Lenka Martinová

A cell-free nanofiber composite scaffold regenerated osteochondral defects in miniature pigs

The aim of the study was to evaluate the effect of a cell-free hyaluronate/type I collagen/fibrin composite scaffold containing polyvinyl alcohol (PVA) nanofibers enriched with liposomes, basic fibroblast growth factor (bFGF) and insulin on the regeneration of osteochondral defects. A novel drug delivery system was developed on the basis of the intake effect of liposomes encapsulated in PVA nanofibers. Time-controlled release of insulin and bFGF improved MSC viability in vitro. Nanofibers functionalized with liposomes also improved the mechanical characteristics of the composite gel scaffold. In addition, time-controlled release of insulin and bFGF stimulated MSC recruitment from bone marrow in vivo. Cell-free composite scaffolds containing PVA nanofibers enriched with liposomes, bFGF, and insulin were implanted into seven osteochondral defects of miniature pigs. Control defects were left untreated. After 12 weeks, the composite scaffold had enhanced osteochondral regeneration towards hyaline cartilage and/or fibrocartilage compared with untreated defects that were filled predominantly with fibrous tissue. The cell-free composite scaffold containing PVA nanofibers, liposomes and growth factors enhanced migration of the cells into the defect, and their differentiation into chondrocytes; the scaffold was able to enhance the regeneration of osteochondral defects in minipigs.

Controlled Morphology of Porous Polyvinyl Butyral Nanofibers

A simple and effective method for the fabrication of porous nanofibers based on the solvent evaporation methods in one-step electrospinning process from the commercial polyvinyl butyral (PVB) is presented. The obtained nanofibers are prevalently amorphous with diameters ranging from 150 to 4350 nm and specific surface area of approximately 2–20 m2/g. Pore size with irregular shape of the porous PVB fibers ranged approximately from 50 to 200 nm. The effects of polymer solution concentration, composition of the solvents mixture, and applied voltage on fiber diameter and morphology were investigated. The theoretical approach for the choice of poor and good solvents for PVB was explained by the application Hansen solubility parameter (HSP) and two-dimensional graph. Three basic conditions for the production of porous PVB nanofibers were defined: (i) application of good/poor solvent mixture for spinning solution, (ii) differences of the evaporation rate between good/poor solvent, and (iii) correct ratios of good/poor solvent (v/v). The diameter of prepared porous PVB fibers decreased as the polymer concentration was lowered and with higher applied voltage. These nanofiber sheets with porous PVB fibers could be a good candidate for high-efficiency filter materials in comparison to smooth fibers without pores.

Electrospun Chitosan Based Nanofibers

The new electrospinning technology NanospiderTM, offering a real potential for industrial production of nanofibers, is used for the preparation of nanofiber sheets from aqueous solutions of polymer blends. The nanofiber sheets are prepared from a mixture of chitosan and polyethylenoxide (PEO) and using the novel continual electrospinning process (Jirsak et al., 2005, www.nanospider.cz) affords a network with typical fiber diameters that are less than 500 nm. Effects of solvents, molecular weight of both polymers, monovalent salt, surfactant and composition of chitosan blend on electrospinning are also studied. The optimal conditions for electrospinning by the NanospiderTM technology, including applied high voltage, distance between both electrodes, air temperature and air humidity, are also found. The crosslinking of the nanofiber sheet is achieved by heat treatment. The morphology of electrospun fibers is observed by using a scanning electron microscope (SEM). Chitosan in the nanofiber sheets format has a great potential to be widely used in various applications derived from its biocompatibility and biodegradability.

A simple drug anchoring microfiber scaffold for chondrocyte seeding and proliferation

The structural properties of microfiber meshes made from poly(2-hydroxyethyl methacrylate) (PHEMA) were found to significantly depend on the chemical composition and subsequent cross-linking and nebulization processes. PHEMA microfibres showed promise as scaffolds for chondrocyte seeding and proliferation. Moreover, the peak liposome adhesion to PHEMA microfiber scaffolds observed in our study resulted in the development of a simple drug anchoring system. Attached foetal bovine serum-loaded liposomes significantly improved both chondrocyte adhesion and proliferation. In conclusion, fibrous scaffolds from PHEMA are promising materials for tissue engineering and, in combination with liposomes, can serve as a simple drug delivery tool.

Polyamide 6/chitosan nanofibers as support for the immobilization of Trametes versicolor laccase for the elimination of endocrine disrupting chemicals.

In recent years, there has been an increase in efforts to improve wastewater treatment as the concentration of dangerous pollutants, such as endocrine disrupting chemicals, in wastewater increases. These compounds, which mimic the effect of hormones, have a negative impact on human health and are not easily removed from water. One way to effectively eliminate these pollutants is to use enzymatically activated materials. In this study, we report on the use of laccase from the white rot fungus Trametes versicolor immobilized onto polyamide 6/chitosan (PA6/CHIT) nanofibers modified using two different spacers (bovine serum albumin and hexamethylenediamine). We then tested the ability of the PA6/CHIT-laccase biocatalysts to eliminate a mixture containing 50μM of two endocrine disrupting chemicals: bisphenol A and 17α-ethinylestradiol. The PA6/CHIT nanofiber matrix used in this study not only proved to be a suitable carrier for immobilized and modified laccase but was also efficient in the removal of a mixture of endocrine disrupting chemicals in three treatment cycles.

Fabrication of silk nanofibres with needle and roller electrospinning methods

In this study, silk nanofibres were prepared by electrospinning from silk fibroin in a mixture of formic acid and calcium chloride. A needle and a rotating cylinder were used as fibre generators in the spinning process. The influences of the spinning electrode and spinning parameters (silk concentration and applied voltage) on the spinning process, morphology of the obtained fibres, and the production rate of the spinning process were examined. The concentration of the spinning solution influenced the diameter of the silk electrospun fibres, with an increase in the concentration increasing the diameters of the fibres in both spinning systems. The diameters of the electrospun fibres produced by roller electrospinning were greater than those produced by needle electrospinning. Moreover, increasing the concentration of the silk solution and the applied voltage in the spinning process improved the production rate in roller electrospinning but had less influence on the production rate in needle electrospinning.

Electrospinning of the hydrophilic poly (2-hydroxyethyl methacrylate) and its copolymers with 2-ethoxyethyl methacrylate

The goal was to electrospin 2-hydroxyethyl methacrylate — based biocompatible polymers and prepare submicron fibres (nanofibers) for biomedicinal applications. Syntheses of poly(2-hydroxyethyl methacrylate) (HEMA) and its copolymer with 2-ethoxyethyl methacrylate (EOEMA), and their characterization by viscometry and molecular weight are described. Their relation to electrospinning is discussed. Electrospinning of HEMA homopolymer from water-ethanol is successful for molecular weights 6.31 × 105 and 1.80 × 106 g/mol. Electrospinning of HEMA/EOEMA copolymers is feasible from ethanol.

Structure–property relationships in Sterculia urens/polyvinyl alcohol electrospun composite nanofibres

Sterculia urens (Gum Karaya) based polyvinyl alcohol (PVA) composite nanofibres have been successfully electrospun after chemical modification of S. urens to increase its solubility. The effect of deacetylated S. urens (DGK) on the morphology, structure, crystallization behaviour and thermal stability was studied for spuned fibres before and after spinning post treatment. An apparent increase in the PVA crystallinity were observed in the PVA-DGK composite nanofibres indicating S. urens induced crystallization of PVA. The pure PVA nanofibre and the nanofibres of PVA-DGK composites were introduced to post electrospinning heat treatment at 150°C for 15 min. The presence of sterculia gum reduced the fibre diameter and distribution of the nanofibres due to the increased stretching of the fibres during spinning. Switching of the thermal behaviour occurs due to post spinning heat treatments.

macroporous hydrogels based on 2-hydroxyethyl methacrylate. Part 7: Methods of preparation and comparison of resulting physical properties

Abstract Five methods of preparation of macroporous hydrogels are described and compared: precipitation polymerization, polymerization in presence of salt, polymerization in presence of gas-releasing compound, lyophilization and electrospinning. Crosslinked copolymers based on 2-hydroxyethyl methacrylate were selected as model hydrogels. Hydrogels were characterized by SEM microscopy, porosity, communicating/non-communicating pore ratio, pore sizes and their distributions. The advantages and drawbacks of the methods of preparation, modification of hydrogel properties, reproducibility and issues related to their preparation are discussed. The most convenient method was preparation in presence of salts. One type of porous hydrogel was based on a hydrogel matrix composed of nanofibers prepared by electrospinning method. The nanofibers have shown unique properties due to their large specific surface. The least suitable method seems to be the preparation of porous hydrogels by polymerization using gas (nitrogen) releasing initiator, 2,2´-azobisisobutyronitrile. The use of prepared porous hydrogels is intended especially for scaffolds in tissue engineering.

Nanofiber Sheets with the Superabsorbent Properties

The new electrospinning technology NanospiderTM offering a realistic potential for industrial production was used for creation of nanofiber sheets from aqueous solutions of partially neutralized poly(acrylic) acid with crosslinking agent. Produced nanofiber sheet was crosslinked by heat treatment. Absorption capacity and rate of absorption were tested and compared with superabsorbent particles and commercial superabsorbent fibers. The morphology of electrospun fibers was observed using a scanning electron microscope (SEM). Possibilities of fiber diameter influence were studied.