Tri-layered elastomeric scaffolds for engineering heart valve leaflets

Modulating biomechanical and integrating biochemical cues to foster adaptive remodeling of tissue engineered matrices for cardiovascular implants

Cardiovascular disease remains one of the leading causes of mortality in the Western world. Congenital heart disease affects nearly 1 % of newborns, with approximately one-fourth requiring reconstructive surgery during their lifetime. Current cardiovascular replacement options have significant limitations. Their inability to grow poses particular challenges for pediatric patients. Tissue Engineered Matrix (TEM)-based in situ constructs, with their self-repair and growth potential, offer a promising solution to overcome the limitations of current clinically used replacement options. Various functionalization strategies, involving the integration of biomechanical or biochemical components to enhance biocompatibility, have been developed for Tissue Engineered Vascular Grafts (TEVG) and Tissue Engineered Heart Valves (TEHV) to foster their capacity for in vivo remodeling. In this review, we present the current state of clinical translation for TEVG and TEHV, and provide a comprehensive overview of biomechanical and biochemical functionalization strategies for TEVG and TEHV. We discuss the rationale for functionalization, the implementation of functionalization cues in TEM-based TEVG and TEHV, and the interrelatedness of biomechanical and biochemical cues in the in vivo response. Finally, we address the challenges associated with functionalization and discuss how interdisciplinary research, especially when combined with in silico models, could enhance the translation of these strategies into clinical applications. STATEMENT OF SIGNIFICANCE: Cardiovascular disease remains one of the leading causes of mortality, with current replacements being unable to grow and regenerate. In this review, we present the current state of clinical translation for tissue engineered vascular grafts (TEVG) and heart valves (TEHV). Particularly, we discuss the rationale and implementation for functionalization cues in tissue engineered matrix-based TEVGs and TEHVs, and for the first time we introduce the interrelatedness of biomechanical and biochemical cues in the in-vivo response. These insights pave the way for next-generation cardiovascular implants that promise better durability, biocompatibility, and growth potential. Finally, we address the challenges associated with functionalization and discuss how interdisciplinary research, especially when combined with in silico models, could enhance the translation of these strategies into clinical applications .

Smooth leaflets with curved belly and attachment edge profiles promote adaptive remodeling in tissue-engineered heart valves: an in silico study

Tissue-engineered heart valves (TEHVs) are promising valve replacements due to their potential to regenerate into living heart valves, capable of growth and adaptation. Previous TEHVs showed promising results, but often developed progressive leaflet retraction in the long term. In a prior proof-of-concept study, we demonstrated that a novel geometry with more native-like mechanical behavior could give rise to more adaptive remodeling, thereby minimizing leaflet retraction in vivo. In the current study, we aimed to systematically analyze the impact of TEHV geometry on in vivo remodeling under both pulmonary and aortic conditions. Using a bio-inspired in silico framework, we predicted cell-driven, mechano-mediated remodeling in TEHVs post-implantation. Two parameterized valve designs were evaluated under both pulmonary and aortic pressure conditions. The results indicate that a valve design with smooth leaflets, a curved belly profile, and medium to wide attachment edge effectively minimizes stress concentrations and reduces the risk of valve insufficiency in both conditions. Additionally, this design should be tailored to specific hemodynamic conditions to prevent retraction in pulmonary applications and excessive stress concentrations in aortic applications. These insights provide essential guidelines for optimizing TEHV designs, aiming to promote functional remodeling and maintain valve functionality over time, thereby advancing the development of next-generation TEHVs with enhanced long-term outcomes.

Cardiovascular patches applied in congenital cardiac surgery: Current materials and prospects

Congenital Heart Defects (CHDs) are the most common congenital anomalies, affecting between 4 and 75 per 1000 live births. Cardiovascular patches (CVPs) are frequently used as part of the surgical armamentarium to reconstruct cardiovascular structures to correct CHDs in pediatric patients. This review aims to evaluate the history of cardiovascular patches, currently available options, clinical applications, and important features of these patches. Performance and outcomes of different patch materials are assessed to provide reference points for clinicians. The target audience includes clinicians seeking data on clinical performance as they make choices between different patch products, as well as scientists and engineers working to develop patches or synthesize new patch materials.

A Biomimetic Leaflet Scaffold for Aortic Valve Remodeling

Heart valve disease poses a significant clinical challenge, especially in pediatric populations, due to the inability of existing valve replacements to grow or respond biologically to their microenvironment. Tissue-engineered heart valves (TEHVs) provide a solution by facilitating patient-specific models for self-repair and remodeling. In this study, a 3D-bioprinted TEHV is designed to emulate the trilayer leaflet structure of an aortic valve. A cell-laden hydrogel scaffold made from gelatin methacrylate and polyethylene glycol diacrylate (GelMA/PEGDA) incorporates valvular interstitial-like (VIC-like) cells, being reinforced with a layer of polycaprolactone (PCL). The composition of the hydrogel scaffold remains stable over 7 days, having increased mechanical strength compared to pure GelMA. The scaffold maintains VIC-like cell function and promotes extracellular matrix (ECM) protein expression up to 14 days under two dynamic culture conditions: shear stress and stretching; replicating heart valve behavior within a more physiological-like setting and suggesting remodeling potential via ECM synthesis. This TEHV offers a promising avenue for valve replacements, closely replicating the structural and functional attributes of a native aortic valve, leading to mechanical and biological integration through biomaterial-cellular interactions.

Exploring Electrospun Scaffold Innovations in Cardiovascular Therapy: A Review of Electrospinning in Cardiovascular Disease

Cardiovascular disease (CVD) remains the leading cause of mortality worldwide. In particular, patients who suffer from ischemic heart disease (IHD) that is not amenable to surgical or percutaneous revascularization techniques have limited treatment options. Furthermore, after revascularization is successfully implemented, there are a number of pathophysiological changes to the myocardium, including but not limited to ischemia-reperfusion injury, necrosis, altered inflammation, tissue remodeling, and dyskinetic wall motion. Electrospinning, a nanofiber scaffold fabrication technique, has recently emerged as an attractive option as a potential therapeutic platform for the treatment of cardiovascular disease. Electrospun scaffolds made of biocompatible materials have the ability to mimic the native extracellular matrix and are compatible with drug delivery. These inherent properties, combined with ease of customization and a low cost of production, have made electrospun scaffolds an active area of research for the treatment of cardiovascular disease. In this review, we aim to discuss the current state of electrospinning from the fundamentals of scaffold creation to the current role of electrospun materials as both bioengineered extracellular matrices and drug delivery vehicles in the treatment of CVD, with a special emphasis on the potential clinical applications in myocardial ischemia.

Strategies for Development of Synthetic Heart Valve Tissue Engineering Scaffolds

The current clinical solutions, including mechanical and bioprosthetic valves for valvular heart diseases, are plagued by coagulation, calcification, nondurability, and the inability to grow with patients. The tissue engineering approach attempts to resolve these shortcomings by producing heart valve scaffolds that may deliver patients a life-long solution. Heart valve scaffolds serve as a three-dimensional support structure made of biocompatible materials that provide adequate porosity for cell infiltration, and nutrient and waste transport, sponsor cell adhesion, proliferation, and differentiation, and allow for extracellular matrix production that together contributes to the generation of functional neotissue. The foundation of successful heart valve tissue engineering is replicating native heart valve architecture, mechanics, and cellular attributes through appropriate biomaterials and scaffold designs. This article reviews biomaterials, the fabrication of heart valve scaffolds, and their in-vitro and in-vivo evaluations applied for heart valve tissue engineering.

Bio-Inspired Fiber Reinforcement for Aortic Valves: Scaffold Production Process and Characterization

The application of tissue-engineered heart valves in the high-pressure circulatory system is still challenging. One possible solution is the development of biohybrid scaffolds with textile reinforcement to achieve improved mechanical properties. In this article, we present a manufacturing process of bio-inspired fiber reinforcement for an aortic valve scaffold. The reinforcement structure consists of polyvinylidene difluoride monofilament fibers that are biomimetically arranged by a novel winding process. The fibers were embedded and fixated into electrospun polycarbonate urethane on a cylindrical collector. The scaffold was characterized by biaxial tensile strength, bending stiffness, burst pressure and hemodynamically in a mock circulation system. The produced fiber-reinforced scaffold showed adequate acute mechanical and hemodynamic properties. The transvalvular pressure gradient was 3.02 ± 0.26 mmHg with an effective orifice area of 2.12 ± 0.22 cm2. The valves sustained aortic conditions, fulfilling the ISO-5840 standards. The fiber-reinforced scaffold failed in a circumferential direction at a stress of 461.64 ± 58.87 N/m and a strain of 49.43 ± 7.53%. These values were above the levels of tested native heart valve tissue. Overall, we demonstrated a novel manufacturing approach to develop a fiber-reinforced biomimetic scaffold for aortic heart valve tissue engineering. The characterization showed that this approach is promising for an in situ valve replacement.

Research trends in cardiovascular tissue engineering from 1992 to 2022: a bibliometric analysis

Background

Cardiovascular tissue engineering (CTE) is a promising technique to treat incurable cardiovascular diseases, such as myocardial infarction and ischemic cardiomyopathy. Plenty of studies related to CTE have been published in the last 30 years. However, an analysis of the research status, trends, and potential directions in this field is still lacking. The present study applies a bibliometric analysis to reveal CTE research trends and potential directions.

Methods

On 5 August 2022, research articles and review papers on CTE were searched from the Web of Science Core Collection with inclusion and exclusion criteria. Publication trends, research directions, and visual maps in this field were obtained using Excel (Microsoft 2009), VOSviewer, and Citespace software.

Results

A total of 2,273 documents from 1992 to 2022 were included in the final analysis. Publications on CTE showed an upward trend from 1992 [number of publications (Np):1] to 2021 (Np:165). The United States (Np: 916, number of citations: 152,377, H-index: 124) contributed the most publications and citations in this field. Research on CTE has a wide distribution of disciplines, led by engineering (Np: 788, number of citations: 40,563, H-index: 105). "Functional maturation" [red cluster, average published year (APY): 2018.63, 30 times], "cell-derived cardiomyocytes" (red cluster, APY: 2018.43, 46 times), "composite scaffolds" (green cluster, APY: 2018.54, 41 times), and "maturation" (red cluster, APY: 2018.17, 84 times) are the main emerging keywords in this area.

Conclusion

Research on CTE is a hot research topic. The United States is a dominant player in CTE research. Interdisciplinary collaboration has played a critical role in the progress of CTE. Studies on functional maturation and the development of novel biologically relevant materials and related applications will be the potential research directions in this field.

Fibrin gel enhanced trilayer structure in cell-cultured constructs

Efficient cell seeding and subsequent support from a substrate ensure optimal cell growth and neotissue development during tissue engineering, including heart valve tissue engineering. Fibrin gel as a cell carrier may provide high cell seeding efficiency and adhesion property, improved cellular interaction, and structural support to enhance cellular growth in trilayer polycaprolactone (PCL) substrates that mimic the structure of native heart valve leaflets. This cell carrier gel coupled with a trilayer PCL substrate may enable the production of native-like cell-cultured leaflet constructs suitable for heart valve tissue engineering. In this study, we seeded valvular interstitial cells onto trilayer PCL substrates with fibrin gel as a cell carrier and cultured them for 1 month in vitro to determine if this gel can improve cell proliferation and production of extracellular matrix within the trilayer cell-cultured constructs. We observed that the fibrin gel enhanced cellular proliferation, their vimentin expression, and collagen and glycosaminoglycan production, leading to improved structure and mechanical properties of the developing PCL cell-cultured constructs. Fibrin gel as a cell carrier significantly improved the orientations of the cells and their produced tissue materials within trilayer PCL substrates that mimic the structure of native heart valve leaflets and, thus, may be highly beneficial for developing functional tissue-engineered leaflet constructs.

Elastomeric Trilayer Substrates with Native-like Mechanical Properties for Heart Valve Leaflet Tissue Engineering

Heart valve leaflets have a complex trilayered structure with layer-specific orientations, anisotropic tensile properties, and elastomeric characteristics that are difficult to mimic collectively. Previously, trilayer leaflet substrates intended for heart valve tissue engineering were developed with nonelastomeric biomaterials that cannot deliver native-like mechanical properties. In this study, by electrospinning polycaprolactone (PCL) polymer and poly(l-lactide-co-ε-caprolactone) (PLCL) copolymer, we created elastomeric trilayer PCL/PLCL leaflet substrates with native-like tensile, flexural, and anisotropic properties and compared them with trilayer PCL leaflet substrates (as control) to find their effectiveness in heart valve leaflet tissue engineering. These substrates were seeded with porcine valvular interstitial cells (PVICs) and cultured for 1 month in static conditions to produce cell-cultured constructs. The PCL/PLCL substrates had lower crystallinity and hydrophobicity but higher anisotropy and flexibility than PCL leaflet substrates. These attributes contributed to more significant cell proliferation, infiltration, extracellular matrix production, and superior gene expression in the PCL/PLCL cell-cultured constructs than in the PCL cell-cultured constructs. Further, the PCL/PLCL constructs showed better resistance to calcification than PCL constructs. Trilayer PCL/PLCL leaflet substrates with native-like mechanical and flexural properties could significantly improve heart valve tissue engineering.

Recent Advancements in Polyurethane-based Tissue Engineering

In tissue engineering, polyurethane-based implants have gained significant traction because of their high compatibility and inertness. The implants therefore show fewer side effects and lasts longer. Also, the mechanical properties can be tuned and morphed into a particular shape, owing to which polyurethanes show immense versatility. In the last 3 years, scientists have devised methods to enhance the strength of and induce dynamic properties in polyurethanes, and these developments offer an immense opportunity to use them in tissue engineering. The focus of this review is on applications of polyurethane implants for biomedical application with detailed analysis of hard tissue implants like bone tissues and soft tissues like cartilage, muscles, skeletal tissues, and blood vessels. The synthetic routes for the preparation of scaffolds have been discussed to gain a better understanding of the issues that arise regarding toxicity. The focus here is also on concerns regarding the biocompatibility of the implants, given that the precursors and byproducts are poisonous.

Polymeric Heart Valves Will Displace Mechanical and Tissue Heart Valves: A New Era for the Medical Devices

The development of a novel artificial heart valve with outstanding durability and safety has remained a challenge since the first mechanical heart valve entered the market 65 years ago. Recent progress in high-molecular compounds opened new horizons in overcoming major drawbacks of mechanical and tissue heart valves (dysfunction and failure, tissue degradation, calcification, high immunogenic potential, and high risk of thrombosis), providing new insights into the development of an ideal artificial heart valve. Polymeric heart valves can best mimic the tissue-level mechanical behavior of the native valves. This review summarizes the evolution of polymeric heart valves and the state-of-the-art approaches to their development, fabrication, and manufacturing. The review discusses the biocompatibility and durability testing of previously investigated polymeric materials and presents the most recent developments, including the first human clinical trials of LifePolymer. New promising functional polymers, nanocomposite biomaterials, and valve designs are discussed in terms of their potential application in the development of an ideal polymeric heart valve. The superiority and inferiority of nanocomposite and hybrid materials to non-modified polymers are reported. The review proposes several concepts potentially suitable to address the above-mentioned challenges arising in the R&D of polymeric heart valves from the properties, structure, and surface of polymeric materials. Additive manufacturing, nanotechnology, anisotropy control, machine learning, and advanced modeling tools have given the green light to set new directions for polymeric heart valves.

Engineering Heart Valve Interfaces Using Melt Electrowriting: Biomimetic Design Strategies from Multi-Modal Imaging

Interfaces within biological tissues not only connect different regions but also contribute to the overall functionality of the tissue. This is especially true in the case of the aortic heart valve. Here, melt electrowriting (MEW) is used to engineer complex, user-defined, interfaces for heart valve scaffolds. First, a multi-modal imaging investigation into the interfacial regions of the valve reveals differences in collagen orientation, density, and recruitment in previously unexplored regions including the commissure and inter-leaflet triangle. Overlapping, suturing, and continuous printing methods for interfacing MEW scaffolds are then investigated for their morphological, tensile, and flexural properties, demonstrating the superior performance of continuous interfaces. G-codes for MEW scaffolds with complex interfaces are designed and generated using a novel software and graphical user interface. Finally, a singular MEW scaffold for the interfacial region of the aortic heart valve is presented incorporating continuous interfaces, gradient porosities, variable layer numbers across regions, and tailored fiber orientations inspired by the collagen distribution and orientation from the multi-modal imaging study. The scaffold exhibits similar yield strain, hysteresis, and relaxation behavior to porcine heart valves. This work demonstrates the ability of a bioinspired approach for MEW scaffold design to address the functional complexity of biological tissues.

An in vitro fibrotic liver lobule model through sequential cell-seeding of HSCs and HepG2 on 3D-printed poly(glycerol sebacate) acrylate scaffolds

Cirrhosis is a major cause of global morbidity and mortality, and significantly leads to a heightened risk of liver cancer. Despite decades of efforts in seeking for cures for cirrhosis, this disease remains irreversible. To assist in the advancement of understanding toward cirrhosis as well as therapeutic options, various disease models, each with different strengths, are developed. With the development of three-dimensional (3D) cell culture in recent years, more realistic biochemical properties are observed in 3D cell models, which have gradually taken over the responsibilities of traditional 2D cell culture, and are expected to replace some of the animal models in the near future. Here, we propose a 3D fibrotic liver model inspired by liver lobules. In the model, 3D-printed poly(glycerol sebacate) acrylate (PGSA) scaffolds facilitated the formation of 3D tissues and guided the deposition of fibrotic structures. Through the sequential seeding of hepatic stellate cells (HSCs), HepG2 and HSCs, fibrotic septum-like tissues were created on PGSA scaffolds. As albumin secretion is considered a rather important function of the liver and is found only among hepatic cells, the detection of albumin secretion up to 30 days indicates the mimicking of basic liver functions. Moreover, the in vivo fibrotic tissue shows a high similarity to fibrotic septa. Finally, via complete encapsulation of HSCs, a down-regulated albumin secretion profile was observed in the capped model, which is a metabolic indicator that is important for the prognosis for liver cirrhosis. Looking forward, the incorporation of the vasculature will further upgrade the model into a sound tool for liver research and associated treatments.

Anisotropicity and flexibility in trilayered microfibrous substrates promote heart valve leaflet tissue engineering

Heart valve leaflet substrates with native trilayer and anisotropic structures are crucial for successful heart valve tissue engineering. In this study, we used the electrospinning technique to produce trilayer microfibrous leaflet substrates using two biocompatible and biodegradable polymers-poly (L-lactic acid) (PLLA) and polycaprolactone (PCL), separately. Different polymer concentrations for each layer were applied to bring a high degree of mechanical and structural anisotropy to the substrates. PCL leaflet substrates exhibited lower unidirectional tensile properties than PLLA leaflet substrates. However, the PLLA substrates exhibited a lower flexural modulus than the PCL substrates. These substrates were seeded with porcine valvular interstitial cells (PVICs) and cultured for one month in static conditions. Both substrates exhibited cellular adhesion and proliferation, resulting in the production of tissue-engineered constructs. The PLLA tissue-engineered constructs had more cellular growth than the PCL tissue-engineered constructs. The PLLA substrates showed higher hydrophilicity, lower crystallinity, and more significant anisotropy than PCL substrates, which may have enhanced their interactions with PVICs. Analysis of gene expression showed higherα-smooth muscle actin and collagen type 1 expression in PLLA tissue-engineered constructs than in PCL tissue-engineered constructs. The differences in anisotropic and flexural properties may have accounted for the different cellular behaviors in these two individual polymer substrates.

Fabricating a Low-Cost, Microscopy-Compatible Mechanical Testing Device

Most commercially-available mechanical testing devices are bulky, expensive, and unable to evaluate changes in sample microstructure under load. This leaves a crucial gap in understanding between material structure and bulk mechanical properties. Our objective was to fabricate a mechanical testing device small enough to fit in most upright or inverted microscopy stages and able to position samples to allow for simultaneous mechanical and microstructural characterization. Parts were 3D printed using the hobbyist-friendly Fused Filament Fabrication technique, then assembled with commercial fasteners and translation components to create a mechanical testing device that utilized the deflection of plastic posts to determine sample reaction forces under applied strain. Video of sample deformation was analyzed using a custom processing script to calculate stress and strain behavior in an automated and high-throughput manner. This device was able to perform mechanical characterization with an accuracy comparable to commercial mechanical testing devices for a wide range of nonlinear and viscoelastic samples under dry and hydrated conditions. Additionally, the device showed compatibility with different upright and inverted microscopes and was able to demonstrate accurate mechanical testing results when used with these instruments. We successfully developed a device capable of accurately testing a majority of soft materials in the field of Biomedical Engineering with the ability to perform additional microstructural characterization using microscopy at a price point of $600.

A biomimetic multilayered polymeric material designed for heart valve repair and replacement

Materials currently used to repair or replace a heart valve are not durable. Their limited durability related to structural degeneration or thrombus formation is attributed to their inadequate mechanical properties and biocompatibility profiles. Our hypothesis is that a biostable material that mimics the structure, mechanical and biological properties of native tissue will improve the durability of these leaflets substitutes and in fine improve the patient outcome. Here, we report the development, optimization, and testing of a biomimetic, multilayered material (BMM), designed to replicate the native valve leaflets. Polycarbonate urethane and polycaprolactone have been processed as film, foam, and aligned fibers to replicate the leaflet's architecture and anisotropy, through solution casting, lyophilization, and electrospinning. Compared to the commercialized materials, our BMMs exhibited an anisotropic behavior and a closer mechanical performance to the aortic leaflets. The material exhibited superior biostability in an accelerated oxidization environment. It also displayed better resistance to protein adsorption and calcification in vitro and in vivo. These results will pave the way for a new class of advanced synthetic material with long-term durability for surgical valve repair or replacement.

Advances in three-dimensional bioprinted stem cell-based tissue engineering for cardiovascular regeneration

Three-dimensional (3D) bioprinting of cellular or biological components are an emerging field to develop tissue structures that mimic the spatial, mechanochemical and temporal characteristics of cardiovascular tissues. 3D multi-cellular and multi-domain organotypic biological constructs can better recapitulate in vivo physiology and can be utilized in a variety of applications. Such applications include in vitro cellular studies, high-throughput drug screening, disease modeling, biocompatibility analysis, drug testing and regenerative medicine. A major challenge of 3D bioprinting strategies is the inability of matrix molecules to reconstitute the complexity of the extracellular matrix and the intrinsic cellular morphologies and functions. An important factor is the inclusion of a vascular network to facilitate oxygen and nutrient perfusion in scalable and patterned 3D bioprinted tissues to promote cell viability and functionality. In this review, we summarize the new generation of 3D bioprinting techniques, the kinds of bioinks and printing materials employed for 3D bioprinting, along with the current state-of-the-art in engineered cardiovascular tissue models. We also highlight the translational applications of 3D bioprinting in engineering the myocardium cardiac valves, and vascular grafts. Finally, we discuss current challenges and perspectives of designing effective 3D bioprinted constructs with native vasculature, architecture and functionality for clinical translation and cardiovascular regeneration.

Electrospun nanofibrous membrane for biomedical application

Electrospinning is a simple, cost-effective, flexible, and feasible continuous micro-nano polymer fiber preparation technology that has attracted extensive scientific and industrial interest over the past few decades, owing to its versatility and ability to manufacture highly tunable nanofiber networks. Nanofiber membrane materials prepared using electrospinning have excellent properties suitable for biomedical applications, such as a high specific surface area, strong plasticity, and the ability to manipulate their nanofiber components to obtain the desired properties and functions. With the increasing popularity of nanomaterials in this century, electrospun nanofiber membranes are gradually becoming widely used in various medical fields. Here, the research progress of electrospun nanofiber membrane materials is reviewed, including the basic electrospinning process and the development of the materials as well as their biomedical applications. The main purpose of this review is to discuss the latest research progress on electrospun nanofiber membrane materials and the various new electrospinning technologies that have emerged in recent years for various applications in the medical field. The application of electrospun nanofiber membrane materials in recent years in tissue engineering, wound dressing, cancer diagnosis and treatment, medical protective equipment, and other fields is the main topic of discussion in this review. Finally, the development of electrospun nanofiber membrane materials in the biomedical field is systematically summarized and prospects are discussed. In general, electrospinning has profound prospects in biomedical applications, as it is a practical and flexible technology used for the fabrication of microfibers and nanofibers.

This review summarizes recent research on the application of electrospun nanofiber membranes as tissue engineering materials for the cardiovascular system, motor system, nervous system, and other clinical aspects.

Research on the application of electrospun nanofiber membrane materials as protective products is discussed in the context of the current epidemic situation.

Examples and analyses of recent popular applications in tissue engineering, wound dressing, protective products, and cancer sensors are presented.

Tri-Layered and Gel-Like Nanofibrous Scaffolds with Anisotropic Features for Engineering Heart Valve Leaflets

3D heterogeneous and anisotropic scaffolds that approximate native heart valve tissues are indispensable for the successful construction of tissue engineered heart valves (TEHVs). In this study, novel tri-layered and gel-like nanofibrous scaffolds, consisting of poly(lactic-co-glycolic) acid (PLGA) and poly(aspartic acid) (PASP), are fabricated by a combination of positive/negative conjugate electrospinning and bioactive hydrogel post-processing. The nanofibrous PLGA-PASP scaffolds present tri-layered structures, resulting in anisotropic mechanical properties that are comparable with native heart valve leaflets. Biological tests show that nanofibrous PLGA-PASP scaffolds with high PASP ratios significantly promote the proliferation and collagen and glycosaminoglycans (GAGs) secretions of human aortic valvular interstitial cells (HAVICs), compared to PLGA scaffolds. Importantly, the nanofibrous PLGA-PASP scaffolds are found to effectively inhibit the osteogenic differentiation of HAVICs. Two types of porcine VICs, from young and adult age groups, are further seeded onto the PLGA-PASP scaffolds. The adult VICs secrete higher amounts of collagens and GAGs and undergo a significantly higher level of osteogenic differentiation than young VICs. RNA sequencing analysis indicates that age has a pivotal effect on the VIC behaviors. This study provides important guidance and a reference for the design and development of 3D tri-layered, gel-like nanofibrous PLGA-PASP scaffolds for TEHV applications.

Engineering Efforts to Refine Compatibility and Duration of Aortic Valve Replacements: An Overview of Previous Expectations and New Promises

The absence of pharmacological treatments to reduce or retard the progression of cardiac valve diseases makes replacement with artificial prostheses (mechanical or bio-prosthetic) essential. Given the increasing incidence of cardiac valve pathologies, there is always a more stringent need for valve replacements that offer enhanced performance and durability. Unfortunately, surgical valve replacement with mechanical or biological substitutes still leads to disadvantages over time. In fact, mechanical valves require a lifetime anticoagulation therapy that leads to a rise in thromboembolic complications, while biological valves are still manufactured with non-living tissue, consisting of aldehyde-treated xenograft material (e.g., bovine pericardium) whose integration into the host fails in the mid- to long-term due to unresolved issues regarding immune-compatibility. While various solutions to these shortcomings are currently under scrutiny, the possibility to implant fully biologically compatible valve replacements remains elusive, at least for large-scale deployment. In this regard, the failure in translation of most of the designed tissue engineered heart valves (TEHVs) to a viable clinical solution has played a major role. In this review, we present a comprehensive overview of the TEHVs developed until now, and critically analyze their strengths and limitations emerging from basic research and clinical trials. Starting from these aspects, we will also discuss strategies currently under investigation to produce valve replacements endowed with a true ability to self-repair, remodel and regenerate. We will discuss these new developments not only considering the scientific/technical framework inherent to the design of novel valve prostheses, but also economical and regulatory aspects, which may be crucial for the success of these novel designs.

Tissue Engineered Transcatheter Pulmonary Valved Stent Implantation: Current State and Future Prospect

Patients with the complex congenital heart disease (CHD) are usually associated with right ventricular outflow tract dysfunction and typically require multiple surgical interventions during their lives to relieve the right ventricular outflow tract abnormality. Transcatheter pulmonary valve replacement was used as a non-surgical, less invasive alternative treatment for right ventricular outflow tract dysfunction and has been rapidly developing over the past years. Despite the current favorable results of transcatheter pulmonary valve replacement, many patients eligible for pulmonary valve replacement are still not candidates for transcatheter pulmonary valve replacement. Therefore, one of the significant future challenges is to expand transcatheter pulmonary valve replacement to a broader patient population. This review describes the limitations and problems of existing techniques and focuses on decellularized tissue engineering for pulmonary valve stenting.

Biodegradable Poly-ε-Caprolactone Scaffolds with ECFCs and iMSCs for Tissue-Engineered Heart Valves

Clinically used heart valve prostheses, despite their progress, are still associated with limitations. Biodegradable poly-ε-caprolactone (PCL) nanofiber scaffolds, as a matrix, were seeded with human endothelial colony-forming cells (ECFCs) and human induced-pluripotent stem cells-derived MSCs (iMSCs) for the generation of tissue-engineered heart valves. Cell adhesion, proliferation, and distribution, as well as the effects of coating PCL nanofibers, were analyzed by fluorescence microscopy and SEM. Mechanical properties of seeded PCL scaffolds were investigated under uniaxial loading. iPSCs were used to differentiate into iMSCs via mesoderm. The obtained iMSCs exhibited a comparable phenotype and surface marker expression to adult human MSCs and were capable of multilineage differentiation. EFCFs and MSCs showed good adhesion and distribution on PCL fibers, forming a closed cell cover. Coating of the fibers resulted in an increased cell number only at an early time point; from day 7 of colonization, there was no difference between cell numbers on coated and uncoated PCL fibers. The mechanical properties of PCL scaffolds under uniaxial loading were compared with native porcine pulmonary valve leaflets. The Young's modulus and mean elongation at Fmax of unseeded PCL scaffolds were comparable to those of native leaflets (p = ns.). Colonization of PCL scaffolds with human ECFCs or iMSCs did not alter these properties (p = ns.). However, the native heart valves exhibited a maximum tensile stress at a force of 1.2 ± 0.5 N, whereas it was lower in the unseeded PCL scaffolds (0.6 ± 0.0 N, p < 0.05). A closed cell layer on PCL tissues did not change the values of Fmax (ECFCs: 0.6 ± 0.1 N; iMSCs: 0.7 ± 0.1 N). Here, a successful two-phase protocol, based on the timed use of differentiation factors for efficient differentiation of human iPSCs into iMSCs, was developed. Furthermore, we demonstrated the successful colonization of a biodegradable PCL nanofiber matrix with human ECFCs and iMSCs suitable for the generation of tissue-engineered heart valves. A closed cell cover was already evident after 14 days for ECFCs and 21 days for MSCs. The PCL tissue did not show major mechanical differences compared to native heart valves, which was not altered by short-term surface colonization with human cells in the absence of an extracellular matrix.

Anisotropic elastic behavior of a hydrogel-coated electrospun polyurethane: Suitability for heart valve leaflets

Although xenograft biomaterials have been used for decades in replacement heart valves, they continue to face multiple limitations, including limited durability, mineralization, and restricted design space due to their biological origins. These issues necessitate the need for novel replacement heart valve biomaterials that are durable, non-thrombogenic, and compatible with transcatheter aortic valve replacement devices. In this study, we explored the suitability of an electrospun poly(carbonate urethane) (ES-PCU) mesh coated with a poly(ethylene glycol) diacrylate (PEGDA) hydrogel as a synthetic biomaterial for replacement heart valve leaflets. In this material design, the mesh provides the mechanical support, while the hydrogel provides the required surface hemocompatibility. We conducted a comprehensive study to characterize the structural and mechanical properties of the uncoated mesh as well as the hydrogel-coated mesh (composite biomaterial) over the estimated operational range. We found that the composite biomaterial was functionally robust with reproducible stress-strain behavior within and beyond the functional ranges for replacement heart valves, and was able to withstand the rigors of mechanical evaluation without any observable damage. In addition, the composite biomaterial displayed a wide range of mechanical anisotropic responses, which were governed by fiber orientation of the mesh, which in turn, was controlled with the fabrication process. Finally, we developed a novel constitutive modeling approach to predict the mechanical behavior of the composite biomaterial under in-plane extension and shear deformation modes. This model identified the existence of fiber-fiber mechanical interactions in the mesh that have not previously been reported. Interestingly, there was no evidence of fiber-hydrogel mechanical interactions. This important finding suggests that the hydrogel coating can be optimized for hemocompatibility independent of the structural mechanical responses required by the leaflet. This initial study indicated that the composite biomaterial has mechanical properties well-suited for replacement heart valve applications and that the electrospun mesh microarchitecture and hydrogel biological properties can be optimized independently. It also reveals that the structural mechanisms contributing to the mechanical response are more complicated than what was previously established and paves the pathway for more detailed future studies.

Leaflet Tissue Generation from Microfibrous Heart Valve Leaflet Scaffolds with Native Characteristics

Mechanical and bioprosthetic valves that are currently applied for replacing diseased heart valves are not fully efficient. Heart valve tissue engineering may solve the issues faced by the prosthetic valves in heart valve replacement. The leaflets of native heart valves have a trilayered structure with layer-specific orientations; thus, it is imperative to develop functional leaflet tissue constructs with a native trilayered, oriented structure. Its key solution is to develop leaflet scaffolds with a native morphology and structure. In this study, microfibrous leaflet scaffolds with a native trilayered and oriented structure were developed in an electrospinning system. The scaffolds were implanted for 3 months in rats subcutaneously to study the scaffold efficiencies in generating functional tissue-engineered leaflet constructs. These in vivo tissue-engineered leaflet constructs had a trilayered, oriented structure similar to native leaflets. The tensile properties of constructs indicated that they were able to endure the hydrodynamic load of the native heart valve. Collagen, glycosaminoglycans, and elastin─the predominant extracellular matrix components of native leaflets─were found sufficiently in the leaflet tissue constructs. The residing cells in the leaflet tissue constructs showed vimentin and α-smooth muscle actin expression, i.e., the constructs were in a growing state. Thus, the trilayered, oriented fibrous leaflet scaffolds produced in this study could be useful to develop heart valve scaffolds for successful heart valve replacements.

Three-Dimensional Printing of Patient-Specific Heart Valves: Separating Facts From Fiction and Myth From Reality

The development of prosthetic heart valves by Dr. Charles Hufnagel in 1952 was a major clinical innovation; however, it was not an ideal solution. Mechanical prosthetic heart valves are rigid, immunogenic, require anticoagulation, do not grow with the patient, and have a finite life.¹ An ideal prosthetic valve should overcome all these limitations. Considering the prevalence of valvular heart disorders, there is considerable interest in the creation of patient-specific heart valves. Following the introduction of three-dimensional (3D) printing in 1986 by Chuck Hill, rapid advances in multimodality 3D imaging and modeling have led to a generation of tangible replicas of patient-specific anatomy. The science of organogenesis has gained importance for a multitude of valid reasons: as an alternate source of organs, for realistic drug testing, as an alternative to animal testing, and for transplants that grow with the patient. What scientists imagined to be seemingly impossible in the past now seems just a step away from becoming a reality. However, due to the disruptive nature of this technology, often there are commercially-motivated claims of originality and overstatement of the scope and applicability of 3D printing. It often is difficult to separate fact from fiction and myth from reality. In this manuscript, the authors have reviewed the historic perspective, status of the basic techniques of organogenesis with specific reference to heart valves, and their potential.

Fibrous heart valve leaflet substrate with native-mimicked morphology

Tissue-engineered heart valves are a promising alternative solution to prosthetic valves. However, long-term functionalities of tissue-engineered heart valves depend on the ability to mimic the trilayered, oriented structure of native heart valve leaflets. In this study, using electrospinning, we developed trilayered microfibrous leaflet substrates with morphological characteristics similar to native leaflets. The substrates were implanted subcutaneously in rats to study the effect of their trilayered oriented structure on in vivo tissue engineering. The tissue constructs showed a well-defined structure, with a circumferentially oriented layer, a randomly oriented layer and a radially oriented layer. The extracellular matrix, produced during in vivo tissue engineering, consisted of collagen, glycosaminoglycans, and elastin, all major components of native leaflets. Moreover, the anisotropic tensile properties of the constructs were sufficient to bear the valvular physiological load. Finally, the expression of vimentin and α-smooth muscle actin, at the gene and protein level, was detected in the residing cells, revealing their growing state and their transdifferentiation to myofibroblasts. Our data support a critical role for the trilayered structure and anisotropic properties in functional leaflet tissue constructs, and indicate that the leaflet substrates have the potential for the development of valve scaffolds for heart valve replacements.

Engineering the aortic valve extracellular matrix through stages of development, aging, and disease

For such a thin tissue, the aortic valve possesses an exquisitely complex, multi-layered extracellular matrix (ECM), and disruptions to this structure constitute one of the earliest hallmarks of fibrocalcific aortic valve disease (CAVD). The native valve structure provides a challenging target for engineers to mimic, but the development of advanced, ECM-based scaffolds may enable mechanistic and therapeutic discoveries that are not feasible in other culture or in vivo platforms. This review first discusses the ECM changes that occur during heart valve development, normal aging, onset of early-stage disease, and progression to late-stage disease. We then provide an overview of the bottom-up tissue engineering strategies that have been used to mimic the valvular ECM, and opportunities for advancement in these areas.

A Review: Optimization for Poly(glycerol sebacate) and Fabrication Techniques for Its Centered Scaffolds

Poly(glycerol sebacate) (PGS), an emerging promising thermosetting polymer synthesized from sebacic acid and glycerol, has attracted considerable attention due to its elasticity, biocompatibility, and tunable biodegradation properties. But it also has some drawbacks such as harsh synthesis conditions, rapid degradation rates, and low stiffness. To overcome these challenges and optimize PGS performance, various modification methods and fabrication techniques for PGS-based scaffolds have been developed in recent years. Outlining the current modification approaches of PGS and summarizing the fabrication techniques for PGS-based scaffolds are of great importance to accelerate the development of new materials and enable them to be appropriately used in potential applications. Thus, this review comprehensively overviews PGS derivatives, PGS composites, PGS blends, processing for PGS-based scaffolds, and their related applications. It is envisioned that this review could instruct and inspire the design of the PGS-based materials and facilitate tissue engineering advances into clinical practice.

A novel detergent-based decellularization combined with carbodiimide crosslinking for improving anti-calcification of bioprosthetic heart valve

Currently, valve replacement surgery is the only therapy for the end-stage valvular diseases because of the inability of regeneration for diseased heart valves. Bioprosthetic heart valves (BHVs), which are mainly derived from glutaraldehyde (GA) crosslinked porcine aortic heart valves or bovine pericardium, have been widely used in the last decades. However, it is inevitable that calcification and deterioration may occur within 10-15 years, which are still the main challenges for the BHVs in clinic. In this study, N-Lauroylsarcosine sodium salt (SLS) combined with N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) were utilized to decellularize and crosslink the heart valves instead of GA treatment. The obtained BHVs exhibited excellent extracellular matrix stability and mechanical properties, which were similar with GA treatment. Moreover, the obtained BHVs exhibited betterin vitrobiocompatibilities than GA treatment. After subcutaneous implantation for 30 d, the obtained BHVs showed mitigated immune response and reduced calcification compare with GA treatment. Therefore, all the above results indicated that the treatment of SLS-based decellularization combined with EDC/NHS crosslink should be a promising method to fabricate BHVs which can be used in clinic in future.

Biomaterials in Valvular Heart Diseases

Valvular heart disease (VHD) occurs as the result of valvular malfunction, which can greatly reduce patient's quality of life and if left untreated may lead to death. Different treatment regiments are available for management of this defect, which can be helpful in reducing the symptoms. The global commitment to reduce VHD-related mortality rates has enhanced the need for new therapeutic approaches. During the past decade, development of innovative pharmacological and surgical approaches have dramatically improved the quality of life for VHD patients, yet the search for low cost, more effective, and less invasive approaches is ongoing. The gold standard approach for VHD management is to replace or repair the injured valvular tissue with natural or synthetic biomaterials. Application of these biomaterials for cardiac valve regeneration and repair holds a great promise for treatment of this type of heart disease. The focus of the present review is the current use of different types of biomaterials in treatment of valvular heart diseases.

Mapping current research and identifying hotspots on mesenchymal stem cells in cardiovascular disease

BACKGROUND

Mesenchymal stem cells (MSCs) have important research value and broad application prospects in the cardiovascular disease. This study provides information on the latest progress, evolutionary path, frontier research hotspots, and future research developmental trends in this field.

METHODS

A knowledge map was generated by CiteSpace and VOSviewer analysis software based on data obtained from the literature on MSCs in the cardiovascular field.

RESULTS

The USA and China ranked at the top in terms of the percentage of articles, accounting for 34.306% and 28.550%, respectively. The institution with the highest number of research publications in this field was the University of Miami, followed by the Chinese Academy of Medical Sciences and Harvard University. The research institution with the highest ACI value was Harvard University, followed by the Mayo Clinic and the University of Cincinnati. The top three subjects in terms of the number of published articles were cell biology, cardiovascular system cardiology, and research experimental medicine. The journal with the most publications in this field was Circulation Research, followed by Scientific Reports and Biomaterials. The direction of research on MSCs in the cardiovascular system was divided into four parts: (1) tissue engineering, scaffolds, and extracellular matrix research; (2) cell transplantation, differentiation, proliferation, and signal transduction pathway research; (3) assessment of the efficacy of stem cells from different sources and administration methods in the treatment of acute myocardial infarction, myocardial hypertrophy, and heart failure; and (4) exosomes and extracellular vesicles research. Tissue research is the hotspot and frontier in this field.

CONCLUSION

MSC research has presented a gradual upward trend in the cardiovascular field. Multidisciplinary intersection is a characteristic of this field. Engineering and materials disciplines are particularly valued and have received attention from researchers. The progress in multidisciplinary research will provide motivation and technical support for the development of this field.

Trilayered tissue construct mimicking the orientations of three layers of a native heart valve leaflet

A tissue-engineered heart valve can be an alternative to a prosthetic valve in heart valve replacement; however, it is not fully efficient in terms of long-lasting functionality, as leaflets in engineered valves do not possess the trilayered native leaflet structure. Previously, we developed a flat, trilayered, oriented nanofibrous (TN) scaffold mimicking the trilayered structure and orientation of native heart valve leaflets. In vivo tissue engineering-a practical regenerative medicine technology-can be used to develop an autologous heart valve. Thus, in this study, we used our flat, trilayered, oriented nanofibrous scaffolds to develop trilayered tissue structures with native leaflet orientations through in vivo tissue engineering in a rat model. After 2 months of in vivo tissue engineering, infiltrated cells and their deposited collagen fibrils were found aligned in the circumferential and radial layers, and randomly oriented in the random layer of the scaffolds, i.e., trilayered tissue constructs (TTCs) were developed. Tensile properties of the TTCs were higher than that of the control tissue constructs (without any scaffolds) due to influence of fibers of the scaffolds in tissue engineering. Different extracellular matrix proteins-collagen, glycosaminoglycans, and elastin-that exist in native leaflets were observed in the TTCs. Gene expression of the TTCs indicated that the tissue constructs were in growing stage. There was no sign of calcification in the tissue constructs. The TTCs developed with the flat TN scaffolds indicate that an autologous leaflet-shaped, trilayered tissue construct that can function as a native leaflet can be developed.

Anisotropic Fiber-Reinforced Glycosaminoglycan Hydrogels for Heart Valve Tissue Engineering

This study investigates polymer fiber-reinforced protein-polysaccharide-based hydrogels for heart valve tissue engineering applications. Polycaprolactone and gelatin (3:1) blends were jet-spun to fabricate aligned fibers that possessed fiber diameters in the range found in the native heart valve. These fibers were embedded in methacrylated hydrogels made from gelatin, sodium hyaluronate, and chondroitin sulfate to create fiber-reinforced hydrogel composites (HCs). The fiber-reinforced gelatin glycosaminoglycan (GAG)-based HC possessed interconnected porous structures and porosity higher than fiber-only conditions. These fiber-reinforced HCs exhibited compressive modulus and biaxial mechanical behavior comparable to that of native porcine aortic valves. The fiber-reinforced HCs were able to swell higher and degraded less than the hydrogels. Elution studies revealed that less than 20% of incorporated gelatin methacrylate and GAGs were released over 2 weeks, with a steady-state release after the first day. When cultured with porcine valve interstitial cells (VICs), the fiber-reinforced composites were able to maintain higher cell viability compared with fiber-only samples. Quiescent VICs expressed alpha smooth muscle actin and calponin showing an activated phenotype, along with a few cells expressing the proliferation marker Ki67 and negative expression for RUNX2, an osteogenic marker. Our study demonstrated that compared with the hydrogels and fibers alone, combining both components can yield durable, reinforced composites that mimic heart valve mechanical behavior, while maintaining high cell viability and expressing positive activation as well as proliferation markers.

Cells, Materials, and Fabrication Processes for Cardiac Tissue Engineering

Cardiovascular disease is the number one killer worldwide, with myocardial infarction (MI) responsible for approximately 1 in 6 deaths. The lack of endogenous regenerative capacity, added to the deleterious remodelling programme set into motion by myocardial necrosis, turns MI into a progressively debilitating disease, which current pharmacological therapy cannot halt. The advent of Regenerative Therapies over 2 decades ago kick-started a whole new scientific field whose aim was to prevent or even reverse the pathological processes of MI. As a highly dynamic organ, the heart displays a tight association between 3D structure and function, with the non-cellular components, mainly the cardiac extracellular matrix (ECM), playing both fundamental active and passive roles. Tissue engineering aims to reproduce this tissue architecture and function in order to fabricate replicas able to mimic or even substitute damaged organs. Recent advances in cell reprogramming and refinement of methods for additive manufacturing have played a critical role in the development of clinically relevant engineered cardiovascular tissues. This review focuses on the generation of human cardiac tissues for therapy, paying special attention to human pluripotent stem cells and their derivatives. We provide a perspective on progress in regenerative medicine from the early stages of cell therapy to the present day, as well as an overview of cellular processes, materials and fabrication strategies currently under investigation. Finally, we summarise current clinical applications and reflect on the most urgent needs and gaps to be filled for efficient translation to the clinical arena.

A Pulsatile Flow System to Engineer Aneurysm and Atherosclerosis Mimetic Extracellular Matrix

Alterations of blood flow patterns strongly correlate with arterial wall diseases such as atherosclerosis and aneurysm. Here, a simple, pumpless, close-loop, easy-to-replicate, and miniaturized flow device is introduced to concurrently expose 3D engineered vascular smooth muscle tissues to high-velocity pulsatile flow versus low-velocity disturbed flow conditions. Two flow regimes are distinguished, one that promotes elastin and impairs collagen I assembly, while the other impairs elastin and promotes collagen assembly. This latter extracellular matrix (ECM) composition shares characteristics with aneurysmal or atherosclerotic tissue phenotypes, thus recapitulating crucial hallmarks of flow-induced tissue morphogenesis in vessel walls. It is shown that the mRNA levels of ECM of collagens and elastin are not affected by the differential flow conditions. Instead, the differential gene expression of matrix metalloproteinase (MMP) and their inhibitors (TIMPs) is flow-dependent, and thus drives the alterations in ECM composition. In further support, treatment with doxycycline, an MMP inhibitor and a clinically used drug to treat vascular diseases, halts the effect of low-velocity flow on the ECM remodeling. This illustrates how the platform can be exploited for drug efficacy studies by providing crucial mechanistic insights into how different therapeutic interventions may affect tissue growth and ECM assembly.

Hybrid cardiovascular sourced extracellular matrix scaffolds as possible platforms for vascular tissue engineering

The aim when designing a scaffold is to provide a supportive microenvironment for the native cells, which is generally achieved by structurally and biochemically imitating the native tissue. Decellularized extracellular matrix (ECM) possesses the mechanical and biochemical cues designed to promote native cell survival. However, when decellularized and reprocessed, the ECM loses its cell supporting mechanical integrity and architecture. Herein, we propose dissolving the ECM into a polymer/solvent solution and electrospinning it into a fibrous sheet, thus harnessing the biochemical cues from the ECM and the mechanical integrity of the polymer. Bovine aorta and myocardium were selected as ECM sources. Decellularization was achieved using sodium dodecyl sulfate (SDS), and the ECM was combined with polycaprolactone and hexafluoro-2-propanol for electrospinning. The scaffolds were seeded with human umbilical vein endothelial cells (HUVECs). The study found that the inclusion of aorta ECM increased the scaffold's wettability and subsequently lead to increased HUVEC adherence and proliferation. Interestingly, the inclusion of myocardium ECM had no effect on wettability or cell viability. Furthermore, gene expression and mechanical changes were noted with the addition of ECM. The results from this study show the vast potential of electrospun ECM/polymer bioscaffolds and their use in tissue engineering.

Multi-layer Scaffolds of Poly(caprolactone), Poly(glycerol sebacate) and Bioactive Glasses Manufactured by Combined 3D Printing and Electrospinning

Three-dimensional (3D) printing has been combined with electrospinning to manufacture multi-layered polymer/glass scaffolds that possess multi-scale porosity, are mechanically robust, release bioactive compounds, degrade at a controlled rate and are biocompatible. Fibrous mats of poly (caprolactone) (PCL) and poly (glycerol sebacate) (PGS) have been directly electrospun on one side of 3D-printed grids of PCL-PGS blends containing bioactive glasses (BGs). The excellent adhesion between layers has resulted in composite scaffolds with a Young's modulus of 240-310 MPa, higher than that of 3D-printed grids (125-280 MPa, without the electrospun layer). The scaffolds degraded in vitro by releasing PGS and BGs, reaching a weight loss of ~14% after 56 days of incubation. Although the hydrolysis of PGS resulted in the acidification of the buffer medium (to a pH of 5.3-5.4), the release of alkaline ions from the BGs balanced that out and brought the pH back to 6.0. Cytotoxicity tests performed on fibroblasts showed that the PCL-PGS-BGs constructs were biocompatible, with cell viability of above 125% at day 2. This study demonstrates the fabrication of systems with engineered properties by the synergy of diverse technologies and materials (organic and inorganic) for potential applications in tendon and ligament tissue engineering.

In vivo tissue engineering of a trilayered leaflet-shaped tissue construct

Aim: We aimed to develop a leaflet-shaped trilayered tissue construct mimicking the morphology of native heart valve leaflets. Materials & methods: Electrospinning and in vivo tissue engineering methods were employed. Results: We developed leaflet-shaped microfibrous scaffolds, each with circumferentially, randomly and radially oriented three layers mimicking the trilayered, oriented structure of native leaflets. After 3 months in vivo tissue engineering with the scaffolds, the generated leaflet-shaped tissue constructs had a trilayered structure mimicking the orientations of native heart valve leaflets. Presence of collagen, glycosaminoglycans and elastin seen in native leaflets was observed in the engineered tissue constructs. Conclusion: Trilayered, oriented fibrous scaffolds brought the orientations of the infiltrated cells and their produced extracellular matrix proteins into the constructs.

Poly(Glycerol Sebacate)-Poly(l-Lactide) Nonwovens. Towards Attractive Electrospun Material for Tissue Engineering

Two types of poly(glycerol sebacate) (PGS) prepolymers were synthesized and electrospun with poly(l-lactic acid) (PLA), resulting in bicomponent nonwovens. The obtained materials were pre-heated in a vacuum, at different times, to crosslink PGS and investigate morphological and structural dependencies in that polymeric, electrospun system. As both PGS and PLA are sensitive to pre-heating (crosslinking) conditions, research concerns both components. More interest is focused on the properties of PGS, considering further research for mechanical properties and subsequent experiments with PGS synthesis. Electrospinning of PGS blended with PLA does not bring difficulties, but obtaining elastomeric properties of nonwovens is problematic. Even though PGS has many potential advantages over other polyesters when soft tissue engineering is considered, its full utilization via the electrospinning process is much harder in practice. Further investigations are ongoing, especially with the promising PGS prepolymer with a higher esterification degree and its variations.