Electrospun polycaprolactone/gelatin composites with enhanced cell-matrix interactions as blood vessel endothelial layer scaffolds

Ionically-crosslinked carboxymethyl chitosan scaffolds by additive manufacturing for antimicrobial wound dressing applications

Chitosan chemical functionalization is a powerful tool to provide novel materials for additive manufacturing strategies. The main aim of this study was the employment of computer-aided wet spinning (CAWS) for the first time to design and fabricate carboxymethyl chitosan (CMCS) scaffolds. For this purpose, the synthesis of a chitosan derivative with a high degree of O-substitution (1.07) and water soluble in a large pH range allowed the fabrication of scaffolds with a 3D interconnected porous structure. In particular, the developed scaffolds were composed of CMCS fibers with a small diameter (< 60 μm) and a hollow structure due to a fast non solvent-induced coagulation. Zn2+ ionotropic crosslinking endowed the CMCS scaffolds with stability in aqueous solutions, pH-sensitive water uptake capability, and antimicrobial activity against Escherichia coli and Staphylococcus aureus. In addition, post-printing functionalization through collagen grafting resulted in a decreased stiffness (1.6 ± 0.3 kPa) and a higher elongation at break (101 ± 9 %) of CMCS scaffolds, as well as in their improved ability to support in vitro fibroblast viability and wound healing process. The obtained results encourage therefore further investigation of the developed scaffolds as antimicrobial wound dressing hydrogels for skin regeneration.

Pro-vasculogenic Fibers by PDA-Mediated Surface Functionalization Using Cell-Free Fat Extract (CEFFE)

Formation of adequate vascular network within engineered three-dimensional (3D) tissue substitutes postimplantation remains a major challenge for the success of biomaterials-based tissue regeneration. To better mimic the in vivo angiogenic and vasculogenic processes, nowadays increasing attention is given to the strategy of functionalizing biomaterial scaffolds with multiple bioactive agents. Aimed at engineering electrospun biomimicking fibers with pro-vasculogenic capability, this study was proposed to functionalize electrospun fibers of polycaprolactone/gelatin (PCL/GT) by cell-free fat extract (CEFFE or FE), a newly emerging natural "cocktail" of cytokines and growth factors extracted from human adipose tissue. This was achieved by having the electrospun PCL/GT fiber surface coated with polydopamine (PDA) followed by PDA-mediated immobilization of FE to generate the pro-vasculogenic fibers of FE-PDA@PCL/GT. It was found that the PDA-coated fibrous mat of PCL/GT exhibited a high FE-loading efficiency (∼90%) and enabled the FE to be released in a highly sustained manner. The engineered FE-PDA@PCL/GT fibers possess improved cytocompatibility, as evidenced by the enhanced cellular proliferation, migration, and RNA and protein expressions (e.g., CD31, vWF, VE-cadherin) in the human umbilical vein endothelial cells (huvECs) used. Most importantly, the FE-PDA@PCL/GT fibrous scaffolds were found to enormously stimulate tube formation in vitro, microvascular development in the in ovo chick chorioallantoic membrane (CAM) assay, and vascularization of 3D construct in a rat subcutaneous embedding model. This study highlights the potential of currently engineered pro-vasculogenic fibers as a versatile platform for engineering vascularized biomaterial constructs for functional tissue regeneration.

Physicochemical, in vitro and in vivo evaluation of VEGF loaded PCL-mPEG and PDGF loaded PCL-Chitosan dual layered vascular grafts

The present study has attempted to evaluate the endothelialization and smooth muscle regeneration efficiency of a novel dual-layer small-diameter vascular graft. Two types of layers (PCL-mPEG-VEGF and PCL-Chitosan-PDGF) were fabricated to find out the best layer giving endothelialization support for the lumen and unique contractile function for outer layer of blood vessels. Platelet-derived growth factor (PDGF) and chitosan were immobilized onto PCL surface by aminolysis-based surface modification technique. Besides, Poly (ethylene glycol) methyl ether (mPEG) and vascular endothelial growth factor (VEGF) were directly blended with PCL. Morphological analysis of membranes ensured consistency of average fibers diameter with native extracellular matrix. A favorable interaction of PCL-mPEG-VEGF with cow pulmonary endothelial cells (CPAEs) and PCL-Chitosan-PDGF with rat bone marrow mesenchymal stem cells (RBMSCs) was obtained during in vitro study. Controlled growth factor release patterns were found from both layers. Further, PCL-mPEG-VEGF exhibited endothelial markers expression properties from RBMSCs. Up-regulation of SMCs markers expression was significantly ensured by the PCL-Chitosan-PDGF membrane. Thus, PCL-mPEG-VEGF and PCL-Chitosan-PDGF were preferred as inner and outer layers respectively of a finally prepared tubular hybrid tissue engineered small diameter vascular graft. Finally, the dual-layer vascular graft was implanted onto a rat abdominal aorta model for 2 months. The extracted samples exhibited the presence of endothelial marker (ICAM 1) in the inner layer and smooth muscle cell marker (αSMA) in the outer layer as well as substantial amount of collagen deposition was observed in the both layers.

In Vitro Investigation of Gelatin/Polycaprolactone Nanofibers in Modulating Human Gingival Mesenchymal Stromal Cells

The aesthetic constancy and functional stability of periodontium largely depend on the presence of healthy mucogingival tissue. Soft tissue management is crucial to the success of periodontal surgery. Recently, synthetic substitute materials have been proposed to be used for soft tissue augmentation, but the tissue compatibility of these materials needs to be further investigated. This study aims to assess the in vitro responses of human gingival mesenchymal stromal cells (hG-MSCs) cultured on a Gelatin/Polycaprolactone prototype (GPP) and volume-stable collagen matrix (VSCM). hG-MSCs were cultured onto the GPP, VSCM, or plastic for 3, 7, and 14 days. The proliferation and/or viability were measured by cell counting kit-8 assay and resazurin-based toxicity assay. Cell morphology and adhesion were evaluated by microscopy. The gene expression of collagen type I, alpha1 (COL1A1), α-smooth muscle actin (α-SMA), fibroblast growth factor (FGF-2), vascular endothelial growth factor A (VEGF-A), transforming growth factor beta-1 (TGF-β1), focal adhesion kinase (FAK), integrin beta-1 (ITG-β1), and interleukin 8 (IL-8) was investigated by RT-qPCR. The levels of VEGF-A, TGF-β1, and IL-8 proteins in conditioned media were tested by ELISA. GPP improved both cell proliferation and viability compared to VSCM. The cells grown on GPP exhibited a distinct morphology and attachment performance. COL1A1, α-SMA, VEGF-A, FGF-2, and FAK were positively modulated in hG-MSCs on GPP at different investigation times. GPP increased the gene expression of TGF-β1 but had no effect on protein production. The level of ITG-β1 had no significant changes in cells seeded on GPP at 7 days. At 3 days, notable differences in VEGF-A, TGF-β1, and α-SMA expression levels were observed between cells seeded on GPP and those on VSCM. Meanwhile, GPP showed higher COL1A1 expression compared to VSCM after 14 days, whereas VSCM demonstrated a more significant upregulation in the production of IL-8. Taken together, our data suggest that GPP electrospun nanofibers have great potential as substitutes for soft tissue regeneration in successful periodontal surgery.

Development of Biocompatible 3D-Printed Artificial Blood Vessels through Multidimensional Approaches

Within the human body, the intricate network of blood vessels plays a pivotal role in transporting nutrients and oxygen and maintaining homeostasis. Bioprinting is an innovative technology with the potential to revolutionize this field by constructing complex multicellular structures. This technique offers the advantage of depositing individual cells, growth factors, and biochemical signals, thereby facilitating the growth of functional blood vessels. Despite the challenges in fabricating vascularized constructs, bioprinting has emerged as an advance in organ engineering. The continuous evolution of bioprinting technology and biomaterial knowledge provides an avenue to overcome the hurdles associated with vascularized tissue fabrication. This article provides an overview of the biofabrication process used to create vascular and vascularized constructs. It delves into the various techniques used in vascular engineering, including extrusion-, droplet-, and laser-based bioprinting methods. Integrating these techniques offers the prospect of crafting artificial blood vessels with remarkable precision and functionality. Therefore, the potential impact of bioprinting in vascular engineering is significant. With technological advances, it holds promise in revolutionizing organ transplantation, tissue engineering, and regenerative medicine. By mimicking the natural complexity of blood vessels, bioprinting brings us one step closer to engineering organs with functional vasculature, ushering in a new era of medical advancement.

ZnO nanoparticles-modified polycaprolactone-gelatin membranes for guided/bone tissue regeneration, antibacterial and osteogenic differentiation properties

Periodontitis is a highly prevalent infectious disease that causes the progressive destruction of the periodontal supporting tissues. If left untreated, it can lead to tooth loss impairing oral function, aesthetics, and the patient's overall quality of life. Guided and Bone Tissue Regeneration (GTR/BTR) are surgical therapies based on the placement of a membrane that prevents epithelial growth into the defect, allowing the periodontal/bone cells (including stem cells) to regenerate or restore the affected tissues. The success of these therapies is commonly affected by the local bacterial colonization of the membrane area and its fast biodegradation, causing postoperative infections and a premature rupture of the membrane limiting the regeneration process. This study presents the antibacterial and osteogenic differentiation properties of polycaprolactone-gelatin (PCL-G) electrospun membranes modified with ZnO nanoparticles (ZnO-NPs). The membranes´ chemical composition, surface roughness, biodegradation, water wettability, and mechanical properties under simulated physiological conditions, were analyzed by the close relationship with their biological properties. The PCL-G membranes modified with 1, 3, and 6% w/w of ZnO-NPs showed a significant reduction in the planktonic and biofilm formation of four clinically relevant bacteria;A. actinomycetemcomitansserotype b, P. gingivalis,E. coli, andS. epidermidis. Additionally, the membranes presented appropriate mechanical properties and biodegradation rates to be potentially used in clinical treatments. Notably, the membranes modified with the lowest concentration of ZnO-NPs (1% w/w) stimulated the production of osteoblast markers and calcium deposits in human bone marrow-derived mesenchymal stem cells (BM-MSC) and were biocompatible to human osteoblasts cells (hFOB). These results suggest that the PCL-G membranes with 1% w/w of ZnO-NPs are high-potential candidates for GTR/BTR treatments, as they were the most effective in terms of better antibacterial effectiveness at a lower NPs-concentration while creating a favorable cellular microenvironment for bone growth.

Chain-End Functionalization of Poly(ε-caprolactone) for Chemical Binding with Gelatin: Binary Electrospun Scaffolds with Improved Physico-Mechanical Characteristics and Cell Adhesive Properties

Composite biocompatible scaffolds, obtained using the electrospinning (ES) technique, are highly promising for biomedical application thanks to their high surface area, porosity, adjustable fiber diameter, and permeability. However, the combination of synthetic biodegradable (such as poly(ε-caprolactone) PCL) and natural (such as gelatin Gt) polymers is complicated by the problem of low compatibility of the components. Previously, this problem was solved by PCL grafting and/or Gt cross-linking after ES molding. In the present study, composite fibrous scaffolds consisting of PCL and Gt were fabricated by the electrospinning (ES) method using non-functionalized PCL1 or NHS-functionalized PCL2 and hexafluoroisopropanol as a solvent. To provide covalent binding between PCL2 and Gt macromolecules, NHS-functionalized methyl glutarate was synthesized and studied in model reactions with components of spinning solution. It was found that selective formation of amide bonds, which provide complete covalent bonding of Gt in PCL/Gt composite, requires the presence of weak acid. With the use of the optimized ES method, fibrous mats with different PCL/Gt ratios were prepared. The sample morphology (SEM), hydrolytic resistance (FT-IR), cell adhesion and viability (MTT assay), cell penetration (fluorescent microscopy), and mechanical characteristics of the samples were studied. PCL2-based films with a Gt content of 20 wt% have demonstrated the best set of properties.

Heat-Stimuli Shape Memory Effect of Poly (ε-Caprolactone)-Cellulose Acetate Composite Tubular Scaffolds

Small-diameter artery disease is the most common clinical occurrence, necessitating the development of small-diameter artificial blood vessels. In this study, seven types of poly(-caprolactone)-cellulose acetate (PCL-CA) composite nanofiber membranes were prepared with different proportions of PCL and CA. The adhesion and growth of Mc3t3-e1 cells were considered to confirm the in vitro cytocompatibility of PCL-CA membranes. A smooth stainless-steel mandrel with a diameter of 4 mm was used to roll up the prepared nanofiber membranes to produce the tubular scaffold with 50 °C hot water. The tubular scaffolds were subjected to axial and circumferential tensile tests. The mechanical performance of the PCL-CA tubular scaffold could be improved by increasing the layers. In addition, the burst pressure (BP) of the tubular scaffolds was increased with the layers, and the BPs of six-layer (2380 ± 36.8 mmHg) and eight-layer (3720 ± 80.5 mmHg) tubular scaffolds were much higher than that of the human saphenous vein (2000 mmHg). The compression shape memory performances of the PCL-CA tubular scaffold with different layers were also investigated to simulate and analyze the contraction and expansion of tubular scaffolds. The experimental results showed that the compression strain of the tubular scaffold in the diameter direction reached 35%, and the ultimate shape recovery rate reached 87%. However, the shape fixity rate and shape recovery rate increased, demonstrating that the optimum number of layers can improve the compression shape memory performance of the tubular scaffold. The results of this study, including comprehensive morphological and mechanical properties and cytocompatibility, indicated the potential applicability of PCL-CA tubular scaffolds as tissue engineering grafts.

Facile synthesis of biogenic silica nanomaterial loaded transparent tragacanth gum hydrogels with improved physicochemical properties and inherent anti-bacterial activity

In this report, biogenic, crystalline (∼60.5 ± 2%) bowknot structured silica nanoparticles (BSNPs) of length ∼ 274 ± 7 nm and width ∼ 36 ± 2 nm were isolated from invasive species viz. Lantana camara. These were then chemically modified using nitrogen containing moieties viz. APTES and CTAB. These modified BSNPs were then used as electrostatic cross-linking agents for the formation of tragacanth gum (TG) hydrogels. The cytocompatible CTAB@BSNP-TG hydrogels documented ∼10-12 fold enhancement in anti-bacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa when compared with TG hydrogels. Disruption of the bacterial membrane by ROS generation and protein leakage were responsible for anti-bacterial activity. A cell migration assay suggested that CTAB@BSNP-TG augmented the cell proliferation of NIH-3T3 cells compared to other TG hydrogels. The present study will pave the path for the development of organic-inorganic hybrid nanocomposite-based hydrogels for anti-bacterial and cell migration applications.

Synergistic Effect of Co-Delivering Ciprofloxacin and Tetracycline Hydrochloride for Promoted Wound Healing by Utilizing Coaxial PCL/Gelatin Nanofiber Membrane

Combining multiple drugs or biologically active substances for wound healing could not only resist the formation of multidrug resistant pathogens, but also achieve better therapeutic effects. Herein, the hydrophobic fluoroquinolone antibiotic ciprofloxacin (CIP) and the hydrophilic broad-spectrum antibiotic tetracycline hydrochloride (TH) were introduced into the coaxial polycaprolactone/gelatin (PCL/GEL) nanofiber mat with CIP loaded into the PCL (core layer) and TH loaded into the GEL (shell layer), developing antibacterial wound dressing with the co-delivering of the two antibiotics (PCL-CIP/GEL-TH). The nanostructure, physical properties, drug release, antibacterial property, and in vitro cytotoxicity were investigated accordingly. The results revealed that the CIP shows a long-lasting release of five days, reaching the releasing rate of 80.71%, while the cumulative drug release of TH reached 83.51% with a rapid release behavior of 12 h. The in vitro antibacterial activity demonstrated that the coaxial nanofiber mesh possesses strong antibacterial activity against E. coli and S. aureus. In addition, the coaxial mats showed superior biocompatibility toward human skin fibroblast cells (hSFCs). This study indicates that the developed PCL-CIP/GEL-TH nanofiber membranes hold enormous potential as wound dressing materials.

Multi-crosslinked hydrogels with instant self-healing and tissue adhesive properties for biomedical applications

Due to the defects like long gelling time, inferior mechanical properties and weak adhesion, in-situ forming hydrogels are still restricted in biomedical applications like viscera rupture and targeted therapy. To address these problems, a new kind of multi-crosslinked hydrogel (G-OKG-DA) consisting of gelatin, oxidized konjac glucomannan (OKG), and dopamine (DA) is proposed in this study. The resulting hybrid hydrogel is endowed with a short gelling time (about 3 min) and injectable capacity. According to the mechanical and adhesive tests, G-OKG-DA hydrogel shows a robust tensile strength of 23.94 kPa, as well as a higher adhesive strength (around 150 kPa) than commercial fibrin glue. In addition, an instant self-healing behavior of G-OKG-DA hydrogel can be found, which is attributed to multi-crosslinking reactions including Schiff-base dynamic covalent bonds between OKG and gelatin, oxidative polymerization of DA, and catechol-mediated chemistry like Michael addition and DA-quinone coupling. Importantly, the multi-crosslinked hydrogel will not compromise its hemocompatibility and cytocompatibility in vitro, suggesting potential applications in biomedical fields as tissue adhesive and implants. This article is protected by copyright. All rights reserved.

Nature-Derived and Synthetic Additives to poly(ɛ-Caprolactone) Nanofibrous Systems for Biomedicine; an Updated Overview

As a low cost, biocompatible, and bioresorbable synthetic polymer, poly (ɛ-caprolactone) (PCL) is widely used for different biomedical applications including drug delivery, wound dressing, and tissue engineering. An extensive range of in vitro and in vivo tests has proven the favourable applicability of PCL in biomedicine, bringing about the FDA approval for a plethora of PCL made medical or drug delivery systems. This popular polymer, widely researched since the 1970s, can be readily processed through various techniques such as 3D printing and electrospinning to create biomimetic and customized medical products. However, low mechanical strength, insufficient number of cellular recognition sites, poor bioactivity, and hydrophobicity are main shortcomings of PCL limiting its broader use for biomedical applications. To maintain and benefit from the high potential of PCL, yet addressing its physicochemical and biological challenges, blending with nature-derived (bio)polymers and incorporation of nanofillers have been extensively investigated. Here, we discuss novel additives that have been meant for enhancement of PCL nanofiber properties and thus for further extension of the PCL nanofiber application domain. The most recent researches (since 2017) have been covered and an updated overview about hybrid PCL nanofibers is presented with focus on those including nature-derived additives, e.g., polysaccharides and proteins, and synthetic additives, e.g., inorganic and carbon nanomaterials.

Limbal Bio-engineered Tissue Employing 3D Nanofiber-Aerogel Scaffold to Facilitate LSCs Growth and Migration

Constrained by the existing scaffold inability to mimic limbal niche, limbal bio-engineered tissue constructed in vitro is challenging to be widely used in clinical practice. Here, 3D nanofiber-aerogel scaffold was fabricated by employing thermal cross-linking electrospinned film Polycaprolactone (PCL) and gelatin (GEL) as the precursor. Benefiting from the cross-linked (160°C, vacuum) structure, the homogenized and lyophilized 3D nanofiber-aerogel scaffold with preferable mechanical strength was capable of refraining the volume collapse in humid vitro. Intriguingly, compared with traditional electrospinning scaffolds, our 3D nanofiber-aerogel scaffolds possessed enhanced water absorption (1100%-1300%), controllable aperture (50-100 μm) and excellent biocompatibility (optical density value, 0.953 ± 0.021). The well-matched aperture and nanostructure of the scaffolds with cells enabled the construction of limbal bio-engineered tissue. It is foreseen that the proposed general method could be extended to various aerogels, providing new opportunities for the development of novel limbal bio-engineered tissue. This article is protected by copyright. All rights reserved.

Regeneration of Subcutaneous Cartilage in a Swine Model Using Autologous Auricular Chondrocytes and Electrospun Nanofiber Membranes Under Conditions of Varying Gelatin/PCL Ratios

The scarcity of ideal biocompatible scaffolds makes the regeneration of cartilage in the subcutaneous environment of large animals difficult. We have previously reported the successful regeneration of good-quality cartilage in a nude mouse model using the electrospun gelatin/polycaprolactone (GT/PCL) nanofiber membranes. The GT/PCL ratios were varied to generate different sets of membranes to conduct the experiments. However, it is unknown whether these GT/PCL membranes can support the process of cartilage regeneration in an immunocompetent large animal model. We seeded swine auricular chondrocytes onto different GT/PCL nanofiber membranes (GT:PCL = 30:70, 50:50, and 70:30) under the sandwich cell-seeding mode. Prior to subcutaneously implanting the samples into an autologous host, they were cultured in vitro over a period of 2 weeks. The results revealed that the nanofiber membranes with different GT/PCL ratios could support the process of subcutaneous cartilage regeneration in an autologous swine model. The maximum extent of homogeneity in the cartilage tissues was achieved when the G5P5 (GT: PC = 50: 50) group was used for the regeneration of cartilage. The formed homogeneous cartilage tissues were characterized by the maximum cartilage formation ratio. The extents of the ingrowth of the fibrous tissues realized and the extents of infiltration of inflammatory cells achieved were found to be the minimum in this case. Quantitative analyses were conducted to determine the wet weight, cartilage-specific extracellular matrix content, and Young’s modulus. The results indicated that the optimal extent of cartilage formation was observed in the G5P5 group. These results indicated that the GT/PCL nanofiber membranes could serve as a potential scaffold for supporting subcutaneous cartilage regeneration under clinical settings. An optimum GT/PCL ratio can promote cartilage formation.

Nanofibrous tissue engineering scaffold with nonlinear elasticity created by controlled curvature and porosity

Micro-crimped fibers have been widely used in the field of tissue repair to mimic the natural tissue structure and mechanical properties. However, the electrospun nanofibrous membrane is a kind of dense structure, which cannot meet the requirements of mechanical properties and permeability. In this study, we prepared nanofibrous scaffold with controllable porosity and crimpness by sacrificing fiber components and releasing residual stress. The results show that the crimpness of the fiber is positively related to the porosity, and with the increase of porosity, the fiber crimpness increases greatly. Meanwhile, the scaffold modulus was reduced by 86% and the elongation at break doubled, which is similar to natural blood vessels. Moreover, it is found that the porous micro-crimped fiber scaffold promotes the adhesion and diffusion of endothelial cells, and facilitates the rapid endothelialization of the scaffold, which has a great potential for practical application.

Design and characterization of small-diameter tissue-engineered blood vessels constructed by electrospun polyurethane-core and gelatin-shell coaxial fiber

Substitution or bypass is the most effective treatment for vascular occlusive diseases.The demand for artificial blood vessels has seen an unprecedented rise due to the limited supply of autologous blood vessels. Tissue engineering is the best approach to provide artificial blood vessels. In this study, a new type of small-diameter artificial blood vessel with good mechanical and biological properties was designed by using electrospinning coaxial fibers. Four groups of coaxial fibers vascular membranes having polyurethane/gelatin core-shell structure were cross-linked by the EDC-NHS system and characterized. The core-shell structure of the coaxial vascular fibers was observed by transmission electron microscope. After the crosslinking, the stress and elastic modulus increased and the elongation decreased, burst pressure of 0.11 group reached the maximum (2844.55 ± 272.65 mmHg) after cross-linking, which acted as the experimental group. Masson staining identified blue-stained ring or elliptical gelatin ingredients in the vascular wall. The cell number in the vascular wall of the coaxial group was found in muscle embedding experiment significantly higher than that of the non-coaxial group at all time points(p < 0.001). Our results showed that the coaxial vascular graft with the ratio of 0.2:0.11 had better mechanical properties (burst pressure reached 2844.55 ± 272.65 mmHg); Meanwhile its biological properties were also outstanding, which was beneficial to cell entry and offered good vascular remodeling performance.Polyurethane (PU); Gelatin (Gel); Polycaprolactone (PCL); polylactic acid (PLA);1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC); N-Hydroxy succinimide (NHS); 4-Morpholine-ethane-sulfonic (MES); phosphate buffered saline (PBS); fetal calf serum (FCS); Minimum Essential Medium (MEM); Dimethyl sulfoxide (DMSO); hematoxylin-eosin (HE).

Effect of sequential electrospinning and co-electrospinning on morphological and fluid mechanical wall properties of polycaprolactone and bovine gelatin scaffolds, for potential use in small diameter vascular grafts

BACKGROUND

Nowadays, the engineering vascular grafts with a diameter less than 6 mm by means of electrospinning, is an attracted alternative technique to create different three-dimensional microenvironments with appropriate physicochemical properties to promote the nutrient transport and to enable the bioactivity, dynamic growth and differentiation of cells. Although the performance of a well-designed porous wall is key for these functional requirements maintaining the mechanical function, yet predicting the flow rate and cellular transport are still not widely understood and many questions remain open about new configurations of wall can be used for modifying the conventional electrospun samples. The aim of the present study was to evaluate the effect of fabrication techniques on scaffolds composed of bovine gelatin and polycaprolactone (PCL) developed by sequential electrospinning and co-electrospinning, on the morphology and fluid-mechanical properties of the porous wall.

METHODOLOGY

For this purpose, small diameter tubular structures were manufactured and experimental tests were performed to characterize the crystallinity, morphology, wettability, permeability, degradability, and mechanical properties. Some samples were cross-linked with Glutaraldehyde (GA) to improve the stability of the gelatin fiber. In addition, it was analyzed how the characteristics of the scaffold favored the levels of cell adhesion and proliferation in an in vitro model of 3T3 fibroblasts in incubation periods of 24, 48 and 72 h.

RESULTS

It was found that in terms of the morphology of tubular scaffolds, the co-electrospun samples had a better alignment with higher values of fiber diameters and apparent pore area than the sequential samples. The static permeability was more significant in the sequential scaffolds and the hydrophilic was higher in the co-electrospun samples. Therefore, the gelatin mass losses were less in the co-electrospun samples, which promote cellular functions. In terms of mechanical properties, no significant differences were observed for different types of samples.

CONCLUSION

This research concluded that the tubular scaffolds generated by sequential and co-electrospinning with modification in the microarchitecture could be used as a vascular graft, as they have better permeability and wettability, interconnected pores, and a circumferential tensile strength similar to native vessel compared to the commercial graft analyzed.

Research progress, models and simulation of electrospinning technology: a review

In recent years, nanomaterials have aroused extensive research interest in the world's material science community. Electrospinning has the advantages of wide range of available raw materials, simple process, small fiber diameter and high porosity. Electrospinning as a nanomaterial preparation technology with obvious advantages has been studied, such as its influencing parameters, physical models and computer simulation. In this review, the influencing parameters, simulation and models of electrospinning technology are summarized. In addition, the progresses in applications of the technology in biomedicine, energy and catalysis are reported. This technology has many applications in many fields, such as electrospun polymers in various aspects of biomedical engineering. The latest achievements in recent years are summarized, and the existing problems and development trends are analyzed and discussed.

Biomedical Applications of Nanofibers

The idea of creating replacement for damaged or diseased tissue, which will mimic the physiological conditions and simultaneously promote regeneration by patients’ own cells, has been a major challenge in the biomedicine for more than a decade. Therefore, nanofibers are a promising solution to address these challenges. Nanofiber technology is an exciting area attracting the attention of many researchers as a potential solution to these current challenges in the biomedical field such as burn and wound care, organ repair, and treatment for osteoporosis and various diseases. Nanofibers mimic the porous topography of natural extracellular matrix (ECM), hence they are advantageous for tissue regeneration . In biomedical engineering, electrospinning exhibits advantages as a tissue engineering scaffolds producer, which can make appropriate resemblance in physical structure with ECM. This is because of the nanometer scale of ECM fibrils in diameter, which can be mimicked by electrospinning procedure as well as its porous structure. In this review, the applications of nanofibers in various biomedical areas such as tissue engineering, wound dressing and facemask, are summarized. It provides opportunities to develop new materials and techniques that improve the ability for developing quick, sensitive and reliable analytical techniques.

Hemolytic, Biocompatible, and Functional Effect of Cellularized Polycaprolactone-Hydrolyzed Collagen Electrospun Membranes for Possible Application as Vascular Implants

In search of bioactive vascular prostheses that exhibit greater biocompatibility through the combination of natural and synthetic polymers, tissue engineering from a biomimetic perspective has proposed the development of three-dimensional structures as therapeutic strategies in the field of cardiovascular medicine. Techniques such as electrospinning allow obtaining of scaffolds that emulate the microarchitecture of the extracellular matrix of native vessels; thus, this study aimed to evaluate the biological influence of microarchitecture on polycaprolactone (PCL) and hydrolyzed collagen (H-Col) electrospun scaffolds, which have a homogeneous (microscale) or heterogeneous (micro-nanoscale) fibrillar structure. The hemolytic, biocompatible, and functional effect of the scaffolds in interaction with an in vitro fibroblast model was determined, in view of its potential use for vascular implants. Scaffolds were characterized by scanning electron microscopy and atomic force microscopy, Fourier transform infrared spectroscopy, wettability, static permeability, tensile test, and degradation. In addition, direct and indirect 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays were used to identify the cell viability of fibroblasts, fluorescence assays were performed to establish morphological changes of the cell nuclei, and the hemolytic effect of the scaffolds was calculated. Results showed that ethanol-treated biocompositescaffolds exhibited mass losses lower than 6.65% and slow wettability and absorption, resulting from an increase in secondary structures that contribute to the crystalline phase of H-Col. The scaffolds demonstrated stable degradation in saline during the incubation period because of the availability of soluble structures in aqueous media, and the inclusion of H-Col increased the elastic properties of the scaffold. As regards hemocompatibility, the scaffolds had hemolysis levels lower than 1%; moreover, in terms of biocompatible characteristics, scaffolds exhibited good adhesion, proliferation, and cell viability and insignificant changes in the circularity of the cell nuclei. However, scaffolds with homogeneous fibers showed cell agglomerates after 48 h of interaction. By contrast, permeability decreased as the incubation period progressed, because of the cellularization of the three-dimensional structure. In conclusion, multiscale scaffolds could exhibit a suitable behavior as a bioactive small-diameter vascular implant.

Advances in Fabricating the Electrospun Biopolymer-Based Biomaterials

Biopolymers formed into a fibrous morphology through electrospinning are of increasing interest in the field of biomedicine due to their intrinsic biocompatibility and biodegradability and their ability to be biomimetic to various fibrous structures present in animal tissues. However, their mechanical properties are often unsatisfactory and their processing may be troublesome. Thus, extensive research interest is focused on improving these qualities. This review article presents the selection of the recent advances in techniques aimed to improve the electrospinnability of various biopolymers (polysaccharides, polynucleotides, peptides, and phospholipids). The electrospinning of single materials, and the variety of co-polymers, with and without additives, is covered. Additionally, various crosslinking strategies are presented. Examples of cytocompatibility, biocompatibility, and antimicrobial properties are analyzed. Special attention is given to whey protein isolate as an example of a novel, promising, green material with good potential in the field of biomedicine. This review ends with a brief summary and outlook for the biomedical applicability of electrospinnable biopolymers.

Selection of different endothelialization modes and different seed cells for tissue-engineered vascular graft

Tissue-engineered vascular grafts (TEVGs) have enormous potential for vascular replacement therapy. However, thrombosis and intimal hyperplasia are important problems associated with TEVGs especially small diameter TEVGs (<6 mm) after transplantation. Endothelialization of TEVGs is a key point to prevent thrombosis. Here, we discuss different types of endothelialization and different seed cells of tissue-engineered vascular grafts. Meanwhile, endothelial heterogeneity is also discussed. Based on it, we provide a new perspective for selecting suitable types of endothelialization and suitable seed cells to improve the long-term patency rate of tissue-engineered vascular grafts with different diameters and lengths.

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The material, diameter and length of tissue-engineered vascular graft are all key factors affecting its long-term patency.

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Endothelialization strategies should consider the different diameters and lengths of tissue-engineered vascular grafts.

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Cell heterogeneity and tissue heterogeneity should be considered in the application of seed cells.

In-vitro Characterization of a Hernia Mesh Featuring a Nanostructured Coating

Abdominal hernia repair is a frequently performed surgical procedure worldwide. Currently, the use of polypropylene (PP) surgical meshes for the repair of abdominal hernias constitutes the primary surgical approach, being widely accepted as superior to primary suture repair. Surgical meshes act as a reinforcement for the weakened or damaged tissues and support tissue restoration. However, implanted meshes could suffer from poor integration with the surrounding tissues. In this context, the present study describes the preliminary evaluation of a PCL-Gel-based nanofibrous coating as an element to develop a multicomponent hernia mesh device (meshPCL-Gel) that could overcome this limitation thanks to the presence of a nanostructured biomimetic substrate for enhanced cell attachment and new tissue formation. Through the electrospinning technique, a commercial PP hernia mesh was coated with a nanofibrous membrane from a polycaprolactone (PCL) and gelatin (Gel) blend (PCL-Gel). Resulting PCL-Gel nanofibers were homogeneous and defect-free, with an average diameter of 0.15 ± 0.04 μm. The presence of Gel decreased PCL hydrophobicity, so that membranes average water contact angle dropped from 138.9 ± 1.1° (PCL) to 99.9 ± 21.6°, while it slightly influenced mechanical properties, which remained comparable to those of PCL (E = 15.7 ± 2.7 MPa, σ R = 7.7 ± 0.6 ε R = 118.8 ± 13.2%). Hydrolytic and enzymatic degradation was conducted on PCL-Gel up to 28 days, with maximum weight losses around 20 and 40%, respectively. The meshPCL-Gel device was obtained with few simple steps, with no influences on the original mechanical properties of the bare mesh, and good stability under physiological conditions. The biocompatibility of meshPCL-Gel was assessed by culturing BJ human fibroblasts on the device, up to 7 days. After 24 h, cells adhered to the nanofibrous substrate, and after 72 h their metabolic activity was about 70% with respect to control cells. The absence of detectable lactate dehydrogenase in the culture medium indicated that no necrosis induction occurred. Hence, the developed nanostructured coating provided the meshPCL-Gel device with chemical and topographical cues similar to the native extracellular matrix ones, that could be exploited for enhancing the biological response and, consequently, mesh integration, in abdominal wall hernia repair.

Elastomeric Electrospun Scaffolds of a Biodegradable Aliphatic Copolyester Containing PEG-Like Sequences for Dynamic Culture of Human Endothelial Cells

In the field of artificial prostheses for damaged vessel replacement, polymeric scaffolds showing the right combination of mechanical performance, biocompatibility, and biodegradability are still demanded. In the present work, poly(butylene-co-triethylene trans-1,4-cyclohexanedicarboxylate), a biodegradable random aliphatic copolyester, has been synthesized and electrospun in form of aligned and random fibers properly designed for vascular applications. The obtained materials were analyzed through tensile and dynamic-mechanical tests, the latter performed under conditions simulating the mechanical contraction of vascular tissue. Furthermore, the in vitro biological characterization, in terms of hemocompatibility and cytocompatibility in static and dynamic conditions, was also carried out. The mechanical properties of the investigated scaffolds fit within the range of physiological properties for medium- and small-caliber blood vessels, and the aligned scaffolds displayed a strain-stiffening behavior typical of the blood vessels. Furthermore, all the produced scaffolds showed constant storage and loss moduli in the investigated timeframe (24 h), demonstrating the stability of the scaffolds under the applied conditions of mechanical deformation. The biological characterization highlighted that the mats showed high hemocompatibility and low probability of thrombus formation; finally, the cytocompatibility tests demonstrated that cyclic stretch of electrospun fibers increased endothelial cell activity and proliferation, in particular on aligned scaffolds.

Quantitative Investigation of the Process Parameters of Electrohydrodynamic Direct-Writing and Their Effects on Fiber Surface Roughness and Cell Adhesion

Electrohydrodynamic (EHD) direct-writing has been widely used to fabricate micro/nanofibers that can serve as a building block in tissue engineering scaffolds. However, the application of EHD direct-writing in tissue engineering is limited by the lack of fundamental knowledge in the correlations among the process parameters, the fiber surface roughness, and the cell adhesion performance. Without a standardized experimental setting and the quantitative database, inconsistent results have been reported. Here, we quantitatively investigate the process–structure–property relationships as the first step towards a better understanding of the EHD direct-writing technology for tissue engineering. Polycaprolactone (PCL) solution is used as a model ink material, and human mesenchymal stem cells (hMSCs) are used to study cell adhesion on PCL fibers. We investigate the different jetting modes defined by the applied voltage, the feed rate, and the nozzle–collector distance. The quantitative effects of process parameters on the fiber surface roughness and the cell adhesion performance are experimentally determined. The quantitative process–structure–property relationships revealed in this study provide guidelines for controlling the surface roughness and the cell adhesion performance of EHD direct-written fibers. This study will facilitate the application of EHD direct-writing in tissue engineering.

Viscosity and degradation controlled injectable hydrogel for esophageal endoscopic submucosal dissection

Endoscopic submucosal dissection (ESD) is a common procedure to treat early and precancerous gastrointestinal lesions. Via submucosal injection, a liquid cushion is created to lift and separate the lesion and malignant part from the muscular layer where the formed indispensable space is convenient for endoscopic incision. Saline is a most common submucosal injection liquid, but the formed liquid pad lasts only a short time, and thus repeated injections increase the potential risk of adverse events. Hydrogels with high osmotic pressure and high viscosity are used as an alternate; however, with some drawbacks such as tissue damage, excessive injection resistance, and high cost. Here, we reported a nature derived hydrogel of gelatin-oxidized alginate (G-OALG). Based on the rheological analysis and compare to commercial endoscopic mucosal resection (EMR) solution (0.25% hyaluronic acid, HA), a designed G-OALG hydrogel of desired concentration and composition showed higher performances in controllable gelation and injectability, higher viscosity and more stable structures. The G-OALG gel also showed lower propulsion resistance than 0.25% HA in the injection force assessment under standard endoscopic instruments, which eased the surgical operation. In addition, the G-OALG hydrogel showed good in vivo degradability biocompatibility. By comparing the results acquired via ESD to normal saline, the G-OALG shows great histocompatibility and excellent endoscopic injectability, and enables create a longer-lasting submucosal cushion. All the features have been confirmed in the living both pig and rat models. The G-OALG could be a promising submucosal injection agent for esophageal ESD.

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Injectable gel with controlled viscosity.

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Injectable gel with controlled degradation.

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Making esophageal submucosal liquid cushion.

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Potential treatment for early esophageal cancer.

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Big animal in-situ imaging.

Considerations in the Development of Small-Diameter Vascular Graft as an Alternative for Bypass and Reconstructive Surgeries: A Review

BACKGROUND

Current design strategies for small diameter vascular grafts (< 6 mm internal diameter; ID) are focused on mimicking native vascular tissue because the commercially available grafts still fail at small diameters, notably due to development of intimal hyperplasia and thrombosis. To overcome these challenges, various design approaches, material selection, and surface modification strategies have been employed to improve the patency of small-diameter grafts.

REVIEW

The purpose of this review is to outline various considerations in the development of small-diameter vascular grafts, including material choice, surface modifications to enhance biocompatibility/endothelialization, and mechanical properties of the graft, that are currently being implanted. Additionally, we have taken into account the general vascular physiology, tissue engineering approaches, and collective achievements of the authors in this area. We reviewed both commercially available synthetic grafts (e-PTFE and PET), elastic polymers such as polyurethane and biodegradable and bioresorbable materials. We included naturally occurring materials by focusing on their potential application in the development of future vascular alternatives.

CONCLUSION

Until now, there are few comprehensive reviews regarding considerations in the design of small-diameter vascular grafts in the literature. Here-in, we have discussed in-depth the various strategies employed to generate engineered vascular graft due to their high demand for vascular surgeries. While some TEVG design strategies have shown greater potential in contrast to autologous or synthetic ePTFE conduits, many are still hindered by high production cost which prevents their widespread adoption. Nonetheless, as tissue engineers continue to develop on their strategies and procedures for improved TEVGs, soon, a reliable engineered graft will be available in the market. Hence, we anticipate a viable TEVG with resorbable property, fabricated via electrospinning approach to hold a greater potential that can overcome the challenges observed in both autologous and allogenic grafts. This is because they can be mechanically tuned, incorporated/surface-functionalized with bioactive molecules and mass-manufactured in a reproducible manner. It is also found that most of the success in engineered vascular graft approaching commercialization is for large vessels rather than small-diameter grafts used as cardiovascular bypass grafts. Consequently, the field of vascular engineering is still available for future innovators that can take up the challenge to create a functional arterial substitute.

3D printing of silk microparticle reinforced polycaprolactone scaffolds for tissue engineering applications

Polycaprolactone (PCL) scaffolds have been widely investigated for tissue engineering applications, however, they exhibit poor cell adhesion and mechanical properties. Subsequently, PCL composites have been produced to improve the material properties. This study utilises a natural material, Bombyx mori silk microparticles (SMP) prepared by milling silk fibre, to produce a composite to enhance the scaffolds properties. Silk is biocompatible and biodegradable with excellent mechanical properties. However, there are no studies using SMPs as a reinforcing agent in a 3D printed thermoplastic polymer scaffold. PCL/SMP (10, 20, 30 wt%) composites were prepared by melt blending. Rheological analysis showed that SMP loading increased the shear thinning and storage modulus of the material. Scaffolds were fabricated using a screw-assisted extrusion-based additive manufacturing system. Scanning electron microscopy and X-ray microtomography was used to determine scaffold morphology. The scaffolds had high interconnectivity with regular printed fibres and pore morphologies within the designed parameters. Compressive mechanical testing showed that the addition of SMP significantly improved the compressive Young's modulus of the scaffolds. The scaffolds were more hydrophobic with the inclusion of SMP which was linked to a decrease in total protein adsorption. Cell behaviour was assessed using human adipose derived mesenchymal stem cells. A cytotoxic effect was observed at higher particle loading (30 wt%) after 7 days of culture. By day 21, 10 wt% loading showed significantly higher cell metabolic activity and proliferation, high cell viability, and cell migration throughout the scaffold. Calcium mineral deposition was observed on the scaffolds during cell culture. Large calcium mineral deposits were observed at 30 wt% and smaller calcium deposits were observed at 10 wt%. This study demonstrates that SMPs incorporated into a PCL scaffold provided effective mechanical reinforcement, improved the rate of degradation, and increased cell proliferation, demonstrating potential suitability for bone tissue engineering applications.

Comparative Study on Protein-Rich Electrospun Fibers for in Vitro Applications

Electrospinning is the leading technology to fabricate fibrous scaffolds that mimic the architecture of the extracellular matrix of natural tissues. In order to improve the biological response, a consolidated trend involves the blending of synthetic polymers with natural proteins to form protein-rich fibers that include selected biochemical cues able to more actively support in vitro cell interaction. In this study, we compared protein-rich fibers fabricated via electrospinning by the blending of poly ε-caprolactone (PCL) with three different proteins, i.e., gelatin, zein, and keratin, respectively. We demonstrated that the peculiar features of the proteins used significantly influence the morphological properties, in terms of fiber size and distribution. Moreover, keratin drastically enhances the fiber hydrophilicity (water contact angle equal to 44.3° ± 3.9°) with positive effects on cell interaction, as confirmed by the higher proliferation of human mesenchymal stem cells (hMSC) until 7 days. By contrast, gelatin and zein not equally contribute to the fiber wettability (water contact angles equal to 95.2° ± 1.2° and 76.3° ± 4.0°, respectively) due to morphological constraints, i.e., broader fiber diameter distribution ascribable to the non-homogeneous presence of the protein along the fibers, or chemical constrains, i.e., large amount of non-polar amino acids. According to in vitro experimental studies, which included SEM and confocal microscopy analyses and vitality assay, we concluded that keratin is the most promising protein to be combined with PCL for the fabrication of biologically instructive fibers for in vitro applications.

Polycaprolactone/Gelatin/Hyaluronic Acid Electrospun Scaffolds to Mimic Glioblastoma Extracellular Matrix

Glioblastoma (GBM), one of the most malignant types of human brain tumor, is resistant to conventional treatments and is associated with poor survival. Since the 3D extracellular matrix (ECM) of GBM microenvironment plays a significant role on the tumor behavior, the engineering of the ECM will help us to get more information on the tumor behavior and to define novel therapeutic strategies. In this study, polycaprolactone (PCL)/gelatin(Gel)/hyaluronic acid(HA) composite scaffolds with aligned and randomly oriented nanofibers were successfully fabricated by electrospinning for mimicking the extracellular matrix of GBM tumor. We investigated the effect of nanotopography and components of fibers on the mechanical, morphological, and hydrophilic properties of electrospun nanofiber as well as their biocompatibility properties. Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) have been used to investigate possible interactions between components. The mean fiber diameter in the nanofiber matrix was increased with the presence of HA at low collector rotation speed. Moreover, the rotational velocity of the collector affected the fiber diameters as well as their homogenous distribution. Water contact angle measurements confirmed that hyaluronic acid-incorporated aligned nanofibers were more hydrophilic than that of random nanofibers. In addition, PCL/Gel/HA nanofibrous scaffold (7.9 MPa) exhibited a significant decrease in tensile strength compared to PCL/Gel nanofibrous mat (19.2 MPa). In-vitro biocompatibilities of nanofiber scaffolds were tested with glioblastoma cells (U251), and the PCL/Gel/HA scaffolds with random nanofiber showed improved cell adhesion and proliferation. On the other hand, PCL/Gel/HA scaffolds with aligned nanofiber were found suitable for enhancing axon growth and elongation supporting intracellular communication. Based on these results, PCL/Gel/HA composite scaffolds are excellent candidates as a biomimetic matrix for GBM and the study of the tumor.

Bioresorbable Polymeric Scaffold in Cardiovascular Applications

Advances in material science and innovative medical technologies have allowed the development of less invasive interventional procedures for deploying implant devices, including scaffolds for cardiac tissue engineering. Biodegradable materials (e.g., resorbable polymers) are employed in devices that are only needed for a transient period. In the case of coronary stents, the device is only required for 6-8 months before positive remodelling takes place. Hence, biodegradable polymeric stents have been considered to promote this positive remodelling and eliminate the issue of permanent caging of the vessel. In tissue engineering, the role of the scaffold is to support favourable cell-scaffold interaction to stimulate formation of functional tissue. The ideal outcome is for the cells to produce their own extracellular matrix over time and eventually replace the implanted scaffold or tissue engineered construct. Synthetic biodegradable polymers are the favoured candidates as scaffolds, because their degradation rates can be manipulated over a broad time scale, and they may be functionalised easily. This review presents an overview of coronary heart disease, the limitations of current interventions and how biomaterials can be used to potentially circumvent these shortcomings in bioresorbable stents, vascular grafts and cardiac patches. The material specifications, type of polymers used, current progress and future challenges for each application will be discussed in this manuscript.

Proteins and Peptides as Important Modifiers of the Polymer Scaffolds for Tissue Engineering Applications-A Review

Polymer scaffolds constitute a very interesting strategy for tissue engineering. Even though they are generally non-toxic, in some cases, they may not provide suitable support for cell adhesion, proliferation, and differentiation, which decelerates tissue regeneration. To improve biological properties, scaffolds are frequently enriched with bioactive molecules, inter alia extracellular matrix proteins, adhesive peptides, growth factors, hormones, and cytokines. Although there are many papers describing synthesis and properties of polymer scaffolds enriched with proteins or peptides, few reviews comprehensively summarize these bioactive molecules. Thus, this review presents the current knowledge about the most important proteins and peptides used for modification of polymer scaffolds for tissue engineering. This paper also describes the influence of addition of proteins and peptides on physicochemical, mechanical, and biological properties of polymer scaffolds. Moreover, this article sums up the major applications of some biodegradable natural and synthetic polymer scaffolds modified with proteins and peptides, which have been developed within the past five years.

Antibacterial composite membranes of polycaprolactone/gelatin loaded with zinc oxide nanoparticles for guided tissue regeneration

The bacterial colonization of absorbable membranes used for guided tissue regeneration (GTR), as well as their rapid degradation that can cause their rupture, are considered the major reasons for clinical failure. To address this, composite membranes of polycaprolactone (PCL) and gelatin (Gel) loaded with zinc oxide nanoparticles (ZnO-NPs; 1, 3 and 6 wt% relative to PCL content) were fabricated by electrospinning. To fabricate homogeneous fibrillar membranes, acetic acid was used as a sole common solvent to enhance the miscibility of PCL and Gel in the electrospinning solutions. The effects of ZnO-NPs in the physico-chemical, mechanical and in vitro biological properties of composite membranes were studied. The composite membranes showed adequate mechanical properties to offer a satisfactory clinical manipulation and an excellent conformability to the defect site while their degradation rate seemed to be appropriate to allow successful regeneration of periodontal defects. The presence of ZnO-NPs in the composite membranes significantly decreased the planktonic and the biofilm growth of the Staphylococcus aureus over time. Finally, the viability of human osteoblasts and human gingival fibroblasts exposed to the composite membranes with 1 and 3 wt% of ZnO-NPs indicated that those membranes are not expected to negatively influence the ability of periodontal cells to repopulate the defect site during GTR treatments. The results here obtained suggest that composite membranes of PCL and Gel loaded with ZnO-NPs have the potential to be used as structurally stable GTR membranes with local antibacterial properties intended for enhancing clinical treatments.

Single-step, acid-based fabrication of homogeneous gelatin-polycaprolactone fibrillar scaffolds intended for skin tissue engineering

Blends of natural and synthetic polymers have recently attracted great attention as scaffolds for tissue engineering applications due to their favorable biological and mechanical properties. Nevertheless, phase-separation of blend components is an important challenge facing the development of electrospun homogeneous fibrillar natural-synthetic polymers scaffolds; phase-separation can produce significant detrimental effects for scaffolds fabricated by electrospinning. In the present study, blends of gelatin (Gel; natural polymer) and polycaprolactone (PCL; synthetic polymer), containing 30 and 45 wt% Gel, were prepared using acetic acid as a 'green' sole solvent to straightforwardly produce appropriate single-step Gel-PCL solutions for electrospinning. Miscibility of Gel and PCL in the scaffolds was assessed and the morphology, chemical composition and structural and solid-state properties of the scaffolds were thoroughly investigated. Results showed that the two polymers proved miscible under the single-step solution process used and that the electrospun scaffolds presented suitable properties for potential skin tissue engineering applications. Viability, metabolic activity and protein expression of human fibroblasts cultured on the Gel-PCL scaffolds were evaluated using LIVE/DEAD (calcein/ethidium homodimer), MTT-Formazan and immunocytochemistry assays, respectively. In vitro results showed that the electrospun Gel-PCL scaffolds enhanced cell viability and proliferation in comparison to PCL scaffolds. Furthermore, scaffolds allowed fibroblasts expression of extracellular matrix proteins, tropoelastin and collagen Type I, in a similar way to positive controls. Results indicated the feasibility of the single-step solution process used herein to obtain homogeneous electrospun Gel-PCL scaffolds with Gel content ≥30 wt% and potential properties to be used as scaffolds for skin tissue engineering applications for wound healing.

Co-culture of mesenchymal stem cells and human umbilical vein endothelial cells on heparinized polycaprolactone/gelatin co-spun nanofibers for improved endothelium remodeling

Endothelization of a tissue-engineered substrate is important for its application as an artificial vascular graft. Despite recent advancements in artificial graft fabrication, a graft of <5 mm is difficult to fabricate owing to insufficient endothelization that results in thrombosis after transplantation. We aimed to perform a co-culture of adipose-derived mesenchymal stem cells (MSCs) with human umbilical vein endothelial cells (HUVECs) on antithrombogenic polycaprolactone (PCL)/heparin-gelatin co-spun nanofibers to evaluate the role of co-culturing in promoting quick endothelization of vascular substrates without surface modification by growth factors or other ECM proteins that trigger the endothelization process. Using a co-axial electrospinning technique, we attempted to fabricate our scaffold balancing between mechanical properties and biocompatibility. Antithrombogenic characteristics were then imparted to the fabricated nanofiber substrate by grafting of heparin. Finally, we performed a co-culture of MSCs and HUVECs on the fabricated co-spun nanofiber substrate to obtain proper endothelization of our material under the in-vitro culture. Staining for CD-31 at seven days of culture revealed enhanced CD-31 expression under the co-culture condition; actin staining revealed healthy cobblestone HUVEC morphology, suggesting that MSCs can aid in proper endothelization. Hence, we conclude that co-culture is effective for quick endothelization of vascular substrates.