Browsing by Author "Saunders, Alexia"

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    Chronic electrical stimulation with a peripheral suprachoroidal retinal implant: a preclinical safety study of neuroprotective stimulation.
    (Frontiers, 2024-06-20) Abbott, Carla J; Allen, Penelope J; Williams, Chris E; Williams, Richard A; Epp, Stephanie B; Burns, Owen; Thomas, Ross; Harrison, Mark; Thien, Patrick C; Saunders, Alexia; McGowan, Ceara; Sloan, Caitlin; Luu, Chi D; Nayagam, David A X
    Extraocular electrical stimulation is known to provide neuroprotection for retinal cells in retinal and optic nerve diseases. Currently, the treatment approach requires patients to set up extraocular electrodes and stimulate potentially weekly due to the lack of an implantable stimulation device. Hence, a minimally-invasive implant was developed to provide chronic electrical stimulation to the retina, potentially improving patient compliance for long-term use. The aim of the present study was to determine the surgical and stimulation safety of this novel device designed for neuroprotective stimulation.
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    Development of a surgical procedure for implantation of a prototype suprachoroidal retinal prosthesis
    (John Wiley & Sons Inc, 2014-09) Saunders, Alexia; Williams, Chris; Heriot, Wilson; Briggs, Robert; Yeoh, Jonathan; Nayagam, David; McCombe, Mark; Villalobos, Joel; Burns, Owen; Luu, Chi; Ayton, Lauren; McPhedran, Michelle; Opie, Nicholas; McGowan, Ceara; Shepherd, Robert; Guymer, Robyn; Allen, Penelope
    BACKGROUND: Current surgical techniques for retinal prosthetic implantation require long and complicated surgery, which can increase the risk of complications and adverse outcomes. METHOD: The suprachoroidal position is known to be an easier location to access surgically, and so this study aimed to develop a surgical procedure for implanting a prototype suprachoroidal retinal prosthesis. The array implantation procedure was developed in 14 enucleated eyes. A full-thickness scleral incision was made parallel to the intermuscular septum and superotemporal to the lateral rectus muscle. A pocket was created in the suprachoroidal space, and the moulded electrode array was inserted. The scleral incision was closed and scleral anchor point sutured. In 9 of the 14 eyes examined, the device insertion was obstructed by the posterior ciliary neurovascular bundle. Subsequently, the position of this neurovascular bundle in 10 eyes was characterized. Implantation and lead routing procedure was then developed in six human cadavers. The array was tunnelled forward from behind the pinna to the orbit. Next, a lateral canthotomy was made. Lead fixation was established by creating an orbitotomy drilled in the frontal process of the zygomatic bone. The lateral rectus muscle was detached, and implantation was carried out. Finally, pinna to lateral canthus measurements were taken on 61 patients in order to determine optimal lead length. RESULTS: These results identified potential anatomical obstructions and informed the anatomical fitting of the suprachoroidal retinal prosthesis. CONCLUSION: As a result of this work, a straightforward surgical approach for accurate anatomical suprachoroidal array and lead placement was developed for clinical application.
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    Hermetic diamond capsules for biomedical implants enabled by gold active braze alloys
    (Elsevier, Ltd., 2015-03) Lichter, Samantha; Escudie, Mathilde; Stacey, Alastair; Ganesan, Kumaravelu; Fox, Kate; Ahnood, Arman; Apollo, Nicholas; Kua, Dunstan; Lee, Aaron; McGowan, Ceara; Saunders, Alexia; Burns, Owen; Nayagam, David; Williams, Richard; Garrett, David; Meffin, Hamish; Prawer, Stephen
    As the field of biomedical implants matures the functionality of implants is rapidly increasing. In the field of neural prostheses this is particularly apparent as researchers strive to build devices that interact with highly complex neural systems such as vision, hearing, touch and movement. A retinal implant, for example, is a highly complex device and the surgery, training and rehabilitation requirements involved in deploying such devices are extensive. Ideally, such devices will be implanted only once and will continue to function effectively for the lifetime of the patient. The first and most pivotal factor that determines device longevity is the encapsulation that separates the sensitive electronics of the device from the biological environment. This paper describes the realisation of a free standing device encapsulation made from diamond, the most impervious, long lasting and biochemically inert material known. A process of laser micro-machining and brazing is described detailing the fabrication of hermetic electrical feedthroughs and laser weldable seams using a 96.4% gold active braze alloy, another material renowned for biochemical longevity. Accelerated ageing of the braze alloy, feedthroughs and hermetic capsules yielded no evidence of corrosion and no loss of hermeticity. Samples of the gold braze implanted for 15 weeks, in vivo, caused minimal histopathological reaction and results were comparable to those obtained from medical grade silicone controls. The work described represents a first account of a free standing, fully functional hermetic diamond encapsulation for biomedical implants, enabled by gold active alloy brazing and laser micro-machining.
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    In vivo biocompatibility of boron doped and nitrogen included conductive-diamond for use in medical implants
    (John Wiley & Sons Inc, 2015-01) Garrett, David; Saunders, Alexia; McGowan, Ceara; Specks, Joscha; Ganesan, Kumaravelu; Meffin, Hamish; Williams, Richard; Nayagam, David
    Recently, there has been interest in investigating diamond as a material for use in biomedical implants. Diamond can be rendered electrically conducting by doping with boron or nitrogen. This has led to inclusion of boron doped and nitrogen included diamond elements as electrodes and/or feedthroughs for medical implants. As these conductive device elements are not encapsulated, there is a need to establish their clinical safety for use in implants. This article compares the biocompatibility of electrically conducting boron doped diamond (BDD) and nitrogen included diamond films and electrically insulating poly crystalline diamond films against a silicone negative control and a BDD sample treated with stannous octoate as a positive control. Samples were surgically implanted into the back muscle of a guinea pig for a period of 4-15 weeks, excised and the implant site sectioned and submitted for histological analysis. All forms of diamond exhibited a similar or lower thickness of fibrotic tissue encapsulating compared to the silicone negative control samples. All forms of diamond exhibited similar or lower levels of acute, chronic inflammatory, and foreign body responses compared to the silicone negative control indicating that the materials are well tolerated in vivo. (c) 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2015.
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    In vivo biocompatibility of boron doped and nitrogen included conductive-diamond for use in medical implants
    (Wiley Online Library, 2015-01-21) Garrett, David; Saunders, Alexia; McGowan, Ceara; Specks, Joshua; Ganesan, Kumaravelu; Meffin, Hamish; Williams, Richard; Nayagam, David
    Recently, there has been interest in investigating diamond as a material for use in biomedical implants. Diamond can be rendered electrically conducting by doping with boron or nitrogen. This has led to inclusion of boron doped and nitrogen included diamond elements as electrodes and/or feedthroughs for medical implants. As these conductive device elements are not encapsulated, there is a need to establish their clinical safety for use in implants. This article compares the biocompatibility of electrically conducting boron doped diamond (BDD) and nitrogen included diamond films and electrically insulating poly crystalline diamond films against a silicone negative control and a BDD sample treated with stannous octoate as a positive control. Samples were surgically implanted into the back muscle of a guinea pig for a period of 4-15 weeks, excised and the implant site sectioned and submitted for histological analysis. All forms of diamond exhibited a similar or lower thickness of fibrotic tissue encapsulating compared to the silicone negative control samples. All forms of diamond exhibited similar or lower levels of acute, chronic inflammatory, and foreign body responses compared to the silicone negative control indicating that the materials are well tolerated in vivo.
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    In Vivo Feasibility of Epiretinal Stimulation Using Ultrananocrystalline Diamond 1 Electrodes
    (IOP Publishing, 2020-07) Shivdasani, Mohit; Evans, Mihailo; Burns, Owen; Yeoh, Jonathon; Allen, Penelope; Nayagam, David; Villalobos, Joel; Abbott, Carla; Luu, Chi; Opie, Nicholas; Sabu, Anu; Saunders, Alexia; McPhedran, Michelle; Cardamone, Lisa; McGowan, Ceara; Maxim, Vanessa; Williams, Richard; Fox, Kate; Cicione, Rosemary; Garrett, David; Ahnood, Arman; Ganesan, Kumaravelu; Meffin, Hamish; Burkitt, Anthony; Prawer, Steven; Williams, Chris; Shepherd, Robert
    PURPOSE: Due to their increased proximity to retinal ganglion cells (RGCs), epiretinal visual prostheses present the opportunity for eliciting phosphenes with low thresholds through direct RGC activation. This study characterised the in vivo performance of a novel prototype monolithic epiretinal prosthesis, containing Nitrogen incorporated ultrananocrystalline (N-UNCD) diamond electrodes. METHODS: A prototype implant containing up to twenty-five 120×120 µm N-UNCD electrodes was implanted into 16 anaesthetised cats and attached to the retina either using a single tack or via magnetic coupling with a suprachoroidally placed magnet. Multiunit responses to retinal stimulation using charge-balanced biphasic current pulses were recorded acutely in the visual cortex using a multichannel planar array. Several stimulus parameters were varied including; the stimulating electrode, stimulus polarity, phase duration, return configuration and the number of electrodes stimulated simultaneously. RESULTS: The rigid nature of the device and its form factor necessitated complex surgical procedures. Surgeries were considered successful in 10/16 animals and cortical responses to single electrode stimulation obtained in 8 animals. Clinical imaging and histological outcomes showed severe retinal trauma caused by the device in-situ in many instances. Cortical measures were found to significantly depend on the surgical outcomes of individual experiments, phase duration, return configuration and the number of electrodes stimulated simultaneously, but not stimulus polarity. Cortical thresholds were also found to increase over time within an experiment. CONCLUSIONS: The study successfully demonstrated that an epiretinal prosthesis containing diamond electrodes could produce cortical activity with high precision, albeit only in a small number of cases. Both surgical approaches were highly challenging in terms of reliable and consistent attachment to and stabilisation against the retina, and often resulted in severe retinal trauma. There are key challenges (device form factor and attachment technique) to be resolved for such a device to progress towards clinical application, as current surgical techniques are unable to address these issues.
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    Safety and efficacy of explanting or replacing suprachoroidal electrode arrays in a feline model
    (John Wiley and Sons, 2015-04) Leung, Ronald; Nayagam, David; Williams, Richard; Allen, Penelope; Salinas-La Rosa, Cesar; Shivdasani, Mohit; Ayton, Lauren; Basa, Meri; Yeoh, Jonathan; Saunders, Alexia; Shepherd, Robert; Williams, Chris
    BACKGROUND: A key requirement for retinal prostheses is the ability for safe removal or replacement. We examined whether suprachoroidal electrode arrays can be removed or replaced after implantation. METHODS: Suprachoroidal electrode arrays were unilaterally implanted into 13 adult felines. After 1 month, arrays were surgically explanted (n = 6), replaced (n = 5) or undisturbed (n = 2). The retina was assessed periodically using fundus photography and optical coherence tomography. Three months after the initial implantation, the function of replaced or undisturbed arrays was assessed by measuring the responses of the visual cortex to retinal electrical stimulation. The histopathology of tissues surrounding the implant was examined. RESULTS: Array explantation or replacement was successful in all cases. Fundus photography showed localized disruption to the tapetum lucidum near the implant's tip in seven subjects following implantation. Although optical coherence tomography showed localized retinal changes, there were no widespread statistically significant differences in the thickness of the retinal layers or choroid. The distance between the electrodes and retina increased after device replacement but returned to control values within eight weeks (P < 0.03). Staphylomas developed near the scleral wound in five animals after device explantation. Device replacement did not alter the cortical evoked potential threshold. Histopathology showed localized outer nuclear layer thinning, tapetal disruption and pseudo-rosette formation, but the overall retinal morphology was preserved. CONCLUSIONS: It is feasible to remove or replace conformable medical grade silicone electrode arrays implanted suprachoroidally. The scleral wound requires careful closure to minimize the risk of staphylomas.