Three-dimensional electrospun ECM-based hybrid scaffolds for cardiovascular tissue engineering

Low-cost FDM 3D-printed modular electrospray/electrospinning setup for biomedical applications

Here, we report on the inexpensive fabrication of an electrospray/electrospinning setup by fused deposition modelling (FDM) 3D printing and provide the files and parameters needed to print this versatile device. Both electrospray and electrospinning technologies are widely used for pharmaceutical, healthcare and bioengineering applications. The setup was designed to be modular, thus its parts can be exchanged easily. The design provides a safe setup, ensuring that the users are not exposed to the high voltage parts of the setup. PLA, PVA, and a thermoplastic elastomer filament were used for the 3D printing. The filament cost was $100 USD and the rig was printed in 6 days. An Ultimaker 3 FDM 3D printer was used with dual print heads, and the PVA was used as a water-soluble support structure. The end part of the setup had several gas channels, allowing a uniform gas flowing against the direction of the nanoparticles/nanofibers, enhancing the drying process by enhancing the evaporation rate. The setup was tested in both electrospray and electrospinning modes successfully. Both the .sldprt and .stl files are provided for free download.

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.

Nanostructured degradable macroporous hydrogel scaffolds with controllable internal morphologies via reactive electrospinning

Creating micro/nanostructured hydrogels with tunable morphologies under cell-friendly processing conditions would enable rational engineering of hydrogel scaffolds for targeted biomedical applications. Herein, an all-aqueous single-step reactive electrospinning method is applied to prepare hydrogel networks with controlled morphologies on both the nanoscale and the microscale. Hydrazide and aldehyde-functionalized poly(oligo ethylene glycol methacrylate) (POEGMA) are co-spun from a double barrel syringe together with poly(ethylene oxide) (PEO) as an electrospinning aid. By varying the concentrations and molecular weights of PEO and/or POEGMA, various morphologies from pure fibers to beaded fibers to bead network morphologies with tunable bead sizes can be fabricated, all of which remain monolithically stable in water due to the dynamic covalent crosslinks formed within the gel structure. The rates and magnitudes of swelling, degradation, and mechanics of the resulting scaffolds can be tuned by independently controlling gel morphologies on the nanoscale (i.e. crosslink density within the gel) and the microscale (i.e. the network structure formed), with an atypical independence of swelling relative to the mechanics and degradation rate observed. Furthermore, the internal morphology of the networks is demonstrated to systematically alter both the cell responses within the scaffolds and the rate of protein release from the scaffolds, with small fibers showing optimal cell proliferation, bead networks exhibiting the slowest protein release kinetics and very high maintained cell viabilities post-electrospinning, and beaded fibers showing intermediate properties. STATEMENT OF SIGNIFICANCE: Controlling the internal structure of hydrogels is critical to successfully applying hydrogels in biomedical applications such as tissue engineering or cell/drug delivery. However, current techniques to fabricate hydrogel scaffolds typically require additives or gelation processes that are poorly compatible with cells and/or require multi-step processes. In this paper, we describe the fabrication of hydrogel scaffolds with tunable feature sizes (from nanometer to micrometer scale) and structures (from all fibers to bead/fiber mixtures to a new "bead network" morphology) using a reactive electrospinning strategy leveraging dynamic hydrazone crosslinking. We show single-step cell/protein loading and systematic control over cell proliferation and protein release kinetics by systematically manipulating the scaffold morphologies and feature sizes, allowing facile customization of scaffold properties for targeted applications.

Nanofiber membranes as biomimetic and mechanically stable surface coatings

Elastomers have been extensively exploited to study cell physiology in fields such as mechanobiology, however, their intrinsic high hydrophobicity renders their surfaces incompatible for prolonged cell adhesion and proliferation. Electrospun fiber networks on the other side provide a promising environment for enhanced cell adhesion and growth due to their architecture closely mimicking the structure of the extracellular matrix present within tissues of the human body. Here, we explored the stable integration of electrospun fibers onto the surfaces of elastomeric materials to promote cytocompatibility of these composites. Elastomers based on room temperature vulcanizing silicone (RTV), polydimethylsiloxane (PDMS) as well as functionalized PDMS-based materials were chosen as wafer substrates for attachment of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDFhfp) fibers, a well-known antithrombotic polymer. Electrospinning the fibers onto uncured interfaces acted as bonding agents on the wafers, enabling penetration and formation of a stable bond between the fibers surfaces and the elastomers after curing the interface. Dimensional analysis revealed a relationship between peeling force, intrusion depth and the elastic modulus of the wafers. A design parameter Π_α was extrapolated to be used as a predictive tool of the peeling force when intrusion depth of PVDFhfp fibers and elastic modulus of the wafers are known. Cultivating fibroblasts on these hybrid membranes showed cell attachment and growth over 7 days regardless of the composition of the substrate, confirming high cytocompatibility for all composite materials. The presented approach opens avenues to establish nanofiber morphologies as a novel, stable surface texturing tool for tissue engineering, cell biology, medical devices and textiles.

Piezoelectric Scaffolds as Smart Materials for Neural Tissue Engineering

Injury to the central or peripheral nervous systems leads to the loss of cognitive and/or sensorimotor capabilities, which still lacks an effective treatment. Tissue engineering in the post-injury brain represents a promising option for cellular replacement and rescue, providing a cell scaffold for either transplanted or resident cells. Tissue engineering relies on scaffolds for supporting cell differentiation and growth with recent emphasis on stimuli responsive scaffolds, sometimes called smart scaffolds. One of the representatives of this material group is piezoelectric scaffolds, being able to generate electrical charges under mechanical stimulation, which creates a real prospect for using such scaffolds in non-invasive therapy of neural tissue. This paper summarizes the recent knowledge on piezoelectric materials used for tissue engineering, especially neural tissue engineering. The most used materials for tissue engineering strategies are reported together with the main achievements, challenges, and future needs for research and actual therapies. This review provides thus a compilation of the most relevant results and strategies and serves as a starting point for novel research pathways in the most relevant and challenging open questions.

Altered processing enhances the efficacy of small-diameter silk fibroin vascular grafts

Current synthetic vascular grafts are not suitable for use in low-diameter applications. Silk fibroin is a promising natural graft material which may be an effective alternative. In this study, we compared two electrospun silk grafts with different manufacturing processes, using either water or hexafluoroisopropanol (HFIP) as solvent. This resulted in markedly different Young's modulus, ultimate tensile strength and burst pressure, with HFIP spun grafts observed to have thicker fibres, and greater stiffness and strength relative to water spun. Assessment in a rat abdominal aorta grafting model showed significantly faster endothelialisation of the HFIP spun graft relative to water spun. Neointimal hyperplasia in the HFIP graft also stabilised significantly earlier, correlated with an earlier SMC phenotype switch from synthetic to contractile, increasing extracellular matrix protein density. An initial examination of the macrophage response showed that HFIP spun conduits promoted an anti-inflammatory M2 phenotype at early timepoints while reducing the pro-inflammatory M1 phenotype relative to water spun grafts. These observations demonstrate the important role of the manufacturing process and physical graft properties in determining the physiological response. Our study is the first to comprehensively study these differences for silk in a long-term rodent model.

Elasticity of fiber meshes from multiblock copolymers influences endothelial cell behavior

BACKGROUND

The behavior of endothelial cells is remarkably influenced by the physical and biochemical signals from their surrounding microenvironments.

OBJECTIVE

Here, the elasticity of fiber meshes was studied as a design parameter of substrates for endothelial cells in order to modulate angiogenesis.

METHODS

Human umbilical vein endothelial cells (HUVECs) were cultured on electrospun fiber meshes made from polyetheresterurethane (PEEU), differing in their elasticity. Cell morphology, proliferation, migration and angiogenesis of endothelial cells on the degradable substrate meshes were characterized.

RESULTS

The aspect ratio of HUVECs cultured on the fiber meshes from PEEU materials increased with increasing stiffness of the materials. HUVECs cultured on fiber meshes with high stiffness (Young's modulus E = 4.5±0.8 MPa) presented a higher proliferation rate and significantly faster migration velocity, as well as higher tube formation capability than the cells cultured on fiber meshes with low stiffness (E = 2.6±0.8 MPa).

CONCLUSIONS

These results suggested that tuning the fiber meshes' elasticity might be a potential strategy for modulating the formation or regeneration of blood vessels.

Polycaprolactone/gelatin-based scaffolds with tailored performance: in vitro and in vivo validation

Nanofibrous scaffolds composed of polycaprolactone (PCL) and gelatin (Ge) were obtained through a hydrolytic assisted electrospinning process. The PCL-to-Ge proportion (100/0 to 20/80), as well as the dissolution time (24, 48, 72, 96, 120 h) into a 1:1 formic/acetic acid solvent before electrospinning were modified to obtain the different samples. A strong influence of these factors on the physicochemical properties of the scaffolds was observed. Higher Ge percentage reduced crystallinity, allowed a uniform morphology and increased water contact angle. The increase in the dissolution time considerably reduced the molar mass and, subsequently, fibre diameter and crystallinity were affected. During in vitro biocompatibility tests, higher cell adhesion and proliferation were found for the 60/40, 50/50 and 40/60 PCL/Ge compositions that was corroborated by MTT assay, fluorescence and microscopy. A weakened structure, more labile to the in vitro degradation in physiologic conditions was found for these compositions with higher dissolution times (72 and 96 h). Particularly, the 40/60 PCL/Ge scaffolds revealed an interesting progressive degradation behaviour as a function of the dissolution time. Moreover, these scaffolds were non-inflammatory, as revealed by the pyrogen test and after the 15-day subcutaneous in vivo implantation in mice. Finally, a reduction of the scar tissue area after infarction was found for the 40/60 PCL/Ge scaffolds electrospun after 72 h implanted in rat hearts. These results are especially interesting and represent a feasible way to avoid undesired inflammatory reactions during the scaffold assimilation.

Fabrication Techniques for Vascular and Vascularized Tissue Engineering

Impaired or damaged blood vessels can occur at all levels in the hierarchy of vascular systems from large vasculatures such as arteries and veins to meso- and microvasculatures such as arterioles, venules, and capillary networks. Vascular tissue engineering has become a promising approach for fabricating small-diameter vascular grafts for occlusive arteries. Vascularized tissue engineering aims to fabricate meso- and microvasculatures for the prevascularization of engineered tissues and organs. The ideal small-diameter vascular graft is biocompatible, bridgeable, and mechanically robust to maintain patency while promoting tissue remodeling. The desirable fabricated meso- and microvasculatures should rapidly integrate with the host blood vessels and allow nutrient and waste exchange throughout the construct after implantation. A number of techniques used, including engineering-based and cell-based approaches, to fabricate these synthetic vasculatures are herein explored, as well as the techniques developed to fabricate hierarchical structures that comprise multiple levels of vasculature.

Hybrid Polyester-Hydrogel Electrospun Scaffolds for Tissue Engineering Applications

Electrospinning is an attractive fabrication process providing a cost-effective and straightforward technic to make extra-cellular matrix (ECM) mimicking scaffolds that can be used to replace or repair injured tissues and organs. Synthetic polymers as poly (ε-caprolactone) (PCL) and poly (ethylene oxide terephthalate)-poly(butylene terephthalate) (PEOT/PBT) have been often used to produce scaffolds due to their good processability, mechanical properties, and suitable biocompatibility. While synthetic polymers can mimic the physical features of native ECM, natural polymers like alginate are better suited to recapitulate its hydrated state or introduce functional groups that are recognized by cells (e.g., -NH2). Thus, this study aims at creating electrospun meshes made of blended synthetic and natural polymers for tissue engineering applications. Polyethylene oxide (PEO), PCL, and PEOT/PBT were used as a carrier of Alginate. Scaffolds were electrospun at different flow rates and distances between spinneret and collector (air gap), and the resulting meshes were characterized in terms of fiber morphology, diameter, and mesh inter-fiber pore size. The fiber diameter increased with increasing flow rate, while there was no substantial influence of the air gap. On the other hand, the mesh pore size increased with increasing air gap, while the effect of flow rate was not significant. Cross-linking and washing of alginate electrospun scaffolds resulted in smaller fiber diameter. These newly developed scaffolds may find useful applications for tissue engineering strategies as they resemble physical and chemical properties of tissue ECM. Human Dermal Fibroblasts were cultured on PCL and PCL/Alginate scaffolds in order to create a dermal substitute.

ECM in Differentiation: A Review of Matrix Structure, Composition and Mechanical Properties

Stem cell regenerative potential owing to the capacity to self-renew as well as differentiate into other cell types is a promising avenue in regenerative medicine. Stem cell niche not only provides physical scaffolding but also possess instructional capacity as it provides a milieu of biophysical and biochemical cues. Extracellular matrix (ECM) has been identified as a major dictator of stem cell lineage, thus understanding the structure of in vivo ECM pertaining to specific tissue differentiation will aid in devising in vitro strategies to improve the differentiation efficiency. In this review, we summarize details about the native architecture, composition and mechanical properties of in vivo ECM of the early embryonic stages and the later adult stages. Native ECM from adult tissues categorized on their origin from respective germ layers are discussed while engineering techniques employed to facilitate differentiation of stem cells into particular lineages are noted. Overall, we emphasize that in vitro strategies need to integrate tissue specific ECM biophysical cues for developing accurate artificial environments for optimizing stem cell differentiation.

In vitro and preclinical characterisation of compressed, macro-porous and collagen coated poly-ε-caprolactone electro-spun scaffolds

Low in macro-porosity electro-spun scaffolds are often associated with foreign body response, whilst macro-porous electro-spun scaffolds have low mechanical integrity. Herein, compressed, macro-porous and collagen (bovine Achilles tendon and human recombinant) coated electro-spun poly-ε-caprolactone scaffolds were developed and their biomechanical, in vitro and in vivo properties were assessed. Collagen coating, independently of the source, did not significantly affect the biomechanical properties of the scaffolds. Although no significant difference in cell viability was observed between the groups, collagen coated scaffolds induced significantly higher DNA concentration. In vivo, no signs of adverse tissue effect were observed in any of the groups and all groups appeared to equally integrate into the subcutaneous tissue. It is evidenced that macro-porous poly-ε-caprolactone electro-spun meshes with adequate mechanical properties and acceptable host response can be developed for biomedical applications.

Blood compatibility assessments of electrospun polyurethane nanocomposites blended with megni oil for tissue engineering applications

Tissue engineering holds as a prominent technique to repair or replace the damaged human parts to recreate its native function. In this research, a novel scaffold based on polyurethane (PU) comprising megni oil was electrospun for tissue engineering applications. The obtained polyurethane blended with megni oil nanofibers were characterized by scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), contact angle measurement and atomic force microscopy (AFM). Furthermore, the blood compatibility of the fabricated nanocomposites evaluated through activated prothrombin time (APTT), partial thromboplastin time (PT) and hemolysis assay to determine the anticoagulant nature. The morphological results showed that the fabricated nanocomposites showed reduced fiber size (789 ± 143.106 nm) than the pristine control (890 ± 116.91 nm). The interaction between PU and megni oil was identified by the hydrogen bond formation evident in the FTIR. The incorporation of megni oil in the PU decreased the wettability behavior (113.3° ± 1.528) and improved the surface roughness (646 nm). Preliminary evaluation of blood compatibility assessments was carried out using APTT, PT and hemolysis assay revealed the enhanced antithrombogenicity nature of the fabricated nanocomposites than the PU. Hence, we conclude that the fabricated new nanocomposite membrane with desirable characteristics which might find potential application in the tissue engineering applications.

Fabricated tropoelastin-silk yarns and woven textiles for diverse tissue engineering applications

Electrospun yarns offer substantial opportunities for the fabrication of elastic scaffolds for flexible tissue engineering applications. Currently available yarns are predominantly made of synthetic elastic materials. Thus scaffolds made from these yarns typically lack cell signaling cues. This can result in poor integration or even rejection on implantation, which drive demands for a new generation of yarns made from natural biologically compatible materials. Here, we present a new type of cell-attractive, highly twisted protein-based yarns made from blended tropoelastin and silk fibroin. These yarns combine physical and biological benefits by being rendered elastic and bioactive through the incorporation of tropoelastin and strengthened through the presence of silk fibroin. Remarkably, the process delivered multi-meter long yarns of tropoelastin-silk mixture that were conducive to fabrication of meshes on hand-made frames. The resulting hydrated meshes are elastic and cell interactive. Furthermore, subcutaneous implantation of the meshes in mice demonstrates their tolerance and persistence over 8 weeks. This combination of mechanical properties, biocompatibility and processability into diverse shapes and patterns underscores the value of these materials and platform technology for tissue engineering applications. STATEMENT OF SIGNIFICANCE: Synthetic yarns are used to fabricate textile materials for various applications such as surgical meshes for hernia repair and pelvic organ prolapse. However, synthetic materials lack the attractive biological and physical cues characteristic of extracellular matrix and there is a demand for materials that can minimize postoperative complications. To address this need, we made yarns from a combination of recombinant human tropoelastin and silk fibroin using a modified electrospinning approach that blended these proteins into functional yarns. Prior to this study, no protein-based yarns using tropoelastin were available for the fabrication of functional textile materials. Multimeter-long, uniform and highly twisted yarns based on these proteins were elastic and cell interactive and demonstrated processing to yield textile fabrics. By using these yarns to weave fabrics, we demonstrate that an elastic human matrix protein blend can deliver a versatile platform technology to make textiles that can be explored for efficacy in tissue repair.

Enhanced mechanical, thermal and biocompatible nature of dual component electrospun nanocomposite for bone tissue engineering

Traditionally, in the Asian continent, oils are a widely accepted choice for alleviating bone-related disorders. The design of scaffolds resembling the extracellular matrix (ECM) is of great significance in bone tissue engineering. In this study, a multicomponent polyurethane (PU), canola oil (CO) and neem oil (NO) scaffold was developed using the electrospinning technique. The fabricated nanofibers were subjected to various physicochemical and biological testing to validate its suitability for bone tissue engineering. Morphological analysis of the multicomponent scaffold showed a reduction in fiber diameter (PU/CO-853 ± 141.27 nm and PU/CO/NO-633 ± 137.54 nm) compared to PU (890 ± 116.911 nm). The existence of CO and NO in PU matrix was confirmed by an infrared spectrum (IR) with the formation of hydrogen bond. PU/CO displayed a mean contact angle of 108.7° ± 0.58 while the PU/CO/NO exhibited hydrophilic nature with an angle of 62.33° ± 2.52. The developed multicomponent also exhibited higher thermal stability and increased mechanical strength compared to the pristine PU. Atomic force microscopy (AFM) analysis depicted lower surface roughness for the nanocomposites (PU/CO-389 nm and PU/CO/NO-323 nm) than the pristine PU (576 nm). Blood compatibility investigation displayed the anticoagulant nature of the composites. Cytocompatibility studies revealed the non-toxic nature of the developed composites with human fibroblast cells (HDF) cells. The newly developed porous PU nanocomposite scaffold comprising CO and NO may serve as a potential candidate for bone tissue engineering.

Quantified forces between HepG2 hepatocarcinoma and WA07 pluripotent stem cells with natural biomaterials correlate with in vitro cell behavior

In vitro cell culture or tissue models that mimic in vivo cellular response have potential in tissue engineering and regenerative medicine, and are a more economical and accurate option for drug toxicity tests than animal experimentation. The design of in vivo-like cell culture models should take into account how the cells interact with the surrounding materials and how these interactions affect the cell behavior. Cell-material interactions are furthermore important in cancer metastasis and tumor progression, so deeper understanding of them can support the development of new cancer treatments. Herein, the colloidal probe microscopy technique was used to quantify the interactions of two cell lines (human pluripotent stem cell line WA07 and human hepatocellular carcinoma cell line HepG2) with natural, xeno-free biomaterials of different chemistry, morphology, and origin. Key components of extracellular matrices -human collagens I and IV, and human recombinant laminin-521-, as well as wood-derived, cellulose nanofibrils -with evidenced potential for 3D cell culture and tissue engineering- were analysed. Both strength of adhesion and force curve profiles depended on biomaterial nature and cell characteristics. The successful growth of the cells on a particular biomaterial required cell-biomaterial adhesion energies above 0.23 nJ/m. The information obtained in this work supports the development of new materials or hybrid scaffolds with tuned cell adhesion properties for tissue engineering, and provides a better understanding of the interactions of normal and cancerous cells with biomaterials in the human body.

Modulating smooth muscle cell response by the release of TGFβ2 from tubular scaffolds for vascular tissue engineering

Tissue engineering has gained considerable attention in the development of small diameter tissue engineered vascular grafts (TEVGs) for treating coronary heart disease. A properly designed acellular and biodegradable TEVG must encourage the infiltration and growth of vascular smooth muscle cells (SMCs). Our group has previously shown that increasing levels of TGFβ2 can differentially modulate SMC migration and proliferation. In this study, tubular electrospun scaffolds loaded with TGFβ2 were fabricated using various ratios of gelatin/polycaprolactone (PCL), resulting in scaffolds with porous nano-woven architecture suitable for tissue ingrowth. Scaffold morphology, degradation rate, TGβ2 release kinetics, and bioactivity were assessed. TGFβ2 was successfully integrated into the electrospun biomaterial that resulted in a differential release profile depending on the gelatin/PCL ratio over the course of 42 days. Higher TGFβ2 elution was obtained in scaffolds with higher gelatin content, which may be related to the biodegradation of gelatin in culture media. The biological activity of the released TGFβ2 was evaluated by its ability to affect SMC proliferation as a function of its concentration. SMCs seeded on TGFβ2-loaded scaffolds also showed higher densities and infiltration after 5 days in culture as compared to scaffolds without TGFβ2. Our results demonstrate that the ratio of synthetic and natural polymers in electrospun blends can be used to tune the release of TGFβ2. This method can be used to intelligently modulate the SMC response in gelatin/PCL scaffolds making the TGFβ2-loaded conduits attractive for cardiovascular tissue engineering applications.

Modulating smooth muscle cell response by the release of TGFβ2 from tubular scaffolds for vascular tissue engineering

Tissue engineering has gained considerable attention in the development of small diameter tissue engineered vascular grafts (TEVGs) for treating coronary heart disease. A properly designed acellular and biodegradable TEVG must encourage the infiltration and growth of vascular smooth muscle cells (SMCs). Our group has previously shown that increasing levels of TGFβ2 can differentially modulate SMC migration and proliferation. In this study, tubular electrospun scaffolds loaded with TGFβ2 were fabricated using various ratios of gelatin/polycaprolactone (PCL), resulting in scaffolds with porous nano-woven architecture suitable for tissue ingrowth. Scaffold morphology, degradation rate, TGβ2 release kinetics, and bioactivity were assessed. TGFβ2 was successfully integrated into the electrospun biomaterial that resulted in a differential release profile depending on the gelatin/PCL ratio over the course of 42 days. Higher TGFβ2 elution was obtained in scaffolds with higher gelatin content, which may be related to the biodegradation of gelatin in culture media. The biological activity of the released TGFβ2 was evaluated by its ability to affect SMC proliferation as a function of its concentration. SMCs seeded on TGFβ2-loaded scaffolds also showed higher densities and infiltration after 5 days in culture as compared to scaffolds without TGFβ2. Our results demonstrate that the ratio of synthetic and natural polymers in electrospun blends can be used to tune the release of TGFβ2. This method can be used to intelligently modulate the SMC response in gelatin/PCL scaffolds making the TGFβ2-loaded conduits attractive for cardiovascular tissue engineering applications.

Collagen type I and hyaluronic acid based hybrid scaffolds for heart valve tissue engineering

Tissue engineers have achieved limited success so far in designing an ideal scaffold for aortic valve; scaffolds lack in mechanical compatibility, appropriate degradation rate, and microstructural similarity. This paper, therefore, has demonstrated a carbodiimide-based sequential crosslinking technique to prepare aortic valve extracellular matrix mimicking (ECM) hybrid scaffolds from collagen type I and hyaluronic acid (HA), the building blocks of heart valve ECM, with tailorable crosslinking densities. Swelling studies revealed that crosslinking densities of parent networks increased with increasing the concentration of the crosslinking agents whereas crosslinking densities of hybrid scaffolds averaged from those of parent collagen and HA networks. Hybrid scaffolds also offered a wide range of pore size (66-126 μm) which fulfilled the criteria for valvular tissue regeneration. Scanning electron microscopy and images of Alcian blue-Periodic acid Schiff stained samples suggested that our crosslinking technique yielded an ECM mimicking microstructure with interlaced bands of collagen and HA in the hybrid scaffolds. The mutually reinforcing networks of collagen and HA also resulted in increased bending moduli up to 1660 kPa which spanned the range of natural aortic valves. Cardio sphere-derived cells (CDCs) from rat hearts showed that crosslinking density affected the available cell attachment sites on the surface of the scaffold. Increased bending moduli of CDCs seeded scaffolds up to two folds (2-6 kPa) as compared to the non-seeded scaffolds (1 kPa) suggested that an increase in crosslinking density of the scaffolds could not only increase the in vitro bending modulus but also prevented its disintegration in the cell culture medium.

Poly(propylene fumarate)-based materials: Synthesis, functionalization, properties, device fabrication and biomedical applications

Poly(propylene fumarate) (PPF) is a biodegradable polymer that has been investigated extensively over the last three decades. It has led many scientists to synthesize and fabricate a variety of PPF-based materials for biomedical applications due to its controllable mechanical properties, tunable degradation and biocompatibility. This review provides a comprehensive overview of the progress made in improving PPF synthesis, resin formulation, crosslinking, device fabrication and post polymerization modification. Further, we highlight the influence of these parameters on biodegradation, biocompatibility, and their use in a number of regenerative medicine applications, especially bone tissue engineering. In particular, the use of 3D printing techniques for the fabrication of PPF-based scaffolds is extensively reviewed. The recent invention of a ring-opening polymerization method affords precise control of PPF molecular mass, molecular mass distribution (Ɖ_M) and viscosity. Low Ɖ_M facilitates time-certain resorption of 3D printed structures. Novel post-polymerization and post-printing functionalization methods have accelerated the expansion of biomedical applications that utilize PPF-based materials. Finally, we shed light on evolving uses of PPF-based materials for orthopedics/bone tissue engineering and other biomedical applications, including its use as a hydrogel for bioprinting.

Functionalized core/shell nanofibers for the differentiation of mesenchymal stem cells for vascular tissue engineering

AIM

Atherosclerosis is a common cardiovascular disease causing medical problems globally leading to coronary artery bypass surgery. The present study is to fabricate core/shell nanofibers to encapsulate VEGF for the differentiation of mesenchymal stem cells (MSCs) into smooth muscle cells to develop vascular grafts.

MATERIALS & METHODS

The fabricated core/shell nanofibers contained polycaprolactone/gelatin as the shell, and silk fibroin/VEGF as the core materials.

RESULTS

The results observed that the core/shell nanofibers interact to differentiate MSCs into smooth muscle cells by the expression of vascular smooth muscle cell (VSMC) contractile proteins α-actinin, myosin and F-actin.

CONCLUSION

The functionalized polycaprolactone/gelatin/silk fibroin/VEGF (250 ng) core/shell nanofibers were fabricated for the controlled release of VEGF in a persistent manner for the differentiation of MSCs into smooth muscle cells for vascular tissue engineering.

Investigation of the batch-to-batch inconsistencies of Collagen in PCL-Collagen nanofibers

The application of tissue engineered constructs is an approach in regenerative therapies to support regeneration of damaged muscular tissue. Therefore the development of highly aligned electrospun scaffolds based on polycaprolactone (PCL) and collagen enables a versatile development towards tailor made applications. However, the application of natural polymers like collagen brings the risk of batch-to-batch inconsistencies, which influence the reproducibility of the electrospinning process. Aligned PCL-Collagen nanofibers were fabricated via electrospinning using benign solvents. The spinnability of different collagen batches and polymer concentrations in diluted acetic acid as solvent was investigated. Furthermore spinning parameters and fiber morphology were investigated in order to determine the most stable spinning conditions and analyze the batch-to-batch variations. Finally the effect of the solution temperature and the time of pure collagen in solution were investigated, to complete the analysis of the influences on the spinning behavior.

Non-invasive characterization of hybrid gelatin:poly-l-lactide electrospun scaffolds using second harmonic generation and multiphoton imaging

Hybrid scaffolds composed of synthetic polymers and naturally occurring components have become more relevant in the field of tissue engineering and regenerative medicine. Synthetic polymers are responsible for scaffold durability, strength and structural integrity; however, often do not provide biological signals. Introducing a biological component leads to more advanced and biocompatible scaffolds. In order to use these scaffolds as implants, a deeper knowledge of material characteristics and the impact of the biological component on the scaffold mechanical properties are required. Furthermore, it is necessary to implement fast, easy and non-invasive methods to determine material characteristics. In this work, we aimed to generate gelatin-poly-l-lactide (PLA) hybrids via electrospinning with defined, controllable and tunable scaffold characteristics. Using Raman microspectroscopy, we demonstrated the effectiveness of the cross-linking reaction and evaluated the increasing PLA content in the hybrid scaffolds with a non-invasive approach. Using multiphoton microscopy, we showed that gelatin fibers electrospun from a fluorinated solvent exhibit a second harmonic generation (SHG) signal typical for collagen-like structures. Compared to pure gelatin, where the SHG signal vanishes after cross-linking, the signal could be preserved in the hybrid scaffolds even after cross-linking. Furthermore, we non-invasively imaged cellular growth of human dermal fibroblasts on the hybrid electrospun scaffolds and performed fluorescence lifetime imaging microscopy on the cell-seeded hybrids, where we were able to discriminate between cells and scaffolds. Here, we successfully employed non-invasive methods to evaluate scaffold characteristics and investigate cell-material interactions.

Solution fibre spinning technique for the fabrication of tuneable decellularised matrix-laden fibres and fibrous micromembranes

Recreating tissue-specific microenvironments of the extracellular matrix (ECM) in vitro is of broad interest for the fields of tissue engineering and organ-on-a-chip. Here, we present biofunctional ECM protein fibres and suspended membranes, with tuneable biochemical, mechanical and topographical properties. This soft and entirely biologic membrane scaffold, formed by micro-nano-fibres using low voltage electrospinning, displays three unique characteristics for potential cell culture applications: high-content of key ECM proteins, single-layered mesh membrane, and flexibility for in situ integration into a range of device setups. Extracellular matrix (ECM) powder derived from urinary bladder, was used to fabricate the ECM-laden fibres and membranes. The highest ECM concentration in the dry protein fibre was 50 wt%, with the rest consisting of gelatin. Key ECM proteins, including collagen IV, laminin, and fibronectin, were shown to be preserved post the biofabrication process. The single fibre tensile Young's modulus can be tuned for over two orders of magnitude between ∼600 kPa and 50 MPa depending on the ECM content. Combining the fibre mesh printing with 3D printed or microfabricated structures, culture devices were constructed for endothelial layer formation, and a trans-membrane co-culture formed by glomerular cell types of podocytes and glomerular endothelial cells, demonstrating feasibility of the membrane culture. Our cell culture observation points to the importance of membrane mechanical property and re-modelling ability as a factor for soft membrane-based cell cultures. The ECM-laden fibres and membranes presented here would see potential applications in in vitro assays, and tailoring structure and biological functions of tissue engineering scaffolds.

STATEMENT OF SIGNIFICANCE

Recreating tissue-specific microenvironments of the extracellular matrix (ECM) is of broad interest for the fields of tissue engineering and organ-on-a-chip. Both the biochemical and biophysical signatures of the engineered ECM interplay to affect cell response. Currently, there are limited biomaterials processing methods which allow to design ECM membrane properties flexibly and rapidly. Solvents and additives used in many existing processes also induced unwanted ECM protein degradation and toxic residues. This paper presents a solution fibre spinning technique, where careful selection of the solution combination led to well-preserved ECM proteins with tuneable composition. This technique also provides a highly versatile approach to fabricate ECM fibres and membranes, leading to designable fibre Young's modulus for over two orders of magnitude.

Tailoring the gelatin/chitosan electrospun scaffold for application in skin tissue engineering: an in vitro study

The nanofibrous structure containing protein and polysaccharide has good potential in tissue engineering. The present work aims to study the role of chitosan in gelatin/chitosan nanofibrous scaffolds fabricated through electrospinning process under optimized condition. The performance of chitosan in gelatin/chitosan nanofibrous scaffolds was evaluated by mechanical tests, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and in vitro cell culture on scaffolds with different gelatin/chitosan blend ratios. To assay the influence of chitosan ratio on biocompatibility of the electrospun gelatin/chitosan scaffolds for skin tissue engineering, the culturing of the human dermal fibroblast cells (HDF) on nanofibers in terms of attachment, morphology and proliferation was evaluated. Morphological observation showed that HDF cells were attached and spread well on highly porous gelatin/chitosan nanofibrous scaffolds displaying spindle-like shapes and stretching. The fibrous morphologies of electrospun gelatin/chitosan scaffolds in culture medium were maintained during 7 days. Cell proliferation on electrospun gelatin/chitosan scaffolds was quantified by MTS assay, which revealed the positive effect of chitosan content (around 30%) as well as the nanofibrous structure on the biocompatibility (cell proliferation and attachment) of substrates.

Sustained release of herbal drugs using biodegradable scaffold for faster wound healing and better patient compliance

Electrospun scaffold has been developed using biodegradable polymer and age old herbal drug for efficient wound healing patch with much better patient compliance. Positively charged smaller particle size (40 nm) of the drug has been prepared for greater penetration through epidermal barrier to enhance the wound healing activity of drug. Controlled drug release has been understood in terms of interactions between the components through spectroscopic techniques and calorimetric studies. In-vivo study using albino rats shows better wound healing efficiency of scaffold in terms of higher wound area contraction, minimum inflammation, faster epithelialization and vascularization. Cellular studies also endorse the scaffold as better biomaterial. Clinical studies also demonstrate fast healing of different type of wounds in presence of all three wound dressing materials with histological evidences. The complete biodegradation of the patch confirms its green nature of the developed patch.

A review on fabricating tissue scaffolds using vat photopolymerization

Vat Photopolymerization (stereolithography, SLA), an Additive Manufacturing (AM) or 3D printing technology, holds particular promise for the fabrication of tissue scaffolds for use in regenerative medicine. Unlike traditional tissue scaffold fabrication techniques, SLA is capable of fabricating designed scaffolds through the selective photopolymerization of a photopolymer resin on the micron scale. SLA offers unprecedented control over scaffold porosity and permeability, as well as pore size, shape, and interconnectivity. Perhaps even more significantly, SLA can be used to fabricate vascular networks that may encourage angio and vasculogenesis. Fulfilling this potential requires the development of new photopolymers, the incorporation of biochemical factors into printed scaffolds, and an understanding of the effects scaffold geometry have on cell viability, proliferation, and differentiation. This review compares SLA to other scaffold fabrication techniques, highlights significant advances in the field, and offers a perspective on the field's challenges and future directions.

STATEMENT OF SIGNIFICANCE

Engineering de novo tissues continues to be challenging due, in part, to our inability to fabricate complex tissue scaffolds that can support cell proliferation and encourage the formation of developed tissue. The goal of this review is to first introduce the reader to traditional and Additive Manufacturing scaffold fabrication techniques. The bulk of this review will then focus on apprising the reader of current research and provide a perspective on the promising use of vat photopolymerization (stereolithography, SLA) for the fabrication of complex tissue scaffolds.

Fabrication and biocompatibility of agarose acetate nanofibrous membrane by electrospinning

In the present paper, agarose acetate (AGA) nanofibrous membranes containing different weight percentages of β-tricalcium phosphate (β-TCP) were successfully developed through electrospinning. The fibers in the nanofibrous membranes had a rough surface due to the β-TCP particles which were uniformly dispersed within or on the surface of AGA fibers. Rat-bone marrow-derived mesenchymal stem cells (rBMSCs) were cultured on the AGA based nanofibrous membranes while showed a good adhesion and proliferation. It was found that more rBMSCs were differentiated to osteoblast-like cells on the β-TCP containing nanofibrous membranes compared with the single AGA membrane, and more alkaline phosphatase (ALP) and mineralized matrix could be detected when rBMSCs were cultured on the β-TCP containing nanofibrous membranes. The nanofibrous membranes were implanted into Sprague-Dawley (SD) rats for biocompatibility test. Gross examination and histological analysis of the AGA based nanofibrous membranes results showed that there was less inflammatory response. All of experimental results suggested that the AGA based nanofibrous membranes had the great potential application in bone tissue engineering.

Novel Conducting and Biodegradable Copolymers with Noncytotoxic Properties toward Embryonic Stem Cells

Electroactive biomaterials that are easily processed as scaffolds with good biocompatibility for tissue regeneration are difficult to design. Herein, the synthesis and characterization of a variety of novel electroactive, biodegradable biomaterials based on poly(3,4-ethylenedioxythiphene) copolymerized with poly(d,l lactic acid) (PEDOT-co-PDLLA) are presented. These copolymers were obtained using (2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)methanol (EDOT-OH) as an initiator in a lactide ring-opening polymerization reaction, resulting in EDOT-PDLLA macromonomer. Conducting PEDOT-co-PDLLA copolymers (in three different proportions) were achieved by chemical copolymerization with 3,4-ethylenedioxythiophene (EDOT) monomers and persulfate oxidant. The PEDOT-co-PDLLA copolymers were structurally characterized by 1H NMR and Fourier transform infrared spectroscopy. Cyclic voltammetry confirmed the electroactive character of the materials, and conductivity measurements were performed via electrochemical impedance spectroscopy. In vitro biodegradability was evaluated using proteinase K over 35 days, showing 29-46% (w/w) biodegradation. Noncytotoxicity was assessed by adhesion, migration, and proliferation assays using embryonic stem cells (E14.tg2a); excellent neuronal differentiation was observed. These novel electroactive and biodegradable PEDOT-co-PDLLA copolymers present surface chemistry and charge density properties that make them potentially useful as scaffold materials in different fields of applications, especially for neuronal tissue engineering.

Development and blood compatibility assessment of electrospun polyvinyl alcohol blended with metallocene polyethylene and plectranthus amboinicus (PVA/mPE/PA) for bone tissue engineering

Introduction

Currently, the design of extracellular matrix (ECM) with nanoscale properties in bone tissue engineering is challenging. For bone tissue engineering, the ECM must have certain properties such as being nontoxic, highly porous, and should not cause foreign body reactions.

Materials and methods

In this study, the hybrid scaffold based on polyvinyl alcohol (PVA) blended with metallocene polyethylene (mPE) and plectranthus amboinicus (PA) was fabricated for bone tissue engineering via electrospinning. The fabricated hybrid nanocomposites were characterized by scanning electron microscopy (SEM), Fourier transform and infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), contact angle measurement, and atomic force microscopy (AFM). Furthermore, activated partial thromboplastin time (APTT), prothrombin time (PT), and hemolytic assays were used to investigate the blood compatibility of the prepared hybrid nanocomposites.

Results

The prepared hybrid nanocomposites showed reduced fiber diameter (238±45 nm) and also increased porosity (87%) with decreased pore diameter (340±86 nm) compared with pure PVA. The interactions between PVA, mPE, and PA were identified by the formation of the additional peaks as revealed in FTIR. Furthermore, the prepared hybrid nanocomposites showed a decreased contact angle of 51°±1.32° indicating a hydrophilic nature and exhibited lower thermal stability compared to pristine PVA. Moreover, the mechanical results revealed that the electrospun scaffold showed an improved tensile strength of 3.55±0.29 MPa compared with the pristine PVA (1.8±0.52 MPa). The prepared hybrid nanocomposites showed delayed blood clotting as noted in APTT and PT assays indicating better blood compatibility. Moreover, the hemolysis assay revealed that the hybrid nanocomposites exhibited a low hemolytic index of 0.6% compared with pure PVA, which was 1.6% suggesting the safety of the developed nanocomposite to red blood cells (RBCs).

Conclusion

The prepared nanocomposites exhibited better physico-chemical properties, sufficient porosity, mechanical strength, and blood compatibility, which favors it as a valuable candidate in bone tissue engineering for repairing the bone defects.

New Three-Dimensional Poly(decanediol-co-tricarballylate) Elastomeric Fibrous Mesh Fabricated by Photoreactive Electrospinning for Cardiac Tissue Engineering Applications

Reactive electrospinning is capable of efficiently producing in situ crosslinked scaffolds resembling the natural extracellular matrix with tunable characteristics. In this study, we aimed to synthesize, characterize, and investigate the in vitro cytocompatibility of electrospun fibers of acrylated poly(1,10-decanediol-co-tricarballylate) copolymer prepared utilizing the photoreactive electrospinning process with ultraviolet radiation for crosslinking, to be used for cardiac tissue engineering applications. Chemical, thermal, and morphological characterization confirmed the successful synthesis of the polymer used for production of the electrospun fibrous scaffolds with more than 70% porosity. Mechanical testing confirmed the elastomeric nature of the fibers required to withstand cardiac contraction and relaxation. The cell viability assay showed no significant cytotoxicity of the fibers on cultured cardiomyoblasts and the cell-scaffolds interaction study showed a significant increase in cell attachment and growth on the electrospun fibers compared to the reference. This data suggests that the newly synthesized fibrous scaffold constitutes a promising candidate for cardiac tissue engineering applications.

Construction of scaffolds composed of acellular cardiac extracellular matrix for myocardial tissue engineering

High rates of mortality and morbidity stemming from cardiovascular diseases unveil extreme limitations in current therapies despite enormous advances in medical and pharmaceutical sciences. Following myocardial infarction (MI), parts of myocardium undergo irreversible remodeling and is substituted by a scar tissue which eventually leads to heart failure (HF). To address this issue, cardiac patches have been utilized to initiate myocardial regeneration. In this study, a porous cardiac patch is fabricated using a mixture of decellularized myocardium extracellular matrix (ECM) and chitosan (CS). Results of rheological measurements, SEM, biodegradation test, and MTT assay showed that the scaffold composed of 3.5% (w/w) CS and 0.5% ECM has the best potential in providing cardiac progenitor cells (CPCs) with a suitable microenvironmental condition for both attachment and growth. This study demonstrates that the fabricated scaffold is capable of transmitting both mechanical and chemical cues that is native to myocardial tissue and supports efficient growth of the CPCs.

3D bioprinting and decellularized ECM-based biomaterials for in vitro CV tissue engineering

Advanced extrusion-based 3D printing strategies allow the rapid fabrication of complex anatomically relevant architectures. Moreover, they have the potential to fabricate 3D-bioprinted cardiac constructs by depositing cardiac cells with appropriate biomaterials. Heart-derived decellularized extracellular matrices containing a complex mixture of various extracellular molecules provide a comprehensive microenvironmental niche similar to native cardiac tissue. Nonetheless, a major concern persists pertaining to insufficient vascularization and mimicking of the complex 3D architectural features, which can be tackled using 3D printing approaches. In this review, we discuss the advantage and application of decellularized extracellular matrix-based hydrogels for the 3D printing of engineered cardiac tissues. We also briefly talk about the integration of electroactive materials within cardiac patches to improve the myocardium's electrophysiological properties.

Decellularized heart ECM hydrogel using supercritical carbon dioxide for improved angiogenesis

Initial angiogenesis within the first 3 days is critical for healing ischemic diseases such as myocardial infarction. Recently, decellularized extracellular matrix (dECM) has been reported to provide tissue-derived ECM components and can be used as a scaffold for cell delivery for angiogenesis in tissue engineering. Decellularization by various detergents such as sodium dodecyl sulfate (SDS) and triton X-100 can remove the cell nuclei in tissue organs. However, this leads to ECM structure denaturation, decreased presence of various ECM proteins and cytokines, and loss of mechanical properties. To overcome these limitations, in this study, we developed a supercritical carbon dioxide and ethanol co-solvent (scCO₂-EtOH) decellularization method, which is a detergent-free system that prevents ECM structure disruption and retains various angiogenic proteins in the heart dECM, and tested on rat heart tissues. The heart tissue was placed into the scCO₂ reactor and decellularized at 37 °C and 350 bar. After scCO₂-EtOH treatment, the effects were evaluated by DNA, collagen, and glycosaminoglycan (GAG) quantification and hematoxylin and eosin and immunofluorescence staining to determine the absence of nucleic acids and preservation of heart ECM components. Similar to the native group, the scCO₂-EtOH group contained more ECM components such as collagen, GAGs, collagen I, laminin, and fibronectin and angiogenic factors including vascular endothelial growth factor, fibroblast growth factor, and platelet-derived growth factor and others in comparison to the detergent group. In addition, to estimate angiogenesis of the dECM hydrogels, the neutralized dECM solution was injected in a rat subcutaneous layer (n = 6 in each group: collagen, scCO₂-EOH, and detergent group), after which the solution naturally formed gelation in the subcutaneous layer. After 3 days, the gels were harvested and estimated by immunofluorescence staining and the ImageJ program for angiogenesis analysis. Consequently, blood vessel formation and density of vWF and α-SMA in the scCO₂-EtOH group were significantly greater than that in the collagen group. Here we suggest that heart-derived decellularized extracellular matrix (dECM) with scCO₂-EtOH treatment is a highly promising angiogenic material for healing in ischemic disease.

STATEMENT OF SIGNIFICANCE

Supercritical carbon dioxide (scCO₂) in a supercritical phase has low viscosity and high diffusivity between gas and liquid properties and is known to be affordable, non-toxic, and eco-friendly. Therefore, scCO₂ extraction technology has been extensively used in commercial and industrial fields. Recently, decellularized extracellular matrix (dECM) was applied to tissue engineering and regenerative medicine as a scaffold, therapeutic material, and bio-ink for 3D printing. Moreover, the general decellularization method using detergents has limitations including eliminating tissue-derived ECM components and disrupting their structures after decellularization. To overcome these limitations, heart tissues were treated with scCO₂-EtOH for decellularization, resulting in preserving of tissue due to the various ECM and angiogenic factors derived. In addition, initiation of angiogenesis was highly induced even after 3 days of injection.

A tissue-mimetic nano-fibrillar hybrid injectable hydrogel for potential soft tissue engineering applications

While collagen type I (Col-I) is commonly used as a structural component of biomaterials, collagen type III (Col-III), another fibril forming collagen ubiquitous in many soft tissues, has not previously been used. In the present study, the novel concept of an injectable hydrogel with semi-interpenetrating polymeric networks of heterotypic collagen fibrils, with tissue-specific Col-III to Col-I ratios, in a glycol-chitosan matrix was investigated. Col-III was introduced as a component of the novel hydrogel, inspired by its co-presence with Col-I in many soft tissues, its influence on the Col-I fibrillogenesis in terms of diameter and mechanics, and its established role in regulating scar formation. The hydrogel has a nano-fibrillar porous structure, and is mechanically stable under continuous dynamic stimulation. It was found to provide a longer half-life of about 35 days than similar hyaluronic acid-based hydrogels, and to support cell implantation in terms of viability, metabolic activity, adhesion and migration. The specific case of pure Col-III fibrils in a glycol-chitosan matrix was investigated. The proposed hydrogels meet many essential requirements for soft tissue engineering applications, particularly for mechanically challenged tissues such as vocal folds and heart valves.

Structured Macroporous Hydrogels: Progress, Challenges, and Opportunities

Structured macroporous hydrogels that have controllable porosities on both the nanoscale and the microscale offer both the swelling and interfacial properties of bulk hydrogels as well as the transport properties of "hard" macroporous materials. While a variety of techniques such as solvent casting, freeze drying, gas foaming, and phase separation have been developed to fabricate structured macroporous hydrogels, the typically weak mechanics and isotropic pore structures achieved as well as the required use of solvent/additives in the preparation process all limit the potential applications of these materials, particularly in biomedical contexts. This review highlights recent developments in the field of structured macroporous hydrogels aiming to increase network strength, create anisotropy and directionality within the networks, and utilize solvent-free or additive-free fabrication methods. Such functional materials are well suited for not only biomedical applications like tissue engineering and drug delivery but also selective filtration, environmental sorption, and the physical templating of secondary networks.