Electrospun PGS:PCL microfibers align human valvular interstitial cells and provide tunable scaffold anisotropy

A lipid activated color switchable probe for the imaging of diseased aortic valves

Lipid deposition has been considered one of the key factors in the occurrence of valvular heart disease (VHD) and a great potential target for the diagnosis of VHD. However, the development of lipid imaging technologies and efficient lipid specific probes is in urgent demand. In this work, we have prepared a lipid droplets (LDs) targeted fluorescence probe CPTM based on a push-pull electronic structure for the imaging of diseased aortic valves. CPTM showed obvious twisted intramolecular charge transfer (TICT) effect and its emission changed from 600 nm in water to 508 nm in oil. CPTM not only exhibited good biocompatibility and high photostability, but also impressive LDs specific imaging performance in human primary valvular interstitial cells and human diseased aortic valves. Moreover, the dynamic changes of intracellular LDs could be monitor in real-time after staining with CPTM. These results were expected to offer new ideals for the designing of novel LDs specific probes for further bioimaging applications.

Melt-electrowriting-enabled anisotropic scaffolds loaded with valve interstitial cells for heart valve tissue Engineering

Tissue engineered heart valves (TEHVs) demonstrates the potential for tissue growth and remodel, offering particular benefit for pediatric patients. A significant challenge in designing functional TEHV lies in replicating the anisotropic mechanical properties of native valve leaflets. To establish a biomimetic TEHV model, we employed melt-electrowriting (MEW) technology to fabricate an anisotropic PCL scaffold. By integrating the anisotropic MEW-PCL scaffold with bioactive hydrogels (GelMA/ChsMA), we successfully crafted an elastic scaffold with tunable mechanical properties closely mirroring the structure and mechanical characteristics of natural heart valves. This scaffold not only supports the growth of valvular interstitial cells (VICs) within a 3D culture but also fosters the remodeling of extracellular matrix of VICs. The in vitro experiments demonstrated that the introduction of ChsMA improved the hemocompatibility and endothelialization of TEHV scaffold. The in vivo experiments revealed that, compared to their non-hydrogel counterparts, the PCL-GelMA/ChsMA scaffold, when implanted into SD rats, significantly suppressed immune reactions and calcification. In comparison with the PCL scaffold, the PCL-GelMA/ChsMA scaffold exhibited higher bioactivity and superior biocompatibility. The amalgamation of MEW technology and biomimetic design approaches provides a new paradigm for manufacturing scaffolds with highly controllable microstructures, biocompatibility, and anisotropic mechanical properties required for the fabrication of TEHVs.

Electrospun Scaffolds are Not Necessarily Always Made of Nanofibers as Demonstrated by Polymeric Heart Valves for Tissue Engineering

In the last 30 years, there are ≈60 000 publications about electrospun nanofibers, but it is still unclear whether nanoscale fibers are really necessary for electrospun tissue engineering scaffolds. The present report puts forward this argument and reveals that compared with electrospun nanofibers, microfibers with diameter of ≈3 µm (named as "oligo-micro fiber") are more appropriate for tissue engineering scaffolds owing to their better cell infiltration ability caused by larger pores with available nuclear deformation. To further increase pore sizes, electrospun poly(ε-caprolactone) (PCL) scaffolds are fabricated using latticed collectors with meshes. Fiber orientation leads to sufficient mechanical strength albeit increases porosity. The latticed scaffolds exhibit good biocompatibility and improve cell infiltration. Under aortic conditions in vitro, the performances of latticed scaffolds are satisfactory in terms of the acute systolic hemodynamic functionality, except for the higher regurgitation fraction caused by the enlarged pores. This hierarchical electrospun scaffold with sparse fibers in macropores and oligo-micro fibers in filaments provides new insights into the design of tissue engineering scaffolds, and tissue engineering may provide living heart valves with regenerative capabilities for patients with severe valve disease in the future.

Polyglycerol sebacate-based elastomeric materials for arterial regeneration

Synthetic vascular grafts are commonly used in patients with severe occlusive arterial disease when autologous grafts are not an option. Commercially available synthetic grafts are confronted with challenging outcomes: they have a lower patency rate than autologous grafts and are currently unable to promote arterial regeneration. Polyglycerol sebacate (PGS), a non-toxic polymer with a tunable degradation profile, has shown promising results as a small-diameter vascular graft component that can support the formation of neoarteries. In this review, we first present an overview of the synthesis and modification of PGS followed by an examination of its mechanical properties. We then report on the performance, degradation, regeneration, and remodeling of PGS-based small-diameter vascular grafts, with a focus on efforts to reduce thrombosis, prevent dilation, and promote cellular residency and extracellular matrix regeneration that resembles the native artery in spatial distribution and organization. We also highlight recent advances in the incorporation of novel in situ cell sources for arterial regeneration and their potential application in PGS-based vascular grafts. Finally, we compare vascular grafts fabricated using PGS-based materials with other elastomeric alternatives.

Nonwoven Reinforced Photocurable Poly(glycerol sebacate)-Based Hydrogels

Implantable hydrogels should ideally possess mechanical properties matched to the surrounding tissues to enable adequate mechanical function while regeneration occurs. This can be challenging, especially when degradable systems with a high water content and hydrolysable chemical bonds are required in anatomical sites under constant mechanical stimulation, e.g., a foot ulcer cavity. In these circumstances, the design of hydrogel composites is a promising strategy for providing controlled structural features and macroscopic properties over time. To explore this strategy, the synthesis of a new photocurable elastomeric polymer, poly(glycerol-co-sebacic acid-co-lactic acid-co-polyethylene glycol) acrylate (PGSLPA), is investigated, along with its processing into UV-cured hydrogels, electrospun nonwovens and fibre-reinforced variants, without the need for a high temperature curing step or the use of hazardous solvents. The mechanical properties of bioresorbable PGSLPA hydrogels were studied with and without electrospun nonwoven reinforcement and with varied layered configurations, aiming to determine the effects of the microstructure on the bulk compressive strength and elasticity. The nonwoven reinforced PGSLPA hydrogels exhibited a 60% increase in compressive strength and an 80% increase in elastic moduli compared to the fibre-free PGSLPA samples. The mechanical properties of the fibre-reinforced hydrogels could also be modulated by altering the layering arrangement of the nonwoven and hydrogel phase. The nanofibre-reinforced PGSLPA hydrogels also exhibited good elastic recovery, as evidenced by the hysteresis in compression fatigue stress-strain evaluations showing a return to the original dimensions.

A novel biomimetic nanofibrous cardiac tissue engineering scaffold with adjustable mechanical and electrical properties based on poly(glycerol sebacate) and polyaniline

Biomaterial tissue engineering scaffolds play a critical role in providing mechanical support, promoting cells growth and proliferation. However, due to the insulation and inappropriate stiffness of most biomaterials, there is an unmet need to engineer a biomimetic nanofibrous cardiac tissue engineering scaffold with tailorable mechanical and electrical properties. Here, we demonstrate for the first time the feasibility to generate a novel type of biocompatible fibrous scaffolds by blending elastic poly(glycerol sebacate) (PGS) and conductive polyaniline (PANI) with the help of a nontoxic carrier polymer, poly (vinyl alcohol) (PVA). Aligned and random PGS/PANI scaffolds are successfully obtained after electrospinning, cross-linking, water and ethanol wash. Incorporating of different concentrations of PANI into PGS fibers, the fibrous sheets show enhanced conductivity and slower degradation rates while maintaining the favorable hemocompatibility. The elastic modulus of the PGS/PANI scaffolds is in the range of 0.65-2.18 MPa under wet conditions, which is similar to that of natural myocardium. All of these fibrous mats show good cell viability and were able to promote adhesion and proliferation of H9c2 cells. Furthermore, the in vivo host responses of both random and aligned scaffolds confirm their good biocompatibility. Therefore, these PGS/PANI scaffolds have great potential for cardiac tissue engineering.

Self-organizing behaviors of cardiovascular cells on synthetic nanofiber scaffolds

In tissues and organs, the extracellular matrix (ECM) helps maintain inter- and intracellular architectures that sustain the structure-function relationships defining physiological homeostasis. Combining fiber scaffolds and cells to form engineered tissues is a means of replicating these relationships. Engineered tissues' fiber scaffolds are designed to mimic the topology and chemical composition of the ECM network. Here, we asked how cells found in the heart compare in their propensity to align their cytoskeleton and self-organize in response to topological cues in fibrous scaffolds. We studied cardiomyocytes, valvular interstitial cells, and vascular endothelial cells as they adapted their inter- and intracellular architectures to the extracellular space. We used focused rotary jet spinning to manufacture aligned fibrous scaffolds to mimic the length scale and three-dimensional (3D) nature of the native ECM in the muscular, valvular, and vascular tissues of the heart. The representative cardiovascular cell types were seeded onto fiber scaffolds and infiltrated the fibrous network. We measured different cell types' propensity for cytoskeletal alignment in response to fiber scaffolds with differing levels of anisotropy. The results indicated that valvular interstitial cells on moderately anisotropic substrates have a higher propensity for cytoskeletal alignment than cardiomyocytes and vascular endothelial cells. However, all cell types displayed similar levels of alignment on more extreme (isotropic and highly anisotropic) fiber scaffold organizations. These data suggest that in the hierarchy of signals that dictate the spatiotemporal organization of a tissue, geometric cues within the ECM and cellular networks may homogenize behaviors across cell populations and demographics.

Elastomeric Polyesters in Cardiovascular Tissue Engineering and Organs-on-a-Chip

Cardiovascular tissue constructs provide unique design requirements due to their functional responses to substrate mechanical properties and cyclic stretching behavior of cardiac tissue that requires the use of durable elastic materials. Given the diversity of polyester synthesis approaches, an opportunity exists to develop a new class of biocompatible, elastic, and immunomodulatory cardiovascular polymers. Furthermore, elastomeric polyester materials have the capability to provide tailored biomechanical synergy with native tissue and hence reduce inflammatory response in vivo and better support tissue maturation in vitro. In this review, we highlight underlying chemistry and design strategies of polyester elastomers optimized for cardiac tissue scaffolds. The major advantages of these materials such as their tunable elasticity, desirable biodegradation, and potential for incorporation of bioactive compounds are further expanded. Unique fabrication methods using polyester materials such as micromolding, 3D stamping, electrospinning, laser ablation, and 3D printing are discussed. Moreover, applications of these biomaterials in cardiovascular organ-on-a-chip devices and patches are analyzed. Finally, we outline unaddressed challenges in the field that need further study to enable the impactful translation of soft polyesters to clinical applications.

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.

Designing Biocompatible Tissue Engineered Heart Valves In Situ: JACC Review Topic of the Week

Valvular heart disease is a globally prevalent cause of morbidity and mortality, with both congenital and acquired clinical presentations. Tissue engineered heart valves (TEHVs) have the potential to radically shift the treatment landscape for valvular disease by functioning as life-long valve replacements that overcome the current limitations of bioprosthetic and mechanical valves. TEHVs are envisioned to meet these goals by functioning as bioinstructive scaffolds that guide the in situ generation of autologous valves capable of growth, repair, and remodeling within the patient. Despite their promise, clinical translation of in situ TEHVs has proven challenging largely because of the unpredictable and patient-specific nature of the TEHV and host interaction following implantation. In light of this challenge, we propose a framework for the development and clinical translation of biocompatible TEHVs, wherein the native valvular environment actively informs the valve's design parameters and sets the benchmarks by which it is functionally evaluated.

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.

Elastomeric, bioadhesive and pH-responsive amphiphilic copolymers based on direct crosslinking of poly(glycerol sebacate)-co-polyethylene glycol

Poly(glycerol sebacate) (PGS), a synthetic biorubber, is characterised by its biocompatibility, high elasticity and tunable mechanical properties; however, its inherent hydrophobicity and insolubility in water make it unsuitable for use in advanced biomaterials like hydrogels fabrication. Here, we developed new hydrophilic PGS-based copolymers that enable hydrogel formation through use of two different types of polyethylene glycol (PEG), polyethylene glycol (PEG2) or glycerol ethoxylate (PEG3), combined at different ratios. A two-step polycondensation reaction was used to produce poly(glycerol sebacate)-co-polyethylene glycol (PGS-co-PEG) copolymers that were then crosslinked thermally without the use of initiators or crosslinkers, resulting in PGS-co-PEG2 and PGS-co-PEG3 amphiphilic polymers. It has been illustrated that the properties of PGS-co-PEG copolymers can be controlled by altering the type and amount of PEG. PGS-co-PEG copolymers containing PEG ≥ 40% showed high swelling, flexibility, stretching, bioadhesion and biocompatibility, and good enzymatic degradation and mechanical properties. Also, the addition of PEG created hydrogels that demonstrated pH-responsive behaviours, which can be used for bioapplications requiring responding to physicochemical dynamics. Interestingly, PGS-co-40PEG2 and PGS-co-60PEG3 had the highest shear strengths, 340.4 ± 49.7 kPa and 336.0 ± 35.1 kPa, and these are within the range of commercially available sealants or bioglues. Due to the versatile multifunctionalities of these new copolymer hydrogels, they can have great potential in soft tissue engineering and biomedicine.

Generating robust human valvular interstitial cell cultures: Protocol and considerations

Research in heart valve biology is a growing field that has yet to elucidate the fundamentals of valve disease. Human valvular interstitial cells (hVICs) are the best option for studying the cellular mechanisms behind valvular pathologies. However, there is a wide range of isolation procedures for these cells published in the literature. To what extent various isolation methods, patient pathologies, and seeding densities influence the behaviour of hVICs remains unclear. Here, we present an optimised method of hVIC isolation from diseased human valves donated at the time of surgery. We show that two rounds of 1000 U/mL collagenase digestion for not >2 h results in a phenotypically stable cell culture with a near complete absence of endothelial cell contamination. We also suggest that cells should be seeded at 10,000 cells/cm² for experimentation. We found that patient pathology does not affect the success of the isolation procedure, and that instead, successful cultures are predicted by ensuring >500 mg valve tissue as starting material.

De novo dual functional 3D scaffold using computational simulation with controlled drug release

A novel and facile synthesis is made of cotton-like three-dimensional (3D) fibrous scaffold containing spatiotemporally defined patterns of simvastatin (SIM) optimized for angiogenesis-coupled osteogenesis. Herein, we demonstrate the 3D fiber deposition mechanism in detail during the electrospinning process via computer simulation. The 3D fibrous scaffolds were functionalized with hydroxyapatite nanoparticles (HA - NPs) to induce the biomineralization process mimicking the natural apatite layer. The morphology, physiochemical properties, biomimetic mineralization, and drug release of the as-fabricated 3D fibrous scaffolds of simvastatin-loaded poly (ɛ-caprolactone) poly (glycerol-sebacate) hydroxyapatite nanoparticles (3D - PGHS) were investigated. The effects of simvastatin on the osteogenic differentiation of human mesenchymal stem cells (hMSCs) and angiogenesis in human umbilical vein endothelial cells (HUVECs) were assessed. The results showed that the 3D - PGHS both enhanced the expression of osteogenic markers including ALP, RUNX2, and COLA1 in hMSCs, and promoted the migration and tube formation of HUVECs. This finding demonstrates the potential of 3D scaffold-loaded SIM as a putative point-of-care therapy for tightly controlled tissue regeneration.

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.

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.

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.

Critical review on microfibrous composites for applications in chemical engineering

Microfibrous composites (MCs) are novel materials with unique structures and excellent functional properties, showing great potential in industrial applications. The investigation of the physicochemical properties of MCs is significant for accommodating the rapid development of high-efficiency chemical engineering industries. In this review, the characteristics, synthesis and applications of different types of previously reported MCs are discussed according to the constituent fibres, including polymers, metals and nonmetals. Among the different types of MCs, polymer MCs have a facile synthesis process and adjustable fibre composition, making them suitable for many complex situations. The high thermal and electrical conductivity of metal MCs enables their application in strong exothermic, endothermic and electrochemical reactions. Nonmetallic MCs are usually stable and corrosion resistant when reducing and oxidizing environments. The disadvantages of MCs, such as complicated synthesis processes compared to those of particles or powders, high cost, insufficient thorough study, and unsatisfactory regeneration effects, are also summarized. As a result, a more systematic investigation of MCs remains necessary. Despite the advantages and great application potential of microfibrous composites, much effort remains necessary to advance them to the industrial level in the chemical engineering industry.

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.

Fabrication of Thick and Anisotropic Cardiac Tissue on Nanofibrous Substrate for Repairing Infarcted Myocardium

In this chapter, we introduce the method for fabricating thick and anisotropic cardiac tissue for heart regeneration. Aligned and biodegradable nanofiber can be prepared by electrospinning Food and Drug Administration-approved poly (lactic-co-glycolic acid) on a rotating drum. After the nanofibers are transferred on to a polydimethylsiloxane frame, the cardiomyocytes could be plated on the nanofiber to form thick and anisotropic cardiac tissue rapidly. Cardiac tissue-like construct could be easily created by one-step method, and transplanted onto the hearts of myocardium infarction models and lead to their functional recovery.

In Situ Remodeling Overrules Bioinspired Scaffold Architecture of Supramolecular Elastomeric Tissue-Engineered Heart Valves

In situ tissue engineering that uses resorbable synthetic heart valve scaffolds is an affordable and practical approach for heart valve replacement; therefore, it is attractive for clinical use. This study showed no consistent collagen organization in the predefined direction of electrospun scaffolds made from a resorbable supramolecular elastomer with random or circumferentially aligned fibers, after 12 months of implantation in sheep. These unexpected findings and the observed intervalvular variability highlight the need for a mechanistic understanding of the long-term in situ remodeling processes in large animal models to improve predictability of outcome toward robust and safe clinical application.

Electrospun PCL/PGS Composite Fibers Incorporating Bioactive Glass Particles for Soft Tissue Engineering Applications

Poly(glycerol-sebacate) (PGS) and poly(epsilon caprolactone) (PCL) have been widely investigated for biomedical applications in combination with the electrospinning process. Among others, one advantage of this blend is its suitability to be processed with benign solvents for electrospinning. In this work, the suitability of PGS/PCL polymers for the fabrication of composite fibers incorporating bioactive glass (BG) particles was investigated. Composite electrospun fibers containing silicate or borosilicate glass particles (13-93 and 13-93BS, respectively) were obtained and characterized. Neat PCL and PCL composite electrospun fibers were used as control to investigate the possible effect of the presence of PGS and the influence of the bioactive glass particles. In fact, with the addition of PGS an increase in the average fiber diameter was observed, while in all the composite fibers, the presence of BG particles induced an increase in the fiber diameter distribution, without changing significantly the average fiber diameter. Results confirmed that the blended fibers are hydrophilic, while the addition of BG particles does not affect fiber wettability. Degradation test and acellular bioactivity test highlight the release of the BG particles from all composite fibers, relevant for all applications related to therapeutic ion release, i.e., wound healing. Because of weak interface between the incorporated BG particles and the polymeric fibers, mechanical properties were not improved in the composite fibers. Promising results were obtained from preliminary biological tests for potential use of the developed mats for soft tissue engineering applications.

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.

The Potential Impact and Timeline of Engineering on Congenital Interventions

Congenital interventional cardiology has seen rapid growth in recent decades due to the expansion of available medical devices. Percutaneous interventions have become standard of care for many common congenital conditions. Unfortunately, patients with congenital heart disease often require multiple interventions throughout their lifespan. The availability of transcatheter devices that are biodegradable, biocompatible, durable, scalable, and can be delivered in the smallest sized patients will rely on continued advances in engineering. The development pipeline for these devices will require contributions of many individuals in academia and industry including experts in material science and tissue engineering. Advances in tissue engineering, bioresorbable technology, and even new nanotechnologies and nitinol fabrication techniques which may have an impact on the field of transcatheter congenital device in the next decade are summarized in this review. This review highlights recent advances in the engineering of transcatheter-based therapies and discusses future opportunities for engineering of transcatheter devices.

Kartogenin-loaded coaxial PGS/PCL aligned nanofibers for cartilage tissue engineering

Electrospinning is a valuable technology for cartilage tissue engineering (CTE) due to its ability to produce fibrous scaffolds mimicking the nanoscale and alignment of collagen fibers present within the superficial zone of articular cartilage. Coaxial electrospinning allows the fabrication of core-shell fibers able to incorporate and release bioactive molecules (e.g., drugs or growth factors) in a controlled manner. Herein, we used coaxial electrospinning to produce coaxial poly(glycerol sebacate) (PGS)/poly(caprolactone) (PCL) aligned nanofibers (core:PGS/shell:PCL). The obtained scaffolds were characterized in terms of their structure, chemical composition, thermal properties, mechanical performance and in vitro degradation kinetics, in comparison to monoaxial PCL aligned fibers and respective non-aligned controls. All the electrospun scaffolds produced presented average fiber diameters within the nanometer-scale and the core-shell structure of the composite fibers was clearly confirmed by TEM. Additionally, fiber alignment significantly increased (>2-fold) the elastic modulus of both coaxial and monoxial scaffolds. Kartogenin (KGN), a small molecule known to promote mesenchymal stem/stromal cells (MSC) chondrogenesis, was loaded into the core PGS solution to generate coaxial PGS-KGN/PCL nanofibers. The KGN release kinetics and scaffold biological performance were evaluated in comparison to KGN-loaded monoaxial fibers and respective non-loaded controls. Coaxial PGS-KGN/PCL nanofibers showed a more controlled and sustained KGN release over 21 days than monoaxial PCL-KGN nanofibers. When cultured with human bone marrow MSC in incomplete chondrogenic medium (without TGF-β3), KGN-loaded scaffolds enhanced significantly cell proliferation and chondrogenic differentiation, as suggested by the increased sGAG amounts and chondrogenic markers gene expression levels. Overall, these findings highlight the potential of using coaxial PGS-KGN/PCL aligned nanofibers as a bioactive scaffold for CTE applications.

Self-assembled structures of halloysite nanotubes: towards the development of high-performance biomedical materials

Halloysite nanotubes (HNTs), 1D natural tubular nanoparticles, exhibit a high aspect ratio, empty lumen, high adsorption ability, good biocompatibility, and high biosafety, which have attracted researchers' attention in applications of the biomedical area. HNTs can be readily dispersed in water due to their negatively charged surface and good hydrophilicity. The unique rod-like structure and surface properties give HNTs assembly ability into ordered hierarchical structures. In this review, the self-assembly approaches of HNTs including evaporation induced self-assembly by a "coffee-ring" mechanism, shear force induced self-assembly, and electric field force induced self-assembly were introduced. In addition, HNT self-assembly on polymeric substrates and biological substrates including hair, cells, and zebrafish embryos was discussed. These assembly processes are related to noncovalent interactions such as electrostatic, hydrogen bonding, and van der Waals forces or electron-transfer reactions. Moreover, the applications of self-assembled HNT patterns in biomedical areas such as capture of circulating tumor cells, guiding oriented cell growth, controlling cell germination, and delivery of drugs or nutrients were discussed and highlighted. Finally, challenges and future directions of assembly of HNTs were introduced. This review will inspire researchers in the design and fabrication of functional biodevices based on HNTs for tissue engineering, cancer diagnosis/therapy, and personal healthcare products.

Trilayered tissue structure with leaflet-like orientations developed through in vivo tissue engineering

A tissue-engineered heart valve can be an alternative to current mechanical or bioprosthetic valves that face limitations, especially in pediatric patients. However, it remains challenging to produce a functional tissue-engineered heart valve with three leaflets mimicking the trilayered, oriented structure of a native valve leaflet. In our previous study, a flat, trilayered nanofibrous substrate mimicking the orientations of three layers in a native leaflet-circumferential, random and radial orientations in fibrosa, spongiosa and ventricularis layers, respectively, was developed through electrospinning. In this study, we sought to develop a trilayered tissue structure mimicking the orientations of a native valve leaflet through in vivo tissue engineering, a practical regenerative medicine technology that can be used to develop an autologous heart valve. Thus, the nanofibrous substrate was placed inside the closed trileaflet-shaped cavity of a mold and implanted subcutaneously in a rat model for in vivo tissue engineering. After two months, the explanted tissue construct had a trilayered structure mimicking the orientations of a native valve leaflet. The infiltrated cells and their deposited collagen fibrils were oriented along the nanofibers in each layer of the substrate. Besides collagen, presence of glycosaminoglycans and elastin in the construct was observed.

Digital Design and Automated Fabrication of Bespoke Collagen Microfiber Scaffolds

A great variety of natural and synthetic polymer materials have been utilized in soft tissue engineering as extracellular matrix (ECM) materials. Natural polymers, such as collagen and fibrin hydrogels, have experienced especially broad adoption due to the high density of cell adhesion sites compared to their synthetic counterparts, ready availability, and ease of use. However, these and other hydrogels lack the structural and mechanical anisotropy that define the ECM in many tissues, such as skeletal and cardiac muscle, tendon, and cartilage. Herein, we present a facile, low-cost, and automated method of preparing collagen microfibers, organizing these fibers into precisely controlled mesh designs, and embedding these meshes in a bulk hydrogel, creating a composite biomaterial suitable for a wide variety of tissue engineering and regenerative medicine applications. With the assistance of custom software tools described herein, mesh patterns are designed by a digital graphical user interface and translated into protocols that are executed by a custom mesh collection and organization device. We demonstrate a high degree of precision and reproducibility in both fiber and mesh fabrication, evaluate single fiber mechanical properties, and provide evidence of collagen self-assembly in the microfibers under standard cell culture conditions. This work offers a powerful, flexible platform for the study of tissue engineering and cell material interactions, as well as the development of therapeutic biomaterials in the form of custom collagen microfiber patterns that will be accessible to all through the methods and techniques described here. Impact Statement Collagen microfiber meshes have immediate and broad applications in tissue engineering research and show high potential for later use in clinical therapeutics due to their compositional similarities to native extracellular matrix and tunable structural and mechanical characteristics. Physical and biological characterizations of these meshes demonstrate physiologically relevant mechanical properties, native-like collagen structure, and cytocompatibility. The methods presented herein not only describe a process through which custom collagen microfiber meshes can be fabricated but also provide the reader with detailed device plans and software tools to produce their own bespoke meshes through a precise, consistent, and automated process.

Promoting neural cell proliferation and differentiation by incorporating lignin into electrospun poly(vinyl alcohol) and poly(glycerol sebacate) fibers

Electrospinning of natural and synthetic polymers open a new practical approach to tissue engineering by producing fibers. In this study, aligned electrospun poly(vinyl alcohol) (PVA)-poly(glycerol sebacate) (PGS) fibers with various percentages of lignin (0, 1, 3, and 5%wt) fabricated for nerve tissue engineering. The effect of the different amount of lignin on the morphology and diameter of the fibers was investigated by scanning electron microscopy (SEM). The physicochemical properties of fibers were studied using FTIR, tensile strain, contact angle, water uptake, and degradation test. MTT assay and SEM were employed to evaluate PC12 cell proliferation and adhesion, respectively. Immunocytochemistry and gene expression were utilized to study how the lignin affected on cell differentiation. The results revealed the smooth with a uniform diameter of the fabricated fibers, and the increased amount of lignin reduced the fiber diameter from 530 to 370 nm. The modulus of elasticity increased from 0.1 to 0.4 MPa by increasing the lignin percentage. The PC12 cell culture indicated that the lignin enhanced cell proliferation. The mRNA expression level for Gfap, β-Tub III, and Map2 and immunocytochemistry (Map2) revealed the positive effect of lignin on neural cell differentiation. Finally, the results suggest PVA-PGS/5% lignin as a promising material for nerve tissue engineering.

Biomimetic cardiovascular platforms for in vitro disease modeling and therapeutic validation

Bioengineered tissues have become increasingly more sophisticated owing to recent advancements in the fields of biomaterials, microfabrication, microfluidics, genetic engineering, and stem cell and developmental biology. In the coming years, the ability to engineer artificial constructs that accurately mimic the compositional, architectural, and functional properties of human tissues, will profoundly impact the therapeutic and diagnostic aspects of the healthcare industry. In this regard, bioengineered cardiac tissues are of particular importance due to the extremely limited ability of the myocardium to self-regenerate, as well as the remarkably high mortality associated with cardiovascular diseases worldwide. As novel microphysiological systems make the transition from bench to bedside, their implementation in high throughput drug screening, personalized diagnostics, disease modeling, and targeted therapy validation will bring forth a paradigm shift in the clinical management of cardiovascular diseases. Here, we will review the current state of the art in experimental in vitro platforms for next generation diagnostics and therapy validation. We will describe recent advancements in the development of smart biomaterials, biofabrication techniques, and stem cell engineering, aimed at recapitulating cardiovascular function at the tissue- and organ levels. In addition, integrative and multidisciplinary approaches to engineer biomimetic cardiovascular constructs with unprecedented human and clinical relevance will be discussed. We will comment on the implementation of these platforms in high throughput drug screening, in vitro disease modeling and therapy validation. Lastly, future perspectives will be provided on how these biomimetic platforms will aid in the transition towards patient centered diagnostics, and the development of personalized targeted therapeutics.

A facile method for fabricating a three-dimensional aligned fibrous scaffold for vascular application

Collection of circumferentially aligned and 3D fibrous scaffold on a newly designed electrospinning auxiliary jig. The aligned fibres served as a signaling modality to induce cell alignment and the maintenance of a contractile phenotype for hSMCs.

Electrospun nanofibrous thermoplastic polyurethane/poly(glycerol sebacate) hybrid scaffolds for vocal fold tissue engineering applications

Vocal fold tissue engineering requires biomimetic scaffolds with an appropriate matrix stiffness closely matching that of the natural vocal folds to maintain function. Traditionally, poly(ɛ‑caprolactone) (PCL) and thermoplastic polyurethane (TPU) have been employed as the primary matrix materials for vocal fold electrospun scaffolds. However, not all of the scaffolds fabricated thus far matched the human vocal fold tissues. Poly(glycerol sebacate) (PGS) is a non-cytotoxic and biodegradable soft elastomer that has shown promising results for soft tissue engineering applications. However, no work has been done to employ this biomaterial to construct vocal fold scaffolds. In this study, PGS has been synthesized and blended with thermoplastic polyurethane (TPU) to produce vocal fold scaffolds with improved hydrophilicity and compliance by electrospinning. The resulting scaffolds were found to have mechanical properties mimicking those of the vocal fold lamina propria extracellular matrix (ECM). An unusual leaf-like structure was obtained when using 1,1,1,3,3,3‑hexafluoroisopropanol (HFIP) as the solvent. Other suitable fibrous scaffolds were also obtained when using acetic acid and 2,2,2‑trifluoroethanol (TFE) as binary solvents. A biological evaluation of these TPU/PGS scaffolds showed better cell spreading and significantly improved cell proliferation as compared to TPU-only scaffolds (p < 0.01), thereby suggesting potential applications for vocal fold tissue engineering.

Cell Sources for Tissue Engineering Strategies to Treat Calcific Valve Disease

Cardiovascular calcification is an independent risk factor and an established predictor of adverse cardiovascular events. Despite concomitant factors leading to atherosclerosis and heart valve disease (VHD), the latter has been identified as an independent pathological entity. Calcific aortic valve stenosis is the most common form of VDH resulting of either congenital malformations or senile “degeneration.” About 2% of the population over 65 years is affected by aortic valve stenosis which represents a major cause of morbidity and mortality in the elderly. A multifactorial, complex and active heterotopic bone-like formation process, including extracellular matrix remodeling, osteogenesis and angiogenesis, drives heart valve “degeneration” and calcification, finally causing left ventricle outflow obstruction. Surgical heart valve replacement is the current therapeutic option for those patients diagnosed with severe VHD representing more than 20% of all cardiac surgeries nowadays. Tissue Engineering of Heart Valves (TEHV) is emerging as a valuable alternative for definitive treatment of VHD and promises to overcome either the chronic oral anticoagulation or the time-dependent deterioration and reintervention of current mechanical or biological prosthesis, respectively. Among the plethora of approaches and stablished techniques for TEHV, utilization of different cell sources may confer of additional properties, desirable and not, which need to be considered before moving from the bench to the bedside. This review aims to provide a critical appraisal of current knowledge about calcific VHD and to discuss the pros and cons of the main cell sources tested in studies addressing in vitro TEHV.