Restoring Upper Extremity Mobility through Functional Neuromuscular Stimulation using Macro Sieve Electrodes

The last decade has seen the advent of brain computer interfaces able to extract precise motor intentions from cortical activity of human subjects. It is possible to convert captured motor intentions into movement through coordinated, artificially induced, neuromuscular stimulation using peripheral nerve interfaces. Our lab has developed and tested a new type of peripheral nerve electrode called the Macro-Sieve electrode which exhibits excellent chronic stability and recruitment selectivity. Work presented in this thesis uses computational modeling to study the interaction between Macro-Sieve electrodes and regenerated peripheral nerves. It provides a detailed understanding of how regenerated fibers, both on an individual level and on a population level respond differently to functional electrical stimulation compared to non-disrupted axons. Despite significant efforts devoted to developing novel regenerative peripheral interfaces, the degree of spatial clustering between functionally related fibers in regenerated nerves is poorly understood. In this thesis, bioelectrical modeling is also used to predict the degree of topographical organization in regenerated nerve trunks. In addition, theoretical limits of the recruitment selectivity of the device is explored and a set of optimal stimulation paradigms used to selectively activate fibers in different regions of the nerve are determined. Finally, the bioelectrical model of the interface/nerve is integrated with a biomechanical model of the macaque upper limb to study the feasibility of using macro-sieve electrodes to achieve upper limb mobilization

Regenerated sciatic nerve axons stimulated through a chronically implanted macro-sieve electrode

Sieve electrodes provide a chronic interface for stimulating peripheral nerve axons. Yet, successful utilization requires robust axonal regeneration through the implanted electrode. The present study determined the effect of large transit zones in enhancing axonal regeneration and revealed an intimate neural interface with an implanted sieve electrode. Fabrication of the polyimide sieve electrodes employed sacrificial photolithography. The manufactured macro-sieve electrode (MSE) contained nine large transit zones with areas of ~0.285 mm2 surrounded by eight Pt-Ir metallized electrode sites. Prior to implantation, saline or glial derived neurotropic factor (GDNF) was injected into nerve guidance silicone-conduits with or without a MSE. The MSE assembly or a nerve guidance conduit was implanted between transected ends of the sciatic nerve in adult male Lewis rats. At 3 months’ post-operation, fiber counts were similar through both implant types. Likewise, stimulation of nerves regenerated through a MSE or an open silicone conduit evoked comparable muscle forces. These results showed that nerve regeneration was comparable through MSE transit zones and an open conduit. GDNF had a minimal positive effect on the quality and morphology of fibers regenerating through the MSE; thus, the MSE may reduce reliance on GDNF to augment axonal regeneration. Selective stimulation of several individual muscles was achieved through monopolar stimulation of individual electrodes sites suggesting that the MSE might be an optimal platform for functional neuromuscular stimulation

A fully implantable pacemaker for the mouse: from battery to wireless power.

Animal models have become a popular platform for the investigation of the molecular and systemic mechanisms of pathological cardiovascular physiology. Chronic pacing studies with implantable pacemakers in large animals have led to useful models of heart failure and atrial fibrillation. Unfortunately, molecular and genetic studies in these large animal models are often prohibitively expensive or not available. Conversely, the mouse is an excellent species for studying molecular mechanisms of cardiovascular disease through genetic engineering. However, the large size of available pacemakers does not lend itself to chronic pacing in mice. Here, we present the design for a novel, fully implantable wireless-powered pacemaker for mice capable of long-term (>30 days) pacing. This design is compared to a traditional battery-powered pacemaker to demonstrate critical advantages achieved through wireless inductive power transfer and control. Battery-powered and wireless-powered pacemakers were fabricated from standard electronic components in our laboratory. Mice (n = 24) were implanted with endocardial, battery-powered devices (n = 14) and epicardial, wireless-powered devices (n = 10). Wireless-powered devices were associated with reduced implant mortality and more reliable device function compared to battery-powered devices. Eight of 14 (57.1%) mice implanted with battery-powered pacemakers died following device implantation compared to 1 of 10 (10%) mice implanted with wireless-powered pacemakers. Moreover, device function was achieved for 30 days with the wireless-powered device compared to 6 days with the battery-powered device. The wireless-powered pacemaker system presented herein will allow electrophysiology studies in numerous genetically engineered mouse models as well as rapid pacing-induced heart failure and atrial arrhythmia in mice

Bench top and <i>in vivo</i> testing of battery powered pacemaker.

<p>(a) Current (blue) and voltage (gray) traces from the pacing catheter. (b) Frequency Response Analysis of distal and proximal pacing catheter electrodes (c) Lead II ECG recording in a mouse heart during sinus rhythm and right ventricular pacing by the battery-powered pacemaker over 5 days.</p

Assembly process of wireless powered pacemaker.

<p>(a) Platinum wire is attached to the circuit board, wound together, and coiled with a 0.5 cc syringe. (b) A bead of Silastic is placed on a piece of parafilm(1). The device is placed on the bead(2), coated with an additional layer of Silastic(3), and topped with a piece of gas permeable film(4). (c) Final product. (d) Artistic rendering of external transmitter interacting with abdominally implanted receiver in mouse.</p

<i>In vivo</i> testing of wireless pacemaker.

<p>(a) Lead II ECG during normal sinus rhythm (top) and during LV apical pacing (bottom). (b) Pacing pulse width threshold of wireless device over 30 days for all mice with stable capture. Solid red line shows linear regression on mean pulse width thresholds. Dashed black lines show 95% confidence interval bounds for the regression.</p

Comparison of battery-powered and wireless-powered pacemakers.

<p>Comparison of battery-powered and wireless-powered pacemakers.</p

Layout of the wireless-powered pacemaker.

<p>(a) Circuit layout of transmitter (top) and receiver (bottom). (b) Pulsed input into transmitter from pulse generator. (c) Output from transmitter. (d) Uncapped output from receiver. (e) Capped output from receiver. (f) Receiver output decreases minimally up to 5 cm from the transmitter coil. See text for further details.</p

Parts list for wireless transmitter and receiver circuits.

<p>Parts list for wireless transmitter and receiver circuits.</p

Channeled Autonomy: The Joint Effects of Autonomy and Feedback on Team Performance Through Organizational Goal Clarity

Past research suggests that autonomy has highly variable effects on team performance, and that one explanation for this pattern of findings is that autonomous teams fall into a state of disorder where they lack clarity regarding the goals of the broader organization. Following this perspective, the authors develop a model proposing that performance feedback coupled with high autonomy enables teams to have greater clarity of the organization???s goals, which in turn increases team performance. This model was tested on 110 teams in a defense industry manufacturing firm in South Korea using mediated-moderation techniques. Results indicate that highly autonomous teams that receive a high degree of performance feedback outperform other teams because of their heightened level of organizational goal clarity. In contrast, highly autonomous teams that receive low levels of feedback perform at the lowest levels compared to other teams because of a lack of organizational goal clarity. The authors discuss the implications of these findings for theory, research, and practice.clos