Graeme Clark Collection
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ItemThe multi-channel cochlear implant: past, present and future perspectives.(Informa UK Limited, 2009)Initial research demonstrated that only low frequencies could be mimicked with rate of electrical stimulation, and thus multi-channel rather than single-channel stimulation was required for the place coding of the mid-high speech frequencies. Place coding of mid-high frequencies was best achieved with electrodes inside the cochlea. Furthermore, correct biomechanical properties of a multiple electrode bundle were required for it to pass around the cochlear spiral to the speech frequency region. Biological studies showed too that intra-cochlear electrodes could be used with minimal trauma, safe electrical stimulus parameters, and methods to prevent inner ear infection and meningitis. The crucial discoveries for coding speech with electrical stimulation have been based on the discovery of: 1) the fact the brain processes frequency information along spatial and temporal channels, and 2) that the first patient experienced vowels when stimulating different electrodes that corresponded to the place of excitation for single formant vowels in people with normal hearing. The inaugural and subsequent speech processing strategies extracted frequencies of special importance for speech intelligibility, and transmitted the information along place coding channels. The voicing frequency and/or amplitude, was coded as temporal information across these spatial channels. As a result a great majority of severely-to-profoundly deaf people with previous hearing can not only communicate when electrical stimulation is combined with lipreading, but with electrical stimulation alone. In addition, the benefits of binaural hearing with bilateral cochlear implants or an implant in one ear and hearing aid in the other ear have been realized. Related psychophysical research has discovered the basic perceptual skills that process the complex patterns of brain excitation that underlie speech recognition both in the one ear as well as bilateral implants.In addition the development of the perceptual skills in the maturing child for speech recognition, have been discovered. In the future high fidelity sound should be achieved by providing the fine temporo-spatial patterns of excitation and preserving the peripheral nerve network. This could require the release of nerve growth factors and the development of electrodes using nanotechnology.
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ItemNo Preview AvailablePersonal reflections on the multichannel cochlear implant and a view of the future(JOURNAL REHAB RES & DEV, 2008)The multichannel cochlear implant is the first neural prosthesis to effectively and safely bring electronic technology into a direct physiological relation with the central nervous system and human consciousness. It is also the first cochlear implant to give speech understanding to tens of thousands of persons with profound deafness and spoken language to children born deaf in more than 80 countries. In so doing, it is the first major advance in research and technology to help deaf children communicate since Sign Language of the Deaf was developed at the Paris deaf school (L'Institut National de Jeunes Sourds de Paris) >200 years ago. Furthermore, biomedical research has been fundamental for ensuring that the multielectrode implant is safe as well as effective. More recent research has also shown that bilateral implants confer the benefits of binaural hearing. Future research using nanotechnology should see high-fidelity sound received, which would help deaf persons communicate in noise and enjoy music. Research should also lead to implants in ears with useful hearing.
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ItemNo Preview AvailableCan we prevent cochlear implant recipients from developing pneumococcal meningitis?(Oxford University Press (OUP), 2008-01-01)The restoration of hearing to persons with severely or profoundly impaired hearing by means of a cochlear implant is one of the great achievements of bionics applied to medicine. However, pneumococcal meningitis in implant recipients has received high profile public attention as a result of the US Food and Drug Administration's public health notification and recent media attention. Worldwide, 118 of the 60,000 people who received cochlear implants over the past 20 years have acquired meningitis, causing deep concern in the international medical community. This review provides answers to pediatricians, internists, and infectious diseases doctors who have patients with cochlear implants and who have questions about the safety of the cochlear implant from both the clinical and scientific research perspectives. Both clinical and laboratory research support the notion that pneumococcal meningitis is more likely in patients who receive cochlear implantation, and that the surgical insertion technique and the cochlear implant design should be nontraumatic, and that all cochlear implant recipients should be offered vaccination against Streptococcus pneumoniae.
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ItemPromoting neurite outgrowth from spiral ganglion neuron explants using polypyrrole/BDNF-coated electrodes(WILEY, 2009-10)Release of neurotrophin-3 (NT3) and brain-derived neurotrophic factor (BDNF) from hair cells in the cochlea is essential for the survival of spiral ganglion neurons (SGNs). Loss of hair cells associated with a sensorineural hearing loss therefore results in degeneration of SGNs, potentially reducing the performance of a cochlear implant. Exogenous replacement of either or both neurotrophins protects SGNs from degeneration after deafness. We previously incorporated NT3 into the conducting polymer polypyrrole (Ppy) synthesized with para-toluene sulfonate (pTS) to investigate whether Ppy/pTS/NT3-coated cochlear implant electrodes could provide both neurotrophic support and electrical stimulation for SGNs. Enhanced and controlled release of NT3 was achieved when Ppy/pTS/NT3-coated electrodes were subjected to electrical stimulation. Here we describe the release dynamics and biological properties of Ppy/pTS with incorporated BDNF. Release studies demonstrated slow passive diffusion of BDNF from Ppy/pTS/BDNF, with electrical stimulation significantly enhancing BDNF release over 7 days. A 3-day SGN explant assay found that neurite outgrowth from explants was 12.3-fold greater when polymers contained BDNF (p < 0.001), although electrical stimulation did not increase neurite outgrowth further. The versatility of Ppy to store and release neurotrophins, conduct electrical charge, and act as a substrate for nerve-electrode interactions is discussed for specialized applications such as cochlear implants.
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ItemConducting polymers, dual neurotrophins and pulsed electrical stimulation - Dramatic effects on neurite outgrowth(ELSEVIER SCIENCE BV, 2010-01-25)In this study the synergistic effect of delivering two neurotrophins simultaneously to encourage neuron survival and neurite elongation was explored. Neurotrophin-3 (NT-3) and brain-derived neurotrophic factor (BDNF) were incorporated into polypyrrole (PPy) during electrosynthesis and the amounts incorporated and released were determined using iodine-125 ((125)I) radio-labelled neurotrophins. Neurite outgrowth from cochlear neural explants grown on the conducting polymer was equivalent to that on tissue culture plastic but significantly improved with the incorporation of NT-3 and BDNF. Neurite outgrowth from explants grown on polymers containing both NT-3 and BDNF showed significant improvement over PPy doped only with NT-3, due to the synergistic effect of both neurotrophins. Neurite outgrowth was significantly improved when the polymer containing both neurotrophins was electrically stimulated. It is envisaged that when applied to the cochlear implant, these conducting and novel polymer films will provide a biocompatible substrate for storage and release of neurotrophins to help protect auditory neurons from degradation after sensorineural hearing loss and encourage neurite outgrowth towards the electrodes.
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ItemCreating conductive structures for cell growth: Growth and alignment of myogenic cell types on polythiophenes(WILEY-BLACKWELL, 2010-10)Conducting polymers provide suitable substrates for the in vitro study of excitable cells, including skeletal muscle cells, due to their inherent conductivity and electroactivity. The thiophene family of conducting polymers offers unique flexibility for tailoring of polymer properties as a result of the ease of functionalization of the parent monomer. This article describes the preparation of films and electrospun fibers from an ester-functionalized organic solvent-soluble polythiophene (poly-octanoic acid 2-thiophen-3-yl-ethyl ester) and details the changes in properties that result from post-polymerization hydrolysis of the ester linkage. The polymer films supported the proliferation and differentiation of both primary and transformed skeletal muscle myoblasts. In addition, aligned electrospun fibers formed from the polymers provided scaffolds for the guided differentiation of linearly aligned primary myotubes, suggesting their suitability as three-dimensional substrates for the in vitro engineering of skeletal muscle tissue.
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ItemWet-Spun Biodegradable Fibers on Conducting Platforms: Novel Architectures for Muscle Regeneration(WILEY-V C H VERLAG GMBH, 2009-11-09)Abstract Novel biosynthetic platforms supporting ex vivo growth of partially differentiated muscle cells in an aligned linear orientation that is consistent with the structural requirements of muscle tissue are described. These platforms consist of biodegradable polymer fibers spatially aligned on a conducting polymer substrate. Long multinucleated myotubes are formed from differentiation of adherent myoblasts, which align longitudinally to the fiber axis to form linear cell‐seeded biosynthetic fiber constructs. The biodegradable polymer fibers bearing undifferentiated myoblasts can be detached from the substrate following culture. The ability to remove the muscle cell‐seeded polymer fibers when required provides the means to use the biodegradable fibers as linear muscle‐seeded scaffold components suitable for in vivo implantation into muscle. These fibers are shown to promote differentiation of muscle cells in a highly organized linear unbranched format in vitro and thereby potentially facilitate more stable integration into recipient tissue, providing structural support and mechanical protection for the donor cells. In addition, the conducting substrate on which the fibers are placed provides the potential to develop electrical stimulation paradigms for optimizing the ex vivo growth and synchronization of muscle cells on the biodegradable fibers prior to implantation into diseased or damaged muscle tissue.
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ItemA Conducting-Polymer Platform with Biodegradable Fibers for Stimulation and Guidance of Axonal Growth(WILEY-V C H VERLAG GMBH, 2009-11-20)A biosynthetic platform composed of a conducting polypyrrole sheet embedded with unidirectional biodegradable polymer fibers is described (see image; scale bar = 50 µm). Such hybrid systems can promote rapid directional nerve growth for neuro-regenerative scaffolds and act as interfaces between the electronic circuitry of medical bionic devices and the nervous system.
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ItemPneumococcal meningitis post-cochlear implantation: preventative measures.(Wiley, 2010-11)OBJECTIVE: Both clinical data and laboratory studies demonstrated the risk of pneumococcal meningitis post-cochlear implantation. This review examines strategies to prevent post-implant meningitis. DATA SOURCES: Medline/PubMed database; English articles after 1980. Search terms: cochlear implants, pneumococcus meningitis, streptococcus pneumonia, immunization, prevention. REVIEW METHODS: Narrative review. All articles relating to post-implant meningitis without any restriction in study designs were assessed and information extracted. RESULTS: The presence of inner ear trauma as a result of surgical technique or cochlear implant electrode array design was associated with a higher risk of post-implant meningitis. Laboratory data demonstrated the effectiveness of pneumococcal vaccination in preventing meningitis induced via the hematogenous route of infection. Fibrous sealing around the electrode array at the cochleostomy site, and the use of antibiotic-coated electrode array reduced the risk of meningitis induced via an otogenic route. CONCLUSION: The recent scientific data support the U.S. Food and Drug Administration recommendation of pneumococcal vaccination for the prevention of meningitis in implant recipients. Nontraumatic cochlear implant design, surgical technique, and an adequate fibrous seal around the cochleostomy site further reduce the risk of meningitis.
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ItemPneumococcal meningitis post-cochlear implantation: potential routes of infection and pathophysiology.(Wiley, 2010-11)OBJECTIVE: This review describes the current concept of pneumococcal meningitis in cochlear implant recipients based on recent laboratory studies. It examines possible routes of Streptococcus pneumoniae infection to the meninges in cochlear implant recipients. It also provides insights into fundamental questions concerning the pathophysiology of pneumococcal meningitis in implant recipients. DATA SOURCES: Medline/PubMed database; English articles after 1960. Search terms: cochlear implants, meningitis, pneumococcus, streptococcus pneumonia. REVIEW METHODS: Narrative review. All articles relating to post-implant meningitis without any restriction in study designs were assessed and information extracted. RESULTS: The incidence of pneumococcal meningitis in cochlear implant recipients is greater than that of an age-matched cohort in the general population. Based on the current clinical literature, it is difficult to determine whether cochlear implantation per se increases the risk of meningitis in subjects with no existing risk factors for acquiring the disease. As this question cannot be answered in humans, the study of implant-related infection must involve the use of laboratory animals in order for the research findings to be applicable to a clinical situation. The laboratory research demonstrated the routes of infection and the effects of the cochlear implant in lowering the threshold for pneumococcal meningitis. CONCLUSION: The laboratory data complement the existing clinical data on the risk of pneumococcal meningitis post-cochlear implantation.