Electrospun cellulose acetate nanofibers: The present status and gamut of biotechnological applications

Cellulose acetate (CA) has been a material of choice for spectrum of utilities across different domains ranging from high absorbing diapers to membrane filters. Electrospinning has conferred a whole new perspective to polymeric materials including CA in the context of multifarious applications across myriad of niches. In the present review, we try to bring out the recent trend (focused over last five years' progress) of research on electrospun CA fibers of nanoscale regime in the context of developmental strategies of their blends and nanocomposites for advanced applications. In the realm of biotechnology, electrospun CA fibers have found applications in biomolecule immobilization, tissue engineering, bio-sensing, nutraceutical delivery, bioseparation, crop protection, bioremediation and in the development of anti-counterfeiting and pH sensitive material, photocatalytic self-cleaning textile, temperature-adaptable fabric, and antimicrobial mats, amongst others. The present review discusses these diverse applications of electrospun CA nanofibers.     

三维取向PLGA神经导管促进坐骨神经再生的实验研究

目的：探讨应用改进静电纺丝技术一次成型制备三维（3D）取向聚乳酸与聚羟基乙酸共聚物（PLGA）纳米神经导管的可行性,检测其对坐骨神经再生的促进作用。方法：应用改进的静电纺丝技术制备无缝取向PLGA纳米神经导管,通过扫描电镜和透射电镜检测支架的纳米结构;分别制备取向和非取向纳米纤维支架修复13mm坐骨神经缺损模型。36只成年SD大鼠随机分为3组（每组12只）,A组：非取向PLGA神经导管组（阴性对照）;B组：取向PLGA神经导管组,C组：自体神经移植组（阳性对照）,于术后3月通过大体观察、行走足印分析、腓肠肌萎缩率、电生理检测、组织形态学检测、透射电镜检测及图像分析,评价无缝取向PLGA纳米神经导管修复坐骨神经缺损的效果。结果：神经导管修复神经缺损三月后,大体观察显示神经导管结构完整,无坍塌和断裂;各组再生神经均有通过神经导管长入远端。B组与C组的腓肠肌萎缩率和神经电传导速度无统计学差异（P〈0.05）,均优于A组。B组与C组再生神经纤维数量及成熟程度均要明显优于A组。结论：无缝取向PLGA纳米神经导管能够诱导并促进神经再生,提高坐骨神经再生的质量,有望成为自体神经移植的替代物。     

Improved infiltration of stem cells on electrospun nanofibers

Nanofibrous scaffolds have been recently used in the field of tissue engineering because of their nano-size structure which promotes cell attachment, function, proliferation and infiltration. In this study, nanofibrous polyethersulfone (PES) scaffolds was prepared via electrospinning. The scaffolds were surface modified by plasma treatment and collagen grafting. The surface changes then investigated by contact angle measurements and FTIR-ATR. The results proved grafting of the collagen on nanofibers surface and increased hydrophilicity after plasma treatment and collagen grafting. The cell interaction study was done using stem cells because of their ability to differentiate to different kinds of cell lines. The cells had normal morphology on nanofibers and showed very high infiltration through collagen grafted PES nanofibers. This infiltration capability is very useful and needed to make 3D scaffolds in tissue engineering.     

三维取向PLGA神经导管促进坐骨神经再生的实验研究

目的:探讨应用改进静电纺丝技术一次成型制备三维(3D)取向聚乳酸与聚羟基乙酸共聚物(PLGA)纳米神经导管的可行性,检测其对坐骨神经再生的促进作用。方法:应用改进的静电纺丝技术制备无缝取向PLGA纳米神经导管,通过扫描电镜和透射电镜检测支架的纳米结构;分别制备取向和非取向纳米纤维支架修复13mm坐骨神经缺损模型。36只成年SD大鼠随机分为3组(每组12只),A组:非取向PLGA神经导管组(阴性对照);B组:取向PLGA神经导管组,C组:自体神经移植组(阳性对照),于术后3月通过大体观察、行走足印分析、腓肠肌萎缩率、电生理检测、组织形态学检测、透射电镜检测及图像分析,评价无缝取向PLGA纳米神经导管修复坐骨神经缺损的效果。结果:神经导管修复神经缺损三月后,大体观察显示神经导管结构完整,无坍塌和断裂;各组再生神经均有通过神经导管长入远端。B组与C组的腓肠肌萎缩率和神经电传导速度无统计学差异(P0.05),均优于A组。B组与C组再生神经纤维数量及成熟程度均要明显优于A组。结论:无缝取向PLGA纳米神经导管能够诱导并促进神经再生,提高坐骨神经再生的质量,有望成为自体神经移植的替代物。     

RF hydrazine plasma modification of chitosan for antibacterial activity and nanofiber applications

Chitosan nano powders were modified using RF hydrazine plasma produced at low pressure (26.66 Pa) with 13.56 MHz frequency at a power of 100 W for 30 min. Characterization and investigation of the properties of plasma-modified chitosan (PMCh) and non-modified chitosan (Ch) were carried out using an optical monochromator, FTIR, florescence analysis, TGA, SEM, and X-ray techniques. FTIR spectra of PMCh indicated a band broadening at 3436 cm⁻¹ that confirmed increasing functional groups based on H-bonding. The number of NH₂ groups was determined from fluorescence analysis. TGA analysis shows that the moisture absorption is three times higher in the PMCh structure. Ch and PMCh in PVA solutions were used to produce nanofibers by the electrospinning method; average fiber diameters were 480 and 280 nm for Ch and PMCh, respectively. It was found that the antibacterial effect of PMCh is better than the Ch for Gram-positive strains.     

Formation of silk fibroin matrices with different texture and its cellular response to normal human keratinocytes

Three forms of silk fibroin (SF) matrices, woven (microfiber), non-woven (nanofiber), and film form, were used to perform a conformational analysis and cell culture using normal human oral keratinocytes (NHOK). To obtain the SF microfiber (SF-M) matrix, natural grey silk was degummed, while the SF film (SF-F) and nanofiber (SF-N) matrices were prepared by casting and electrospinning the formic acid solutions of the regenerated SF, respectively. For insolubilization, as-prepared SF-F and SF-N matrices were chemically treated with an aqueous methanol solution of 50%. The conformational structures of as-prepared and chemically treated SF matrices were investigated using attenuated total reflectance infrared spectroscopy (ATR-IR) and solid-state ¹³C CP/MAS nuclear magnetic resonance (NMR) spectroscopy. The as-cast SF-F matrix formed a mainly β-sheet structure that was similar to the SF-M matrix, whereas the as-spun SF-N matrix had a random coil conformation as the predominant secondary structure. Conformational transitions from random coil to β-sheet of the as-spun SF-N occurred rapidly within 10 min following aqueous methanol treatment, and were confirmed by solid-state ¹³C NMR analysis. To assess the cytocompatibility and cells behavior on the different textures of SF, we examined the cell attachment and spreading of NHOK that was seeded onto the SF matrices, as well as the interaction between the cells and SF matrices. Our results indicate that the SF nanofiber matrix may be more preferable than SF film and SF microfiber matrices for biomedical applications, such as wound dressings and scaffolds for tissue engineering.     

Chitosan nanofiber scaffold enhances hepatocyte adhesion and function

To enhance cell attachment and promote liver functions of hepatocytes cultured in bioreactors, a chitosan nanofiber scaffold was designed and prepared via electrospinning. Effects of the scaffold on hepatocyte adhesion, viability and function were then investigated. Data showed that hepatocytes on chitosan nanofiber scaffold exhibited better viability and tighter cell-substrate contact than cells on regular chitosan film. In addition, urea synthesis, albumin secretion and cytochrome P450 activity of hepatocytes on chitosan nanofiber scaffold were all 1.5 to 2 folds higher than the controls. Glycogen synthesis was also increased as compared with the controls. These results suggested the potential application of this chitosan nanofiber scaffold as a suitable substratum for hepatocyte culturing in bioreactors.     

Determination of the parameters affecting electrospun chitosan fiber size distribution and morphology

The production of chitosan nanofiber mats by electrospinning presents serious difficulties due to the lack of suitable solvents and the strong influence of processing parameters on the fiber properties. Two are the main problems to be solved: to control the properties of the solution in order to obtain large area uniform fiber mats by having a stable flow rate and to avoid sparks during the process, damaging the fiber mats. In this work chitosan electrospun mats have been prepared form solutions of trifluoroacetic acid/dichloromethane mixtures, allowing solving the aforementioned problems. Mats with uniform fibers of submicron diameters without beads were obtained. Further, the influence of the different solution and process parameters on the mean fiber diameter and on the width of the distribution of the fiber sizes has been assessed. Solvent composition, needle diameter, applied voltage and traveling distance were the parameters considered in this study.     

Critical Role of Silicon in Directing the Bio-inspired Mineralization of Gelatin in the Presence of Hydroxyapatite

Significant progress has been made on understanding the critical role of organic components in directing the collagen mineralization.We hypothesize that the inorganic trace elements might also play important role in the mineralization of collagenous matrix.To this aim,we systematically compared the in-vitro biomineralization behaviors of gelatin,gelatin-HA and gelatin-SiHA electrospun membranes.The results indicated that the presence of Si ions played a striking influence on the nucleation behaviors and mineralized structures.The gelatin-SiHA samples demonstrated more homogeneous nucleation within the gelatin fiber and growth along the fiber direction,in comparison with the heterogeneous nucleation and growth of spherulitic clusters on top of the nanofiber surface,i.e.extrafibrillar mineralization.The likely shift of the nucleation mode to the intrafibrillar mineralization in the presence of Si ions led to good alignment of apatite c-axis with the long axis of the nanofiber,resulting in a mineralization process and microstructure that were closer to those in natural bone.Cellular response analysis indicated that Si incorporation improved the MSC attachment and cytoskeleton organization.Such findings might have important implication in both understanding the complex mechanisms involved in collagen mineralization and optimal designing of advanced bio-inspired materials with potential superior mechanical and biological properties.     

Stable and continuous long-term enzymatic reaction using an enzyme–nanofiber composite

This study shows the preparation and application of enzyme–nanofiber composites for long-term stable operation. The enzyme–nanofiber composite was prepared by coating an enzyme aggregate, the esterase from Rhizopus oryzae, on the surface of the nanofibers. After immobilization on the nanofiber, the apparent K _m for the immobilized esterase was 1.48-fold higher than that of the free esterase, with values of 0.98 and 1.35 mM for the free and immobilized enzymes, respectively. It was found that enzyme–nanofiber was very stable, even when the fibers were shaken in glass vials, preserving 80% of the initial activity for 100 days. In addition, the enzyme–nanofiber composite was used repeatedly in 30 cycles of substrate hydrolysis and still remained active. Consequently, the esterase–nanofiber composite was employed within a continuous reactor system to evaluate its use in a long-term and stable continuous substrate hydrolysis reaction. It was found that the production of p-nitrophenol was stable for at least 400 h. This study demonstrates that the enzyme–nanofiber composite can be used in both repeated-batch mode and a continuous mode for a long-term stable operation.