Electrospun PELCL membranes loaded with QK peptide for enhancement of vascular endothelial cell growth

One of the major challenges in tissue engineering of small-diameter vascular grafts is to inhibit intimal hyperplasia and keep long-term patency after implantation. Rapid endothelialization of the grafts could be an effective approach. In this study, QK, a peptide mimicking vascular endothelial growth factor, was selected as the bioactive substrate and loaded in electrospun membranes for enhancement of vascular endothelial cell growth. In detail, QK peptide was firstly introduced with poly(ethylene glycol) diacrylate into a thiolated chitosan solution that could transfer into hydrogel. Then, suspensions or emulsions of poly(ethylene glycol)-b-poly(l-lactide-co-ε-caprolactone) (PELCL) containing QK peptide (with or without chitosan hydrogel) were electrospun into fibrous membranes. For comparison, the electrospun PELCL membrane without QK was also fabricated. Results of release behaviors showed that the electrospun membranes, especially that contained chitosan hydrogel prepared by suspension electrospinning, could successfully encapsulate QK peptide and maintain its secondary structure after released. In vitro cell culture studies exhibited that the release of QK peptide could accelerate the proliferation of vascular endothelial cells in the 9 days. It was suggested that the electrospun PELCL membranes loaded with QK peptide might have potential applications in vascular tissue engineering.     

X-ray diffraction methods to determine crystallinity and preferred orientation of lithium disilicate in Li-Zn-silicate glass-ceramic fibres

Three X-ray diffraction methods for the evaluation of the microstructural features shown by glass-ceramic fibres obtained by various heat treatments have been developed and discussed. Fibres made of a Li-Zn-silicate glass of the following chemical composition were investigated (mol%): SiO₂ 66.75, Li₂O 23.45, ZnO 8.00, K₂O 1.00, P₂O₅ 0.80. The first method is devoted to measure the preferred crystal orientation of lithium disilicate crystals which begin to grow starting from 580°C with thec-axis lying preferentially normal to the fibre external surface. This method has employed a four-circle diffractometer by means of which the intensity distribution of the equatorial 002 X-ray reflection could be evaluated. The other two methods regard the crystallinity content determination of lithium disilicate formed at 590°C as well as at 620°C either after a nucleation step at 480°C or at 500°C, or without any nucleation treatment. These two methods, namely the Hermans and Weidinger and the Wakelin, Virgin and Crystal methods, have been transferred for the first time from the organic polymer science to glass-ceramic materials. The results obtained with both methods have been compared together and have been found in good agreement.     

Process optimization and alignment of PVA/FeCl<Subscript>3</Subscript> nano composite fibres by electrospinning

This paper describes the result of investigation on PVA/FeCl₃ nano composites fibres prepared by the electrospinning process. The effects of instrument parameters including solution concentration, electric voltage, tip–target distance, flow rate parameters on the morphology of electrospun PVA/FeCl₃ fibres were evaluated. The produced composite fibres were characterized by scanning electron microscopy (SEM) and transmission electron microscope (TEM). Fibre mats of (PVA)/FeCl₃ composite thin fibres, in the diameter of 500–1100 nm, were prepared by electrospinning. These microscopies show detailed morphologies of PVA/FeCl₃ nano composites incorporating magnetic power. These novel composite fibres could be used in biomedical, catalyst and magnetic purpose.     

Comparative performance of collagen nanofibers electrospun from different solvents and stabilized by different crosslinkers

Collagen electrospun scaffolds well reproduce the structure of the extracellular matrix (ECM) of natural tissues by coupling high biomimetism of the biological material with the fibrous morphology of the protein. Structural properties of collagen electrospun fibers are still a debated subject and there are conflicting reports in the literature addressing the presence of ultrastructure of collagen in electrospun fibers. In this work collagen type I was successfully electrospun from two different solvents, trifluoroethanol (TFE) and dilute acetic acid (AcOH). Characterization of collagen fibers was performed by means of SEM, ATR-IR, Circular Dichroism and WAXD. We demonstrated that collagen fibers contained a very low amount of triple helix with respect to pristine collagen (18 and 16 % in fibers electrospun from AcOH and TFE, respectively) and that triple helix denaturation occurred during polymer dissolution. Collagen scaffolds were crosslinked by using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), a commonly employed crosslinker for electrospun collagen, and 1,4-butanediol diglycidyl ether (BDDGE), that was tested for the first time in this work as crosslinking agent for collagen in the form of electrospun fibers. We demonstrated that BDDGE successfully crosslinked collagen and preserved at the same time the scaffold fibrous morphology, while scaffolds crosslinked with EDC completely lost their porous structure. Mesenchymal stem cell experiments demonstrated that collagen scaffolds crosslinked with BDDGE are biocompatible and support cell attachment.     

Endotoxins affect diverse biological activity of chitosans in matters of hemocompatibility and cytocompatibility

Chitosan is used in several pharmaceutical and medical applications, owing to its good cytocompatibility and hemocompatibility. However, there are conflicting reports regarding the biological activities of chitosan with some studies reporting anti-inflammatory properties while others report pro-inflammatory properties. In this regards we analyzed the endotoxin content in five different chitosans and examined these chitosans with their different deacetylation degrees for their hemocompatibility and cytocompatibility. Therefore, we incubated primary human endothelial cells or whole blood with different chitosan concentrations and studied the protein and mRNA expression of different inflammatory markers or cytokines. Our data indicate a correlation of the endotoxin content and cytokine up-regulation in whole blood for Poly-Morpho-Nuclear (PMN)-Elastase, soluble terminal complement complex SC5b-9, complement component C5/C5a, granulocyte colony-stimulating factor, Interleukin-8 (IL), IL-10, IL-13, IL-17E, Il-32α and monocyte chemotactic protein-1. In contrast, the incubation of low endotoxin containing chitosans with primary endothelial cells resulted in increased expression of E-selectin, intercellular adhesion molecule-1, vascular cell adhesion protein-1, IL-1β, IL-6 and IL-8 in endothelial cells. We suggest that the endotoxin content in chitosan plays a major role in the biological activity of chitosan. Therefore, we strongly recommend analysis of the endotoxin concentration in chitosan, before further determining if it has pro- or anti-inflammatory properties or if it is applicable for pharmaceutical and medical fields.     

Straw-reinforced polyester composites

Annual crop fibres are rich in cellulose and they are a cheap and rapidly renewable source of fibres with potential for polymer reinforcement. Straw fibres have been incorporated in a polyester resin matrix and the properties of the fibre and composite determined. The fibres have a Young's modulus of approximately 8 GN m^?2 and an effective density of 5.1 kN m^?3 when combined with resin. Useful composites can be formulated with an optimum fibre volume fraction of about 0.61, resulting in a flexural stiffness of 7.3 GN m^?2 and flexural strength of 56 MN m^?2. The specific flexural stiffness is about 2.5 times greater than that of polyester resin and about half that of softwoods and GRP. The work of fracture measured in impact is about half that of softwoods. It is envisaged that alternative methods for processing the fibres and the use of a phenolic resin matrix will improve the composite properties further. Straw-based composites are suitable as core material for structural board products.     

Blow spun strontium zirconate fibres produced from a sol-gel precursor

A zirconium sol was produced from the hydrolysis and immediate peptization of a zirconium alkoxide, which was found to be stable with the addition of a large proportion of a strontium salt, even up to equimolar amounts. Get fibres were successfully blow spun from this doped sol, which on subsequent heating produced ceramic fibres of orthorhombic strontium zirconate. The fibres were characterized by various techniques. The fibres were found to begin forming SrZrO₃ at 400°C and were present as single phase orthorhombic strontium zirconate at 800°C and above. The ceramic fibres had no discernible grain structure and the average crystallite size was calculated to be only 20 nm at this temperature, but the fibres contained small surface pores (< 0.2 m) which continued to increase in size on subsequent heating, resulting in a weak and brittle fibre. Therefore, more investigation is required into sintering and the development of high temperature properties.     

Carbon fibre composites with rubber toughened matrices

In carbon fibre reinforced plastics (CFRP), the initial resistance to crack propagation parallel to fibres is determined largely by the matrix toughness. The fracture toughness (G _IC) of an epoxide resin can be increased considerably by the addition of butadieneacrylonitrile co-polymers (CTBN). These cause the precipitation of small spheres of a second phase and, for example, increaseG _IC from ～ 300 to ～ 3000 J m^?2 on the addition of 9 wt% CTBN. The large increases obtained in bulk resins are not obtained in CFRP, instead significant but modest increases are achieved. The suppression of toughness is related to the thickness of resin film through which the crack propagates.     

Comparative evaluation of N-glass and E-glass fibres with special reference to their use in FRP composites

The abilities of E-glass and N-glass fibres and of composites based on them to withstand degradative effects in boiling water or in boiling aqueous solutions of HCl (10%), NaOH (0.5%) and NaCl (10%) have been evaluated on a comparative basis by following the loss or retention of strength properties (tensile/flexural) with the time of the respective degradative exposure. The degradative effects under different chemical environments for the composites were also analysed with the help of SEM micrographs of the composites before and after the specific degradative treatments. Analysis of strength properties and retention of strength and of the micrographs clearly indicates that N glass is highly superior to E glass, and the former imparts a much higher order of stability to composites in different chemical environments despite substantial initial advantages in the strength properties for E-glass fibre and composites based on this fibre.     

Morphological and chemical characterization of microfabricated fibres for biological applications

Monodisperse fibres and particulates of different materials with controllable three-dimensional shape, size and chemical composition are of interest in research on toxic respirable fibres as well as wear debris around orthopaedic implants. We have previously demonstrated the production of well-controlled, metal and oxide microfabricated fibres having dimensions 0.1 to 10 m. While our previous results focused on how controlled fibres can be prepared by microfabrication methods, this paper evaluates property–production relationships for microfabricated fibres. Here we have briefly reviewed the production of 0.1 m×0.5 m×10 m microfabricated fibres made by electron beam lithography from evaporated titanium or silicon oxide films using a double lift-off method. We have also analysed the properties of these fibres with respect to morphology and chemical composition, and how they are affected by variations in the production process. Two different solution types have been used to place fibres into liquid suspension and to clean and sterilize them for biological testing. One method involves the use of organic solvents; the other a hydroxide solution and water. While fibre dimensions appear to be material-specific, differences can be corrected for by compensation of the size of the lithographic pattern. Similarly the crystallinity of fibres is material-specific, as is to be expected of evaporated thin films, but should be possible to modify by varying deposition parameters or heat treating, for example. Of the cleaning methods used, the one using an aqueous hydroxide solution is preferred over solvent cleaning, as it is easier to perform and appears to be more effective at removing resist from the fibre suspension.     

Preparation of multiple oxide BaTiO3 fibres by the sol-gel method

Multiple oxide BaTiO₃ gel fibres were prepared by the sol-gel method from Ba(OC₂H₅)₂-Ti(O-isoC₃H₇)₄-H₂O-C₂H₅OH-CH₃COOH and Ba(CH₃COO)₂-Ti(O-isoC₃H₇)₄-H₂O-CH₃COOH solutions. Relatively long gel fibres of 10cm length were obtained from both solutions in the limited composition region. The latter solution in particular showed a spinnability even when it contained no water. Therefore, the occurrence of spinnability of the solution was considered to be due to the formation of linear polymers composed of bridging acetate groups such as TiO-C(CH₃)-O-Ti rather than metalloxane bonding as Ti-O-Ti. Addition of water to the solutions seems to break the bridging acetate bonds and replace some of them by bridging oxygen bonds. The as-drawn gel fibres which were X-ray amorphous crystallized into BaTiO₃ ceramic fibres of 5mm average length upon heating above 600 ° C. However, the gel fibres drawn from the sols without water became powdery on heating because of the lack of Ti-O-Ti metalloxane bonds. The crystallization behaviour of the BaTiO₃ gel fibres is discussed based on the infrared spectroscopy, X-ray diffraction analysis and thermogravimetric-differential thermal analysis.     

Fracture of aluminium-coated carbon fibres

A degradation in the ultimate tensile strength (UTS) of aluminium-coated carbon fibres was associated with the formation of a reaction layer of aluminium carbide during annealing treatments 475° C for high tensile fibres (HT) and 550° C for high modulus fibres (HM). It was established that for a given annealing treatment, the UTS depended on the square root of the original coating thickness and proposed that fracture was controlled by cracks in the aluminium carbide, with a specific surface energy () and intrinsic crack length (c ₀) of 2.33 J m^–2 and 30 nm for HT fibres, and of 0.64 to 0.77 J m^–2 and 20 nm for HM fibres.     

Preparation of NbN fibres by nitridation of sol-gel derived Nb2O5 fibres

Nbn fibres were prepared by nitriding sol-gel-derived Nb₂O₅ fibres. Precursor niobium-oxide-gel fibres were obtained by spinning viscous sots prepared through acid-catalysed hydrolysis of niobium penta-ethoxide, Nb(OC₂H₅)₅. It was found that the spinnability of the sols depended on the water/alkoxide and the acid/alkoxide ratios. The niobium-oxide-gel fibres thus obtained were converted to niobium nitride by heat-treatment in a NH₃ gas above 800°C. Characterization of these fibres was carried out using X-ray powder diffraction, Auger electron spectroscopy and scanning electron microscopy. The nitride fibres obtained at 1050°C were mostly of stoichiometric -NbN phase, and they showed a transition to a superconducting state at around 11 K.     

Control of nanostructures in PVA,PVA/chitosan blends and PCL through electrospinning

Aqueous solutions of polyvinyl alcohol (PVA) were electrospun and its characteristics were studied as a function of applied potential, tip-target distance and solution flow rate. Solutions of PVA and chitosan were homogeneously mixed and electrospun to result in blend nanofibres and their properties were investigated. Conditions were revealed under which multiscale bi-modal fibres could be electrospun in a single step, producing structures that have potential applications in tissue engineering. Electrospun fibres having a bimodal size distribution of poly(caprolactone) (PCL) were also fabricated using a modified electrospinning setup. Nanofibrous microporous PVA scaffolds were fabricated using a cryogenic grinding method with subsequent compaction. Such multiscale porous structures would offer ideal matrices for tissue engineering applications.     

Nanogold and nanosilver composites with lignin-containing cellulose fibres

The formation of nanogold and nanosilver composites with cellulose paper fibres and the associated lignin component together with their antimicrobial properties are presented. This follows on from the proprietary technology of Johnston et al. [1] wherein they used nanogold and nanosilver entities in wool fibres to provide novel colourfast colourants in textiles with additional effective antimicrobial and catalytic properties. The nanogold and nanosilver are formed and bound directly onto the unbleached lignin-containing paper fibres without the use of an external linker molecule. For this, the lignin was found to play an essential role and hence the methodology presented is applicable only to cellulose in the form of unbleached kraft fibres and mechanical pulp. The phenol and possibly the aromatic methoxy groups of the lignin are considered to reduce Au³⁺ to Au⁰ and Ag⁺ to Ag⁰, respectively, and bind the nanogold and nanosilver to the fibre surface. SEM images and UV–Visible spectra confirm the formation of nanogold and nanosilver on the fibre surface. Changes in the IR spectra are consistent with the above role of the phenol and methoxy groups. The resulting nanogold—unbleached kraft fibres are purple and the nanosilver—unbleached kraft fibres are yellow due to the surface plasmon resonance effects of nanogold and nanosilver respectively. The nanogold—unbleached kraft fibres and particularly the nanosilver—unbleached kraft fibres exhibit very effective antimicrobial properties at low levels of gold and at very low levels of silver. In this way we have been able to produce novel nanogold paper and nanosilver paper fibres and products which collectively exhibit the properties of the nanomaterials and the fibre substrates in a synergistic way. This provides the opportunity for developing new functional paper products for antimicrobial packaging, medical dressings, and clothing.     

The mechanics of stretch-graphitization of glassy carbon fibres

The mechanics of stretch-graphitization of glassy carbon fibres made from two pitch precursors was studied by determining the plastic deformation characteristics of monofilaments during their elongation to 50% strain in a continuous apparatus. By monitoring fibre tension under various processing conditions and analysing deformation profiles quenched into extending fibres, the temperature and strain-rate dependence of induced fibre stresses has been obtained. Over the temperature range 2200 to 3000° C and strainrate range 3.0×10^?4 to 2.5×10^?1 sec^?1, tensile stresses in the glassy carbon fibres ranged from 7000 to 50 000 psi. The deformation can be described by the empirical equation \(\dot \varepsilon = A\sigma ^n \) exp (? ΔH/RT), where A is a constant, n=8.6±1 and ΔH ～ 290±50 kcal mole^?1, independent of temperature and strain-rate, for both fibre types. The apparent activation energy is consistent with the controlling operation of a microfibrillar reorientation process, accompanied by atomic diffusion (ordering). The high strain-rate stress dependence, indicating an apparent activation volume ～ 4000 ų, also suggests a molecular-scale rate-limiting process. Results are compared with those of various high temperature processes in carbonaceous solids and deformation in organic polymers and it is suggested that stretch-graphitization can be considered analogous to the affine drawing of amorphous polymer fibres.     

Comparison of the performance of natural latex membranes prepared with different procedures and PTFE membrane in guided bone regeneration (GBR) in rabbits

This work assessed the performance of membranes made of natural latex extracted from Hevea brasiliensis prepared with three different methods: polymerized immediately after collection without the use of ammonia (L1); polymerized after preservation in ammonia solution (L2); and polymerized after storage in ammonia, followed by Soxhlet technique for the extraction of substances (L3). Polytetrafluoroethylene (PTFE) membrane was used as control. Two 10-mm diameter bone defects were surgically made in the calvaria of thirty adult male New Zealand rabbits. Defects (total n = 60) were treated with guided bone regeneration (GBR) using L1, L2, L3 or PTFE membranes (n = 15 for each membrane). Ten animals were euthanized after 7, 20 and 60 days postoperatively so that five samples (n = 5) of each treatment were collected at each time, and bone regeneration was assessed microscopically. The microscopic analysis revealed defects filled with blood clot and new bone formation at the margins of the defect in all 7-day samples, while 20-day defects were mainly filled with fibrous connective tissue. After 60 days defects covered with L1 membranes showed a significantly larger bone formation area in comparison to the other groups (P < 0.05, ANOVA, Tukey). Additionally, bone tissue hypersensitization for L1 and PTFE membranes was also investigated in six additional rabbits. The animals were subjected to the same surgical procedure for the confection of one 10-mm diameter bone defect that was treated with L1 (n = 3) or PTFE (n = 3). Fifty-three days later, a second surgery was performed to make a second defect, which was treated with the same type of membrane used in the first surgery. Seven days later, the animals were euthanized and samples analyzed. No differences among L1 and PTFE samples collected from sensitized and non-sensitized animals were found (P > 0.05, Kruskal–Wallis). Therefore, the results demonstrated that latex membranes presented performance comparable to PTFE membranes, and that L1 membranes induced higher bone formation. L1 and PTFE membranes produced no hypersensitization in the bone tissue.     

Preparation of ultra-oriented,high-strength filaments of polyethylene

A strong, transparent high-density polyethylene morphology has been produced in an Instron capillary rheometer by orientation and pressure near the polymer ambient melting point, 130 to 136? C. The multiple and interrelated variables for extrusion of this special morphology have been considered and tested. Capillaries of four different dimensions were employed. The formation of the transparent polyethylene was found to be the result of neither molten-state shear nor simple cold-drawing. It is initiated by the transition from molten flow to cold-drawing in which pre-oriented crystals are drawn within the capillary and entrance region under pressure and shear. Long strands of high perfection have been produced. Prior art, however, has not permitted continuous production. Differential Scanning Calorimetry on the transparent strands shows the existence of a higher melting structure in an inner core, and that a higher extrusion pressure and temperature gives a higher melting ultra-oriented polyethylene strand.     

Inviscid melt-spun high-temperature alumina-magnesia fibres

Al₂O₃-MgO (AM) fibres containing 98.16 wt% Al₂O₃ and 1.84 wt% MgO, were produced via inviscid melt spinning. By using scanning electron microscopy it was found that the as-spun AM fibres were hollow and their surfaces were very rough. The X-ray diffraction pattern of the as-spun AM fibre showed -Al₂O₃ as a major phase and -Al₂O₃ as a minor phase. The DTA curve of the as-spun AM fibre showed a single endothermic peak representing the phase transformation of -Al₂O₃ to -Al₂O₃. This phase transformation was readily confirmed by analysing the X-ray diffraction pattern of heat-treated AM fibres.