| 1. |
- Asplund, Maria, 1978-, et al.
(författare)
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Biocompatibility of PEDOT/biomolecular composites intended for neural communication electrodes
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Annan publikation (populärvet., debatt m.m.)abstract
- 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.
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| 2. |
- Asplund, Maria, 1978-, et al.
(författare)
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Composite biomolecule/PEDOT materials for neural electrodes
- 2008
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Ingår i: Biointerphases. - NY : American Institute of Physics. - 1559-4106 .- 1934-8630. ; 3:3, s. 83-93
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Tidskriftsartikel (refereegranskat)abstract
- Electrodes intended for neural communication must be designed to meet boththe electrochemical and biological requirements essential for long term functionality. Metallic electrode materials have been found inadequate to meet theserequirements and therefore conducting polymers for neural electrodes have emergedas a field of interest. One clear advantage with polymerelectrodes is the possibility to tailor the material to haveoptimal biomechanical and chemical properties for certain applications. To identifyand evaluate new materials for neural communication electrodes, three chargedbiomolecules, fibrinogen, hyaluronic acid (HA), and heparin are used ascounterions in the electrochemical polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT). The resultingmaterial is evaluated electrochemically and the amount of exposed biomoleculeon the surface is quantified. PEDOT:biomolecule surfaces are also studiedwith static contact angle measurements as well as scanning electronmicroscopy and compared to surfaces of PEDOT electrochemically deposited withsurfactant counterion polystyrene sulphonate (PSS). Electrochemical measurements show that PEDOT:heparinand PEDOT:HA, both have the electrochemical properties required for neuralelectrodes, and PEDOT:heparin also compares well to PEDOT:PSS. PEDOT:fibrinogen isfound less suitable as neural electrode material.
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| 3. |
- Asplund, Maria, 1978-
(författare)
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Conjugated Polymers for Neural Interfaces : Prospects, possibilities and future challenges
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Within the field of neuroprosthetics the possibility to use implanted electrodes for communication with the nervous system is explored. Much effort is put into the material aspects of the electrode implant to increase charge injection capacity, suppress foreign body response and build micro sized electrode arrays allowing close contact with neurons. Conducting polymers, in particular poly(3,4-ethylene dioxythiophene) (PEDOT), have been suggested as materials highly interesting for such neural communication electrodes. The possibility to tailor the material both mechanically and biochemically to suit specific applications, is a substantial benefit with polymers when compared to metals. PEDOT also have hybrid charge transfer properties, including both electronic and ionic conduction, which allow for highly efficient charge injection. Part of this thesis describes a method of tailoring PEDOT through exchanging the counter ion used in electropolymerisation process. Commonly used surfactants can thereby be excluded and instead, different biomolecules can be incorporated into the polymer. The electrochemical characteristics of the polymer film depend on the ion. PEDOT electropolymerised with heparin was here determined to have the most advantageous properties. In vitro methods were applied to confirm non-cytotoxicity of the formed PEDOT:biomolecular composites. In addition, biocompatibility was affirmed for PEDOT:heparin by evaluation of inflammatory response and neuron density when implanted in rodent cortex. One advantage with PEDOT often stated, is its high stability compared to other conducting polymers. A battery of tests simulating the biological environment was therefore applied to investigate this stability, and especially the influence of the incorporated heparin. These tests showed that there was a decline in the electroactivity of PEDOT over time. This also applied in phosphate buffered saline at body temperature and in the absence of other stressors. The time course of degradation also differed depending on whether the counter ion was the surfactant polystyrene sulphonate or heparin, with a slightly better stability for the former. One possibility with PEDOT, often overlooked for biological applications, is the use of its semi conducting properties in order to include logic functions in the implant. This thesis presents the concept of using PEDOT electrochemical transistors to construct textile electrode arrays with in-built multiplexing. Using the electrolyte mediated interaction between adjacent PEDOT coated fibres to switch the polymer coat between conducting and non conducting states, then transistor function can be included in the conducting textile. Analogue circuit simulations based on experimentally found transistor characteristics proved the feasibility of these textile arrays. Developments of better polymer coatings, electrolytes and encapsulation techniques for this technology, were also identified to be essential steps in order to make these devices truly useful. In summary, this work shows the potential of PEDOT to improve neural interfaces in several ways. Some weaknesses of the polymer and the polymer electronics are presented and this, together with the epidemiological data, should point in the direction for future studies within this field.
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| 4. |
- Asplund, Maria, 1978-, et al.
(författare)
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Incidence of traumatic peripheral nerve injuries and amputations in Sweden between 1998 and 2006
- 2008
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Ingår i: Neuroepidemiology. - Basel : Kargel, AG. - 0251-5350 .- 1423-0208.
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Tidskriftsartikel (refereegranskat)abstract
- Background: To define the epidemiological pattern of nerve injuries and traumatic amputations in Sweden, 1998-2006, and investigate possible targets for emerging neural engineering and neuroprosthetic technologies. Methods: The Swedish Hospital Discharge Register was used as basis of information, including data from all public in-patient care, excluding out-patient data. ICD-10 codes were screened for nerve injuries and traumatic amputations of high incidence or in-patient care time. Selected codes, causing factors, age and gender distribution were discussed in detail, and potential targets for tailored solutions were identified. Results: Incidence rate was determined to 13.9 for nerve injuries and 5.21 for amputations per 100 000 person-yrs. The majority of injuries occurred at wrist and hand level although it could be concluded that these are often minor injuries requiring less than a week of hospitalization. The single most care consuming nerve injury was brachial plexus injury constituting, in average, 68 injuries and 960 hospital days annually. When minor amputations of fingers and toes were disregarded, most frequent site of amputation was between knee and ankle (24 patients / year). Conclusions: Based on analysis of incidence and care time, we find that brachial plexus injuries and lower leg amputations should be primary targets of these new technologies.
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| 5. |
- Asplund, Maria, 1978-, et al.
(författare)
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Wire electronics and woven logic, as a potential technology for neuroelectronic implants
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Annan publikation (populärvet., debatt m.m.)abstract
- 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.
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| 6. |
- Chen, Xing, et al.
(författare)
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Chronic stability of a neuroprosthesis comprising multiple adjacent Utah arrays in monkeys
- 2023
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Ingår i: Journal of Neural Engineering. - 1741-2560 .- 1741-2552. ; 20:3
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Tidskriftsartikel (refereegranskat)abstract
- Objective. Electrical stimulation of visual cortex via a neuroprosthesis induces the perception of dots of light ('phosphenes'), potentially allowing recognition of simple shapes even after decades of blindness. However, restoration of functional vision requires large numbers of electrodes, and chronic, clinical implantation of intracortical electrodes in the visual cortex has only been achieved using devices of up to 96 channels. We evaluated the efficacy and stability of a 1024-channel neuroprosthesis system in non-human primates (NHPs) over more than 3 years to assess its suitability for long-term vision restoration. Approach. We implanted 16 microelectrode arrays (Utah arrays) consisting of 8 x 8 electrodes with iridium oxide tips in the primary visual cortex (V1) and visual area 4 (V4) of two sighted macaques. We monitored the animals' health and measured electrode impedances and neuronal signal quality by calculating signal-to-noise ratios of visually driven neuronal activity, peak-to-peak voltages of the waveforms of action potentials, and the number of channels with high-amplitude signals. We delivered cortical microstimulation and determined the minimum current that could be perceived, monitoring the number of channels that successfully yielded phosphenes. We also examined the influence of the implant on a visual task after 2-3 years of implantation and determined the integrity of the brain tissue with a histological analysis 3-3.5 years post-implantation. Main results. The monkeys remained healthy throughout the implantation period and the device retained its mechanical integrity and electrical conductivity. However, we observed decreasing signal quality with time, declining numbers of phosphene-evoking electrodes, decreases in electrode impedances, and impaired performance on a visual task at visual field locations corresponding to implanted cortical regions. Current thresholds increased with time in one of the two animals. The histological analysis revealed encapsulation of arrays and cortical degeneration. Scanning electron microscopy on one array revealed degradation of IrOx coating and higher impedances for electrodes with broken tips. Significance. Long-term implantation of a high-channel-count device in NHP visual cortex was accompanied by deformation of cortical tissue and decreased stimulation efficacy and signal quality over time. We conclude that improvements in device biocompatibility and/or refinement of implantation techniques are needed before future clinical use is feasible.
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| 7. |
- Eidenskog, Maria, 1981-, et al.
(författare)
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Changing the world one engineer at a time – unmaking the traditional engineering education when introducing sustainability subjects
- 2023
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Ingår i: International Journal of Sustainability in Higher Education. - : EMERALD GROUP PUBLISHING LTD. - 1467-6370 .- 1758-6739. ; 24:9, s. 70-84
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The information technology (IT) sector has been seen as central to society's transformation to a more just and sustainable society, which underlines teachers’ responsibility to foster engineers who can contribute specifically to such ends. This study aims to report an effort to significantly update an existing engineering programme in IT with this ambition and to analyse the effects and challenges associated with the transformation.Design/methodology/approach: This study is based on a combination of action-oriented research based on implementing key changes to the curriculum; empirical investigations including surveys and interviews with students and teachers, and analysis of these; and a science and technology studies-inspired analysis.Findings: Respondents were generally positive towards adding topics relating to sustainability. However, in the unmaking of traditional engineering subjects, changes created a conflict between core versus soft subjects in which the core subjects tended to gain the upper hand. This conflict can be turned into productive discussions by focusing on what kinds of engineers the authors’ educate and how students can be introduced to societal problems as an integrated part of their education.Practical implications: This study can be helpful for educators in the engineering domain to support them in their efforts to transition from a (narrow) focus on traditional disciplines to one where the bettering of society is at the core.Originality/value: This study provides a novel approach to the transformation of engineering education through a theoretical analysis seldom used in studies of higher education on a novel case study.
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| 8. |
- Eklöf, Johan, 1978, et al.
(författare)
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The importance of grazing intensity and frequency for physiological responses of the tropical seagrass Thalassia hemprichii
- 2008
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Ingår i: Aquatic Botany. - : Elsevier BV. - 0304-3770. ; 89, s. 337-340
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Tidskriftsartikel (refereegranskat)abstract
- Seagrass grazing is an intrinsic disturbance in primarily tropical and subtropical areas. While there is a general parabolic response in seagrass growth to grazing intensity, there is less knowledge on the role of grazing frequency, as well as potential interactions between grazing intensity and frequency. This study experimentally investigated physiological responses in Thalassia hemprichii to simulated (leaf cutting) grazing regimes with different intensities (25% vs. 75%) and frequencies (I times vs. 3 times) over 35 days in Chwaka Bay (Zanzibar, Tanzania). The results showed that the two high-intensity treatments (75% removal) had 37-41% lower growth rate than the low-intensity/low-frequency treatment, and rhizome sugar and starch content were both affected in a similar way. A 36% lower starch content in the simulated low-intensity/high-frequency regime (25% x 3) compared to the one of low-intensity/low-frequency (25% x I) also shows an interaction between grazing intensity and frequency. This suggests that high-intensity (and to some extent frequency) grazing regimes, in comparison to low-intensity regimes, could negatively affect T. hemprichii growth, energy reserves, and thereby the ability to deal with additional stress like light limitation or grazing. (C) 2008 Elsevier B.V. All rights reserved.
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| 9. |
- Lewis, Christopher M., et al.
(författare)
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Recording Quality Is Systematically Related to Electrode Impedance
- 2024
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Ingår i: Advanced healthcare materials. - 2192-2640 .- 2192-2659. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- Extracellular recordings with planar microelectrodes are the gold standard technique for recording the fast action potentials of neurons in the intact brain. The introduction of microfabrication techniques has revolutionized the in vivo recording of neuronal activity and introduced high-density, multi-electrode arrays that increase the spatial resolution of recordings and the number of neurons that can be simultaneously recorded. Despite these innovations, there is still debate about the ideal electrical transfer characteristics of extracellular electrodes. This uncertainty is partly due to the lack of systematic studies comparing electrodes with different characteristics, particularly for chronically implanted arrays over extended time periods. Here a high-density, flexible, and thin-film array is fabricated and tested, containing four distinct electrode types differing in surface material and surface topology and, thus, impedance. It is found that recording quality is strongly related to electrode impedance with signal amplitude and unit yield negatively correlated to impedance. Electrode impedances are stable for the duration of the experiment (up to 12 weeks) and recording quality does not deteriorate. The findings support the expectation from the theory that recording quality will increase as impedance decreases.
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| 10. |
- Orlemann, Corinne, et al.
(författare)
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Flexible Polymer Electrodes for Stable Prosthetic Visual Perception in Mice
- 2024
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Ingår i: Advanced healthcare materials. - 2192-2640 .- 2192-2659. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- Brain interfaces that can stimulate neurons, cause minimal damage, and work for a long time will be central for future neuroprosthetics. Here, the long-term performance of highly flexible, thin polyimide shanks with several small (<15 µm) electrodes during electrical microstimulation of the visual cortex, is reported. The electrodes exhibit a remarkable stability when several billions of electrical pulses are applied in vitro. When the devices are implanted in the primary visual cortex (area V1) of mice and the animals are trained to detect electrical microstimulation, it is found that the perceptual thresholds are 2–20 microamperes (µA), which is far below the maximal currents that the electrodes can withstand. The long-term functionality of the devices in vivo is excellent, with stable performance for up to more than a year and little damage to the brain tissue. These results demonstrate the potential of thin floating electrodes for the long-term restoration of lost sensory functions.
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