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  • 1.
    Asplund, Maria
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Hamedi, Mahiar
    Forchheimer, Robert
    Inganäs, Olle
    von Holst, Hans
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Wire electronics and woven logic, as a potential technology for neuroelectronic implantsManuscript (Other (popular science, discussion, etc.))
    Abstract [en]

    New strategies to improve neuron coupling to neuroelectronic implants are needed. In particular, to maintain functional coupling between implant and neurons, foreign body response like encapsulation must me minimized. Apart from modifying materials to mitigate encapsulation it has been shown that with extremely thin structures, encapsulation will be less pronounced. We here utilize wire electrochemical transistors (WECTs) using conducting polymer coated fibers. Monofilaments down to 10 μm can be successfully coated and weaved into complex networks with built in logic functions, so called textile logic. Such systems can control signal patterns at a large number of electrode terminals from a few addressing fibres. Not only is fibre size in the range where less encapsulation is expected but textiles are known to make successful implants because of their soft and flexible mechanical properties. Further, textile fabrication provides versatility and even three dimensional networks are possible. Three possible architectures for neuroelectronic systems are discussed. WECTs are sensitive to dehydration and materials for better durability or improved encapsulation is needed for stable performance in biological environments.

  • 2.
    Asplund, Maria
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Thaning, Elin
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Lundberg, Johan
    Sandberg-Nordqvist, Ann-Christin
    Kostyszyn, Beata
    Inganäs, Olle
    von Holst, Hans
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Biocompatibility of PEDOT/biomolecular composites intended for neural communication electrodesManuscript (Other (popular science, discussion, etc.))
    Abstract [en]

    Electrodes of the conjugated polymer poly(3,4-ethylene dioxythiophene) (PEDOT) have been shown to possess very attractive electrochemical properties for functional electrical stimulation (FES) or recording in the nervous system. Biomolecules already present in nervous tissue, added as counter ions in PEDOT electropolymerisation, could be a route to further improve the biomaterial properties of PEDOT, eliminating the need of surfactant counter ions like docedyl benzene sulphonate (DBS) or polystyrene sulphonate (PSS) in the polymerisation process. Such PEDOT/biomolecular composites using heparin, or hyaluronic acid, have been electrochemically investigated in a previous study and have been shown to retain the attractive electrochemical properties already proven for PEDOT:PSS.

     

    The aim of the present study is to evaluate biocompatibility of these PEDOT/biomolecular composites in vitro and also evaluate PEDOT:heparin biocompatibility in cortical tissue in vivo. Hereby, we also aim to identify a suitable test protocol, that can be used in future evaluations when further material developments are made.

     

    Material toxicity was first tested on cell lines, both through a standardised agarose overlay assay on L929 fibroblasts, and through elution tests on human neuroblastoma SH-SY5Y cells. Subsequently, a biocompatibility in vivo test was performed using PEDOT:heparin coated platinum probes implanted in the cerebral cortex of Sprague-Dawley rats. Tissue was collected at three weeks and six weeks of implantation and evaluated by immunohistochemistry.

     

    No cytotoxic response was seen to any of the PEDOT:biomolecular composites tested here. Furthermore, elution tests were found to be a practical and effective way of screening materials for toxicity and had a clear advantage over the agarose overlay assay, which was difficult to apply on other cell types than fibroblasts. Elution tests would therefore be recommendable as a screening method, at all stages of material development. In the in vivo tests, the stiffness of the platinum substrate was a significant problem, and extensive glial scarring was seen in most cases irrespective of implant material. However, quantification of immunological response through distance measurements from implant site to closest neuron, and counting of macrophage densities in proximity to polymer surface, was comparable to those of platinum controls. These results indicate that PEDOT:heparin surfaces were as compatible with cortical tissue as pure platinum controls.

  • 3.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    The rotation axis of the left ventricle - A new concept derived from ultrasound data in healthy individualsManuscript (preprint) (Other (popular science, discussion, etc.))
    Abstract [en]

    Different modalities have been used to describe the circumferential motion of the left ventricle (LV) and studies have indicated LV twist to be an additional integral component in LV function. So far, only amplitudes of rotation have been reported, whereas the rotation pattern of the LV has not been fully described. However, data from a previous study on regional rotation have indicated that the axis around which the LV rotates, is not congruent to the longitudinal axis of the LV. The aim of the present study was to develop an ultrasound-based method to calculate the rotation axis of the LV in a three-dimensional aspect throughout the cardiac cycle and to apply it in a group of healthy individuals. An algorithm for calculation of rotation axes at the basal, mid-, apical and transitional levels of the LV was developed. By constructing a simplified model of the LV, based on rotation amplitudes measured at the basal, mid- and apical levels, rotation planes with similar values of rotation could be calculated at each level. The transition plane was defined as where the rotation values shifted from positive to negative. An overview of the rotation pattern was achieved by displaying data on deflection (angle between the rotation axis and the longitudinal axis of the LV) and direction (defined as the angle in a short-axis view of the LV with zero degrees at the lateral wall and increasing angles counterclockwise) of the rotation axes throughout the cardiac cycle. The deflection differed significantly from zero in all tested time points, i.e. the rotation axis was not congruent to the longitudinal axis of the LV. Rayleigh’s test for uniformity demonstrated a significant mean direction for each of the axes for the majority of the tested time points. Thus, the axis of rotation at different levels of the LV displayed a physiological pattern, where also stability of rotation could be assessed. Furthermore, the angle and level of the transition plane could be described over time. This new way of assessing rotational function provides further insight into the complexity of LV mechanics. The method has acceptable reproducibility but the potential clinical use of this method needs to be validated in further studies.

  • 4.
    Thaning, Elin
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701).
    Asplund, Maria
    KTH, School of Technology and Health (STH).
    Nyberg, Tobias
    KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701).
    Inganäs, Olle
    von Holst, Hans
    KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701).
    Stability of PEDOT materials intended for implantsManuscript (Other (popular science, discussion, etc.))
    Abstract [en]

    This study presents a set of experiments designed to study the stability over time of the conducting polymer poly(3,4-ethylene dioxythiophene) (PEDOT), under simulated physiological conditions. Especially, the influence of switching the counter ion used in electropolymerisation, from surfactant polystyrene sulphonate (PSS) to heparin, was investigated. Electropolymerised PEDOT was exposed to different solutions at 37 °C over a 5-6 weeks study period. Two methods were used to study changes over time, spectroscopy and cyclic voltammetry. Phosphate buffer solution (PBS) and diluted hydrogen peroxide (H2O2) (0.01 M) were used to simulate in vivo environment. Some PEDOT electrodes in PBS were also subject to voltage pulsing to further stress the material.

     

    The vast part of the samples of both types lost both electroactivity and optical absorbance within the study period, when exposed to H2O2. An overall slightly higher stability of PEDOT:PSS compared to PEDOT:heparin could be seen. The time dependence of the decline also differed, with a linear decrease of electroactivity for PEDOT:heparin while for PEDOT:PSS a comparably stable appearance initially, followed by a marked decrease after 8-15 days.

     

    Polymers were relatively stable in PBS throughout the study period, with around 80% of electroactivity remaining after five weeks. Disregarding a slight drop in electroactivity during the first day, voltage pulsing in PBS did not increase degradation (tested over 11 days). Delamination of PEDOT exposed to PBS was however a significant problem, especially for polymer on ITO substrates.

     

    PEDOT is sensitive to oxidising agents, also in the dilute concentrations used here, and counter ion influences the time course of degradation. Even without oxidising agents, some decline in electroactivity can be expected and it is unclear whether this decrease will continue over time, or if the polymer will stabilise. Such stabilisation was however not seen within the five weeks studied here. Delamination of polymer is likely to be a problem on implantation, especially with unwisely chosen substrates, and might be an even more serious threat to long term applications than degradation in biological fluids.

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