Engraving the Surface of Electrospun Microfibers with Nanoscale Grooves Promotes the Outgrowth of Neurites and the Migration of Schwann Cells

We report a simple method based upon coaxial electrospinning for the fabrication of aligned microfibers engraved with nanoscale grooves to promote neurite outgrowth and cell migration. The success of this method relies on the immiscibility between poly(?‐caprolactone) (PCL) and poly(vinyl pyrrolidone) (PVP) in 2,2,2‐trifluoroethanol (TFE) for the generation of PVP/TFE pockets on the surface of a PCL jet. The pockets are stretched and elongated along with the jet, eventually resulting in the formation of nanoscale grooves upon the removal of PVP. The presence of nanoscale grooves greatly enhances the outgrowth of neurites from both PC12 cells and chick embryonic dorsal root ganglia (DRG) bodies, as well as the migration of Schwann cells. The enhancements can be maximized by optimizing the dimensions of the grooves for potential use in applications involving neurite extension and wound closure.     

Photothermal Welding,Melting, and Patterned Expansion of Nonwoven Mats of Polymer Nanofibers for Biomedical and Printing Applications

We report a simple method for the photothermal welding of nonwoven mats of electrospun nanofibers by introducing a near‐infrared (NIR) dye such as indocyanine green. By leveraging the strong photothermal effect of the dye, the nanofibers can be readily welded at their cross points or even over‐welded (i.e., melted and/or fused together) to transform the porous mat into a solid film upon exposure to a NIR laser. While welding at the cross points greatly improves the mechanical strength of a nonwoven mat of nanofibers, melting and fusion of the nanofibers can be employed to fabricate a novel class of photothermal papers for laser writing or printing without chemicals or toner particles. By using a photomask, we can integrate photothermal welding with the gas foaming technique to pattern and then expand nonwoven mats into 3D scaffolds with well‐defined structures. This method can be applied to different combinations of polymers and dyes, if they can be co‐dissolved in a suitable solvent for electrospinning.     

Photothermal Welding,Melting, and Patterned Expansion of Nonwoven Mats of Polymer Nanofibers for Biomedical and Printing Applications

We report a simple method for the photothermal welding of nonwoven mats of electrospun nanofibers by introducing a near‐infrared (NIR) dye such as indocyanine green. By leveraging the strong photothermal effect of the dye, the nanofibers can be readily welded at their cross points or even over‐welded (i.e., melted and/or fused together) to transform the porous mat into a solid film upon exposure to a NIR laser. While welding at the cross points greatly improves the mechanical strength of a nonwoven mat of nanofibers, melting and fusion of the nanofibers can be employed to fabricate a novel class of photothermal papers for laser writing or printing without chemicals or toner particles. By using a photomask, we can integrate photothermal welding with the gas foaming technique to pattern and then expand nonwoven mats into 3D scaffolds with well‐defined structures. This method can be applied to different combinations of polymers and dyes, if they can be co‐dissolved in a suitable solvent for electrospinning.     

Double‐layered composite nanofibers and their mechanical performance

Continuous polymer nanofibers are available through electrospinning, but most have the same structure in their cross section. This article focuses on the fabrication and the structural and mechanical characterization of pencil‐like double‐layered composite nanofibers coaxially electrospun from solutions of two different biodegradable materials, i.e., gelatin and poly(ε‐caprolactone) (PCL). Transmission electron microscopy and water contact angle measurements confirmed that a gelatin inner fiber was wrapped with a PCL outer layer. Possible applications of such nanofibers include a controlled degradation rate when used as a medical device in human body. It has been found that the tensile performance of the composite nanofibers was better than those of both the pure constituent, i.e. gelatin and PCL, nanofibers alone. The ultimate strength and ultimate strain of the composite nanofibers with 7.5% w/v gelatin in the core and 10% w/v PCL as shell were at least 68% and 244% higher, respectively, than those of the same concentration pure gelatin and PCL nanofibers. Thus, a coaxial electrospinning technique as used in this article can be applicable, not only in developing functionalized nanofibers but also in elevating their mechanical property. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2852–2861, 2005     

Enhancing the Mechanical Properties of Electrospun Nanofiber Mats through Controllable Welding at the Cross Points

This communication describes a simple and effective method for welding electrospun nanofibers at the cross points to enhance the mechanical properties of their nonwoven mats. The welding is achieved by placing a nonwoven mat of the nanofibers in a capped vial with the vapor of a proper solvent. For polycaprolactone (PCL) nanofibers, the solvent is dichloromethane (DCM). The welding can be managed in a controllable fashion by simply varying the partial pressure of DCM and/or the exposure time. Relative to the pristine nanofiber mat, the mechanical strength of the welded PCL nanofiber mat can be increased by as much as 200%. Meanwhile, such a treatment does not cause any major structural changes, including morphology, fiber diameter, and pore size. This study provides a generic method for improving the mechanical properties of nonwoven nanofiber mats, holding great potential in various applications.

     

Highly porous core-shell polymeric fiber network

Core-shell nanofibers are of great interest in the field of tissue engineering and cell biology. We fabricated porous core-shell fiber networks using an electrospinning system with a water-immersed collector. We hypothesized that the phase separation and solvent evaporation process would enable the control of the pore formation on the core-shell fiber networks. To synthesize porous core-shell fiber networks, we used polycaprolactone (PCL) and gelatin. Quantitative analysis showed that the sizes of gelatin-PCL core-shell nanofibers increased with PCL concentrations. We also observed that the shapes of the pores created on the PCL fiber networks were elongated, whereas the gelatin-PCL core-shell fiber networks had circular pores. The surface areas of porous nanofibers were larger than those of the nonporous nanofibers due to the highly volatile solvent and phase separation process. The porous core-shell fiber network was also used as a matrix to culture various cell types, such as embryonic stem cells, breast cancer cells, and fibroblast cells. Therefore, this porous core-shell polymeric fiber network could be a potentially powerful tool for tissue engineering and biological applications.     

Regulation of neurite outgrowth by intermittent irradiation of visible light

The effect of neurite outgrowth of PC12 cells on collagen-coated glass plates under intermittent light irradiation at 525 nm and 0.4 mW/cm2 of intensity was investigated. Neurite outgrowth of PC12 cells was significantly suppressed when PC12 cells were cultivated under intermittent light irradiation with a total irradiation time of more than 2 min/h. No temperature increase was observed in the culture medium under either continuous or intermittent light irradiation. Therefore, suppression of neurite outgrowth under light irradiation was not due to the increase of temperature in the culture medium, but rather the effect of light on the PC12 cells, especially the signal transmittance of light to PC12 cells. The light irradiation interval also affected the neurite outgrowth of PC12 cells when the total irradiation time was constant. A high extension ratio of neurite outgrowth was observed under a long time interval of nonirradiation between light irradiations (1 min of irradiation every hour) as compared with frequent light irradiation intervals (5 s of irradiation every 5 min) with the same total irradiation period per hour. The neurite outgrowth ratio was thought to be dependent on the light intensity, the total time of light irradiation in the intermittent light irradiation, and the interval of light irradiation in the intermittent light irradiation.     

Fabrication of poly(ϵ-caprolactone)/paclitaxel (core)/chitosan/zein/multi-walled carbon nanotubes/doxorubicin (shell) nanofibers against MCF-7 breast cancer

In the present study, paclitaxel (PTX), multi-walled carbon nanotubes (MWCNTs), and doxorubicin (DOX) have been simultaneously doped into the poly(ϵ-caprolactone) (PCL)/chitosan/zein core-shell nanofibers to increase its cytotoxicity for MCF-7 breast cancers killing. The physico-chemical properties of synthesized nanofibers were determined by scanning electron microscope, Fourier-transform infrared spectroscopy, tensile strength, and degradation rate determinations. The in vitro release studies demonstrated the sustained release of drugs from core-shell nanofibrous scaffold. The cytotoxicity and compatibility of core-shell nanofibers were investigated by their treating with MCF-7 breast cancer cells and L929 normal cells, respectively. PCL/PTX/chitosan/zein/MWCNTs/DOX core-shell nanofibers containing 1 wt% MWCNTs, 100 μg ml⁻¹ DOX and 100 μg ml⁻¹ PTX had a high biocompatibility with a 84% MCF-7 cancer cells killing. The in vivo studies revealed the synergic effects of MWCNTs and anticancer drugs on the tumor inhibition. This method could be considered as a new way for developing of MWCNTs loaded-nanofibers for cancer treatment in future.     

Neuroactive Peptide Nanofibers for Regeneration of Spinal Cord after Injury

The highly complex nature of spinal cord injuries (SCIs) requires design of novel biomaterials that can stimulate cellular regeneration and functional recovery. Promising SCI treatments use biomaterial scaffolds, which provide bioactive cues to the cells in order to trigger neural regeneration in the spinal cord. In this work, the use of peptide nanofibers is demonstrated, presenting protein binding and cellular adhesion epitopes in a rat model of SCI. The self‐assembling peptide molecules are designed to form nanofibers, which display heparan sulfate mimetic and laminin mimetic epitopes to the cells in the spinal cord. These neuroactive nanofibers are found to support adhesion and viability of dorsal root ganglion neurons as well as neurite outgrowth in vitro and enhance tissue integrity after 6 weeks of injury in vivo. Treatment with the peptide nanofiber scaffolds also show significant behavioral improvement. These results demonstrate that it is possible to facilitate regeneration especially in the white matter of the spinal cord, which is usually damaged during the accidents using bioactive 3D nanostructures displaying high densities of laminin and heparan sulfate‐mimetic epitopes on their surfaces.     

Improved survival of cardiac cells on surface modified electrospun nanofibers

Polycaprolactone (PCL) is a popular synthetic polymer used in the field of cardiac tissue engineering (CTE) due to its non-toxic degraded by products and low cost manufacturing method. However, hydrophobic nature of this material limits its wide spread application in different cell interaction processes. Therefore, current study aims to chemically modify PCL made random and aligned nanofibers with collagen coating mimicking the oriented matrix of the cardiac cells. Morphological and chemical properties of the electrospun PCL nanofibers were evaluated by SEM, FTIR, XRD and water contact angle measurement. Results indicated that the anisotropic characteristics of aligned nanofibers promoted cell attachment and alignment, which closely match the requirements of native cardiac cells. Thus, aligned nanofibers could be preferred for cardiac tissue regeneration and defects over random nanofibers.     

Syntheses and evaluation of biodegradable multifunctional polymer networks

The biodegradable, injectable and in situ crosslinkable polymer networks based upon di(propylene fumarate)-dimethacrylate (DPFDMA) and polycaprolactone trimethacrylate (PCLTMA), were prepared and characterized. The polymer networks were initiated by photopolymerization. The initial compressive (CS) and diametral tensile strengths (DTS) of the networks materials were determined and used to evaluate the effects of PCLTMA/DPFDMA ratios on the degradation behavior. The networks exhibited initial DTS values ranging from 2.5 to 9.3 MPa and CS values ranging from 1.8 to 146.0 MPa. The increase of PCLTMA in the formulation led to an increase in viscosity and DTS. The degree of conversions and polymerization shrinkage of the resins ranged from 60% to 72% and 5.1% to 6.4%, respectively. After 6 month, PCL300TMA/DPFDMA resins at a ratio of 100/0, 75/25 and 25/75 lost 70%, 87% and 46% of their initial CS, respectively, while PCL900TMA/DPFDMA and PCL300TMA/PCL900TMA resins at 75/25 lost 100% and 83% of their initial CS, respectively.     

The role of chalcones: helichrysetin,xanthohumol, and flavokawin-C in promoting neurite outgrowth in PC12 Adh cells

Chalcones are a group of compounds widely distributed in plant kingdom. The aim of this study was to assess the neurite outgrowth stimulatory activity of selected chalcones, namely helichrysetin, xanthohumol and flavokawin-C. Using adherent rat pheochromocytoma (PC12 Adh) cells, the chalcones were subjected to neurite outgrowth assay and the extracellular nerve growth factor (NGF) levels were determined. Xanthohumol (10 μg/mL) displayed the highest (p < 0.05) percentage of neurite-bearing PC12 Adh cells and the highest (p < 0.05) NGF level in the culture medium of xanthohumol-treated cells. While, helichrysetin induced a moderately high numbers of neurite-bearing cells, flavokawin-C did not stimulate neurite outgrowth. This work supports the potential use of xanthohumol as a potential neuroactive compound to stimulate neurite outgrowth.     

p190RhoGAP and Rap-dependent RhoGAP (ARAP3) inactivate RhoA in response to nerve growth factor leading to neurite outgrowth from PC12 cells

Rat pheochromocytoma (PC12) cells have been used to investigate neurite outgrowth. Nerve growth factor (NGF) has been well known to induce neurite outgrowth from PC12 cells. RhoA belongs to Ras-related small GTP-binding proteins, which regulate a variety of cellular processes, including cell morphology alteration, actin dynamics, and cell migration. NGF suppressed GTP-RhoA levels after 12 h in PC12 cells and was consistently required for a long time to induce neurite outgrowth. Constitutively active (CA)-RhoA suppressed neurite outgrowth from PC12 cells in response to NGF, whereas dominant-negative (DN)-RhoA stimulated it, suggesting that RhoA inactivation is essential for neurite outgrowth. Here, we investigated the mechanism of RhoA inactivation. DN-p190RhoGAP abrogated neurite outgrowth, whereas wild-type (WT)-p190RhoGAP and WT-Src synergistically stimulated it along with accelerating RhoA inactivation, suggesting that p190RhoGAP, which can be activated by Src, is a major component in inhibiting RhoA in response to NGF in PC12 cells. Contrary to RhoA, Rap1 was activated by NGF, and DN-Rap1 suppressed neurite outgrowth, suggesting that Rap1 is also essential for neurite outgrowth. RhoA was co-immunoprecipitated with Rap1, suggesting that Rap1 interacts with RhoA. Furthermore, a DN-Rap-dependent RhoGAP (ARAP3) prevented RhoA inactivation, abolishing neurite formation from PC12 cells in response to NGF. These results suggest that NGF activates Rap1, which, in turn, up-regulates ARAP3 leading to RhoA inactivation and neurite outgrowth from PC12 cells. Taken together, p190RhoGAP and ARAP3 seem to be two main factors inhibiting RhoA activity during neurite outgrowth in PC12 cells in response to NGF.     

Investigation of nanomechanical and morphological properties of silane-modified halloysite clay nanotubes reinforced polycaprolactone bio-composite nanofibers by atomic force microscopy

There is remarkable interest in the fabrication of polymeric composite nano/micro-fibers by electrospinning for many applications ranging from bioengineering to water/air filtration. In almost all of these applications, the mechanical properties of both the polymer fibers and their assemblies, are significant. In this study, unmodified, 3-Glycidoxypropyltrimethoxysilane (GPTMS) or 3-Aminopropyltriethoxysilane (APTES) modified halloysite clay nanotube (HNT) reinforced polycaprolactone (PCL) nanofibers were successfully synthesized via the electrospinning. The morphology and mechanical features of the obtained electrospun fibers were investigated by atomic force microscopy (AFM) and AFM-based nanoindentation for single fibers in nanoscale, respectively. Besides, scanning electron microscopy and tensile strength tests were used to investigate whole fibrous structures in microscale. The AFMresults, accompanied by SEM and tensile strength, support the conclusion that silane-modification affected positively the morphology and mechanical characteristics of electrospun PCL nanofibers. Therefore, it was concluded that the morphological and mechanical features from the single fibers in the nanofiber mats were related to the whole fibrous structure.     

Alkali‐Mediated Miscibility of Gelatin/Polycaprolactone for Electrospinning Homogeneous Composite Nanofibers for Tissue Scaffolding

Electrospun natural‐synthetic composite nanofibers, which possess favorable biological and mechanical properties, have gained widespread attention in tissue engineering. However, the development of biomimetic nanofibers of hybrids remains a huge challenge due to phase separation of the polymer blends. Here, aqueous sodium hydroxide (NaOH) solution is proposed to modulate the miscibility of a representative natural‐synthetic hybrid of gelatin (GT) and polycaprolactone (PCL) for electrospinning homogeneous composite nanofibers. Alkali‐doped GT/PCL solutions and nanofibers examined at macroscopic, microscopic, and internal molecular levels demonstrate appropriate miscibility of GT and PCL after introducing the alkali dopant. Particularly, homogeneous GT/PCL nanofibers with smooth surface and uniform diameter are obtained when aqueous NaOH solution with a concentration of 10 m is used. The fibers become more hydrophilic and possess improved mechanical properties both in dry and wet conditions. Moreover, biocompatibility experiments show that stem cells adhere to and proliferate better on the alkali‐modified nanofibers than the untreated one. This study provides a facile and effective approach to solve the phase separation issue of the synthetic‐natural hybrid GT/PCL and establishes a correlation of compositionally and morphologically homogeneous composite nanofibers with respect to cell responses.     

Insulin immobilized PCL‐cellulose acetate micro‐nanostructured fibrous scaffolds for tendon tissue engineering

Use of growth factors as biochemical molecules to elicit cellular differentiation is a common strategy in tissue engineering. However, limitations associated with growth factors, such as short half‐life, high effective physiological doses, and high costs, have prompted the search for growth factor alternatives, such as growth factor mimics and other proteins. This work explores the use of insulin protein as a biochemical factor to aid in tendon healing and differentiation of cells on a biomimetic electrospun micro‐nanostructured scaffold. Dose response studies were conducted using human mesenchymal stem cells (MSCs) in basal media supplemented with varied insulin concentrations. A dose of 100‐ng/mL insulin showed increased expression of tendon markers. Synthetic‐natural blends of various ratios of polycaprolactone (PCL) and cellulose acetate (CA) were used to fabricate micro‐nanofibers to balance physicochemical properties of the scaffolds in terms of mechanical strength, hydrophilicity, and insulin delivery. A 75:25 ratio of PCL:CA was found to be optimal in promoting cellular attachment and insulin immobilization. Insulin immobilized fiber matrices also showed increased expression of tendon phenotypic markers by MSCs similar to findings with insulin supplemented media, indicating preservation of insulin bioactivity. Insulin functionalized scaffolds may have potential applications in tendon healing and regeneration.     

Desorption-limited mechanism of release from polymer nanofibers

This work examines the release of a model water-soluble compound from electrospun polymer nanofiber assemblies. Such release attracts attention in relation to biomedical applications, such as controlled drug delivery. It is also important for stem cell attachment and differentiation on biocompatible electrospun nanofiber scaffolds containing growth factors, which have been encapsulated by means of electrospinning. Typically, the release mechanism has been attributed to solid-state diffusion of the encapsulated compound from the fibers into the surrounding aqueous bath. Under this assumption, a 100% release of the encapsulated compound is expected in a certain (long) time. The present work focuses on certain cases where complete release does not happen, which suggests that solid-state diffusion may not be the primary mechanism at play. We show that in such cases the release rate can be explained by desorption of the embedded compound from nanopores in the fibers or from the outer surface of the fibers in contact with the water bath. After release, the water-soluble compound rapidly diffuses in water, whereas the release rate is determined by the limiting desorption stage. A model system of Rhodamine 610 chloride fluorescent dye embedded in electrospun monolithic poly(methylmethacrylate) (PMMA) or poly(caprolactone) (PCL) nanofibers, in nanofibers electrospun from PMMA/PCL blends, or in core-shell PMMA/PCL nanofibers is studied. Both the experimental results and theory point at the above mentioned desorption-related mechanism, and the predicted characteristic time, release rate, and effective diffusion coefficient agree fairly well with the experimental data. A practically important outcome of this surface release mechanism is that only the compound on the fiber and pore surfaces can be released, whereas the material encapsulated in the bulk cannot be freed within the time scales characteristic of the present experiments (days to months). Consequently, in such cases, complete release is impossible. We also demonstrate how the release rate can be manipulated by the polymer content and molecular weight affecting nanoporosity and the desorption enthalpy, as well as by the nanofiber structure (monolithic fibers, fibers from polymer blends, and core-shell fibers). In particular, it is shown that, by manipulating the above parameters, release times from tens of hours to months can be attained.     

Short and simple peptide-based pH-sensitive hydrogel for antitumor drug delivery

Since self-assembled peptide hydrogels can solve the problems such as low solubility, poor selectivity and serious adverse effects of traditional chemotherapy drugs, they have been widely used as carrier materials for drug delivery. In this study, we developed a novel and injectable drug delivery platform for the antitumor drug doxorubicin(DOX) using a p H-responsive ionic-complementary octapeptide FOE.This octapeptide could self-assemble into stable hydrogel under neutral conditions, while disa...     

Fabrication of random and aligned electrospun nanofibers containing graphene oxide for skeletal muscle cells scaffold

Graphene oxide (GO)‐based materials have been explored in biomedical applications as active engineered materials for diagnosis and therapy. Although a large number of studies have been carried out in the last years, aspects involving the orientation and elongation of cells on GO immobilized on polymeric nanofibers are still scarce. We investigated the interactions between skeletal muscle cells and GO immobilized on random and aligned electrospun nanofibers of poly(caprolactone) (PCL), a biocompatible and biodegradable polymer. Oxygen plasma was employed to modify the nanofiber polymer surface to enhance the interactions between the PCL fibers and GO. Scanning electron microscopy and confocal microscopy revealed the morphology and orientation of skeletal muscle cells (C2C12 cells) on random and aligned GO/PCL nanofibers. The approach employed here is useful to investigate the interaction of skeletal muscle cells with biocompatible polymer nanofibers modified with GO intended for cell scaffolds and tissue engineering.     

将源药包覆到聚己内酯超细纤维的芯部

采用同轴共纺技术,分别将白藜芦醇(Resveratrol,RT)和硫酸庆大霉素(Gentamycin Sulfate,GS)源药包覆在生物可降解的聚己内酯(PCL)超细(直径为几百纳米)纤维芯部.研究了这种纤维的制备过程以及它们的微观结构.这种复合纳米纤维可在医疗新产品开发中发挥作用,如用于制备新的羊肠线(体内手术伤口缝合线)或伤口敷布.