Biomedical Engineering - Research Publications

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    Wearable Transmitter Coil Design for Inductive Wireless Power Transfer to Implantable Devices.
    Tai, Y-D ; Widdicombe, B ; Unnithan, RR ; Grayden, DB ; John, SE (IEEE, 2023-07)
    Wireless endovascular sensors and stimulators are emerging biomedical technologies for applications such as endovascular pressure monitoring, hyperthermia, and neural stimulations. Recently, coil-shaped stents have been proposed for inductive power transfer to endovascular devices using the stent as a receiver. However, less work has been done on the external transmitter components, so the maximum power transferable remains unknown. In this work, we design and evaluate a wearable transmitter coil that allows 50 mW power transfer in simulation.Clinical Relevance-This allows more accurate measurements and precise control of endovascular devices.
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    Computational Fluid Dynamics of Stent-Mounted Neural Interfaces in an Idealized Cerebral Venous Sinus.
    Qi, W ; Ooi, A ; Grayden, DB ; John, SE (IEEE, 2023-07)
    Hemodynamic changes in stented blood vessels play a critical role in stent-associated complications. The majority of work on the hemodynamics of stented blood vessels has focused on coronary arteries but not cerebral venous sinuses. With the emergence of endovascular electrophysiology, there is a growing interest in stenting cerebral blood vessels. We investigated the hemodynamic impact of a stent-mounted neural interface inside the cerebral venous sinus. The stent was virtually implanted into an idealized superior sagittal sinus (SSS) model. Local venous blood flow was simulated. Results showed that blood flow was altered by the stent, generating recirculation and low wall shear stress (WSS) around the device. However, the effect of the electrodes on blood flow was not prominent due to their small size. This is an early exploration of the hemodynamics of a stent-mounted neural interface. Future work will shed light on the key factors that influence blood flow and stenting outcomes.Clinical Relevance-The study investigates blood flow through a stent-based electrode array inside the cerebral venous sinus. The hemodynamic impact of the stent can provide insight into neointimal growth and thrombus formation.
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    Establishing the Calibration Curve of a Compressive Ophthalmodynamometry Device.
    Kaplan, MA ; Bui, BV ; Ayton, LN ; Nguyen, B ; Grayden, DB ; John, S (IEEE, 2023-07)
    The relationship between externally applied force and intraocular pressure was determined using an ex-vivo porcine eye model (N=9). Eyes were indented through the sclera with a convex ophthalmodynamometry head (ODM). Intraocular pressure and ophthalmodynamometric force were simultaneously recorded to establish a calibration curve of this indenter head. A calibration coefficient of 0.140 ± 0.009 mmHg/mN was established and was shown to be highly linear (r = 0.998 ± 0.002). Repeat application of ODM resulted in a 0.010 ± 0.002 mmHg/mN increase to the calibration coefficient.Clinical Relevance- ODM has been highlighted as a potential method of non-invasively estimating intracranial pressure. This study provides relevant data for the practical performance of ODM with similar compressive devices.
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    Predictive Shared Control of Robotic Arms Using Simulated Brain-Computer Interface Inputs
    Kokorin, K ; Mu, J ; John, SE ; Grayden, DB (IEEE, 2023)
    Low decoding accuracy makes brain-computer interface (BCI) control of a robotic arm difficult. Shared control (SC) can overcome limitations of a BCI by leveraging external sensor data and generating commands to assist the user. Our study explored whether reaching targets with a robot end-effector was easier using SC rather than direct control (DC). We simulated a motor imagery BCI using a joystick with noise introduced to explicitly control interface accuracy to be 65% or 79%. Compared to DC, our prediction-based implementation of SC led to a significant reduction in the trajectory length of successful reaches for 4 (3) out of 5 targets using the 65% (79%) accurate interface, with failure rates being equivalent to DC for 2 (1) out of 5 targets. Therefore, this implementation of SC is likely to improve reaching efficiency but at the cost of more failures. Additionally, the NASA Task Load Index results suggest SC reduced user workload.Clinical relevance-Shared control can minimise the impact of BCI decoder errors on robot motion, making robotic arm control using noninvasive BCIs more viable.
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    Electrochemistry in a Two- or Three-Electrode Configuration to Understand Monopolar or Bipolar Configurations of Platinum Bionic Implants
    Harris, AR ; Grayden, DB ; John, SE (MDPI, 2023-04)
    Electrodes are used in vivo for chemical sensing, electrophysiological recording, and stimulation of tissue. The electrode configuration used in vivo is often optimised for a specific anatomy and biological or clinical outcomes, not electrochemical performance. Electrode materials and geometries are constrained by biostability and biocompatibility issues and may be required to function clinically for decades. We performed benchtop electrochemistry, with changes in reference electrode, smaller counter-electrode sizes, and three- or two-electrode configurations. We detail the effects different electrode configurations have on typical electroanalytical techniques used on implanted electrodes. Changes in reference electrode required correction by application of an offset potential. In a two-electrode configuration with similar working and reference/counter-electrode sizes, the electrochemical response was dictated by the rate-limiting charge transfer step at either electrode. This could invalidate calibration curves, standard analytical methods, and equations, and prevent use of commercial simulation software. We provide methods for determining if an electrode configuration is affecting the in vivo electrochemical response. We recommend sufficient details be provided in experimental sections on electronics, electrode configuration, and their calibration to justify results and discussion. In conclusion, the experimental limitations of performing in vivo electrochemistry may dictate what types of measurements and analyses are possible, such as obtaining relative rather than absolute measurements.
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    Computational modeling of endovascular peripheral nerve stimulation using a stent-mounted electrode array
    Liu, JY ; Grayden, DB ; Keast, JR ; John, SE (IOP Publishing Ltd, 2023-06-01)
    Objective.Endovascular neuromodulation has attracted substantial interest in recent years as a minimally invasive approach to treat neurological disorders. In this study, we investigated with a computational model the feasibility of stimulating peripheral nerves with an endovascular stent-mounted electrode array.Approach.Anatomically realistic FEM models were constructed for the pudendal and vagal neurovascular bundles. The electromagnetic fields generated from electrical stimuli were computed using Sim4Life NEURON models to predict dynamic axonal responses.Main results.The models predict that the stimulation thresholds of the endovascular stent-electrode array configurations tested are comparable to that of ring electrodes and are dependent on the inter-electrode distance and orientation of the device. Arranging multiple electrodes along the longitudinal axis of the nerve lowers surface charge density without sacrificing axon recruitment, whereas arranging electrodes along the circumference of the blood vessel reduces the risk of misalignment but lowers axon recruitment.Significance.Overall, this study predicts that the endovascular stent-electrode array is a feasible stimulation option for peripheral nerves, and the electrode array can be flexibly optimized to achieve the lowest stimulation threshold.
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    Vascular remodeling in sheep implanted with endovascular neural interface
    John, SE ; Donegan, S ; Scordas, TC ; Qi, W ; Sharma, P ; Liyanage, K ; Wilson, S ; Birchall, I ; Ooi, A ; Oxley, TJ ; May, CN ; Grayden, DB ; Opie, NL (IOP Publishing Ltd, 2022-10-01)
    Objective.The aim of this work was to assess vascular remodeling after the placement of an endovascular neural interface (ENI) in the superior sagittal sinus (SSS) of sheep. We also assessed the efficacy of neural recording using an ENI.Approach.The study used histological analysis to assess the composition of the foreign body response. Micro-CT images were analyzed to assess the profiles of the foreign body response and create a model of a blood vessel. Computational fluid dynamic modeling was performed on a reconstructed blood vessel to evaluate the blood flow within the vessel. Recording of brain activity in sheep was used to evaluate efficacy of neural recordings.Main results.Histological analysis showed accumulated extracellular matrix material in and around the implanted ENI. The extracellular matrix contained numerous macrophages, foreign body giant cells, and new vascular channels lined by endothelium. Image analysis of CT slices demonstrated an uneven narrowing of the SSS lumen proportional to the stent material within the blood vessel. However, the foreign body response did not occlude blood flow. The ENI was able to record epileptiform spiking activity with distinct spike morphologies.Significance. This is the first study to show high-resolution tissue profiles, the histological response to an implanted ENI and blood flow dynamic modeling based on blood vessels implanted with an ENI. The results from this study can be used to guide surgical planning and future ENI designs; stent oversizing parameters to blood vessel diameter should be considered to minimize detrimental vascular remodeling.
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    Longwave infrared multispectral image sensor system using aluminum-germanium plasmonic filter arrays
    Shaik, NEK ; Widdicombe, B ; Sun, D ; John, SEE ; Ryu, D ; Nirmalathas, A ; Unnithan, RRR (TSINGHUA UNIV PRESS, 2023-07)
    Abstract A multispectral camera records image data in various wavelengths across the electromagnetic spectrum to acquire additional information that a conventional camera fails to capture. With the advent of high-resolution image sensors and color filter technologies, multispectral imagers in the visible wavelengths have become popular with increasing commercial viability in the last decade. However, multispectral imaging in longwave infrared (LWIR, 8–14 μm) is still an emerging area due to the limited availability of optical materials, filter technologies, and high-resolution sensors. Images from LWIR multispectral cameras can capture emission spectra of objects to extract additional information that a human eye fails to capture and thus have important applications in precision agriculture, forestry, medicine, and object identification. In this work, we experimentally demonstrate an LWIR multispectral image sensor with three wavelength bands using optical elements made of an aluminum (Al)-based plasmonic filter array sandwiched in germanium (Ge). To realize the multispectral sensor, the filter arrays are then integrated into a three-dimensional (3D) printed wheel stacked on a low-resolution monochrome thermal sensor. Our prototype device is calibrated using a blackbody and its thermal output has been enhanced with computer vision methods. By applying a state-of-the-art deep learning method, we have also reconstructed multispectral images to a better spatial resolution. Scientifically, our work demonstrates a versatile spectral thermography technique for detecting target signatures in the LWIR range and other advanced spectral analyses.
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    Non-Invasive Measurement of Intracranial Pressure Through Application of Venous Ophthalmodynamometry.
    Lo, L ; Zhao, D ; Ayton, L ; Grayden, D ; Bui, B ; Morokoff, A ; John, S (IEEE, 2021-11)
    Non-invasive intracranial pressure (ICP) monitoring is possible using venous ophthalmodynamometry to observe a pulsation in retinal blood vessels when intraocular pressure (IOP) exceeds ICP. Here, we identify features in the eye - optic disc and retinal blood vessel locations - and identify pulsation in large retinal blood vessels. The relationship between force and the magnitude of pulsation is used to estimate ICP when force is applied to the eye to gradually increase IOP over time. This approach yields 77% accuracy in automatically observing vessel pulsation.Clinical Relevance - Non-invasive ICP monitoring is desirable to improve patient outcome by reducing potential trauma and complications associated with invasive assessment with intracranial sensors or lumbar puncture.
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    Enhancing student learning through trans-disciplinary project-based assessment in bioengineering
    Lam, L ; Cochrane, T ; Rajagopal, V ; Davey, K ; John, S (Auckland University of Technology (AUT) Library, 2021)
    Pecha Kucha presentation for the SoTEL 2021 Symposium from the Bionic Limb project team at the University of Melbourne. https://sotel.nz