Design of a wearable device for conditional neuromodulation of the pudendal nerve

After spinal cord injury, the normal functions of the lower urinary tract may be disrupted. Namely, incontinence and concurrent voiding problems may ensue. The troublesome side effects of the drugs, infection due to catheterisation, and the costs and risks associated with more invasive treatments indicate the need for alternative forms of treatment. The pudendal nerve neuromodulation may provide such an alternative. The unique aspect of this technique is that depending on the stimulus frequency it may result in micturition-like or continence-like reflexes. Also, the stimulus current can be applied trans-rectally, meaning that a minimally-invasive wearable solution may be developed. The major limitation of such a solution is the high level of the required stimulus current to activate the nerve trans-rectally. The efficacy of the trans-rectal neuromodulation of the pudendal may be increased by only applying the stimulus when needed, when employed to tackle incontinence. The electromyogram signal from the external anal sphincter may be used to detect the onset of hyper-reflexive contractions of the bladder. The ability of recording this signal can be readily incorporated in the neuromodulation device due to the proximity of the structures. However, the recording electrodes should be designed for an efficacious and chronic recording. Thus, the main objective of this thesis was to design and optimise the neuromodulation and recording electrodes on the said device. A volume conductor model of such a device in situ was developed and used in tandem with a double layer cable model of nerve fibres to minimise the stimulus current. It was demonstrated that a considerable reduction in the stimulus current may be achieved even when the variations of the nerve trajectory in different individuals are considered. Using computational models and experimental measurements, a recording assembly was identified for an efficacious recording of the electromyogram from the external anal sphincter

Effect of nerve variations on the stimulus current level in a wearable neuromodulator for migraine: A modeling study

Migraine is a socioeconomic burden, whose pharmaceutical and invasive treatment methods may have troublesome side-effects. A wearable neuromodulator targeting frontal nerve branches of trigeminal nerve may provide an effective solution to suppress or treat migraine. Such solutions have had limited efficacies. In this paper, using computational models, the relationship of this lack of efficacy to some neural variations is investigated. The results indicate that due to neuro-anatomic variations, different current levels may be required to achieve a sufficient level of neural stimulation. Thus, an optimized design should consider such variations across the patient group

Electrically pumped silicon waveguide light sources

We report simulations of electrically pumped waveguide emitters in which the emissive layer contains silicon nanoclusters and erbium ions. Plasmonic coupling to metallic or semi-metallic overlayers provides enhancement of the radiative rate of erbium ions, enabling high quantum efficiency emission. Using 2D and 3D finite difference time domain (FDTD) simulations we show that up to 75% of the light emitted from the active layer can be coupled into a nanowire silicon rib waveguide. Our results suggest that such devices, which can readily be fabricated using CMOS processing techniques, pave the way for viable waveguide optical sources to be realized in silicon photonics

Design of sEMG assembly to detect external anal sphincter activity: a proof of concept

Objective: Conditional trans-rectal stimulation of the pudendal nerve could provide a viable solution to treat hyperreflexive bladder in spinal cord injury. A set threshold of the amplitude estimate of the external anal sphincter surface electromyography (sEMG) may be used as the trigger signal. The efficacy of such a device should be tested in a large scale clinical trial. As such a probe should remain in situ for several hours while patients attend to their daily routine, the recording electrodes should be designed to be large enough to maintain good contact while observing design constraints. The objective of this study was to arrive at a design for intra-anal sEMG recording electrodes for the subsequent clinical trials while deriving the possible recording and processing parameters. 
 Approach: Having in mind existing solutions and based on theoretical and anatomical considerations, a set of four multi-electrode probes were designed and developed. These were tested in a healthy subject and the measured sEMG traces were recorded and appropriately processed.
 Main results: It was shown that while comparatively large electrodes record sEMG traces that are not sufficiently correlated with the external anal sphincter contractions, smaller electrodes may not maintain a stable electrode tissue contact. It was shown that 3 mm wide and 1 cm long electrodes with 5 mm inter-electrode spacing, in agreement with Nyquist sampling, placed 1 cm from the orifice may intra-anally record a sEMG trace sufficiently correlated with external anal sphincter activity.
 Significance: The outcome of this study can be used in any biofeedback, treatment or diagnostic application where the activity of the external anal sphincter sEMG should be detected for an extended period of time