Fabrication of chitosan/silk fibroin composite nanofibers for wound-dressing applications.

Chitosan, a naturally occurring polysaccharide with abundant resources, has been extensively exploited for various biomedical applications, typically as wound dressings owing to its unique biocompatibility, good biodegradability and excellent antibacterial properties. In this work, composite nanofibrous membranes of chitosan (CS) and silk fibroin (SF) were successfully fabricated by electrospinning. The morphology of electrospun blend nanofibers was observed by scanning electron microscopy (SEM) and the fiber diameters decreased with the increasing percentage of chitosan. Further, the mechanical test illustrated that the addition of silk fibroin enhanced the mechanical properties of CS/SF nanofibers. The antibacterial activities against Escherichia coli (Gram negative) and Staphylococcus aureus (Gram positive) were evaluated by the turbidity measurement method; and results suggest that the antibacterial effect of composite nanofibers varied on the type of bacteria. Furthermore, the biocompatibility of murine fibroblast on as-prepared nanofibrous membranes was investigated by hematoxylin and eosin (H&E) staining and MTT assays in vitro, and the membranes were found to promote the cell attachment and proliferation. These results suggest that as-prepared chitosan/silk fibroin (CS/SF) composite nanofibrous membranes could be a promising candidate for wound healing applications.

Preparation of core-shell biodegradable microfibers for long-term drug delivery.

A coaxial electrospun technique to fabricate core-shell microfibers (MFs) for drug delivery application is described. In one-step, Paclitaxel (PTX)-loaded poly(L-lactic acid-co-epsilon-caprolactone) (75:25) (P(LLA-CL)(core/shell)) was electrospun into MFs using 2,2,2-trifluoroethanol as the solvent. The physical and chemical properties of electrospun fibers were characterized by various techniques, such as scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, and Fourier-transform infrared. The fiber diameter depended on both the polymer concentration and the flow ratio of PTX to P(LLA-CL). The encapsulation efficiency and in vitro release profile were measured using high performance liquid chromatography methods. PTX released from the MFs in a short burst over 24 h followed by very slow release over the following 60 days. In addition, the cytotoxicity of PTX-loaded P(LLA-CL) MFs was evaluated using 3-[4,5-dimehyl-2-thiazolyl]-2, 5-diphenyl-2H-tetrazolium bromide assay on HeLa cell lines. These results indicate that PTX could be released from P(LLA-CL) fibers in a steady manner and effectively inhibit the activity of HeLa cells.

Fabrication and characterization of chitosan coated braided PLLA wire using aligned electrospun fibers.

The development of functionalized braided wires coated with chitosan that can be used for tissue suturing and tissue regeneration is the subject of this work. Poly(L: -lactic acid) (PLLA) braided wires were successfully fabricated by combining an electrospinning technique and alignment collection with a mini-type braiding method. The resulting PLLA wires with and without chitosan coating were characterized through a variety of methods including scanning electron microscopy (SEM), X-ray photoelectronic spectra (XPS) and tensile mechanical testing. Hemolytic property, kinetic hemostasis behavior, platelet adhesion, erythrocyte adhesion, and water uptake ability of the wires were explored. The results showed that a nearly comparable mechanical behavior of the braided wires with some commercial suture could be obtained with well-aligned fibers, and no significant difference in tensile performances were recognized with and without the introduction of chitosan. The PLLA wires coated with chitosan were found to have better prohemostatic activity than those without a chitosan coating.

Fabrication of drug-loaded electrospun aligned fibrous threads for suture applications.

In this work, drug-loaded fibers and threads were successfully fabricated by combining electrospinning with aligned fibers collection. Two different electrospinning processes, that is, blend and coaxial electrospinning, to incorporate a model drug tetracycline hydrochloride (TCH) into poly(L-lactic acid) (PLLA) fibers have been used and compared with each other. The resulting composite ultrafine fibers and threads were characterized through scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, and tensile testing. It has been shown that average diameters of the fibers made from the same polymer concentration depended on the processing method. The blend TCH/PLLA fibers showed the smallest fiber diameter, whereas neat PLLA fibers and core-shell TCH-PLLA fibers showed a larger proximal average diameter. Higher rotating speed of a wheel collector is helpful for obtaining better-aligned fibers. Both the polymer and the drug in the electrospun fibers have poor crystalline property. In vitro release study indicated that threads made from the core-shell fibers could suppress the initial burst release and provide a sustained drug release useful for the release of growth factor or other therapeutic drugs. On the other hand, the threads from the blend fibers produced a large initial burst release that may be used to prevent bacteria infection. A combination of these results suggests that electrospinning technique provides a novel way to fabricate medical agents-loaded fibrous threads for tissue suturing and tissue regeneration applications.

The expression of Bcl-XL, Bcl-XS and p27Kip1 in topotecan-induced apoptosis in hepatoblastoma HepG2 cell line.

BACKGROUND: To assess the efficacy of topotecan, a topoisomerase I specific inhibitor in S-phase, the reagent-induced apoptosis and cytotoxicity as well as related proteins expression, had been preliminarily investigated in human hepatoblastoma HepG2 cells. METHODS: Microculture tetrazolium assay (MTT), HE staining, transmission electron microscopy (TEM), flow cytometry (FCM), quantitative immunocytochemistry (QI), gene tranfection and RNAi technology were employed to carry out the exploration. RESULTS: Topotecan could potently kill HepG2 cells via inducing apoptosis and demonstrated strong cytotoxicity in a time, dose-dependent manner with IC50 of about 95 mu g/L. According to morphologic observation and FCM analyses, it was confirmed that the drug treatment, causing significant S-phase arrest, could trigger a typical interphase apoptosis, the main traits of which were identified as chromatin pycnosis and cytoplasm condensation. It was shown that the expression of Bcl-XL was simultaneously down-regulated with the up-regulation of Bcl-XS in cytoplasm, which was possibly a key downstream event following the topotecan-induced DNA damage in nucleus. The expression level of p27Kip1, a negative regulator in cell cycle at G1/S transient, was also elevated. Transfection of pcDNA 3.1-p27Kip1 into HepG2 cells could abrogate the cytotoxicity in a degree while silence of p27Kip1 with siRNA in drug treatments could significantly increased the chemosensitivity, strongly indicating that the up-regulation of p27Kip1 was not an apoptosis-promoting, but a self-rescue response against drug by moderate G0/G1 arrest. CONCLUSION: Topotecan had potent cytotoxicity against HepG2 cells by triggering an interphase apoptosis possibly mediated by increasing the ratio of Bcl-XS/Bcl-XL. Up-regulation of p27Kip1in TPT treatments could be a protective response for self-rescue and silence of the gene markedly augmented TPT cytotoxicity. Therefore, the experiment in vitro could provide a new idea for the clinical chemotherapy based on the combination of traditional drugs with the specific-siRNA targeted on the protective response gene.

Encapsulating drugs in biodegradable ultrafine fibers through co-axial electrospinning.

This article describes an electrospinning process to fabricate double-layered ultrafine fibers. A bioabsorbable polymer, Polycaprolactone (PCL), was used as the outer layer or the shell and two medically pure drugs, Resveratrol (RT, a kind of antioxidant) and Gentamycin Sulfate (GS, an antibiotic), were used as the inner layers or the cores. Morphology and microstructure of the ultrafine fibers were characterized by scanning electron microscope (SEM) and transmission electron microscopy (TEM), whereas mechanical performance of them was understood through tensile test. In vitro degradation rates of the nanofibrous membranes were determined by measuring their weight loss when immersed in pH 7.4 phosphate-buffered saline (PBS) mixed with certain amount of Pseudomonas lipase for a maximum of 7 days. The drug release behaviors of the RT and GS were measured using a high performance liquid chromatography (HPLC) and ultraviolet-visible (UV-vis) spectroscopy, respectively. It has been found that the drug solutions without any fiber-forming additive could be encapsulated in the PCL ultrafine fibers, although they alone cannot be made into a fiber form. Beads on the fiber surface influenced the tensile behavior of the ultrafine fibers remarkably. When the core solvent was miscible with the shell solvent, higher drug concentration decreased the bead formation and thus favored the mechanical performance. The situation, however, became different if the two solvents were immiscible with each other. The degradation rate was closely related to hydrophilicity of the drugs in the cores. Higher hydrophilicity apparently led to faster degradation. The release profiles of the RT and GS exhibited a sustained release characteristic, with no burst release phenomenon.

Preliminarily investigating the polymorphism of self-organized actin filament in vitro by atomic force microscope.

With the atomic force microscope (AFM), we preliminarily investigated the large-scale structure of actin filaments formed in low concentration protein solution (5 microg/ml) via self-organization without the presence of any F-actin dynamic interfering factors (such as phalloidin) in vitro. It was found that the G-actin could be polymerized into ordered filamentous structures with different diameter from the slimmest filament of single F-actin to giant filament in tree-like branched aggregates. The observed polymerized actin filaments, to which our most intense attention was attracted, was discretely distributed and showed obvious polymorphism distinctly different from those in the presence of phalloidin or actin binding proteins (fimbrin, gelsolin, etc.) in previous experiments. Latter structures were mainly composed of single F-actin and/or multifilaments clearly consisting of several single F-actin. The experimental results clearly demonstrated that non-interference with the F-actin intrinsic dynamics in self-organizing could lead to the polymorphism of actin filamentous structures, and further analysis implied that the disturbance of normal F-actin dynamics by many factors could prevent the emergence of structural polymorphism, more often than not, give rise to formation of specific structures instead and different interference would bring about various particular structures under certain conditions.