Fibrous Constructs Research Articles

Patterned Electrospinning: A Method of Generating Defined Fibrous Constructs Influencing Cell Adhesion and Retention.

A critical component of tissue engineering is the ability to functionally replace native tissue stroma. Electrospinning is a technique capable of forming fibrous constructs with a high surface area for increased cell-material interaction and enhanced biocompatibility. However, physical and biological properties of electrospun scaffolds are limited by design controllability on a macroscale. We developed a methodology for generating electrospun scaffolds with defined patterns and topographic features to influence physical properties and biological interactions. Five unique design electrospinning target collectors were fabricated to allow for generation of defined polymeric scaffold patterns including lines, sinusoids, squares, zigzags, and solid. Poly(lactic-co-glycolic) acid was electrospun under identical conditions utilizing these varied targets, and constructs generated were examined as to their physical configuration, mechanical and chemical properties, and their ability to foster vascular smooth muscle cell adhesion and retention at 24 h. Modifying collector designs led to significant differences in fiber target coverage ranging from 300 mm2 for solid (100% of the target area) to 217.8 mm2 for lines (72.6% of the target area). Measured fiber excess, residual open area, and contact angle (hydrophobicity) followed the same trend as fiber target coverage with respect to the collector pattern: lines > sinusoids > squares > zigzags > solid. Similarly, the line design allowed for the greatest cell adhesion and retention (258 ± 31 cells), whereas solid exhibited the lowest (150 ± 15 cells); p < 0.05. There was a strong direct correlation of cell adhesion to construct residual open area (R2 = 0.94), normalized fiber excess (R2 = 0.99), and fiber grammage (R2 = 0.72), with an inverse relationship to fiber target coverage (R2 = 0.94). Our results demonstrate the ability to utilize patterned collectors for modifying macroscopic and microscopic electrospun scaffold features, which directly impact cell adhesion and retention, offering translational utility for designing specific tissue constructs.

Biodegradable wet-spun fibers modified with antimicrobial agents for potential applications in biomedical engineering

Wet-spinning is a non-solvent induced phase inversion technique that allows the production of continuous polymeric microfibers, with a uniform morphology, based on the principle of precipitation. It allows the production of 3D fibrous constructs with an intricated architecture that facilitates cell infiltration, something that is very limited in electrospun nanofibrous mats, thus increasing its interest in biomedicine. Wet-spun scaffolds are also more easily processed and can be loaded with a variety of biomolecules of interest. Antimicrobial agents that display a broad spectrum of activity against bacteria, fungi and viruses have been combined with such constructs demonstrating great potential to fight infections. In the present work, we explore the use of wet-spinning to process both natural and synthetic biodegradable polymers in the form of microfibers, and the necessary processes to modify their surface to increase their antimicrobial profile. The synergistic potential of specialized biomolecules within wet-spun fibrous architectures are also highlighted.

Fabrication of chitosan-polyvinyl alcohol and silk electrospun fiber seeded with differentiated keratinocyte for skin tissue regeneration in animal wound model

Hybrid fibrous mat containing cell interactive molecules offers the ability to deliver the cells and drugs in wound bed, which will help to achieve a high therapeutic treatment. In this study, a co-electrospun hybrid of polyvinyl alcohol (PVA), chitosan (Ch) and silk fibrous mat was developed and their wound healing potential by localizing bone marrow mesenchymal stem cells (MSCs)-derived keratinocytes on it was evaluated in vitro and in vivo. It was expected that fabricated hybrid construct could promote wound healing due to its structure, physical, biological specifications. The fabricated fibrous mats were characterized for their structural, mechanical and biochemical properties. The shape uniformity and pore size of fibers showed smooth and homogenous structures of them. Fourier transform infrared spectroscopy (FTIR) verified all typical absorption characteristics of Ch-PVA + Silk polymers as well as Ch-PVA or pure PVA substrates. The contact angle and wettability measurement of fibers showed that mats found moderate hydrophilicity by addition of Ch and silk substrates compared with PVA alone. The mechanical features of Ch-PVA + Silk fibrous mat increase significantly through co-electrospun process as well as hybridization of these synthetic and natural polymers. Higher degrees of cellular attachment and proliferation obtained on Ch-PVA + Silk fibers compared with PVA and Ch-PVA fibers. In terms of the capability of Ch-PVA + Silk fibers and MSC-derived keratinocytes, histological analysis and skin regeneration results showed this novel fibrous construct could be suggested as a skin substitute in the repair of injured skin and regenerative medicine applications.

Tensile Properties of Composite Reinforced with Three-Dimensional Printed Fibers.

This study used melt-electrospinning writing to fabricate three-dimensional fiber constructs by embedding them in a polyvinyl alcohol (PVA) matrix to obtain thin composite films. Fourier transform infrared spectroscopy (FTIR) and dynamic scanning calorimetry (DSC) were used to demonstrate an interaction between the polycaprolactone (PCL) fibrous phase and the PVA matrix phase. Following this, the mechanical deformation behavior of the composite was investigated, and the effect of reinforcement with three-dimensional fibrous constructs was illustrated. The specific strength of the composite was found to be five times higher than the specific strength of the neat PVA matrix. Additionally, the specific toughness of the composite was determined to be roughly four times higher than the specific toughness determined for the neat PVA matrix. These results demonstrate the potential of using melt-electrospinning writing for producing three-dimensional fibrous constructs for composite reinforcement purposes.

Tandem electrospinning for heterogeneous nanofiber patterns

Smart nanofibrillar constructs can be a promising technological solution for many emerging and established fields, facilitating the potential impact of nano-scale strategies to address relevant technological challenges. As a fabrication technique, electrospinning (ESP) is relatively well-known, accessible, economic, and fast, though until now has shown limitation over control and design of the fibrillar constructs which can be produced. Here, we introduce ‘Tandem Electrospinning’ (T-ESP), a novel technique able to create increasingly complex patterns of fibrous polymeric constructs on a micro and nano-scale. Modifying a standard ESP configuration results in a focusing electric field that is able to spatially define the deposition pattern of multiple polymer jets simultaneously. Additional spatially defined heterogeneity is achieved by tuning polymer solution properties to obtain a gradient of fiber alignment. Heterogeneous fibrous meshes are created with either random, aligned, or a divergent fiber patterns. This approach holds potential for many fields, with application examples shown for tissue engineering and separation technologies. The technique outlined here provides a rapid, versatile, and accessible method for polymeric nanofabrication of patterned heterogeneous fibrous constructs. Polymer properties are also shown to dictate fiber alignment, providing further insight into the mechanisms involved in the electrospinning fabrication process.

A Facile Method for Controlled Fabrication of Hybrid Silver Nanoparticle-Poly(-caprolactone) Fibrous Constructs with Antimicrobial Properties.

Infection is one of the major factors affecting wound healing. The use of polymeric fibrous constructs or scaffolds with encapsulated biologically active components has shown great potential in topical wound care as wound dressings to expedite wound healing process; however, there is a limitation in precise control over the release of active components. Therefore, in this study, the authors developed a facile method for controlled fabrication of poly(-caprolactone) (PCL) microfibrous constructs with silver (Ag) nanoparticles as antibacterial agent by single capillary electrospinning. By optimizing spinning parameters, the PCL microfibrous constructs were fabricated. The encapsulation of Ag nanoparticles within the PCL microfibers was confirmed using microstructural analysis. The encapsulation efficacy and release profile of Ag was evaluated in vitro. The diffusion study further revealed the controlled release and optimal bioavailability of Ag during the experimental period. in vitro assessment of antibacterial activity of electrospun hybrid constructs showed a high antibacterial activity and an inhibitory effect on the growth of both staphylococcus aureus and escherichia coli bacteria when compared to PCL and their efficiency of antibacterial activity also varied with respect to the percent of encapsulated Ag nanoparticles. This kind of Ag nanoparticles-loaded PCL microfibrous constructs may be considered for wound care applications.

Fibrous composite material for textile heart valve design: in vitro assessment.

With over 150,000 implantations performed over the world, transcatheter aortic valve replacement (TAVR) has become a surgical technique, which largely competes with open surgery valve replacement for an increasing number of patients. The success of the procedure favors the research toward synthetic valve leaflet materials as an alternative to biological tissues, whose durability remains unknown. In particular, fibrous constructions have recently proven to be durable in vivo over a 6-month period of time in animal sheep models. Exaggerated fibrotic tissue formation remains, however, a critical issue to be addressed. This work investigates the design of a composite fibrous construction combining a woven polyethylene terephthalate (PET) layer and a non-woven PET mat, which are expected to provide, respectively, strength and appropriate topography toward limited fibrotic tissue ingrowth. For this purpose, a specific equipment has been developed to produce non-woven PET mats made from fibers with small diameter. These mats were assembled with woven PET substrates using various assembling techniques in order to obtain hybrid fibrous constructions. The physical and mechanical properties of the obtained materials were assessed and valve samples were manufactured to be tested in vitro for hydrodynamic performances. The results show that the composite fibrous construction is characterized by properties suitable for the valve leaflet function, but the durability of the assembling is however limited under accelerated cyclic loading.

Development of random and ordered composite fiber hybrid technologies for controlled release functions

Fibrous technologies (such as membranes, films, patches and filters) and their enabling engineering platforms have gained considerable interest over the last decade. In this study, novel fibrous constructs from a unique engineering platform were developed based on hybrid electrohydrodynamic (EHD) technology; incorporating functional and bioactive materials within random and aligned fibrous formulation geometries. Complex constructs were engineered using 3D printing (polycaprolactone, PCL, for sustained delivery) and electrospinning (polyvinylpyrrolidone, PVP, for rapid release) in an intercalating material layer-by-layer format using a side-by-side technological approach. Here, structure generation proceeded with deposition of ordered PCL fibers enabling well-defined void size and overall dimension, after which randomly spun PVP fibers formed a construct overcoat (as a membrane). Differences between polymer dissolution rate, hydrophilicity, mechanical properties and functional material hosting (and linked external auxiliary magnetic field trigger) provided opportunities to modulate antibiotic drug (tetracycline hydrochloride, TE-HCl) release. In vitro cell studies using human umbilical vein blood vessel cell line demonstrated device biocompatibility and Escherichia Coli (E. coli) was selected to demonstrate anti-bacterial function. Overall, a new hybrid engineering platform to prepare customizable and exciting multi-faceted drug release constructs is elucidated.

Robust hydrophobic polyurethane fibrous membranes with tunable porous structure for waterproof and breathable application

In this work, novel nanofibrous membranes with waterproof and breathable (W&B) performance were successfully fabricated by the combination of electrospinning and surface modification technology. This fibrous membranes consisted of polyurethane (PU), NaCl, and fluoroalkylsilane (FAS). Firstly, The fibrous construction and porous structure of fibrous membranes were regulated by tuning the NaCl concentrations in PU solutions. Then, the obtained PU/NaCl fibrous membranes were further modified with fluoroalkylsilane (FAS) to improve hydrophobic property. The synergistic effect of porous structure and hydrophobicity on waterproof and breathable performance was investigated. Furthermore, the mechanical property of fibrous membranes was deeply analysed on the basis of macromolecule orientation and adhesive structure. Benefiting from the optimized porous structure and hydrophobic modification, the resultant fibrous membranes exhibited excellent waterproof (hydrostatic pressure of 1261 Mbar), breathable (water vapor transmission (WVT) rate of 9.06 kg m−2 d−1 and air permeability of 4.8 mm s−1) performance, as well as high tensile strength (breakage stress of 10.4 MPa), suggesting a promising candidate for various applications, especially in protective clothing.

Evaluation of changes in thermodiffusion properties of mineral wool resulting from treatment with water and re-drying

The work presents the formulation of inverse problem that allows to estimate the basic parameters describing coupled thermodiffusion of moisture in porous fibrous material and construction of the measuring stand in order to obtain the necessary data to carry out calculations for this purpose. This approach was used to evaluate the changes in the thermodiffusion properties of stone wool samples for the indoor applications that were treated with water and re-dried. In the mathematical model, one introduced a simplification that coupling in the thermodiffusion process is unilateral and includes only the influence of heat transport on moisture transport.

Sandwich-structured composite fibrous membranes with tunable porous structure for waterproof, breathable, and oil-water separation applications

HypothesisIn general, microporous membranes with waterproofness, breathability, and oil-water separation performance are prepared from hydrophobic raw materials and demonstrated to exhibit an interconnected porous structure. Hence, constructing porous and gradient-structured composite membranes by integrating robust hydrophobic/lipophilic polyvinylidene fluoride (PVDF) and breathable polyurethane (PU) microporous membranes could help realize a selective separation process. ExperimentHere, novel polyvinylidene fluoride-carbon nanotube/polyurethane/polyvinylidene fluoride-carbon nanotube (PVDF-CNT/PU/PVDF-CNT) sandwich-structured microporous membranes were fabricated by sequential electrospinning. The influence of the thickness ratios of PVDF/PU/PVDF and carbon nanotube (CNT) content on the fibrous construction, porous structure, and wettability of the composite membranes was systematically studied by scanning electron microscopy (SEM), pore size, porosity and contact angle. Significantly, the effect of the fibrous construction, porous structure, and wettability on the waterproofness, breathability, and oil-water separation ability of the composite membranes was investigated. FindingsThe novel separation system proved the ‘complementary effect’ between the PVDF and PU membranes. Further, because of the elaborate gradient construction, superior porous structure, and robust hydrophobicity-oleophilicity, the resultant membranes exhibited moderate waterproofness (38 kPa) and excellent breathability (8.63 kg m−2 d−1), and oil-water separation, confirming that they could be promising alternatives for numerous practical applications, such as protective clothing, treatment of oil-contaminated water, and membrane distillation.

Materials and Fabrication Methods for Biofabrication

Within tissue engineering and regenerative medicine, Biofabrication is a young and dynamically evolving field of research [1]. It aims at the automated generation of hierarchical tissue-like structures from cells and materials through Bioprinting or Bioassembly. This approach has the potential to overcome a number of classical challenges relating to organization, personalized shape and mechanical integrity of generated constructs. Although this has allowed achieving some remarkable successes, it has recently become evident that the lack of variety in printable hydrogel systems is one major drawback for the complete field [2]. In order to be suitable for Biofabrication, hydrogels have to comply with a number of prerequisites with regards to rheological behavior and especially stabilization of the printed structure instantly after printing, while at the same time allowing the cells to proliferate. Also fabrication techniques are often not ideal and need to be optimized for the printing of anatomical structures. This lecture will briefly introduce the field and the major printing techniques, as well as the most important demands on materials and fabrication techniques. It will then introduce a new method for the rational design of thermoplast fibre constructs by the combination of melt electrospinning with automated movement of the collector (Melt electrospinning writing). This technique allows for the generation of highly regular fibrous constructs with pore sizes in cellular dimensions and fibre diameters down to submicrometer [3]. Printing of anatomical structures that would not be accessible otherwise will be demonstrated at one example. The lecture will then focus on printable hydrogels. Thiolene cross-linking of poly(glycidyl-co-allylglycidylether) based 3D plotted hydrogels will be introduced [4] as alternative to the often used free radical polymerization to stabilize printed hydrogel structures with high resolution and reproducibility. Furthermore, a purely physically cross-linked system based on recombinant spider silk proteins will be introduced [5], in which beta-sheet interactions facilitate good printability and stability of the constructs.

Sliding Fibers: Slidable, Injectable, and Gel-like Electrospun Nanofibers as Versatile Cell Carriers.

Designing biomaterial systems that can mimic fibrous, natural extracellular matrix is crucial for enhancing the efficacy of various therapeutic tools. Herein, a smart technology of three-dimensional electrospun fibers that can be injected in a minimally invasive manner was developed. Open surgery is currently the only route of administration of conventional electrospun fibers into the body. Coordinating electrospun fibers with a lubricating hydrogel produced fibrous constructs referred to as slidable, injectable, and gel-like (SLIDING) fibers. These SLIDING fibers could pass smoothly through a catheter and fill any cavity while maintaining their fibrous morphology. Their injectable features were derived from their distinctive rheological characteristics, which were presumably caused by the combinatorial effects of mobile electrospun fibers and lubricating hydrogels. The resulting injectable fibers fostered a highly favorable environment for human neural stem cell (hNSC) proliferation and neurosphere formation within the fibrous structures without compromising hNSC viability. SLIDING fibers demonstrated superior performance as cell carriers in animal stroke models subjected to the middle cerebral artery occlusion (MCAO) stroke model. In this model, SLIDING fiber application extended the survival rate of administered hNSCs by blocking microglial infiltration at the early, acute inflammatory stage. The development of SLIDING fibers will increase the clinical significance of fiber-based scaffolds in many biomedical fields and will broaden their applicability.

Processing and surface modification of polymer nanofibers for biological scaffolds: a review.

Polymeric fibrous constructs possess high surface area-to-volume ratios when compared with solid substrates and are quite commonly used as tissue engineering and cell growth scaffolds. An overview of important design and material considerations for fibrous scaffolds as well as an outline of both established and emerging solution- and melt-based fabrication techniques is provided. Innovative post-process surface modification avenues using "click" chemistry with both single and dual active cues as well as gradient cues, which maintain the fibrous structure are described. By combining process parameters with post-process surface modification, researchers have been able to selectively tune cellular response after seeding and culturing on fibrous constructs.

Three-dimensional multilayered fibrous constructs for wound healing applications.

Electrospun materials are promising scaffolds due to their light-weight, high surface-area and low-cost fabrication, however, such scaffolds are commonly obtained as ultrathin two-dimensional non-woven meshes, lacking on topographical specificity and surface side-dependent properties. Herein, it is reported the production of three-dimensional fibrous materials with an asymmetrical inner structure and engineered surfaces. The manufactured constructs evidence fibrous-based microsized conical protrusions [length: (10 ± 3) × 10(2) μm; width: (3.8 ± 0.8) × 10(2) μm] at their top side, with a median peak density of 73 peaks per cm(2), while their bottom side resembles to a non-woven mesh commonly observed in the fabrication of two-dimensional electrospun materials. Regarding their thickness (3.7 ± 0.1 mm) and asymmetric fibrous inner architecture, such materials avoid external liquid absorption while promoting internal liquid uptake. Nevertheless, such constructs also observed the high porosity (89.9%) and surface area (1.44 m(2) g(-1)) characteristic of traditional electrospun mats. Spray layer-by-layer assembly is used to effectively coat the structurally complex materials, allowing to complementary tailor features such as water vapor transmission, swelling ratio and bioactive agent release. Tested as wound dressings, the novel constructs are capable of withstanding (11.0 ± 0.3) × 10(4) kg m(-2) even after 14 days of hydration, while actively promote wound healing (90 ± 0.5% of wound closure within 48 hours) although avoiding cell adhesion on the dressings for a painless removal.

Functional Reconstruction of Tracheal Defects by Protein-Loaded, Cell-Seeded, Fibrous Constructs in Rabbits.

Tracheal stenosis is a life-threatening disease and current treatments include surgical reconstruction with autologous rib cartilage and the highly complex slide tracheoplasty surgical technique. We propose using a sustainable implant, composed of a tunable, fibrous scaffold with encapsulated chondrogenic growth factor (transforming growth factor-beta3 [TGF-β3]) or seeded allogeneic rabbit bone marrow mesenchymal stromal cells (BMSCs). In vivo functionality of these constructs was determined by implanting them in induced tracheal defects in rabbits for 6 or 12 weeks. The scaffolds maintained functional airways in a majority of the cases, with the BMSC-seeded group having an improved survival rate and the Scaffold-only group having a higher occurrence of more patent airways as determined by microcomputed tomography. The BMSC group had a greater accumulation of inflammatory cells over the graft, while also exhibiting normal epithelium, subepithelium, and cartilage formation. Overall, it was concluded that a simple, acellular scaffold is a viable option for tracheal tissue engineering, with the intraoperative addition of cells being an optional variation to the scaffolds.

Textile transcatheter heart valve prosthesis: state of the art

Today, transcatheter aortic valve replacement (TAVR) has become a largely considered alternative technique to surgical valve replacement in patients who are not operable or patients with high risk for open chest surgery. However, the biological valve tissue used in the devices implanted clinically appears to be a fragile material when folded for low-diameter catheter insertion purpose and released in calcified environment with irregular geometry. Textile polyester material is characterised by outstanding folding and strength properties combined with proven biocompatibility. It could therefore be considered to replace biological valve leaflets in the TAVR procedure. Different issues must, however, be addressed concerning the development of the fabric construction in order to make the material compatible with the valve-requested durability. The performances of a textile valve mainly depend on the ability of the fabric to undergo repeated cyclic loading, the ability of the fibrous construction to resist exaggerated tissue ingrowth with leaflet stiffening and the ability to be crimped into the catheter sheet. The purpose of the present work is to present how a polyester fabric material can address these critical issues, and how the material can be tuned in order to optimise the performance of the device.

Electrospun anisotropic architectures and porous structures for tissue engineering.

In order to design scaffolds for tissue engineering with proper architectures, organization and properties, a variety of materials and technologies are being developed. In addition to being biocompatible both in their bulk and degraded forms, scaffolds should not only possess appropriate mechanical properties to provide a suitable stress environment, but also be porous and permeable to permit the ingress of cells and nutrients. In this review, we aim to summarize recent advances in electrospun anisotropic architectures such as aligned fibrous arrays, fibrous yarns and bundles, fibrous tubular structures, and porous structures, as well as their formation mechanisms and mechanical properties. In particular, the potential applications of these structure-controlled fibrous constructs in neural regeneration, vascular grafts, cardiac tissue, skeletal muscle regeneration, tendon repair, and cornea repair are presented. Moreover, the current challenges and future opportunities for the use of these scaffolds in research and clinical practice are proposed.

The Composite Serratus Anterior/Rib Free Flap: A Viable Alternative to the Fibula in Head and Neck Reconstruction

were transferred to non-adherent 24 well plates and cultured in 1 ml of chondrogenic differentiation medium. Cell viability in-vitro was assessed using the LIVE/ DEAD Cell Viability assay. Total DNA content using the Quant-iT PicoGreen kit and sulfated glycosaminoglycans were determined using the Blyscan Kit. Fibrous constructs were examined histologically by staining for deposited extracellular matrix components of sulfated proteoglycans using 0.1% Alcian Blue, Hematoxylin and Eosinophilic stains for cell nuclei and extraneous extracellular matrix material and Picrosirius Red for collagen. Seeded constructs and acellular control constructs were assessed for compressional properties by performing unconfined uniaxial compression testing using an Instron Model 5540 testing machine. All experimental sample groups had a sample size of at least n = 3 for biochemical, histological and mechanical property analyses done on week 5. Data is presented as average standard error mean. Statistical significance was determined by performing Student’s T-test for all data sets with significance accepted at p-value < 0.05. Histological examination of seeded fibrous constructs revealed a greater distribution and amount of cell nuclei, collagen and proteoglycans throughout the cross-section of chondroprogenitor compared to chondrocyte seeded constructs. Chondroprogenitor seeded constructs exhibited higher compressive moduli (417.5 31.2 kPa) compared to chondrocyte seeded constructs (227.7 20.9 kPa). In conclusion, both chondroprogenitors and chondrocytes are viable and able to undergo chondrogenesis on the trilaminar electrospun scaffolds but alter its mechanical properties in different ways. The clinical implication is that with an improved understanding of the different cell types that are viable and factors that affect the mechanical properties of hierarchical scaffolds we are able to tune and tailor the most effective engineered tissue for articular cartilage regeneration.

Monitoring fibrous scaffold guidance of three-dimensional collagen organisation using minimally-invasive second harmonic generation.

The biological and mechanical function of connective tissues is largely determined by controlled cellular alignment and therefore it seems appropriate that tissue-engineered constructs should be architecturally similar to the in vivo tissue targeted for repair or replacement. Collagen organisation dictates the tensile properties of most tissues and so monitoring the deposition of cell-secreted collagen as the construct develops is essential for understanding tissue formation. In this study, electrospun fibres with a random or high degree of orientation, mimicking two types of tissue architecture found in the body, were used to culture human fibroblasts for controlling cell alignment. The minimally-invasive technique of second harmonic generation was used with the aim of monitoring and profiling the deposition and organisation of collagen at different construct depths over time while construct mechanical properties were also determined over the culture period. It was seen that scaffold fibre organisation affected cell migration and orientation up to 21 days which in turn had an effect on collagen organisation. Collagen in random fibrous constructs was deposited in alternating configurations at different depths however a high degree of organisation was observed throughout aligned fibrous constructs orientated in the scaffold fibre direction. Three-dimensional second harmonic generation images showed that deposited collagen was more uniformly distributed in random constructs but aligned constructs were more organised and had higher intensities. The tensile properties of all constructs increased with increasing collagen deposition and were ultimately dictated by collagen organisation. This study highlights the importance of scaffold architecture for controlling the development of well-organised tissue engineered constructs and the usefulness of second harmonic generation imaging for monitoring collagen maturation in a minimally invasive manner.