Electrospun nanofibers: Work for medicine?

Attempts have been made to fabricate nanofibrous scaffolds to mimic the chemical composition and structural properties of the extracellular matrix (ECM) for tissue/organ replacement. Nanofiber scaffolds with various patterns have been successfully produced from synthetic and natural polymers through a relatively simple technique of electrospinning. The resulting patterns can mimic some of the diverse tissue-specific orientation and three-dimensional (3D) fibrous structures. Studies on cell-nanofiber interactions, including studies on stem cells, have revealed the importance of nanotopography on cell adhesion, proliferation and differentiation. Furthermore, clinical application of electrospun nanofibers including wound healing, tissue regeneration, drug delivery and stem cell therapy are highly feasible due to the ease and flexibility of fabrication of making nanofiber with this cost-effective method using electrospinning. In this review, we have highlighted the current state of the art and provided future perspectives on electrospun nanofiber in medical applications.     

Investigation of cancer cell behavior on nanofibrous scaffolds

Tissue engineering and the use of nanofibrous biomaterial scaffolds offer a unique perspective for studying cancer development in vitro. Current in vitro models of tumorigenesis are limited by the use of static, two-dimensional (2D) cell culture monolayers that lack the structural architecture necessary for cell-cell interaction and three-dimensional (3D) scaffolds that are too simplistic for studying basic pathological mechanisms. In this study, two nanofibrous biomaterials that mimic the structure of the extracellular matrix, bacterial cellulose and electrospun polycaprolactone (PCL)/collagen I, were investigated as potential 3D scaffolds for an in vitro cancer model. Multiple cancer cell lines were cultured on each scaffold material and monitored for cell viability, proliferation, adhesion, infiltration, and morphology. Both bacterial cellulose and electrospun PCL/collagen I, which have nano-scale structures on the order of 100-500 nm, have been used in many diverse tissue engineering applications. Cancer cell adhesion and growth were limited on bacterial cellulose, while all cellular processes were enhanced on the electrospun scaffolds. This initial analysis has demonstrated the potential of electrospun PCL/collagen I scaffolds toward the development of an improved 3D in vitro cancer model.     

Poly(L-lactic acid) nanocylinders as nanofibrous structures for macroporous gelatin scaffolds

Electrospun Nanofiber sheets have been shown to mimic the structure of extracellular matrix (ECM). Although these nanofibers have shown great potential for use as tissue engineering scaffolds, it is difficult for the electrospun nanofiber based sheets to be shaped into the desired three-dimensional structure. In this study, poly(L-lactic acid) (PLLA), a biodegradable and biocompatible polyester, was electrospun to produce nanofibers that were treated with an amino group containing base in order to fabricate polymeric nanocylinders. The aspect ratio of the PLLA nanocylinders was tunable by varying the aminolysis time and density of the amino group containing base. The effects of changes in nanofibrous morphology of the PLLA nanocylinders/macro-porous gelatin scaffolds on cell adhesion and proliferation were evaluated. The results revealed different cell morphology, adhesion, and proliferation in the nanocylinders composite gelatin scaffold versus gelatin scaffold alone. Confocal laser scanning microscopy observation showed more spreading and a more flattened cell morphology after NIH3T3 cells were cultured on PLLA nanocylinders/gelatin scaffolds for 10 hours and 4 days. These results indicate that the gelatin/PLLA nanocylinder composite is a promising way to fabricate 3D nanofibrous scaffolds that accelerates cell adhesion and proliferation for tissue engineering.     

Fabrication and characterization of electrospun osteon mimicking scaffolds for bone tissue engineering

Skeletal loss and bone deficiencies are a major worldwide problem with over 600,000 procedures performed in the US alone annually, making bone one of the most transplanted tissues, second to blood only. Bone is a composite tissue composed of organic matrix, inorganic bone mineral, and water. Structurally bone is organized into two distinct types: trabecular (or cancellous) and cortical (or compact) bones. Trabecular bone is characterized by an extensive interconnected network of pores. Cortical bone is composed of tightly packed units, called osteons, oriented parallel along to the axis of the bone. While the majority of scaffolds attempt to replicate the structure of the trabecular bone, fewer attempts have been made to create scaffolds to mimic the structure of cortical bone. The aim of this study was to develop a technique to fabricate scaffolds that mimic the organization of an osteon, the structural unit of cortical bone. We successfully built a rotating stage for PGA fibers and utilized it for collecting electrospun nanofibers and creating scaffolds. Resulting scaffolds consisted of concentric layers of electrospun PLLA or gelatin/PLLA nanofibers wrapped around PGA microfiber core with diameters that ranged from 200 to 600 μm. Scaffolds were mineralized by incubation in 10× simulated body fluid, and scaffolds composed of 10%gelatin/PLLA had significantly higher amounts of calcium phosphate. The electrospun scaffolds also supported cellular attachment and proliferation of MC3T3 cells over the period of 28 days.     

Investigation of 2D and 3D electrospun scaffolds intended for tendon repair

Two-dimensional (2D) electrospun fibre mats have been investigated as fibrous sheets intended as biomaterials scaffolds for tissue repair. It is recognised that tissues are three-dimensional (3D) structures and that optimisation of the fabrication process should include both 2D and 3D scaffolds. Understanding the relative merits of the architecture of 2D and 3D scaffolds for tendon repair is required. This study investigated three different electrospun scaffolds based on poly(ε-caprolactone) fibres intended for repair of injured tendons, referred to as; 2D random sheet, 2D aligned sheet and 3D bundles. 2D aligned fibres and 3D bundles mimicked the parallel arrangement of collagen fibres in natural tendon and 3D bundles further replicated the tertiary layer of a tendon’s hierarchical configuration. 3D bundles demonstrated greatest tensile properties, being significantly stronger and stiffer than 2D aligned and 2D random fibres. All scaffolds supported adhesion and proliferation of tendon fibroblasts. Furthermore, 2D aligned sheets and 3D bundles allowed guidance of the cells into a parallel, longitudinal arrangement, which is similar to tendon cells in the native tissue. With their superior physical properties and ability to better replicate tendon tissue, the 3D electrospun scaffolds warrant greater investigation as synthetic grafts in tendon repair.     

Fabrication of fibrous poly(butylene succinate)/wollastonite/apatite composite scaffolds by electrospinning and biomimetic process

In this paper, a novel kind of Poly(butylene succinate) (PBSU) /wollastonite/apatite composite scaffold was fabricated via electrospinning and biomimetic process. Pure PBSU scaffold and composite scaffolds with 12.5 wt% and 25 wt% wollastonite were firstly fabricated by electrospinning. SEM micrographs showed that all the electrospun scaffolds had homogeneous fibrous structures with interconnected pores and randomly oriented ultrafine fibers. The composite scaffolds were then surface modified using a biomimetic process. SEM and XRD results showed that apatite could deposit on the surfaces of the composite fibers after incubation in SBF and a novel fibrous structure with microspheres composed of worm-like apatite on composite fibers was formed. Incubation time and wollastonite content were found to influence the morphology of the scaffolds during the biomimetic process obviously. Both the amount and the size of the microspheres on the composite scaffolds increased with increased incubation time. After a certain incubation time, microspheres formed on the composite fibers with less wollastonite had a relatively larger size. Therefore, the microstructure of the composite scaffolds could be adjusted by controlling the wollastonite content and the incubation time. All of these results suggest that it is an effective approach to fabricate PBSU/wollastonite/apatite fibrous composite scaffolds with different material content and controllable microstructure for bone tissue engineering.     

Electrospinning of three-dimensional nanofibrous tubes with controllable architectures

This paper reports a novel static method to fabricate three-dimensional (3D) fibrous tubes composed of ultrafine electrospun fibers. By using this unique technique, micro and macro single tubes with multiple micropatterns, multiple interconnected tubes, and many tubes with the same or different sizes, shapes, structures, and patterns can be prepared synchronously. Parameters that could influence the order degree of patterned architectures have also been investigated. It is expected that electrospun tubes with controllable patterned architectures and 3D configurations may be attractive in many biomedical and industrial applications.     

In situ collagen assembly for integrating microfabricated three-dimensional cell-seeded matrices

Microscale fabrication of three-dimensional (3D) extracellular matrices (ECMs) can be used to mimic the often inhomogeneous and anisotropic properties of native tissues and to construct in vitro cellular microenvironments. Cellular contraction of fibrous natural ECMs (such as fibrin and collagen I) can detach matrices from their surroundings and destroy intended geometry. Here, we demonstrate in situ collagen fibre assembly (the nucleation and growth of new collagen fibres from preformed collagen fibres at an interface) to anchor together multiple phases of cell-seeded 3D hydrogel-based matrices against cellular contractile forces. We apply this technique to stably interface multiple microfabricated 3D natural matrices (containing collagen I, Matrigel, fibrin or alginate); each phase can be seeded with cells and designed to permit cell spreading. With collagen-fibre-mediated interfacing, microfabricated 3D matrices maintain stable interfaces (the individual phases do not separate from each other) over long-term culture (at least 3 weeks) and support spatially restricted development of multicellular structures within designed patterns. The technique enables construction of well-defined and stable patterns of a variety of 3D ECMs formed by diverse mechanisms (including temperature-, ion- and enzyme-mediated crosslinking), and presents a simple approach to interface multiple 3D matrices for biological studies and tissue engineering.     

Hemocompatible surface of electrospun nanofibrous scaffolds by ATRP modification

The electrospun scaffolds are potential application in vascular tissue engineering since they can mimic the nano-sized dimension of natural extracellular matrix (ECM). We prepared a fibrous scaffold from polycarbonateurethane (PCU) by electrospinning technology. In order to improve the hydrophilicity and hemocompatibility of the fibrous scaffold, poly(ethylene glycol) methacrylate (PEGMA) was grafted onto the fiber surface by surface-initiated atom transfer radical polymerization (SI-ATRP) method. Although SI-ATRP has been developed and used for surface modification for many years, there are only few studies about the modification of electrospun fiber by this method. The modified fibrous scaffolds were characterized by SEM, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS). The scaffold morphology showed no significant difference when PEGMA was grafted onto the scaffold surface. Based on the water contact angle measurement, the surface hydrophilicity of the scaffold surface was improved significantly after grafting hydrophilic PEGMA (P = 0.0012). The modified surface showed effective resistance for platelet adhesion compared with the unmodified surface. Activated partial thromboplastin time (APTT) of the PCU-g-PEGMA scaffold was much longer than that of the unmodified PCU scaffold. The cyto-compatibility of electrospun nanofibrous scaffolds was tested by human umbilical vein endothelial cells (HUVECs). The images of 7-day cultured cells on the scaffold surface were observed by SEM. The modified scaffolds showed high tendency to induce cell adhesion. Moreover, the cells reached out pseudopodia along the fibrous direction and formed a continuous monolayer. Hemolysis test showed that the grafted chains of PEGMA reduced blood coagulation. These results indicated that the modified electrospun nanofibrous scaffolds were potential application as artificial blood vessels.     

Fabrication of three-dimensional nano, micro and micro/nano scaffolds of porous poly(lactic acid) by electrospinning and comparison of cell infiltration by Z-stacking/three-dimensional projection technique

The use of electrospun extracellular matrix (ECM)-mimicking nanofibrous scaffolds for tissue engineering is limited by poor cellular infiltration. The authors hypothesised that cell penetration could be enhanced in scaffolds by using a hierarchical structure where nano fibres are combined with micron-scale fibres while preserving the overall scaffold architecture. To assess this, we fabricated electrospun porous poly(lactic acid) (PLA) scaffolds having nanoscale, microscale and combined micro/nano architecture and evaluated the structural characteristics and biological response in detail. Although the bioactivity was intermediate to that for nanofibre and microfibre scaffold, a unique result of this study was that the micro/nano combined fibrous scaffold showed improved cell infiltration and distribution than the nanofibrous scaffold. Although the cells were found to be lining the scaffold periphery in the case of nanofibrous scaffold, micro/nano scaffolds had cells dispersed throughout the scaffold. Further, as expected, the addition of nanoparticles of hydroxyapatite (nHAp) improved the bioactivity, although it did not play a significant role in cell penetration. Thus, this strategy of creating a three-dimensional (3D) micro/nano architecture that would increase the porosity of the fibrous scaffold and thereby improving the cell penetration, can be utilised for the generation of functional tissue engineered constructs in vitro.     

Electrospun multifunctional tissue engineering scaffolds

Tissue engineering holds great promises in providing successful treat- ments of human body tissue loss that current methods are unable to treat or unable to achieve satisfactory clinical outcomes. In scaffold-based tissue engineering, a high- performance scaffold underpins the success of a tissue engineering strategy and a major direction in the field is to create multifunctional tissue engineering scaffolds for enhanced biological performance and for regenerating complex body tissues. Electrospinning can produce nanofibrous scaffolds that are highly desirable for tissue engineering. The enormous interest in electrospinning and electrospun fibrous structures by the science, engineering and medical communities has led to various developments of the electrospinning technology and wide investigations of eiectrospun products in many industries, including biomedical engineering, over the past two decades. It is now possible to create novel, multicomponent tissue engineering scaffolds with multiple functions. This article provides a concise review of recant advances in the R ＆ D of electrospun multifunctional tissue engineering scaffolds. It also presents our philosophy and research in the designing and fabrication of electrospun multicomponent scaffolds with multiple functions.     

Crosslinking of the electrospun polyethylene glycol/cellulose acetate composite fibers as shape-stabilized phase change materials

In a previous study, polyethylene glycol/cellulose acetate (PEG/CA) composite ultrafine fibers have been prepared by electrospinning. In order to improve their water-resistant ability and thermal stability for potential thermal storage applications, in this study, the electrospun PEG/CA fibers were crosslinked by using toluene-2, 4-diisocyanate (TDI). The morphology and thermal properties of the crosslinked fibers were investigated via SEM, DSC and TG, respectively. The results showed that the fibrous morphology of the crosslinked fibers was well preserved even after 24 h immersing in deionized water. Meanwhile, the crosslinking also led to an improvement on the thermal stability, but brought a decrease of the enthalpy compared with the original electrospun fibers.     

Mechanical properties of electrospun collagen–chitosan complex single fibers and membrane

Collagen and chitosan blends were fabricated into ultrafine fibers to mimic the native extracellular matrix (ECM). So far less mechanical property investigation of electrospun fibers has been reported because of the small dimensions of micro and nanostructures that pose a tremendous challenge for the experimental study of their mechanical properties. In this paper, the electrospun collagen–chitosan complex single fibers and fibrous membrane were collected and their mechanical properties were investigated with a nano tensile testing system and a universal materials tester, respectively. The mechanical properties were found to be dependent on fiber diameter and the ratio of collagen to chitosan in fibers. Fibers with a smaller diameter had higher strength but lower ductility due to the higher draw ratio that was applied during the electrospinning process. For the electrospun single fibers, the fibers demonstrated excellent tensile ductility at chitosan content of 10% and 20% and the highest tensile strength and Young's modulus at chitosan content from 40% to 60%. For the electrospun fibrous membrane, the ultimate tensile strength of the fibrous membrane decreased with the increase of chitosan content in fibers and the trend in the ultimate tensile elongation is similar to that of the single fiber.     

Fast-dissolving carvacrol/cyclodextrin inclusion complex electrospun fibers with enhanced thermal stability,water solubility,and antioxidant activity

Carvacrol is a known antioxidant molecule and commonly used in food and cosmetics as a flavor and fragrance agent; however, carvacrol has major issues such as high volatility, low water solubility, and stability. In this study, carvacrol/cyclodextrin inclusion complex fibers (carvacrol/CD-IC fibers) were produced via electrospinning in order to enhance thermal stability, water solubility and shelf-life of carvacrol having antioxidant activity. The phase solubility and computational modeling studies showed that carvacrol can form inclusion complexes with two types of modified CDs, hydroxypropyl-β-cyclodextrin (HPβCD) and hydroxypropyl-γ-cyclodextrin (HPγCD). The carvacrol/cyclodextrin inclusion complex electrospun fibers (carvacrol/HPβCD-IC fibers and carvacrol/HPγCD-IC fibers) were obtained as free-standing fibrous webs. Although pure carvacrol is highly volatile, the electrospun carvacrol/CD-IC fibers were quite effective to preserve high amount of carvacrol due to the inclusion complexation. In addition, carvacrol/CD-IC fibers have shown higher temperature stability for carvacrol. Moreover, carvacrol/CD-IC fibers showed more effective antioxidant activity as compared to pure carvacrol. The carvacrol/CD-IC fibrous webs have shown fast-dissolving character in water due to the enhanced water solubility of carvacrol/CD-IC and their ultrafine fiber structure. In short, encapsulation of carvacrol in electrospun CD-IC fibrous webs has shown potentials for food and oral care applications due to free-standing and fast-dissolving character along with high water solubility, high temperature stability and enhanced antioxidant by carvacrol/cyclodextrin inclusion complexation.     

聚丁二酸丁二醇酯调控丝素蛋白超细纤维膜形貌及其力学性能

为了改善静电纺再生丝素蛋白(SF)纤维膜的力学性能,通过静电纺丝技术制备丝素蛋白(SF)/聚丁二酸丁二醇酯(PBS)复合超细纤维膜。通过对用甲醇处理后的具有不同共混比例的超细纤维膜进行FE-SEM、FTIR、XRD和DSC观察测试,分析比较了不同共混比例的复合超细纤维膜的形貌、结构,并进行力学性能测试。结果表明:随着聚丁二酸丁二醇酯共混质量比的增加,复合超细纤维的平均直径从289 nm增大到425 nm;复合超细纤维的结晶性能随之提高;复合超细纤维膜的拉伸破坏应力先减小后增大,拉伸破坏应变逐渐增加;当共混质量比为50/50时,复合超细纤维膜表现出良好的力学性能,拉伸破坏应力接近于16 MPa,破坏应变达到50%。聚丁二酸丁二醇酯可有效调控丝素蛋白超细纤维膜的形貌、结构和力学性能。     

Fabrication of PU/PEGMA crosslinked hybrid scaffolds by in situ UV photopolymerization favoring human endothelial cells growth for vascular tissue engineering

Poly(ethylene glycol) methacrylate (PEGMA) was introduced into a polyurethane (PU) solution in order to prepare electrospun scaffold with improving the biocompatibility by electrospinning technology for potential application as small diameter vascular scaffolds. Crosslinked electrospun PU/PEGMA hybrid nanofibers were fabricated by a reactive electrospinning process with N,N'-methylenebisacrylamide as crosslinker and benzophenone as photoinitiator. The photoinduced polymerization and crosslinking reaction took place simultaneously during the electrospinning process. The electrospinning solutions with various weight ratios of PU/PEGMA were successfully electrospun. No significant difference in the scaffold morphology was found by SEM when PEGMA content was <20 wt%. The crosslinked fibrous scaffolds of PU/PEGMA exhibited higher mechanical strength than the pure PU scaffold. The hydrophilicity of scaffolds was controlled by varying the PU/PEGMA weight ratio. The tissue compatibility of electrospun nanofibrous scaffolds were tested using human umbilical vein endothelial cells (HUVECs). Cell morphology and cell proliferation were measured by SEM, fluorescence microscopy and thiazolyl blue assay (MTT) after 1, 3, 7 days of culture. The results indicated that the cell morphology and proliferation on the crosslinked PU/PEGMA scaffolds were better than that on the pure PU scaffold. Furthermore, the appropriate hydrophilic surface with water contact angle in the range of 55-75° was favorable of improvement the HUVECs adhesion and proliferation. Cells seeded on the crosslinked PU/PEGMA (80/20) scaffolds infiltrated into the scaffolds after 7 days of growth. These results indicated the crosslinked electrospun PU/PEGMA nanofibrous scaffolds were potential substitutes for artificial vascular scaffolds.     

有序电纺纤维膜的制备方法及在组织工程中的应用进展

静电纺丝是一种简单且有效的制备高分子微纳米纤维的方法。近年来,通过电纺装置的控制制备有序纤维膜已成为研究热点,由此构建的电纺纤维膜支架具有独特的结构和生物学性能,有利于细胞的粘附、增殖和分化,在神经、血管、骨与软骨等组织工程及组织修复中具有良好的应用前景。文中对有序电纺纤维膜的制备方法进行了总结,概述了有序电纺纤维膜在...     

Comparative performance of collagen nanofibers electrospun from different solvents and stabilized by different crosslinkers

Collagen electrospun scaffolds well reproduce the structure of the extracellular matrix (ECM) of natural tissues by coupling high biomimetism of the biological material with the fibrous morphology of the protein. Structural properties of collagen electrospun fibers are still a debated subject and there are conflicting reports in the literature addressing the presence of ultrastructure of collagen in electrospun fibers. In this work collagen type I was successfully electrospun from two different solvents, trifluoroethanol (TFE) and dilute acetic acid (AcOH). Characterization of collagen fibers was performed by means of SEM, ATR-IR, Circular Dichroism and WAXD. We demonstrated that collagen fibers contained a very low amount of triple helix with respect to pristine collagen (18 and 16 % in fibers electrospun from AcOH and TFE, respectively) and that triple helix denaturation occurred during polymer dissolution. Collagen scaffolds were crosslinked by using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), a commonly employed crosslinker for electrospun collagen, and 1,4-butanediol diglycidyl ether (BDDGE), that was tested for the first time in this work as crosslinking agent for collagen in the form of electrospun fibers. We demonstrated that BDDGE successfully crosslinked collagen and preserved at the same time the scaffold fibrous morphology, while scaffolds crosslinked with EDC completely lost their porous structure. Mesenchymal stem cell experiments demonstrated that collagen scaffolds crosslinked with BDDGE are biocompatible and support cell attachment.     

Neurite Outgrowth on Nanocomposite Scaffolds Synthesized from PLGA and Carboxylated Carbon Nanotubes

Carbon nanotubes (CNTs) have been suggested as suitable materials for biomedical applications, especially in the neural area. It is essential not only to investigate the biocompatibility of CNTs with the neural system but also to determine proper methods for applying CNTs to neuronal growth. This work represents the first application of CNTs by electrospun poly(D ,L ‐lactic‐co‐glycolic acid) (PLGA) scaffolds for a neural system. We synthesized electrospun nanocomposites of PLGA and single‐walled carbon nanotubes functionalized by carboxylic acid groups (c‐SWNTs), and investigated neurite outgrowth from SH‐SY5Y cells on these nanocomposites as compared to that on fibrous PLGA alone. Cells on our PLGA/c‐SWNT nanocomposite showed significantly enhanced mitochondrial function and neurite outgrowth compared to cells on PLGA alone. We concluded that c‐SWNTs incorporated into fibrous PLGA scaffolds exerted a positive role on the health of neural cells.     

Osteoblast behaviour on in situ photopolymerizable three-dimensional scaffolds based on d,l-lactide and ε-caprolactone: influence of pore volume, pore size and pore shape

Bone marrow cells were cultured on in situ photopolymerizable scaffolds based on D,L-lactide and epsilon-caprolactone. The influence of pore volume, size and shape were evaluated. Bone formation was demonstrated by ALP activity, osteocalcin secretion and histological analysis. TEM at the polymer interface revealed osteoblasts which secreted an extracellular matrix containing matrix vesicles loaded with apatite. Cellular infiltration was possible for scaffolds with a porosity of 70 and gelatin particle size of 250-355 microm. Scaffolds with a porosity less than 70 had the tendency to form a polymer top layer. Although increasing the gelatin particle size to 355-500 microm, leads to infiltration even in scaffolds with a porosity of 60. No infiltration was possible in scaffolds with sodium chloride as porogen. On the contrary, sucrose and gelatin leads to better interconnected scaffolds at the same porosity. Hence, spherical gelatin particles are suitable to use as porogen in photopolymerizable scaffolds.