Poly(vinyl alcohol) (PVA) as a biodegradable hydrophilic polymer has unique properties. It absorbs water and swells easily, but the swelling is inhibited by salts. Its physico-chemical properties ...depend on the degree of hydrolysis. The solubility of PVA in water increases greatly as its degree of hydrolysis increases.
In the current work, new systems for the delivery of ketoprofen as non-steroidal anti-inflammatory drug (NSAID) were developed. New electrospun fibers containing ketoprofen and made from partially and fully hydrolyzed poly(vinyl alcohol) (PVA) were developed as drug delivery system. Moreover, electrospun PVA fibers were stabilized against disintegration in water by treatment with alcohol such as methanol. The release of ketoprofen from the electrospun fibers was determined by UV spectrophotometer at the body temperature (37
°C) and at the room temperature (20
°C). The results showed that upon the treatment of electrospun PVA with alcohol, the burst release was eliminated.
Polydioxanone (PDS) is a colorless, crystalline, bioabsorbable polymer that was first developed specifically for wound closure sutures. The compatibility, degradation rate, and mechanical properties ...(including shape memory) of PDS are of interest when considering the design of tissue engineering scaffolds. This research presents the electrospinning of PDS to fabricate unique nanofibrous structures for a variety of biomedical applications. Electrospinning is a polymer processing technique that utilizes an electric field to form fibers from a polymer solution or melt and allows the fabrication of nanofibrous non-woven structures. Results demonstrate the ability to control the fiber diameter of PDS as a function of solution concentrations and the fiber orientation with our prototype electrospinning apparatus. The results also show dependence between the fiber orientation and the elastic modulus, peak stress, and strain to failure of PDS in a uniaxial model.
Significant challenges must be overcome before the true benefit and economic impact of vascular tissue engineering can be fully realized. Toward that end, we have pioneered the electrospinning of ...micro- and nano-fibrous scaffoldings from the natural polymers collagen and elastin and applied these to development of biomimicking vascular tissue engineered constructs. The vascular wall composition and structure is highly intricate and imparts unique biomechanical properties that challenge the development of a living tissue engineered vascular replacement that can withstand the high pressure and pulsatile environment of the bloodstream. The potential of the novel scaffold presented here for the development of a viable vascular prosthetic meets these stringent requirements in that it can replicate the complex architecture of the blood vessel wall. This replication potential creates an "ideal" environment for subsequent in vitro development of a vascular replacement. The research presented herein provides preliminary data toward the development of electrospun collagen and elastin tissue engineering scaffolds for the development of a three layer vascular construct.
Poly(glycolic acid) (PGA) has a long history as a bioresorbable polymer. Its biocompatibility is widely accepted, yet PGA is often rejected as a soft-tissue scaffold because of fibrous encapsulation. ...The goal of this study was to improve the soft-tissue biocompatibility of PGA by producing scaffolds composed of small-diameter fibers through electrospinning and subjecting these scaffolds to a concentrated hydrochloric acid (HCL) pretreatment. The theory is that small-diameter fibers will elicit a reduced immune response and HCl treatment will improve cellular interactions. Scaffolds were characterized in terms of fiber diameter and pore area via image-analysis software. Biocompatibility was assessed through a WST-1 cell-proliferation assay (in vitro) with the use of rat cardiac fibroblasts and rat intramuscular implantations (in vivo). Fibers produced ranged in diameter from 0.22 to 0.88 microm with pore areas from 1.84 to 13.22 microm(2). The untreated scaffold composed of 0.88-microm fibers was encapsulated in vivo and supported the lowest rates of cell proliferation. On the contrary, the acid pretreated scaffold with 0.22-microm fibers was incorporated into the surrounding tissue and exhibited proliferation rates that exceeded the control populations on tissue-culture plastic. In conclusion, this study has shown the ability to improve the biocompatibility of PGA through acid pretreatment of scaffolds comprised of submicron fiber diameters.
We fabricated and investigated polymeric scaffolds that can substitute for the conjunctival extracellular matrix to provide a substrate for autologous expansion of human conjunctival goblet cells in ...culture.
We fabricated two hydrogels and two silk films: (1) recombinant human collagen (RHC) hydrogel, (2) recombinant human collagen 2-methacryloylxyethyl phosphorylcholine (RHC-MPC) hydrogel, (3) arginine-glycine-aspartic acid (RGD) modified silk, and (4) poly-D-lysine (PDL) coated silk, and four electrospun scaffolds: (1) collagen, (2) poly(acrylic acid) (PAA), (3) poly(caprolactone) (PCL), and (4) poly(vinyl alcohol) (PVA). Coverslips and polyethylene terephthalate (PET) were used for comparison. Human conjunctival explants were cultured on scaffolds for 9 to 15 days. Cell viability, outgrowth area, and the percentage of cells expressing markers for stratified squamous epithelial cells (cytokeratin 4) and goblet cells (cytokeratin 7) were determined.
Most of cells grown on all scaffolds were viable except for PCL in which only 3.6 ± 2.2% of the cells were viable. No cells attached to PVA scaffold. The outgrowth was greatest on PDL-silk and PET. Outgrowth was smallest on PCL. All cells were CK7-positive on RHC-MPC while 84.7 ± 6.9% of cells expressed CK7 on PDL-silk. For PCL, 87.10 ± 3.17% of cells were CK7-positive compared to PET where 67.10 ± 12.08% of cells were CK7-positive cells.
Biopolymer substrates in the form of hydrogels and silk films provided for better adherence, proliferation, and differentiation than the electrospun scaffolds and could be used for conjunctival goblet cell expansion for eventual transplantation once undifferentiated and stratified squamous cells are included. Useful polymer scaffold design characteristics have emerged from this study.
Water uptake, swelling,
1H pulsed gradient spin-echo nuclear magnetic resonance (NMR) and variable temperature and pressure complex impedance/electrical conductivity studies have been carried out on ...sulfonated styrene/ethylene-butylene/styrene (S-SEBS) triblock polymer proton conducting membranes. At the highest water contents, the activation volume calculated from the effect of pressure on the electrical conductivity is negative. Previously reported results for Nafion 117 show the same behavior. In addition, above about 10 wt% water, the diffusion coefficients,
D from NMR and
D
σ
calculated from conductivity data, are similar for S-SEBS. The same result is obtained for Nafion 117. The conclusion is that proton transport at high water content is by molecular diffusion for both materials. For low water contents, however, the materials are significantly different. For low water content S-SEBS,
D and
D
σ
are different while they are the same for Nafion 117. In addition, the variation of the conductivity with temperature for S-SEBS is Arrhenius while that for Nafion 117 is not. Finally, the variation of the electrical conductivity with pressure gives rise to activation volumes on the order of 14 cm
3/mol for S-SEBS while those for Nafion 117 are about four times larger. These results indicate that proton transport in low water content S-SEBS occurs via a thermally activated process (ion motion via energy barriers) that is consistent with the more rigid side chains in that material.
Characterization of electrosprayed Nafion films Sanders, E.H.; McGrady, K.A.; Wnek, G.E. ...
Journal of power sources,
04/2004, Letnik:
129, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
Nafion has long served as a benchmark material when evaluating the performance of proton conducting membranes used in PEM fuel cells. Traditionally, the membranes are either extruded from dry polymer ...or cast from a liquid polymer solvent solution. Recently, a different technique for fabricating membranes has been developed. The new approach exploits electrostatic spraying, or electrospraying, to deposit PEM films, with the longer-term goal of fabricating membrane-electrode assemblies using this technique. The focus of this paper is to compare the proton transport and physical properties of electrosprayed membranes with those of extruded Nafion.
Audio frequency complex impedance studies of the electrosprayed membranes were conducted at a variety of temperatures and pressures over a wide range of membrane water contents. The results are compared with similar data for Nafion 117 and for membranes cast from the electrosprayed solutions. Water uptake, dimensional changes, and electrical conductivity measurements indicate that extruded, cast, and electrosprayed Nafion films are similar, with the exception that the electrosprayed Nafion absorbs as much as 15
wt.% water more than the other two membranes with only a slight increase in conductivity. The activation volumes for electrosprayed Nafion are also consistent with those for Nafion 117 and concur with proposed mechanisms for proton transport in Nafion membranes. As in Nafion 117, a dielectric loss peak appeared in the electrosprayed Nafion at low temperatures after heating in vacuum at 380
K, further demonstrating the similarity between the two materials.
Fibrin and fibrinogen have a well-established track record in tissue engineering due to their innate ability to induce improved cellular interaction and subsequent scaffold remodeling compared to ...synthetic scaffolds. Use of fibrinogen as a primary scaffold component, however, has been limited by traditional processing techniques that render scaffolds with insufficient mechanical properties. The goal of this study was to demonstrate, based on mechanical properties, that electrospun fibrinogen overcomes these limitations and can be successful as a tissue engineering scaffold or wound dressing. Electrospun fibrinogen scaffolds were characterized for fiber diameter and pore area and subsequently tested for uniaxial mechanical properties while dry and hydrated. In addition, uniaxial mechanical testing was conducted on scaffolds treated to regulate scaffold degradation in serum-containing media by supplementing the media with aprotinin or cross-linking the scaffolds with glutaraldehyde vapor. A linear relationship between electrospinning solution concentration and measured fiber diameter was seen; fiber diameters ranged from 120 to 610
nm over electrospinning concentrations of 80 to 140
mg/ml fibrinogen, respectively. Pore areas ranged from 1.3
μm
2 to 13
μm
2 over the same fibrinogen concentrations. Aprotinin in the culture media inhibited scaffold degradation in a predictable fashion, but glutaraldehyde vapor fixation produced less reliable results as evidenced by mechanical property testing. In conclusion, the mechanical characteristics of electrospun fibrinogen strongly support its potential use as a tissue engineering scaffold or wound dressing.
In this work, the ω-amine alkanethiols, cysteamine (CA) and 11-amino-1-undecanethiol (11-AUT), were chemisorbed as self-assembled monolayers (SAMs) onto 250-μm gold microelectrodes that were ...microlithographically fabricated within eight-well cell culture plates and investigated as a means to improve neuron-to-electrode surface attachment (NESA). Dynamic contact angle (DCA) measurements showed similar advancing, θa (69° and 65°), but contrasting receding contact angles, θr (9 and 30°) for CA- and 11-AUT-SAMs, respectively. The corresponding hysteresis (Δθar = 60 and 35°, respectively) indicates the CA-SAM displays greater amphiphilic character than the 11-AUT-SAM. A portion of the greater Δθar for CA-SAMs may arise from surface heterogeneity, as compared to sputter-deposited gold and 11-AUT-SAMs. Tapping mode atomic force microscopy (AFM) confirmed a 6% increase (CA-SAM) and a 22% decrease (11-AUT-SAM) in surface roughness when compared to clean but unmodified, sputter-deposited gold. The extracellular matrix cell adhesion proteins, collagen, fibronectin, and laminin, were covalently coupled to the aminoalkanethiol-decorated gold electrodes via acid−amine heterobifunctional cross-linking. Using fluorescein isothiocyanate-tagged laminin, confocal fluorescence microscopy of both CA- and 11-AUT-SAM-modified and unmodified gold microelectrodes confirmed coupling of the protein to the electrode and was readily distinguishable from nonspecifically adsorbed protein. DCA measurements of laminin physisorbed directly onto gold or covalently immobilized via CA- or 11-AUT-SAM had similar advancing (ca. 63−65°) and receding (ca. 7−9°) contact angles. Tapping mode AFM of these protein-bearing surfaces likewise showed dimerized protein aggregates of similar surface roughness. PC-12 cells cultured to confluence on both unmodified and SAM-modified, protein-derivatized gold microelectrodes were examined by alternating current impedance (50 mV p−t−p at 4 kHz). CA- and 11-AUT-SAM-modified surfaces when serving as a foundation or covalently immobilized adhesion proteins produced highly stable and reproducible temporal impedance responses. On the basis of the magnitude and the reproducibility of the impedance responses, the CA-SAM-modified surfaces were identified as being best suited for optimal neuron-to-electrode contact with laminin. Laminin performed best when compared to collagen and fibronectin. Covalent immobilization of the adhesion-promoting proteins results in enhanced NESA by tightly anchoring cells to the electrode.
PDF
