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PubMed2006

Preparation and encapsulation of highly fluorescent conjugated polymer nanoparticles.

A facile method has been developed to prepare aqueous dispersions of encapsulated conjugated polymer nanoparticles exhibiting high fluorescence brightness. Salient features of the nanoparticles include their small diameter and spherical morphology. Encapsulation of the nanoparticles with a silica shell reduces the rate of photooxidation and allows facile attachment of functional groups for subsequent bioconjugation and nanoparticle assembly. Functionalization of the nanoparticle with amine groups followed by the addition of Au nanoparticles resulted in the formation of nanoparticle assemblies, as evidenced by the efficient quenching of the conjugated polymer fluorescence by the Au nanoparticles.

Fluorescent Dyes↗
PubMed2005

Electroactive polymeric sensors in hand prostheses: bending response of an ionic polymer metal composite.

In stark contrast to the inspiring functionality of the natural hand, limitations of current upper limb prostheses stemming from marginal feedback control, challenges of mechanical design, and lack of sensory capacity, are well-established. This paper provides a critical review of current sensory systems and the potential of a selection of electroactive polymers for sensory applications in hand prostheses. Candidate electroactive polymers are reviewed in terms of their relevant advantages and disadvantages, together with their current implementation in related applications. Empirical analysis of one of the most novel electroactive polymers, ionic polymer metal composites (IPMC), was conducted to demonstrate its potential for prosthetic applications. With linear responses within the operating range typical of hand prostheses, bending angles, and bending rates were accurately measured with 4.4+/-2.5 and 4.8+/-3.5% error, respectively, using the IPMC sensors. With these comparable error rates to traditional resistive bend sensors and a wide range of sensitivities and responses, electroactive polymers offer a promising alternative to more traditional sensory approaches. Their potential role in prosthetics is further heightened by their flexible and formable structure, and their ability to act as both sensors and actuators.

Artificial Limbs↗
PubMed2002

Membranes for biohybrid liver support systems--investigations on hepatocyte attachment, morphology and growth.

The biological properties of four different membranes were studied regarding their possible application in biohybrid liver support systems. Two of them, one made of polyetherimide (PEI), and a second based on polyacrylonitrile-N-vinylpyrollidone co-polymer (P(AN-NVP)), were recently developed in our lab and studied for the first time. Together with pure polyacrylonitrile (PAN) membranes, the three preparations were characterised as ultra-filtration membranes. Their ability to support cell attachment, morphology, proliferation and function of human hepatoblastoma C3A cells was studied. The role of surface morphology for the interaction with hepatocytes was highlighted using a commercial, moderately wettable polyvinylidendifluoride (PVDF) membrane with micro-filtration properties. Comparative investigations showed strongest interaction of C3A cells with PAN membranes, as the focal adhesion contacts were more expressed and cell growth was also high. However, the functional activity in terms of albumin synthesis was reduced. Very similar results were obtained with the most hydrophobic PEI membrane. In contrast, the most hydrophilic membrane P(AN-NVP) was found to provoke stronger homotypic adhesion (E-cadherin expression) of C3A cells and less substratum attachment (focal adhesions), but enhanced albumin secretion. However, proliferation of C3A cells was lowered. Micro-porous PVDF membrane showed very good initial attachment, but the resulting cell material and cell-cell interaction were relatively poor developed. Among four membranes tested, PEI seems to be the most attractive membrane for biohybrid liver devices, as it provides good surface properties for hepatocytes interaction, but in addition it is highly thermostable, which would permit steam sterilisation. No simple relationship, however, between the wettability of the membranes and their ability to support hepatocyte adhesion and function was found in this study.

Acrylic Resins↗
PubMed2006

Transmission infrared spectroscopy as a probe of Nafion film structure: analysis of spectral regions fundamental to understanding hydration effects.

Transmission infrared spectroscopy was applied to investigate properties of the perfluorosulfonated polymer Nafion. Measurements were made on thin films formed by casting the polymer from solution onto ZnSe windows. Effects of water vapor permeation were studied. A complex band structure between 1350 and 1100 cm(-1) was analyzed qualitatively by fitting the region to Gaussian functions. Features associated with vibrational modes of -CF(2) and -SO(3)(-) groups were identified and observed to be sensitive to film hydration. The intensities of bands for the -SO(3)(-) modes increased with film hydration, while bands assignable to -CF(2) modes decreased. The results were applied to interpret infrared difference spectra of Nafion and shed light on the complicated features that appear. Vibrational bands for water were also examined. In partially hydrated films, the stretching mode of the free -OH group for interfacial water present in pores and channels of the polymer and bands for hydrated proton clusters were detected.

Fluorocarbon Polymers↗
PubMed2002

Steady state and time-resolved spectroscopic studies of 7-hydroxyquinoline in various polymeric matrices.

The photophysical behavior of 7-hydroxyquinoline (7HQ) is studied in four polymer matrices, viz. polymethyl methacrylate (PMMA), cellulose acetate (CA), polyvinyl alcohol (PVA) and Nafion-117, at ambient temperature using both steady state and time-domain measurements. The study reveals both ground as well as excited state tautomerization in the case of PVA. In PMMA and CA, the intermolecular hydrogen bond to the host polymer results in proton transfer. Edge excitation red shift (EERS) and excitation and emission wavelength dependent decays are observed for normal emission in PMMA and CA matrices. These results are attributed to the trapping of a normal molecule in different geometries. In Nafion, the results show the presence of 7HQ cationic species trapped in the polymer.

Cellulose↗
PubMed2001

Control of shape and size of vascular smooth muscle cells in vitro by plasma lithography.

The ability to control the shape and size of cells is an important enabling technique for investigating influences of geometrical variables on cell physiology. Herein we present a micropatterning technique ("plasma lithography") that uses photolithography and plasma thin-film polymerization for the fabrication of cell culture substrates with a cell-adhesive pattern on a cell-repellent (non-fouling) background. The micron-level pattern was designed to isolate individual vascular smooth muscle cells (SMC) on areas with a projected area of between 25 and 3600 microm(2) in order to later study their response to cytokine stimulation in dependence of the cell size and shape as an indication for the phenotypic state of the cells. Polyethylene terephthalate substrates were first coated with a non-fouling plasma polymer of tetraglyme (tetraethylene glycol dimethyl ether). In an organic lift-off process, we then fashioned square- and rectangular-shaped islands of a thin fluorocarbon plasma polymer film of approximately 12-nm thickness. Electron spectroscopy for chemical analysis and secondary ion mass spectroscopy were used to optimize the deposition conditions and characterize the resulting polymers. Secondary ion mass spectroscopy imaging was used to visualize the spatial distribution of the polymer components of the micropatterned surfaces. Rat vascular SMC were seeded onto the patterned substrates in serum-free medium to show that the substrates display the desired properties, and that cell shape can indeed be controlled. For long-term maintenance of these cells, the medium was augmented with 10% calf serum after 24 h in culture, and the medium was exchanged every 3 days. After 2 weeks, the cells were still confined to the areas of the adhesive pattern, and when one or more cells spanned more than one island, they did not attach to the intervening tetraethylene glycol dimethyl ether (tetraglyme) background. Spreading-restricted cells formed a well-ordered actin skeleton, which was most dense along the perimeter of the cells. The shape of the nucleus was also influenced by the pattern geometry. These properties make the patterned substrates suitable for investigating if the phenotypic reversion of SMC can be influenced by controlling the shape and size of SMC in vitro.

Animals↗
PubMed2003

Surface modification of poly(vinylidenefluoride) to improve the osteoblast adhesion.

Cell adhesion to biomaterials is mediated primarily by the interaction between surface bound proteins and corresponding receptors on the membrane of the cells. The attachment of fibronectin onto poly(vinylidenefluoride) (PVDF) surface and the application of PVDF as biomaterial in bone contact was the subject of our study. PVDF is a biomaterial established for soft tissue applications. Surface modifications of PVDF were performed by plasma induced graft copolymerisation of acrylic acid or CVD polymerisation of 4-amino[2.2]paracyclophane. The provided functionalised PVDF surface was used to immobilise fibronectin using different techniques. All modification steps were verified by means of X-ray photoelectron spectroscopy (XPS), attenuated total reflection infrared spectroscopy (IR-ATR) and contact angle measurements. Surface topology was studied by atomic force measurements (AFM). Protein adsorption was controlled by enzyme linked immunosorbent assay (ELISA). Cell attachment was enhanced if physically adsorbed fibronectin was used, while enhanced attachment and proliferation were induced by covalently binding fibronectin to the surface modified PVDF.

Acetates↗
PubMed1992

The development of synthetic polymers that resist encrustation on exposure to urine.

The consequences of long-term exposure of synthetic materials to urine have prevented the development of alloplastic replacement of diseased or damaged parts of the urinary tract. Similarly, urethral and ureteric catheters require regular replacement if the complications of encrustation and blockage are to be avoided. The mechanism of encrustation is not understood completely and thus it is unclear why certain materials appear better able to resist encrustation. This study has involved the development of a new encrustation model to provide a reproducible and quantitative assessment of the susceptibility of polymers to encrustation. This model will allow beneficial characteristics of co-polymer design to be recognised, with the aim of finding new materials that are tolerant of exposure to urine. Results of co-polymers examined show that the incorporation of fluorine-containing components confers significant resistance to the formation of encrustation. It is suggested that the physico-chemical properties of polymer surfaces may be important determinants of resistance to encrustation.

Calcium↗
PubMed2003

Relative influence of polymer fiber diameter and surface charge on fibrous capsule thickness and vessel density for single-fiber implants.

Single polypropylene microfibers plasma-coated with polymers of different surface charge [N,N-dimethylaminoethyl methacrylate (NN) (positive charge), methacrylic acid (MA) (negative charge), and hexafluoropropylene (HF) (neutral)] were implanted in the subcutaneous dorsum of Sprague-Dawley rats for 5-week intervals. Thee groups of fiber diameters were used: (I) 1.0 to 5.9 microm; (II) 6.0 to 10.9 microm; and (III) 11.0 to 15.9 microm. Fibrous capsule thickness and blood-vessel density (number of vessels within 100 microm of the fiber) were assessed in tissue sections in the planes of microfiber cross-sections. Results from a multifactorial analysis of variance demonstrated statistically significant main effects (p < 0.05) for microfiber diameter but not for surface-charge coating. The mean differences in capsule thickness among the microfiber diameter groups were: between groups II and I: 5.4 microm; between groups III and I: 10.2 microm; and between groups III and II: 4.7 microm. The mean differences in capsule thickness among surface-charge coatings were: between MA and NN: 0.7 microm; between MA and HF: 1.4 microm; and between NN and HF: 0.7 microm. Many of the 1.0 to 5.9 microm-in-diameter fibers had no capsule and no sign of a foreign-body reaction. For the vessel density analysis, neither microfiber diameter nor surface-charge coating had a statistically significant effect. Thus the geometric feature of microfiber diameter was more important than was surface charge relative to fibrous capsule formation but not relative to local vessel density. This ranking of the relative influence of design features in relation to tissue response provides useful information for prioritization in biomaterial design.

Animals↗
PubMedDate not supplied

[Effect of surface roughness of polymers on thrombus formation].

Thromboresistant properties of fluoroplast-4, lavsan, polymethylmetacrylate, carbon glass, employed in various devices contacting the blood and presenting different degrees of the surface roughness, were studied. The thromboresistant properties of polymers were judged on the ground of modified methods for determining the blood coagulating time, thromboelastograms, with reference to the prothrombin complex factors concentration, the amount of fibrinogen, heparin blood tolerance, the thrombocytes adhesion index, their splitting and flattening. A higher class of the polymer surface roughness was found to raise the thromboresistant properties of the surface. In case of polymers with high mechanical and strength properties the surface roughness is of greater importance in the genesis of thrombosis than in polymers possessing elastic properties.

Biocompatible Materials↗