 31 d in vivo. PLT32o membrane implants retain their dry mass, whereas PGS implants lose 70 percent of their dry mass by day 31. Macrophages are initially recruited to PLT32o and PGS membrane implants but are no longer present by day 31. Facile synthesis and processing in combination with the capability to support heart cells in vitro and in vivo suggest that PLT32o can offer advantages for tissue engineering applications where prolonged in vivo maintenance of 3D structural integrity and elastomeric mechanical behavior are required.

Biomaterials for pluripotent stem cell engineering: From fate determination to vascularization

Recent advancements in material science and engineering may hold the key to overcoming reproducibility and scalability limitations currently hindering the clinical translation of stem cell therapies. Biomaterial assisted differentiation commitment of stem cells and modulation of their in vivo function could have significant impact in stem cell-centred regenerative medicine approaches and next gen technological platforms. Synthetic biomaterials are of particular interest as they provide a consistent, chemically defined, and tunable way of mimicking the physical and chemical properties of the natural tissue or cell environment. Combining emerging biomaterial and biofabrication advancements may finally give researchers the tools to modulate spatiotemporal complexity and engineer more hierarchically complex, physiologically relevant tissue mimics. In this review we highlight recent research advancements in biomaterial assisted pluripotent stem cell (PSC) expansion and three dimensional (3D) tissue formation strategies. Furthermore, since vascularization is a major challenge affecting the in vivo function of engineered tissues, we discuss recent developments in vascularization strategies and assess their ability to produce perfusable and functional vasculature that can be integrated with the host tissue.

Synthesis of polyester urethane urea and fabrication of elastomeric nanofibrous scaffolds for myocardial regeneration

Fabrication of bioactive scaffolds is one of the most promising strategies to reconstruct the infarcted myocardium. In this study, we synthesized polyester urethane urea (PEUU), further blended it with gelatin and fabricated PEUU/G nanofibrous scaffolds. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC) and X-ray diffraction were used for the characterization of the synthesized PEUU and properties of nanofibrous scaffolds were evaluated using scanning electron microscopy (SEM), ATR-FTIR, contact angle measurement, biodegradation test, tensile strength analysis and dynamic mechanical analysis (DMA). In vitro biocompatibility studies were performed using cardiomyocytes. DMA analysis showed that the scaffolds could be reshaped with cyclic deformations and might remain stable in the frequencies of the physiological activity of the heart. On the whole, our study suggests that aligned PEUU/G 70:30 nanofibrous scaffolds meet the required specifications for cardiac tissue engineering and could be used as a promising construct for myocardial regeneration.

Polyol-based biodegradable polyesters: a short review

Catalyst-free thermal polyesterification has recently emerged as a potential strategy for designing biodegradable thermoset polymers, particularly polyol-based polyesters for biomedical applications. These thermoset polyesters are synthesized through polycondensation of polyol and polyacid without the presence of catalyst or solvents. The mechanical properties, degradation rates, crystallinity, hydrophilicity, and biocompatibility can be controlled by adjusting the monomer feed ratios and curing conditions. These polyesters often degrade via surface erosion that allows the polymers to maintain structural integrity throughout hydrolysis. Additionally, polyol-based polyesters demonstrated good biocompatibility as non-toxic catalysts and/or solvents involved in the reaction, and the monomers used are endogenous to human metabolism which can be resorbed and metabolized in various physiological pathways. This review summarizes the polyol-based biodegradable polyesters that were synthesized by catalyst-free polyesterification.

Lorentz contact resonance spectroscopy for nanoscale characterisation of structural and mechanical properties of biological, dental and pharmaceutical materials

Scanning probe microscopy has been widely used to obtain topographical information and to quantify nanostructural properties of different materials. Qualitative and quantitative imaging is of particular interest to study material-material interactions and map surface properties on a nanoscale (i.e. stiffness and viscoelastic properties). These data are essential for the development of new biomedical materials. Currently, there are limited options to map viscoelastic properties of materials at nanoscale and at high resolutions. Lorentz contact resonance (LCR) is an emerging technique, which allows mapping viscoelasticity of samples with stiffness ranging from a few hundred Pa up to several GPa. Here we demonstrate the applicability of LCR to probe and map the viscoelasticity and stiffness of 'soft' (biological sample: cell treated with nanodiamond), 'medium hard' (pharmaceutical sample: pMDI canister) and 'hard' (human teeth enamel) specimens. The results allowed the identification of nanodiamond on the cells and the qualitative assessment of its distribution based on its nanomechanical properties. It also enabled mapping of the mechanical properties of the cell to demonstrate variability of these characteristics in a single cell. Qualitative imaging of an enamel sample demonstrated variations of stiffness across the specimen and precise identification of enamel prisms (higher stiffness) and enamel interrods (lower stiffness). Similarly, mapping of the pMDI canister wall showed that drug particles were adsorbed to the wall. These particles showed differences in stiffness at nanoscale, which suggested variations in surface composition-multiphasic material. LCR technique emerges as a valuable tool for probing viscoelasticity of samples of varying stiffness's.

Porous nanofibrous poly(L-lactic acid) scaffolds supporting cardiovascular progenitor cells for cardiac tissue engineering

Myocardial infarction (MI) is the irreversible necrosis of heart with approximately 1.5 million cases every year in the United States. Tissue engineering offers a promising strategy for cardiac repair after MI. However, the optimal cell source for heart tissue regeneration and the ideal scaffolds to support cell survival, differentiation, and integration, remain to be developed. To address these issues, we developed the technology to induce cardiovascular progenitor cells (CPCs) derived from mouse embryonic stem cells (ESCs) towards desired cardiomyocytes as well as smooth muscle cells and endothelial cells. We fabricated extracellular matrix (ECM)-mimicking nanofibrous poly(l-lactic acid) (PLLA) scaffolds with porous structure of high interconnection for cardiac tissue formation. The CPCs were seeded into the scaffolds to engineer cardiac constructs in vitro. Fluorescence staining and RT-PCR assay showed that the scaffolds facilitated cell attachment, extension, and differentiation. Subcutaneous implantation of the cell/scaffold constructs in a nude mouse model showed that the scaffolds favorably supported survival of the grafted cells and their commitment to the three desired lineages in vivo. Thus, our study suggested that the porous nanofibrous PLLA scaffolds support cardiac tissue formation from CPCs. The integration of CPCs with the nanofibrous PLLA scaffolds represents a promising tissue engineering strategy for cardiac repair.

STATEMENT OF SIGNIFICANCE

Myocardial infarction is the irreversible necrosis of heart with approximately 1.5 million cases every year in the United States. Tissue engineering offers a promising strategy for cardiac repair after MI. However, the optimal cell source for heart tissue regeneration and the ideal scaffolds to support cell survival, differentiation, and integration, remain to be developed. To address these issues, we developed porous nanofibrous PLLA scaffolds that mimic natural extracellular matrix to support cardiac tissue formation from CPCs. The integration of CPCs with the nanofibrous PLLA scaffolds represents a promising tissue engineering strategy for cardiac repair.

Application and Progress of Combined Mesenchymal Stem Cell Transplantation in the Treatment of Ischemic Cardiomyopathy

Treatment of ischemic cardiomyopathy caused by myocardial infarction (MI) using mesenchymal stem cell (MSC) transplantation is a widely researched field, with promising clinical application. However, the low survival rate of transplanted cells has a severe impact on treatment outcome. Currently, research is focused on investigating the strategy of combining genetic engineering, tissue engineering materials, and drug/hypoxia preconditioning to improve ischemic cardiomyopathy treatment outcome using MSC transplantation treatment (MSCTT). This review discusses the application and progress of these techniques.

Biomaterial Approaches for Stem Cell-Based Myocardial Tissue Engineering

Adult and pluripotent stem cells represent a ready supply of cellular raw materials that can be used to generate the functionally mature cells needed to replace damaged or diseased heart tissue. However, the use of stem cells for cardiac regenerative therapies is limited by the low efficiency by which stem cells are differentiated in vitro to cardiac lineages as well as the inability to effectively deliver stem cells and their derivatives to regions of damaged myocardium. In this review, we discuss the various biomaterial-based approaches that are being implemented to direct stem cell fate both in vitro and in vivo. First, we discuss the stem cell types available for cardiac repair and the engineering of naturally and synthetically derived biomaterials to direct their in vitro differentiation to the cell types that comprise heart tissue. Next, we describe biomaterial-based approaches that are being implemented to enhance the in vivo integration and differentiation of stem cells delivered to areas of cardiac damage. Finally, we present emerging trends of using stem cell-based biomaterial approaches to deliver pro-survival factors and fully vascularized tissue to the damaged and diseased cardiac tissue.

Physiologically inspired cardiac scaffolds for tailored in vivo function and heart regeneration

Tissue engineering is well suited for the treatment of cardiac disease due to the limited regenerative capacity of native cardiac tissue and the loss of function associated with endemic cardiac pathologies, such as myocardial infarction and congenital heart defects. However, the physiological complexity of the myocardium imposes extensive requirements on tissue therapies intended for these applications. In recent years, the field of cardiac tissue engineering has been characterized by great innovation and diversity in the fabrication of engineered tissue scaffolds for cardiac repair and regeneration to address these problems. From early approaches that attempted only to deliver cardiac cells in a hydrogel vessel, significant progress has been made in understanding the role of each major component of cardiac living tissue constructs (namely cells, scaffolds, and signaling mechanisms) as they relate to mechanical, biological, and electrical in vivo performance. This improved insight, accompanied by modern material science techniques, allows for the informed development of complex scaffold materials that are optimally designed for cardiac applications. This review provides a background on cardiac physiology as it relates to critical cardiac scaffold characteristics, the degree to which common cardiac scaffold materials fulfill these criteria, and finally an overview of recent in vivo studies that have employed this type of approach.

Highly elastic and suturable electrospun poly(glycerol sebacate) fibrous scaffolds

Poly(glycerol sebacate) (PGS) is a thermally-crosslinked elastomer suitable for tissue regeneration due to its elasticity, degradability, and pro-regenerative inflammatory response. Pores in PGS scaffolds are typically introduced by porogen leaching, which compromises strength. Methods for producing fibrous PGS scaffolds are very limited. Electrospinning is the most widely used method for laboratory scale production of fibrous scaffolds. Electrospinning PGS by itself is challenging, necessitating a carrier polymer which can affect material properties if not removed. We report a simple electrospinning method to produce distinct PGS fibers while maintaining the desired mechanical and cytocompatibility properties of thermally crosslinked PGS. Fibrous PGS demonstrated 5 times higher tensile strength and increased suture retention compared to porous PGS foams. Additionally, similar modulus and elastic recovery were observed. A final advantage of fibrous PGS sheets is the ability to create multi-laminate constructs due to fiber bonding that occurs during thermal crosslinking. Taken together, these highly elastic fibrous PGS scaffolds will enable new approaches in tissue engineering and regenerative medicine.

Clinical applications of naturally derived biopolymer-based scaffolds for regenerative medicine

Naturally derived polymeric biomaterials, such as collagens, silks, elastins, alginates, and fibrins are utilized in tissue engineering due to their biocompatibility, bioactivity, and tunable mechanical and degradation kinetics. The use of these natural biopolymers in biomedical applications is advantageous because they do not release cytotoxic degradation products, are often processed using environmentally-friendly aqueous-based methods, and their degradation rates within biological systems can be manipulated by modifying the starting formulation or processing conditions. For these reasons, many recent in vivo investigations and FDA-approval of new biomaterials for clinical use have utilized natural biopolymers as matrices for cell delivery and as scaffolds for cell-free support of native tissues. This review highlights biopolymer-based scaffolds used in clinical applications for the regeneration and repair of native tissues, with a focus on bone, skeletal muscle, peripheral nerve, cardiac muscle, and cornea substitutes.

Fabrication and characterization of biodegradable polymeric films as a corneal stroma substitute

Background:

Biodegradable elastomeric materials such as poly glycerol sebacate (PGS) have gained much current attention in the field of soft tissue engineering. The present study reports the synthesis of PGS with molar ratios of 1:1, 2:3, and 3:2 of glycerol and sebacic acid via polycondensation reaction and tests the effect of PGS on human corneal epithelial (HCE) cells viability in vitro.

Materials and Methods:

PGS films were prepared by the casting method. We tried to fabricate PGS with different compositions and various properties as being a viable alternative to the corneal stroma in cornea tissue engineering. The chemical properties of the prepared polymer were investigated by means of attenuated total reflectance – Fourier transform infrared spectroscopy (ATR-FTIR) analysis and the in vitro cytotoxicity was investigated by the Alamarblue method.

Results:

The functional groups observed in the PGS FTIR spectrums of PGS with various molar ratios were the same. However, the main difference was the time of completing the cross-linking reaction. The PGS prepared by 2:3 ratio as a molar ratio had the fastest and the 3:2 ratio had the lowest cross-linking rate because of the higher amount of sebacic acid. Results of the Alamarblue cytotoxicity test assay showed no deleterious effect on HCE cell viability and proliferation.

Conclusions:

PGS is a potentially good candidate material for corneal tissue engineering because of its lack of in vitro HCE cell toxicity.

Poly(glycerol sebacate) biomaterial: synthesis and biomedical applications

The recently developed poly(glycerol sebacate) (PGS) has been gaining attraction as a biomaterial for tissue engineering applications.

Hybrid amphiphilic bimodal hydrogels having mechanical and biological recognition characteristics for cardiac tissue engineering

Tissue engineering strategies rely on the favourable microniche scaffolds for 3D cell growth.

In vitro characterization of polyesters of aconitic acid, glycerol, and cinnamic acid for bone tissue engineering

In this study, a novel class of polyesters of glycerol, aconitic acid, and cinnamic acid were synthesized along with their hydroxyapatite (HA) composites, and studied for their potential application in bone defect repair. An osteogenic study was conducted with human adipose derived mesenchymal stem cells (hASCs) to determine the osteoinductive ability of aconitic acid-glycerol (AG) polyesters, AG:HA (80:20), aconitic acid-glycerol-cinnamic acid (AGC) polyesters, and AGC:HA (80:20) to serve as bone scaffolds. The results indicate that AGC scaffolds have the highest mechanical strength in comparison to AG, AG:HA (80:20), and AGC:HA (80:20) scaffolds due to its low porosity. It was determined by cytotoxicity and osteogenesis experiments that hASCs cultured for 21 days on AG:HA (80:20) scaffolds in stromal medium exhibited a greater number of live cells than control PCL:HA composites. Moreover, hASCs cultured on foamed AG:HA (80:20) scaffolds resulted in the highest levels of mineralization, increased alkaline phosphatase (ALP) expression, and the greatest osteocalcin (OCN) expression after 21 days. Overall, AG:HA (100:0 and 80:20) scaffolds had higher mechanical strength and cytocompatibility than the PCL:HA control. In vitro osteogenic study demonstrated that AG:HA (100:0 and 80:20) synthesized using sugarcane industry by-products hold potential as scaffolds for bone tissue engineering applications.

Highly tunable elastomeric silk biomaterials

Elastomeric, fully degradable and biocompatible biomaterials are rare, with current options presenting significant limitations in terms of ease of functionalization and tunable mechanical and degradation properties. We report a new method for covalently crosslinking tyrosine residues in silk proteins, via horseradish peroxidase and hydrogen peroxide, to generate highly elastic hydrogels with tunable properties. The tunable mechanical properties, gelation kinetics and swelling properties of these new protein polymers, in addition to their ability to withstand shear strains on the order of 100%, compressive strains greater than 70% and display stiffness between 200 - 10,000 Pa, covering a significant portion of the properties of native soft tissues. Molecular weight and solvent composition allowed control of material mechanical properties over several orders of magnitude while maintaining high resilience and resistance to fatigue. Encapsulation of human bone marrow derived mesenchymal stem cells (hMSC) showed long term survival and exhibited cell-matrix interactions reflective of both silk concentration and gelation conditions. Further biocompatibility of these materials were demonstrated with in vivo evaluation. These new protein-based elastomeric and degradable hydrogels represent an exciting new biomaterials option, with a unique combination of properties, for tissue engineering and regenerative medicine.

Cardiac Tissue Engineering

The engineering of 3-dimensional (3D) heart muscles has undergone exciting progress for the past decade. Profound advances in human stem cell biology and technology, tissue engineering and material sciences, as well as prevascularization and in vitro assay technologies make the first clinical application of engineered cardiac tissues a realistic option and predict that cardiac tissue engineering techniques will find widespread use in the preclinical research and drug development in the near future. Tasks that need to be solved for this purpose include standardization of human myocyte production protocols, establishment of simple methods for the in vitro vascularization of 3D constructs and better maturation of myocytes, and, finally, thorough definition of the predictive value of these methods for preclinical safety pharmacology. The present article gives an overview of the present state of the art, bottlenecks, and perspectives of cardiac tissue engineering for cardiac repair and in vitro testing.

Engineering the heart: evaluation of conductive nanomaterials for improving implant integration and cardiac function

Recently, carbon nanotubes together with other types of conductive materials have been used to enhance the viability and function of cardiomyocytes in vitro. Here we demonstrated a paradigm to construct ECTs for cardiac repair using conductive nanomaterials. Single walled carbon nanotubes (SWNTs) were incorporated into gelatin hydrogel scaffolds to construct three-dimensional ECTs. We found that SWNTs could provide cellular microenvironment in vitro favorable for cardiac contraction and the expression of electrochemical associated proteins. Upon implantation into the infarct hearts in rats, ECTs structurally integrated with the host myocardium, with different types of cells observed to mutually invade into implants and host tissues. The functional measurements showed that SWNTs were essential to improve the performance of ECTs in inhibiting pathological deterioration of myocardium. This work suggested that conductive nanomaterials hold therapeutic potential in engineering cardiac tissues to repair myocardial infarction.

Towards the generation of patient-specific patches for cardiac repair

Cardiovascular diseases represent the main cause of morbidity and mortality worldwide. Millions of people are affected by such diseases in the industrialized countries, with hundreds of thousands new cases diagnosed every year. Among cardiac diseases, heart failure is the most common end-stage pathology, leading to impaired cardiac output and cardiac performance as a result of the irreversible loss of contractile cardiomyocytes. Tissue engineering holds the promise to provide personalized solutions to the problem of cardiac muscle repair. Indeed, the identification of little reservoirs of stem and progenitor cells within every body district opened new perspectives to the setup of patient-specific protocols for cardiac diseases. Nonetheless, the results of the first pre-clinical and clinical trials in which adult stem/progenitor cells were adopted pointed at the route of delivery to the injured organ as well as at the cell source as the main issues for cardiac tissue engineers. In fact, when adult stem cells were directly injected into the myocardium or delivered through bloodstream to the heart, no or few cells could be found engrafted within host tissue few days after the administration. Renewed enthusiasm was generated by the techniques set up to enrich cardiomyocytes obtained by embryonic stem cells and by the recent disclosure of the protocols to obtain reprogrammed pluripotent cells or reprogrammed cardiomyocytes out of patients' own somatic cells. In this context, additional efforts to setup efficient systems to deliver stem cells to the injured site are required. The application of forefront technologies to fabricate synthetic and hybrid scaffolds to be employed as cell delivery systems and the acknowledgement that surface physical, mechanical, chemical properties can exert specific effects on stem cells per se prompted new enthusiasm in the field. In this respect, a cardiac-specific scaffold should be able to comply with cardiac muscle architecture, be deformable as to indulge and possibly sustain cardiac contraction. As expected, such a scaffold should favor stem cell electromechanical coupling with host tissue, while promoting the vascularization of the newly-formed tissue.

Biomimetic scaffold combined with electrical stimulation and growth factor promotes tissue engineered cardiac development

Toward developing biologically sound models for the study of heart regeneration and disease, we cultured heart cells on a biodegradable, microfabricated poly(glycerol sebacate) (PGS) scaffold designed with micro-structural features and anisotropic mechanical properties to promote cardiac-like tissue architecture. Using this biomimetic system, we studied individual and combined effects of supplemental insulin-like growth factor-1 (IGF-1) and electrical stimulation (ES). On culture day 8, all tissue constructs could be paced and expressed the cardiac protein troponin-T. IGF-1 reduced apoptosis, promoted cell-to-cell connectivity, and lowered excitation threshold, an index of electrophysiological activity. ES promoted formation of tissue-like bundles oriented in parallel to the electrical field and a more than ten-fold increase in matrix metalloprotease-2 (MMP-2) gene expression. The combination of IGF-1 and ES increased 2D projection length, an index of overall contraction strength, and enhanced expression of the gap junction protein connexin-43 and sarcomere development. This culture environment, designed to combine cardiac-like scaffold architecture and biomechanics with molecular and biophysical signals, enabled functional assembly of engineered heart muscle from dissociated cells and could serve as a template for future studies on the hierarchy of various signaling domains relative to cardiac tissue development.

A biodegradable microvessel scaffold as a framework to enable vascular support of engineered tissues

A biodegradable microvessel scaffold comprised of distinct parenchymal and vascular compartments separated by a permeable membrane interface was conceptualized, fabricated, cellularized, and implanted. The device was designed with perfusable microfluidic channels on the order of 100 μm to mimic small blood vessels, and high interfacial area to an adjacent parenchymal space to enable transport between the compartments. Poly(glycerol sebacate) (PGS) elastomer was used to construct the microvessel framework, and various assembly methods were evaluated to ensure robust mechanical integrity. In vitro studies demonstrated the differentiation of human skeletal muscle cells cultured in the parenchymal space, a 90% reduction in muscle cell viability due to trans-membrane transport of a myotoxic drug from the perfusate, and microvessel seeding with human endothelial cells. In vivo studies of scaffolds implanted subcutaneously and intraperitoneally, without or with exogenous cells, into nude rats demonstrated biodegradation of the membrane interface and host blood cell infiltration of the microvessels. This modular, implantable scaffold could serve as a basis for building tissue constructs of increasing scale and clinical relevance.

Enzymatic and oxidative degradation of poly(polyol sebacate)

Poly(glycerol sebacate) (PGS) and poly(xylitol sebacate) (PXS) are biodegradable elastomers with tremendous potential in soft tissue engineering. This study was aimed at exploring the enzymatic degradation mechanisms of these polyesters, using biochemical conditions similar to those occurring in vivo. To this end, PGS and PXS (crosslinked at 130℃ for 2 or 7 (PGS)/12 days (PXS)) were incubated in vitro under physiological conditions in tissue culture media supplemented with either a biodegrading enzyme (esterase), an oxidant species (FeSO4/H2O2 with 0.11 molar ratio of Fe2+/H2O2), an oxidant generating enzyme (xanthine oxidase and xanthine) or combinations of these (FeSO4/H2O2 and esterase, or (v) xanthine oxidase/xanthine and esterase), based on their independent effects on polymer degradation. Testing was performed over 35 days of continuous incubation, during which mechanical properties, mass loss, biomaterial thickness and pH value of the culture medium were determined. Degradation kinetics of both PGS and PXS samples were primarily determined by the degree of crosslink density. Esterase and FeSO4/H2O2 accelerated the degradation of both polymers, by promoting hydrolysis and free-radical degradation, although this action was not affected by the presence of xanthine oxidase and xanthine. Degradation of PGS and PXS is primarily mediated by the action of esterase, with free-radical oxidation playing a secondary role, suggesting that both could synergistically affect the biodegradability of biomaterial implants, under more complex biological conditions.

Mechanically tissue-like elastomeric polymers and their potential as a vehicle to deliver functional cardiomyocytes

One of the major challenges in the field of biomaterials engineering is the replication of the non-linear elasticity observed in soft tissues. In the present study, non-linearly elastic biomaterials were successfully fabricated from a chemically cross-linked elastomeric poly(glycerol sebacate) (PGS) and thermoplastic poly(L-lactic acid) (PLLA) using the core/shell electrospinning technique. The spun fibrous materials, containing a PGS core and PLLA shell, demonstrated J-shaped stress-strain curves, and having ultimate tensile strength, rupture elongation, and stiffness constants respectively comparable to muscle tissue properties. In vitro evaluations also showed that PGS/PLLA fibrous biomaterials possess excellent biocompatibility, capable of supporting human stem-cell-derived cardiomyocytes over several weeks in culture. Therefore, the core/shell electrospun elastomeric materials provide a new potential scaffold to support cells in the therapy of a wide range of soft tissues exposed to cyclic deformation, such as tendon, ligament, cardiac or smooth muscle and lung epithelium.

Localized targeting of biomaterials following myocardial infarction: a foundation to build on

Acute coronary syndromes can give rise to myocardial injury infarction (MI), which in turn promulgates a series of cellular and extracellular events that result in left ventricular (LV) dilation and dysfunction. Localized strategies focused upon interrupting this inexorable process include delivery of bioactive molecules and stem cell derivatives. These localized treatment strategies are often delivered in a biomaterial complex in order to facilitate elution of the bioactive molecules or stem cell engraftment. However, these biomaterials can impart significant and independent effects upon the MI remodeling process. In addition, significant changes in local cell and interstitial biology within the targeted MI region can occur following injection of certain biomaterials, which may hold important considerations when using these materials as matrices for adjuvant drug/cell therapies.

Non-linear elasticity of core/shell spun PGS/PLLA fibres and their effect on cell proliferation

An efficient delivery system is critical for the success of cell therapy. To deliver cells to a dynamic organ, the biomaterial vehicle should mechanically match with the non-linearly elastic host tissue. In this study, non-linearly elastic biomaterials have been fabricated from a chemically crosslinked elastomeric poly(glycerol sebacate) (PGS) and thermoplastic poly(l-lactic acid) (PLLA) using the core/shell electrospinning technique. The spun fibrous materials containing a PGS core and PLLA shell demonstrate J-shaped stress-strain curves, having ultimate tensile strength (UTS), rupture elongation and stiffness constants of 1 ± 0.2 MPa, 25 ± 3% and 12 ± 2, respectively, which are comparable to skin tissue properties reported previously. Our ex vivo and in vivo trials have shown that the elastomeric mesh supports and fosters the growth of enteric neural crest (ENC) progenitor cells, and that the cell-seeded elastomeric fibrous sheet physically remains in intimate contact with guts after grafting, providing the effective delivery of the progenitor cells to an embryonic and post-natal gut environment.

Microwave-assisted rapid synthesis of poly(glycerol-sebacate) elastomers

Poly(glycerol-sebacate) (PGS) was introduced a decade ago as a potential material for soft tissue repair. All of the proposed copolymerization reactions in the literature include a two-stage (prepolymerization and curing) synthesis where the reaction times can take as long as several days. This study, on the other hand, proposes a new route that eliminates these disadvantages and enables a rapid synthesis of PGS elastomers via microwave-assisted prepolymerization in minutes instead of days. No purge gas, catalyst or vacuum is needed in the first prepolymerization step. The curing stage was carried out at 150 °C for 4, 8, 16, and 24 hours. The glass transition temperature (T_g) and melting temperatures for the glycerol and sebacic acid fragments (T_m1 and T_m2 ) of these PGS elastomers were found as -35.61 °C, -15.82 °C, and 61.70 °C, respectively. The Young's modulus and tensile strength values were found as 0.50 ± 0.02 MPa and 0.27 ± 0.06 MPa, respectively.

Injectable photocrosslinkable nanocomposite based on poly(glycerol sebacate) fumarate and hydroxyapatite: development, biocompatibility and bone regeneration in a rat calvarial bone defect model

AIM

An injectable, photocrosslinkable nanocomposite was prepared using a fumarate derivative of poly(glycerol sebacate) and nanohydroxyapatite.

MATERIALS & METHODS

Polymers with varying physical and mechanical properties were synthesized. Furthermore, nanocomposites were developed using a homogenization process by combining nanohydroxyapatite within poly(glycerol sebacate) matrix via photocrosslinking and evaluated both in vitro and in vivo.

RESULTS & DISCUSSION

The nanocomposites were injectable, highly bioactive and biocompatible. Addition of nanohydroxyapatite led to enhanced mechanical properties with an ultimate strength of 8 MPa. The optimized nanocomposite showed good in vitro cell attachment, proliferation and differentiation of rat bone marrow-derived mesenchymal stem cells. The in vivo evaluation in a rat calvarial bone defect model showed significantly high alkaline phosphatase activity and bone regeneration.

CONCLUSION

This injectable, biocompatible and bioactive in situ hardening composite graft was found to be suitable for load-bearing bone regeneration applications using minimally invasive surgery.

Cardiomyocyte regeneration

The heart was initially believed to be a terminally differentiated organ; once the cardiomyocytes died, no recovery could be made to replace the dead cells. However, around a decade ago, the concept of cardiac stem cells (CSCs) in adult hearts was proposed. CSCs differentiate into cardiomyocytes, keeping the heart functioning. Studies have proved the existence of stem cells in the heart. These somatic stem cells have been studied for use in cardiac regeneration. Moreover, recently, induced pluripotent stem cells (iPSCs) were invented, and methodologies have now been developed to induce stable cardiomyocyte differentiation and purification of mature cardiomyocytes. A reprogramming method has also been applied to direct reprogramming using cardiac fibroblasts into cardiomyocytes. Here, we address cardiomyocyte differentiation of CSCs and iPSCs. Furthermore, we describe the potential of CSCs in regenerative biology and regenerative medicine.

Three-dimensional elastomeric scaffolds designed with cardiac-mimetic structural and mechanical features

Tissue-engineered constructs, at the interface of material science, biology, engineering, and medicine, have the capacity to improve outcomes for cardiac patients by providing living cells and degradable biomaterials that can regenerate the native myocardium. With an ultimate goal of both delivering cells and providing mechanical support to the healing heart, we designed three-dimensional (3D) elastomeric scaffolds with (1) stiffnesses and anisotropy mimicking explanted myocardial specimens as predicted by finite-element (FE) modeling, (2) systematically varied combinations of rectangular pore pattern, pore aspect ratio, and strut width, and (3) structural features approaching tissue scale. Based on predicted mechanical properties, three scaffold designs were selected from eight candidates for fabrication from poly(glycerol sebacate) by micromolding from silicon wafers. Large 20×20 mm scaffolds with high aspect ratio features (5:1 strut height:strut width) were reproducibly cast, cured, and demolded at a relatively high throughput. Empirically measured mechanical properties demonstrated that scaffolds were cardiac mimetic and validated FE model predictions. Two-layered scaffolds providing fully interconnected pore networks were fabricated by layer-by-layer assembly. C2C12 myoblasts cultured on one-layered scaffolds exhibited specific patterns of cell elongation and interconnectivity that appeared to be guided by the scaffold pore pattern. Neonatal rat heart cells cultured on two-layered scaffolds for 1 week were contractile, both spontaneously and in response to electrical stimulation, and expressed sarcomeric α-actinin, a cardiac biomarker. This work not only demonstrated several scaffold designs that promoted functional assembly of rat heart cells, but also provided the foundation for further computational and empirical investigations of 3D elastomeric scaffolds for cardiac tissue engineering.

Electrophysiological and contractile function of cardiomyocytes derived from human embryonic stem cells

Human embryonic stem cells have emerged as the prototypical source from which cardiomyocytes can be derived for use in drug discovery and cell therapy. However, such applications require that these cardiomyocytes (hESC-CMs) faithfully recapitulate the physiology of adult cells, especially in relation to their electrophysiological and contractile function. We review what is known about the electrophysiology of hESC-CMs in terms of beating rate, action potential characteristics, ionic currents, and cellular coupling as well as their contractility in terms of calcium cycling and contraction. We also discuss the heterogeneity in cellular phenotypes that arises from variability in cardiac differentiation, maturation, and culture conditions, and summarize present strategies that have been implemented to reduce this heterogeneity. Finally, we present original electrophysiological data from optical maps of hESC-CM clusters.