Dermal Sensory Regenerative Peripheral Nerve Interface for Reestablishing Sensory Nerve Feedback in Peripheral Afferents in the Rat.

BACKGROUND: Without meaningful, intuitive sensory feedback, even the most advanced myoelectric devices require significant cognitive demand to control. The dermal sensory regenerative peripheral nerve interface (DS-RPNI) is a biological interface designed to establish high-fidelity sensory feedback from prosthetic limbs. METHODS: DS-RPNIs were constructed in rats by securing fascicles of residual sensory peripheral nerves into autologous dermal grafts, with the objectives of confirming regeneration of sensory afferents within DS-RPNIs and establishing the reliability of afferent neural response generation with either mechanical or electrical stimulation. RESULTS: Two months after implantation, DS-RPNIs were healthy and displayed well-vascularized dermis with organized axonal collaterals throughout and no evidence of neuroma. Electrophysiologic signals were recorded proximal from DS-RPNI's sural nerve in response to both mechanical and electrical stimuli and compared with (1) full-thickness skin, (2) deepithelialized skin, and (3) transected sural nerves without DS-RPNI. Mechanical indentation of DS-RPNIs evoked compound sensory nerve action potentials (CSNAPs) that were like those evoked during indentation of full-thickness skin. CSNAP firing rates and waveform amplitudes increased in a graded fashion with increased mechanical indentation. Electrical stimuli delivered to DS-RPNIs reliably elicited CSNAPs at low current thresholds, and CSNAPs gradually increased in amplitude with increasing stimulation current. CONCLUSIONS: These findings suggest that afferent nerve fibers successfully reinnervate DS-RPNIs, and that graded stimuli applied to DS-RPNIs produce proximal sensory afferent responses similar to those evoked from normal skin. This confirmation of graded afferent signal transduction through DS-RPNI neural interfaces validate DS-RPNI's potential role of facilitating sensation in human-machine interfacing. CLINICAL RELEVANCE STATEMENT: The DS-RPNI is a novel biotic-abiotic neural interface that allows for transduction of sensory stimuli into neural signals. It is expected to advance the restoration of natural sensation and development of sensorimotor control in prosthetics.

Providing a sense of touch to prosthetic hands.

Each year, approximately 185,000 Americans suffer the devastating loss of a limb. The effects of upper limb amputations are profound because a person's hands are tools for everyday functioning, expressive communication, and other uniquely human attributes. Despite the advancements in prosthetic technology, current upper limb prostheses are still limited in terms of complex motor control and sensory feedback. Sensory feedback is critical to restoring full functionality to amputated patients because it would relieve the cognitive burden of relying solely on visual input to monitor motor commands and provide tremendous psychological benefits. This article reviews the latest innovations in sensory feedback and argues in favor of peripheral nerve interfaces. First, the authors examine the structure of the peripheral nerve and its importance in the development of a sensory interface. Second, the authors discuss advancements in targeted muscle reinnervation and direct neural stimulation by means of intraneural electrodes. The authors then explore the future of prosthetic sensory feedback using innovative technologies for neural signaling, specifically, the sensory regenerative peripheral nerve interface and optogenetics. These breakthroughs pave the way for the development of a prosthetic limb with the ability to feel.

Material characterization of ex vivo prostate tissue via spherical indentation in the clinic.

BACKGROUND: The mechanical characterization of prostate tissue has not received much attention and is often disconnected from the clinic, where samples are readily attained. METHODS: We developed a spherical indenter for the clinic to generate force-displacement data from ex vivo prostate tissue. Indentation velocity, depth, and sphere diameter, and four means of estimating elastic modulus (EM) were validated. EM was then estimated for 26 prostate specimens obtained via prostatectomy and 6 samples obtained from autopsy. Prostatectomy prostates were evaluated clinically upon digital rectal exam and pathologically post-extirpation. FINDINGS: Whole-mount measurements yielded median EM of 43.2 kPa (SD=59.8 kPa). Once sliced into cross-sections, median EM for stage T2 and T3 glands were 30.9 and 71.0 kPa, respectively, but not significantly different. Furthermore, we compared within-organ EM difference for prostates with (median=46.5 kPa, SD=22.2 kPa) and without (median=31.0 kPa, SD=63.1 kPa) palpable abnormalities. INTERPRETATION: This work finds that diseased prostate tissue is stiffer than normal tissue, stiffness increases with disease severity, and large variability exists between samples, even though disease differences within a prostate are detectable. A further study of late-stage cancers would help to strengthen the findings presented in this work.

Psychophysical Detection of Inclusions with the Bare Finger amidst Softness Differentials.

Softness discrimination and the detection of inclusions are important in surgery and other medical tasks. To better understand how the characteristics of an inclusion (size, depth, hardness) and substrate (stiffness) affect their tactile detection and discrimination with the bare finger, we conducted a psychophysics experiment with eighteen participants. The results indicate that within a more pliant substrate (21 kPa), inclusions of 4 mm diameter (20 mm(3) volume) and greater were consistently detectable (above 75% of the time) but only at a depth of 5 mm. Inclusions embedded in stiffer substrates (82 kPa) had to be twice that volume (5 mm diameter, 40 mm(3) volume) to be detectable at the same rate. To analyze which tactile cues most impact stimulus detectability, we utilized logistic regression and generalized estimating equations. The results indicate that substrate stiffness most contributes to inclusion detectability, while the size, depth, and hardness of the stimulus follow in individual importance, respectively. The results seek to aid in the development of clinical tools and information displays and more accurate virtual haptic environments in discrimination of soft tissue.

Using a prostate exam simulator to decipher palpation techniques that facilitate the detection of abnormalities near clinical limits.

INTRODUCTION: Prostate carcinoma (and other prostate irregularities and abnormalities) is detected in part via the digital rectal examination. Training clinicians to use particular palpation techniques may be one way to improve the rates of detection. METHODS: In an experiment of 34 participants with clinical backgrounds, we used a custom-built simulator to determine whether certain finger palpation techniques improved one's ability to detect abnormalities smaller in size and dispersed as multiples over a volume. The intent was to test abnormality cases of clinical relevance near the limits of size perceptibility (ie, 5-mm diameter). The simulator can present abnormalities in various configurations and record finger movement. To characterize finger movement, four palpation techniques were quantitatively defined (global finger movement, local finger movement, average intentional finger pressure, and dominant intentional finger frequency) to represent the qualitative definitions of other researchers. RESULTS: Participants who used more thorough patterns of global finger movement (V and L) ensured that the entire prostate was searched and detected more abnormalities. A higher magnitude of finger pressure was associated with the detection of smaller abnormalities. The local finger movement of firm pressure with varying intensities was most indicative of success and was required to identify the smallest (5-mm diameter) abnormality. When participants used firm pressure with varying intensities, their dominant intentional finger frequency was about 6 Hz. CONCLUSIONS: The use of certain palpation techniques does enable the detection of smaller and more numerous abnormalities, and we seek to abstract these techniques into a systematic protocol for use in the clinic.

Characterizing the range of simulated prostate abnormalities palpable by digital rectal examination.

BACKGROUND: Although the digital rectal exam (DRE) is a common method of screening for prostate cancer and other abnormalities, the limits of ability to perform this hands-on exam are unknown. Perceptible limits are a function of the size, depth, and hardness of abnormalities within a given prostate stiffness. METHODS: To better understand the perceptible limits of the DRE, we conducted a psychophysical study with 18 participants using a custom-built apparatus to simulate prostate tissue and abnormalities of varying size, depth, and hardness. Utilizing a modified version of the psychophysical method of constant stimuli, we uncovered thresholds of absolute detection and variance in ability between examiners. RESULTS: Within silicone-elastomers that mimic normal prostate tissue (21kPa), abnormalities of 4mm diameter (20mm(3) volume) and greater were consistently detectable (above 75% of the time) but only at a depth of 5mm. Abnormalities located in simulated tissue of greater stiffness (82kPa) had to be twice that volume (5mm diameter, 40mm(3) volume) to be detectable at the same rate. CONCLUSIONS: This study finds that the size and depth of abnormalities most influence detectability, while the relative stiffness between abnormalities and substrate also affects detectability for some size/depth combinations. While limits identified here are obtained for idealized substrates, this work is useful for informing the development of training and allowing clinicians to set expectations on performance.

Augmented, pulsating tactile feedback facilitates simulator training of clinical breast examinations.

Haptic training devices can facilitate tactile skill development by providing repeatable exposures to rare stimuli. Extant haptic training simulator research primarily emphasizes realistic stimuli representation; however, the experiments reported herein suggest that providing augmented feedback can improve training effectiveness, even when the feedback is not natural. A novel clinical breast examination training device uses inflated balloons embedded in silicone to simulate breast lumps. Oscillating the balloon water pressure makes the lumps pulsate. The pulsating lumps are easier to detect than the static lumps used in current simulators, and this manipulation seems to effectively introduce trainees to small, deep lumps that are initially difficult to perceive. A study of 48 medical students indicates that training with the dynamic breast model increased the number of lumps detected, F(1, 47) = 9.34, p = .004, decreased the number of false positives, F(1, 47) = 5.78, p = .020, and improved intersimulator skill transfer, F(1, 47) = 26.56, p < .001. The results suggest that at least in this case, augmented, tactile feedback increases training effectiveness, despite the fact that the feedback does not attempt to mimic any physical phenomenon present in the natural stimulus. Applications of this research include training techniques and tools for improved detection of palpable cancers.

Effectiveness of a dynamic breast examination training model to improve clinical breast examination (CBE) skills.

Despite the potential utility of clinical breast examination (CBE), doctors' palpation skills are often inadequate and difficult to train. CBE sensitivity ranges from 39-59%, in part because current training does not effectively teach tactile skills. To address CBE training limitations, we developed a breast examination training model with 15 dynamically controlled lumps, set to desired hardness within underlying rib and muscle structures, in a silicone breast. In an experiment of 48 medical students, training with the dynamic model increased lump detection by 1.35 lumps compared to 0.60 lumps for a traditional breast model (P=0.008), reduced false positives by -0.70 lumps compared to +0.42 lumps (P=0.0277), and demonstrated skill transfer with a 1.17 lump detection improvement on the traditional device compared to only a 0.17 lump detection improvement by traditional device trainees on the dynamic device (P<0.001). Findings demonstrate the advantage of the dynamic model over conventional models in training CBE tactile skills.