Objective A neural interface system has been developed that consists of an implantable stimulator/recorder can with a 15-electrode lead that trifurcates into three bundles of five individual wire longitudinal intrafascicular electrodes. This work evaluated the mechanical fatigue resistance of the branched lead and distributed electrode system under conditions designed to mimic anticipated strain profiles that would be observed after implantation in the human upper arm. Approach Custom test setups and procedures were developed to apply linear or angular strain at four critical stress riser points on the lead and electrode system. Each test was performed to evaluate fatigue under a high repetition/low amplitude paradigm designed to test the effects of arm movement on the leads during activities such as walking, or under a low repetition/high amplitude paradigm designed to test the effects of more strenuous upper arm activities. The tests were performed on representative samples of the implantable lead system for human use. The specimens were fabricated using procedures equivalent to those that will be used during production of human-use implants. Electrical and visual inspections of all test specimens were performed before and after the testing procedures to assess lead integrity. Main Results Measurements obtained before and after applying repetitive strain indicated that all test specimens retained electrical continuity and that electrical impedance remained well below pre-specified thresholds for detection of breakage. Visual inspection under a microscope at 10X magnification did not reveal any signs of damage to the wires or silicone sheathing at the stress riser points. Significance These results demonstrate that the branched lead of this implantable neural interface system has sufficient mechanical fatigue resistance to withstand strain profiles anticipated when the system is implanted in an arm. The novel test setups and paradigms may be useful in testing other lead systems.

Current myoelectric prosthetic limbs are limited in their ability to provide direct sensory feedback to users, which increases attentional demands and reliance on visual cues. Vibrotactile sensory substitution (VSS), which can be used to provide sensory feedback in a non-invasive manner has demonstrated some improvement in myoelectric hand control. In this work, we developed and tested two VSS configurations: one with a single burst-rate modulated actuator and another with a spatially distributed array of five coin tactors. We performed a direct comparative assessment of these two VSS configurations with able-bodied subjects to investigate sensory perception, myoelectric control of grasp force and hand aperture with a prosthesis, and the effects of interface compliance. Six subjects completed a sensory perception experiment under a stimulation only paradigm; sixteen subjects completed experiments to compare VSS performance on perception and graded myoelectric control during grasp force and hand aperture tasks; and ten subjects completed experiments to investigate the effect of mechanical compliance of the myoelectric hand on the ability to control grasp force. Results indicated that sensory perception of vibrotactile feedback was not different for the two VSS configurations in the absence of active myoelectric control, but it was better with feedback from the coin tactor array than with the single actuator during myoelectric control of grasp force. Graded myoelectric control of grasp force and hand aperture was better with feedback from the coin tactor array than with the single actuator, and myoelectric control of grasp force was improved with a compliant grasp interface. Further investigations with VSS should focus on the use of coin tactor arrays by subjects with amputation in real-world settings and on improving control of grasp force by increasing the mechanical compliance of the hand.

Objective. Lack of sensation from a hand or prosthesis can result in substantial functional deficits. Surface electrical stimulation of the peripheral nerves is a promising non-invasive approach to restore lost sensory function. However, the utility of standard surface stimulation methods has been hampered by localized discomfort caused by unintended activation of afferents near the electrodes and limited ability to specifically target underlying neural tissue. The objectives of this work were to develop and evaluate a novel channel-hopping interleaved pulse scheduling (CHIPS) strategy for surface stimulation that is designed to activate deep nerves while reducing activation of fibers near the electrodes. Approach. The median nerve of able-bodied subjects was activated by up to two surface stimulating electrode pairs placed around their right wrist. Subjects received biphasic current pulses either from one electrode pair at a time (single-channel), or interleaved between two electrode pairs (multi-channel). Percept thresholds were characterized for five pulse durations under each approach, and psychophysical questionnaires were used to interrogate the perceived modality, quality and location of evoked sensations. Main results. Stimulation with CHIPS elicited enhanced tactile percepts that were distally referred, while avoiding the distracting sensations and discomfort associated with localized charge densities. These effects were reduced after introduction of large delays between interleaved pulses. Significance. These findings demonstrate that our pulse scheduling strategy can selectively elicit referred sensations that are comfortable, thus overcoming the primary limitations of standard surface stimulation methods. Implementation of this strategy with an array of spatially distributed electrodes may allow for rapid and effective stimulation fitting. The ability to elicit comfortable and referred tactile percepts may enable the use of this neurostimulation strategy to provide meaningful and intuitive feedback from a prosthesis, enhance tactile feedback after sensory loss secondary to nerve damage, and deliver non-invasive stimulation therapies to treat various pain conditions.

Clinical risk factors (CRFs) are established predictors of fracture events. However, the influence of individual CRFs on trabecular mechanical fragility is still a subject of debate. In this study, we aimed to assess differences, adjusted for CRFs, between bone macrostructural parameters measured in ex-vivo specimens from hip fragility fracture patients and osteoarthritis patients, and to determine whether individual CRFs could predict trabecular bone mechanical behavior in hip fragility fractures. Additionally, we also looked for associations between the 10-year risk of major and hip fracture calculated by FRAX and trabecular bone mechanical performance. In this case-control study, a group of fragility fracture patients were compared with a group of osteoarthritis patients, both having undergone hip replacement surgery. A clinical protocol was applied in order to collect CRFs [body mass index (BMI), prior fragility fracture, parental history of hip fracture, long-term use of oral glucocorticoids, rheumatoid arthritis, current smoking, alcohol consumption, age and gender]. The 10-year probability of fracture was calculated. Serum bone turnover markers were determined and dual X-ray absorptiometry performed. Femoral head diameter was evaluated and trabecular bone cylinders were drilled for mechanical testing to determine bone strength, stiffness and toughness. We evaluated 40 hip fragility fracture and 52 osteoarthritis patients. Trabecular bone stiffness was significantly lower (p = 0.042) in hip fragility fracture patients when compared to osteoarthritic individuals, adjusted for age, gender and BMI. No other macrostructural parameter was statistically different between the groups. In hip fragility fracture patients, smoking habits (β = -0.403; p = 0.018) and female gender (β = -0.416; p = 0.008) were independently associated with lower stiffness. In addition, smoking was also independently associated with worse trabecular strength (β = -0.323; p = 0.045), and toughness (β = -0.403; p = 0.018). In these patients, the 10-year risk of major (r = -0.550; p = 0.012) and hip fracture (r = -0.513; p = 0.021) calculated using only CRFs was strongly correlated with femoral neck bone mineral density but not with mechanical performance. Our data showed that among fragility fracture patients active smoking is a predictor of worse intrinsic trabecular mechanical performance, and female gender is also independently associated with lower stiffness. In this population, the 10-year risk of fracture using CRFs with different weights only reflects bone mass loss but not trabecular mechanical properties.