Lingling Tian

Electrospinning of poly(glycerol sebacate)-based nanofibers for nerve tissue engineering

Nerve tissue engineering (TE) requires biomimetic scaffolds providing essential chemical and topographical cues for nerve regeneration. Poly(glycerol sebacate) (PGS) is a biodegradable and elastic polymer that has gained great interest as a TE scaffolding biomaterial. However, uncured PGS is difficult to be electrospun into nanofibers. PGS would, therefore, require the addition of electrospinning agents. In this study, we modified PGS by using atom transfer radical polymerization (ATRP) to synthesize PGS-based copolymers with methyl methacrylate (MMA). The synthesized PGS-PMMA copolymer showed a molecular weight of 82kDa and a glass transition temperature of 115°C. More importantly, the PGS-PMMA could be easily electrospun into nanofiber with a fiber diameter of 167±33nm. Blending gelatin into PGS-PMMA nanofibers was found to increase its hydrophilicity and biocompatibility. Rat PC12 cells were seeded onto the PGS-PMMA/gelatin nanofibers to investigate their potential for nerve regeneration. It was found that gelatin-containing PGS-based nanofibers promoted cell proliferation. The elongated cell morphology observed on such nanofibers indicated that the scaffolds could induce the neurite outgrowth of the nerve stem cells. Overall, our study suggested that the synthesis of PGS-based copolymers might be a promising approach to enhance their processability, and therefore advancing bioscaffold engineering for various TE applications.

Strategies for regeneration of components of nervous system: scaffolds, cells and biomolecules.

Nerve diseases including acute injury such as peripheral nerve injury (PNI), spinal cord injury (SCI) and traumatic brain injury (TBI), and chronic disease like neurodegeneration disease can cause various function disorders of nervous system, such as those relating to memory and voluntary movement. These nerve diseases produce great burden for individual families and the society, for which a lot of efforts have been made. Axonal pathways represent a unidirectional and aligned architecture allowing systematic axonal development within the tissue. Following a traumatic injury, the intricate architecture suffers disruption leading to inhibition of growth and loss of guidance. Due to limited capacity of the body to regenerate axonal pathways, it is desirable to have biomimetic approach that has the capacity to graft a bridge across the lesion while providing optimal mechanical and biochemical cues for tissue regeneration. And for central nervous system injury, one more extra precondition is compulsory: creating a less inhibitory surrounding for axonal growth. Electrospinning is a cost-effective and straightforward technique to fabricate extracellular matrix (ECM)-like nanofibrous structures, with various fibrous forms such as random fibers, aligned fibers, 3D fibrous scaffold and core-shell fibers from a variety of polymers. The diversity and versatility of electrospinning technique, together with functionalizing cues such as neurotrophins, ECM-based proteins and conductive polymers, have gained considerable success for the nerve tissue applications. We are convinced that in the future the stem cell therapy with the support of functionalized electrospun nerve scaffolds could be a promising therapy to cure nerve diseases.

Size- and shape-controlled synthesis of ZnIn2S4 nanocrystals with high photocatalytic performance

A facile route for synthesizing size- and shape-controlled ternary hexagonal ZnIn2S4 nanocrystals with narrow size distributions is developed using oleylamine as the ligand and noncoordinating octadecene as the solvent. Tunable sizes from 2.1 nm to 9.2 nm of the ZnIn2S4 nanocrystals are achieved through manipulation of reaction temperatures. Furthermore, the obtained ZnIn2S4 presents a nanoplate structure by replacing the sulfur powder with thiourea as the sulfur source. Optical measurements of the ZnIn2S4 nanocrystals demonstrate that their optical properties are related to the sizes of the products. The band gap energy varies from 3.28 to 2.35 eV, corresponding to the size from 2.1 nm to 9.2 nm. Compared with the bulk material, the blue-shift of the absorption spectra is mainly due to the size-dependent quantum confined effect. Photodegradation investigation demonstrates that the annealed ZnIn2S4 nanocrystals reveal higher photocatalytic activity for degradation of methylene orange (MO) solution in the visible region than the annealed ZnIn2S4 nanoplates and unannealed ZnIn2S4 nanocrystals.

Coaxial electrospun poly(lactic acid)/silk fibroin nanofibers incorporated with nerve growth factor support the differentiation of neuronal stem cells

Coaxial electrospinning is an explicit method for encapsulation of protein drugs, and the process could preserve the bioactivity of the molecules. In this study, coaxial electrospinning was used to fabricate Poly(Lactic Acid)/Silk Fibroin/Nerve Growth Factor (PS/N) by encapsulating nerve growth factor (NGF) along with Silk Fibroin (SF) as the core of the scaffold. Air plasma treatment was applied to PS/N scaffold to improve the surface hydrophilicity without causing any damage to the nanofibers. Surface characterization of the plasma treated PS/N scaffold (p-PS/N) was carried out by Atomic Force Microscopy, X-ray Photoelectron Spectroscopy and water contact angle test. PC12 cells cultured on both PS/N and p-PS/N scaffolds using Differentiation Medium devoid of NGF expressed neurofilament 200 protein on day 8, suggesting the differentiation potential of PC12 on both the scaffolds. By day 11, the cells cultured on p-PS/N scaffolds using the Differentiation Medium devoid of NGF showed elongated neurites with the length up to 95 μm. Our results suggested the sustained release of NGF, thus demonstrating the fact that the bioactivity of NGF was retained. The p-PS/N scaffolds were able to support the attachment and differentiation of PC12 cells, with ability to function as suitable substrates for nerve tissue engineering.

Drug-loaded emulsion electrospun nanofibers: characterization, drug release and in vitro biocompatibility

Emulsion electrospinning is a flexible and promising technique for encapsulating various drugs into nanofibers. In this work, nanofibrous scaffolds were produced by emulsion electrospinning of either metformin hydrochloride (MH) or metoprolol tartrate (MPT) with poly(e-caprolactone) (PCL) or poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV). The influence of preparation processes and emulsion compositions (polymer/drug/surfactant Span 80) towards the drug release behaviour of the scaffolds, together with their morphology, surface and thermal properties were evaluated. In vitro release studies indicated that the emulsion electrospun nanofibers significantly alleviated the burst release and produced a sustained release of drugs compared to the blended electrospun nanofibers. Between the two polymers studied, PCL demonstrated a better drug delivery carrier compared to PHBV, and MPT incorporated nanofibers showed less burst release than the others. The emulsion electrospun nanofibers were evaluated for their cytotoxicity using human mesenchymal stem cells and the cytotoxicity results showed that the emulsion electrospun MPT/PCL scaffold favoured cell growth compared to other tested scaffolds. Our study shows that emulsion electrospinning could be a better technique than normal blend electrospinning, especially in modulating the drug release properties by regulating the oil phase and water phase of the emulsions to obtain the desired drug release for the drug delivery systems. And PCL may be a better drug delivery carrier than PHBV.

Fabrication of Nerve Growth Factor Encapsulated Aligned Poly(ε-Caprolactone) Nanofibers and Their Assessment as a Potential Neural Tissue Engineering Scaffold

Peripheral nerve injury is a serious clinical problem to be solved. There has been no breakthrough so far and neural tissue engineering offers a promising approach to promote the regeneration of peripheral neural injuries. In this study, emulsion electrospinning technique was introduced as a flexible and promising technique for the fabrication of random (R) and aligned (A) Poly(ε-caprolactone) (PCL)-Nerve Growth Factor (NGF)&Bovine Serum Albumin (BSA) nanofibrous scaffolds [(R/A)-PCL-NGF&BSA], where NGF and BSA were encapsulated in the core while PCL form the shell. Random and aligned pure PCL, PCL-BSA, and PCL-NGF nanofibers were also produced for comparison. The scaffolds were characterized by Field Emission Scanning Electron Microscopy (FESEM) and water contact angle test. Release study showed that, with the addition of stabilizer BSA, a sustained release of NGF from emulsion electrospun PCL nanofibers was observed over 28 days. [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt; MTS] assay revealed that (R/A)-PCL-NGF and (R/A)-PCL-NGF&BSA scaffolds favored cell growth and showed no cytotoxicity to PC12 cells. Laser scanning confocal microscope images exhibited that the A-PCL-NGF&BSA scaffold increased the length of neurites and directed neurites extension along the fiber axis, indicating that the A-PCL-NGF&BSA scaffold has a potential for guiding nerve tissue growth and promoting nerve regeneration.

Evaluation of the potential of rhTGF- β3 encapsulated P(LLA-CL)/collagen nanofibers for tracheal cartilage regeneration using mesenchymal stems cells derived from Wharton's jelly of human umbilical cord.

Tracheal injuries are one of major challenging issues in clinical medicine because of the poor intrinsic ability of tracheal cartilage for repair. Tissue engineering provides an alternative method for the treatment of tracheal defects by generating replacement tracheal structures. In this study, core-shell nanofibrous scaffold was fabricated to encapsulate bovine serum albumin & rhTGF-β3 (recombinant human transforming growth factor-β3) into the core of the nanofibers for tracheal cartilage regeneration. Characterization of the core-shell nanofibrous scaffold was carried out by scanning electron microscope (SEM), transmission electron microscope (TEM), laser scanning confocal microscopy (LSCM), and tensile mechanical test. The rhTGF-β3 released from the scaffolds in a sustained and stable manner for about 2months. The bioactivity of released rhTGF-β3 was evaluated by its effect on the synthesis of type II collagen (COL2) and glycosaminoglycans (GAGs) by chondrocytes. The results suggested that its bioactivity was retained during release process. The proliferation and morphology analyses of mesenchymal stems cells derived from Whartons jelly of human umbilical cord (WMSCs) indicated the good biocompatibility of the fabricated nanofibrous scaffold. Meanwhile, the chondrogenic differentiation of WMSCs cultured on core-shell nanofibrous scaffold was evaluated by real-time qPCR and histological staining. The results suggested that the core-shell nanofibrous scaffold with rhTGF-β3 could promote the chondrogenic differentiation ability of WMSCs. Therefore, WMSCs could be a promising seed cells in the construction of tissue-engineered tracheal cartilage. Overall, the core-shell nanofibrous scaffold could be an effective delivery system for rhTGF-β3 and served as a promising tissue engineered scaffold for tracheal cartilage regeneration.

Synergistic effect of topography, surface chemistry and conductivity of the electrospun nanofibrous scaffold on cellular response of PC12 cells.

Electrospun nanofibrous nerve implants is a promising therapy for peripheral nerve injury, and its performance can be tailored by chemical cues, topographical features as well as electrical properties. In this paper, a surface modified, electrically conductive, aligned nanofibrous scaffold composed of poly (lactic acid) (PLA) and polypyrrole (Ppy), referred to as o-PLAPpy_A, was fabricated for nerve regeneration. The morphology, surface chemistry and hydrophilicity of nanofibers were characterized by Scanning Electron Microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and water contact angle, respectively. The effects of these nanofibers on neuronal differentiation using PC12 cells were evaluated. A hydrophilic surface was created by Poly-ornithine coating, which was able to provide a better environment for cell attachment, and furthermore aligned fibers were proved to be able to guide PC12 cells grow along the fiber direction and be beneficial for neurite outgrowth. The cellular response of PC12 cells to pulsed electrical stimulation was evaluated by NF 200 and alpha tubulin expression, indicating that electrical stimulation with a voltage of 40mV could enhance the neurite outgrowth. The PC12 cells stimulated with electrical shock showed greater level of neurite outgrowth and smaller cell body size. Moreover, the PC12 cells under electrical stimulation showed better viability. In summary, the o-PLAPpy_A nanofibrous scaffold supported the attachment, proliferation and differentiation of PC12 cells in the absence of electrical stimulation, which could be potential candidate for nerve regeneration applications.

The control of beads diameter of bead-on-string electrospun nanofibers and the corresponding release behaviors of embedded drugs

Bead-on-string nanofibers, with appropriate control of the beads diameter, are potential fibrous structures for efficient encapsulation of particle drugs in micron scales and could achieve controlled drug release for tissue engineering applications. In this study, the beads diameter of electrospun bead-on-string nanofibers was controlled by adjusting the concentration of spinning polymer, poly (lactic-co-glycolic acid) (PLGA), and the solvent ratio of chloroform to acetone. The images of the scanning electron microscopy (SEM) suggested that bead-on-string nanofibers could be successfully obtained only with a certain range of PLGA solution concentration. Moreover, with the decrease in the solvent ratio of chloroform to acetone, the range was left-shifted towards a smaller concentration. In addition, increase in the PLGA solution concentration within the range the beads diameter became greater and the shape of the beads changed from oval to slender when increasing the PLGA concentration within the range. The bead-on-string nanofibers with different beads diameter were further used to load micro-particle drugs of tetracycline hydrochloride, as a model drug, to examine the release behavior of nanofibers scaffold. The release profiles of drug loaded bead-on-string nanofibers demonstrated the possibility to alleviate the burst drug release by means of beads diameter control.

Surface Modification of PLLA Nano‐scaffolds with Laminin Multilayer by LbL Assembly for Enhancing Neurite Outgrowth

In this study, PLLA nanofibers are fabricated by electrospinning and their surfaces are modified by laminin/chitosan (LN/CS) polyelectrolyte multilayer. Surface C/N ratio determined by XPS analysis quantitatively indicates of discrete coating layers on the nanofibers. The amount of LN deposited sustainably increases with LbL assembly processing, approximately 60 ng mm(-2) LN per cycle of LN/CS deposition. The LN-modified PLLA scaffolds significantly induce neurite outgrowth of DRG neurons and NSC compared to the pure PLLA nanofibrous scaffolds. Furthermore, higher amounts of LN adsorbed assist in promoting cell proliferation than PLLA as-spun nanofibers. Therefore, a facile and efficient method to modify nano-scaffolds for the construction of a biomimetic scaffold to promote highly efficient neurite outgrowth is presented.