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Transcutaneous electrical nerve stimulation (TENS) setup. (a) schematic representation of transcutaneous electrical nerve stimulation in the context of upper limb sensory restitution. This figure schematically illustrates how an electrode placed on the skin can generate a voltage field within the residual forearm's soft tissue. By placing the electrodes in the appropriate positions, the voltage field can elicit referred and clear sensations from the missing hand, corresponding to median and ulnar nerve innervations, as shown in transparent green and red. This allows for a certain amount of selectivity in the elicited response. (b) shows the exact electrode placements for each of the four subjects. The stimulation parameters (fixed amplitude, range of pulse widths) are also shown. The positions of the electrodes were patient specific.
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According to amputees, sensory feedback is amongst the most important features lacking from commercial prostheses. Although restoration of touch by means of implantable neural interfaces has been achieved, these approaches require surgical interventions, and their long-term usability still needs to be fully investigated. Here, we developed a non-in...
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Context 1
... placing electrodes on the skin (PALS neurostimulation electrodes, Axelgaard, US) in specific areas where the underlying nervous structures are close to the surface of the skin and easily accessible, it is possible to elicit activation of hand afferents, leading mainly to a paresthesia reported over the phantom limb (Fig. 8a). Initially the stimulating and return electrodes were round with a radius of 2.5 cm. In some cases (Subjects 1, 3 and 4), the round stimulation electrodes were cut with scissors to a more oval shape, which resulted in a smaller contact surface with the skin. Figure 8b shows the precise electrode positioning used for each of the four ...
Context 2
... some cases (Subjects 1, 3 and 4), the round stimulation electrodes were cut with scissors to a more oval shape, which resulted in a smaller contact surface with the skin. Figure 8b shows the precise electrode positioning used for each of the four subjects. The electrode placement and stimulation parameters were calibrated during an initial extensive exploration phase. ...
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Tactile sensory feedback would make a significant contribution to the state-of-the-art prosthetic hands for achieving dexterous manipulation over objects. Phantom finger sensation, also called referred sensation of lost fingers, can be noninvasively evoked by transcutaneous electrical nerve stimulation (TENS) of the phantom finger territories (PFTs...
Multimodal sensory feedback from upper-limb prostheses can increase their function and usability. Here we show that intuitive thermal perceptions during cold-object grasping with a prosthesis can be restored in a phantom hand through targeted nerve stimulation via a wearable thin-film thermoelectric device with high cooling power density and speed....
Objective:
Evoked tactile sensation (ETS) elicited by transcutaneous electrical nerve stimulation (TENS) is promising to convey digit-specific sensory information to amputees naturally and non-invasively. Fitting ETS-based sensory feedback to amputees entails customizing coding of multiple sensory information for each stimulation site. This study...
The restoration of sensory feedback in amputees plays a fundamental role in the prosthesis control and in the communication on the afferent channel between hand and brain. The literature shows that transcutaneous electrical nerve stimulation (TENS) can be a promising non-invasive technique to elicit sensory feedback in amputees, especially in the l...
Upper limb amputation severely affects the quality of life of individuals. Therefore, developing closed-loop upper-limb prostheses would enhance the sensory-motor capabilities of the prosthetic user. Considering design priorities based on user needs, the restoration of sensory feedback is one of the most desired features. This study focuses on empl...
Citations
... Amputation may eventually be necessary for some patients. One of the main types of prostheses used to help amputees regain limb function is the myoelectric prosthesis, which uses surface electrodes to collect nerve signals and control the movement of the prosthesis by sending cortical motor signals to the motor nerve of the limb stump according to the needs of the patient [1][2][3][4][5][6]. ...
... To perform the bidirectional control appears feasible to make a compromise to optimally fix both superficial electrodes for sensory feedback and myoelectric sensors on the residual arm of the amputee. It is also important to mention that there could be interference between myoelectric signals and electrical stimulation, but windowing approaches [43] or filtering methods [61] could use to solve this aspect. The feasibility of the closed-loop will be also validated as in the study of Zollo et al. [52], where an algorithm to detect touch and slippage events during manipulation was implemented in the closed-loop control [62]. ...
Upper limb amputation severely affects the quality of life of individuals. Therefore, developing closed-loop upper-limb prostheses would enhance the sensory-motor capabilities of the prosthetic user. Considering design priorities based on user needs, the restoration of sensory feedback is one of the most desired features. This study focuses on employing Transcutaneous Electrical Nerve Stimulation (TENS) as a non-invasive somatotopic stimulation technique for restoring somatic sensations in upper-limb amputees. The aim of this study is to propose two encoding strategies to elicit force and slippage sensations in transradial amputees. The former aims at restoring three different levels of force through a Linear Pulse Amplitude Modulation (LPAM); the latter is devoted to elicit slippage sensations through Apparent Moving Sensation (AMS) by means of three different algorithms, i.e. the Pulse Amplitude Variation (PAV), the Pulse Width Variation (PWV) and Inter-Stimulus Delay Modulation (ISDM). Amputees had to characterize perceived sensations and to perform force and slippage recognition tasks. Results demonstrates that amputees were able to correctly identify low, medium and high levels of force, with an accuracy above the 80% and similarly, to also discriminate the slippage moving direction with a high accuracy above 90%, also highlighting that ISDM would be the most suitable method, among the three AMS strategies to deliver slippage sensations. It was demonstrated for the first time that the developed encoding strategies are effective methods to somatotopically reintroduce in the amputees, by means of TENS, force and slippage sensations.
... Invasive techniques can convey sensory information via direct stimulation of sensory nerves along the afferent pathway at the periphery, spinal cord, and primary somatosensory cortex [10][11][12][13][14]. Surface electrotactile stimulation presents a convenient way to access the sensory nerves but with less intuitive perception and functionality [6], [15], [16], [17]. Somatotopic and quality-matched sensory information may be achieved through mechanical stimulation in specific areas of the stump skin [18], transcutaneous electrical nerve stimulation (TENS) [19], [20] or a cutaneous interface via target reinnervation surgery [21]. However, a somatotopically compatible and reliable non-invasive technique for users of bionic hands is still lacking. ...
... The intensity information in the ETS could be effectively processed by the participants with forearm amputation to recognize compliance of objects regardless of their prior use of a prosthetic hand. The accuracy of participants with ETSbased feedback (90.4%) (Fig. 3D) is comparable with the performance for identification of three different compliance levels with peripheral nerve stimulation at 78.7% [13], transcutaneous electrical nerve stimulation at 60% [20] and spinal cord stimulation at 46% [38]. The median response time of the six participants was 2.37 s, much shorter than 7.91 s observed in identifying two objects of different compliance levels via peripheral nerve stimulation [14]. ...
Sensory feedback provides critical interactive information for the effective use of hand prostheses. Non-invasive neural interfaces allow convenient access to the sensory system, but they communicate a limited amount of sensory information. This study examined a novel approach that leverages a direct and natural sensory afferent pathway, and enables an evoked tactile sensation (ETS) of multiple digits in the projected finger map (PFM) of participants with forearm amputation non-invasively. A bidirectional prosthetic interface was constructed by integrating the non-invasive ETS-based feedback system into a commercial prosthetic hand. The pressure information of five fingers was encoded linearly by the pulse width modulation range of the buzz sensation. We showed that simultaneous perception of multiple digits allowed participants with forearm amputation to identify object length and compliance by using information about contact patterns and force intensity. The ETS enhanced the grasp-and-transport performance of participants with and without prior experience of prosthetic use. The functional test of transport-and-identification further revealed improved execution in classifying object size and compliance using ETS-based feedback. Results demonstrated that the ETS is capable of communicating somatotopically compatible information to participants efficiently, and improves sensory discrimination and closed-loop prosthetic control. This non-invasive sensory interface may establish a viable way to restore sensory ability for prosthetic users who experience the phenomenon of PFM.
... Peripheral nerve stimulation has been used to activate sensory pathways and provide sensory feedback to research subjects [11][12][13][14][15][16][17][18]. Extra-neural cuffs have been demonstrated as an effective chronic method of delivering fascicle-level selectivity. ...
Objective: We intend to chronically restore somatosensation and provide high-fidelity myoelectric control for those with limb loss via a novel, distributed, high-channel-count, implanted system. Approach: We have developed the implanted Somatosensory Electrical Neurostimulation and Sensing (iSens®) system to support peripheral nerve stimulation through up to 64, 96, or 128 electrode contacts with myoelectric recording from 16, 8, or 0 bipolar sites, respectively. The rechargeable central device has Bluetooth® wireless telemetry to communicate to external devices and wired connections for up to four implanted satellite stimulation or recording devices. We characterized the stimulation, recording, battery runtime, and wireless performance and completed safety testing to support its use in human trials. Results: The stimulator operates as expected across a range of parameters and can schedule multiple asynchronous, interleaved pulse trains subject to total charge delivery limits. Recorded signals in saline show negligible stimulus artifact when 10 cm from a 1 mA stimulating source. The wireless telemetry range exceeds 1 m (direction and orientation dependent) in a saline torso phantom. The bandwidth supports 100 Hz bidirectional update rates of stimulation commands and data features or streaming select full bandwidth myoelectric signals. Preliminary first-in-human data validates the bench testing result. Significance: We developed, tested, and clinically implemented an advanced, modular, fully implanted peripheral stimulation and sensing system for somatosensory restoration and myoelectric control. The modularity in electrode type and number, including distributed sensing and stimulation, supports a wide variety of applications; iSens® is a flexible platform to bring peripheral neuromodulation applications to clinical reality. ClinicalTrials.gov ID NCT04430218.
... In their study, changes in the ipsilesional motor theta and alpha power were significantly correlated with finger individuation improvements [16]. Furthermore, in the field of neural prosthetics, several researchers have studied neural markers during sensory retraining interventions, particularly in tactile discrimination tasks [46][47][48][49]. For instance, Su et al. [48] found that alpha band attenuation in the somatosensory cortex was correlated with tactile discrimination performance. ...
A large proportion of stroke survivors suffer from sensory loss, negatively impacting their independence, quality of life, and neurorehabilitation prognosis. Despite the high prevalence of somatosensory impairments, our understanding of somatosensory interventions such as sensory electrical stimulation (SES) in neurorehabilitation is limited. We aimed to study the effectiveness of SES combined with a sensory discrimination task in a well-controlled virtual environment in healthy participants, setting a foundation for its potential application in stroke rehabilitation. We employed electroencephalography (EEG) to gain a better understanding of the underlying neural mechanisms and dynamics associated with sensory training and SES. We conducted a single-session experiment with 26 healthy participants who explored a set of three visually identical virtual textures—haptically rendered by a robotic device and that differed in their spatial period—while physically guided by the robot to identify the odd texture. The experiment consisted of three phases: pre-intervention, intervention, and post-intervention. Half the participants received subthreshold whole-hand SES during the intervention, while the other half received sham stimulation. We evaluated changes in task performance—assessed by the probability of correct responses—before and after intervention and between groups. We also evaluated differences in the exploration behavior, e.g., scanning speed. EEG was employed to examine the effects of the intervention on brain activity, particularly in the alpha frequency band (8–13 Hz) associated with sensory processing. We found that participants in the SES group improved their task performance after intervention and their scanning speed during and after intervention, while the sham group did not improve their task performance. However, the differences in task performance improvements between groups only approached significance. Furthermore, we found that alpha power was sensitive to the effects of SES; participants in the stimulation group exhibited enhanced brain signals associated with improved touch sensitivity likely due to the effects of SES on the central nervous system, while the increase in alpha power for the sham group was less pronounced. Our findings suggest that SES enhances texture discrimination after training and has a positive effect on sensory-related brain areas. Further research involving brain-injured patients is needed to confirm the potential benefit of our solution in neurorehabilitation.
... Two widely used approaches (i.e., training paradigms) for collecting training data for prostheses exist. One training paradigm, herein referred to as "mimic training," relies on amputees' mimicking preprogrammed movements of a prosthesis with their missing hand such that the corresponding muscle activations are correlated to preprogrammed kinematics of the prosthesis (Fig. 1A) [12], [13], [14], [15], [16], [17]. This training method is most popular due to its low cost, ease of use, and availability. ...
Intuitive regression control of prostheses relies on training algorithms to correlate biological recordings to motor intent. The quality of the training dataset is critical to run-time regression performance, but accurately labeling intended hand kinematics after hand amputation is challenging. In this study, we quantified the accuracy and precision of labeling hand kinematics using two common training paradigms: 1) mimic training, where participants mimic predetermined motions of a prosthesis, and 2) mirror training, where participants mirror their contralateral intact hand during synchronized bilateral movements. We first explored this question in healthy non-amputee individuals where the ground-truth kinematics could be readily determined using motion capture. Kinematic data showed that mimic training fails to account for biomechanical coupling and temporal changes in hand posture. Additionally, mirror training exhibited significantly higher accuracy and precision in labeling hand kinematics. These findings suggest that the mirror training approach generates a more faithful, albeit more complex, dataset. Accordingly, mirror training resulted in significantly better offline regression performance when using a large amount of training data and a non-linear neural network. Next, we explored these different training paradigms online, with a cohort of unilateral transradial amputees actively controlling a prosthesis in real-time to complete a functional task. Overall, we found that mirror training resulted in significantly faster task completion speeds and similar subjective workload. These results demonstrate that mirror training can potentially provide more dexterous control through the utilization of task-specific, user-selected training data. Consequently, these findings serve as a valuable guide for the next generation of myoelectric and neuroprostheses leveraging machine learning to provide more dexterous and intuitive control.
... Restoring sensory feedback has the potential to break this vicious cycle, resulting in several health and functional benefits. While sensory feedback restoration has been tested in amputees with both invasive (22)(23)(24)(25) and non-invasive (26)(27)(28)(29)(30)(31)(32) approaches, studies in non-amputated neuropathies such as PN are limited. Oddsson et al (33,34) proposed a solution by providing remapped vibration sensation reflecting plantar pressure measurements at the ankle level. ...
... Oddsson et al (33,34) proposed a solution by providing remapped vibration sensation reflecting plantar pressure measurements at the ankle level. However, vibratory feedback is strongly limited by the bulkiness, rigidity and power consumption of the actuators (35) and the remapped approach requires a learning phase to integrate new information during functional tasks, which prevents patients adoption (29,36). A different approach has been followed by Najafi et al (21,37), who exploited SENSUS, a stimulator designed for pain treatment, to examine therapeutic effectiveness of plantar electrocutaneous stimulation. ...
... Near-natural tactile sensation has been achieved only through invasive neural technologies both at the peripheral level (22,25,67), and at the central level (68)(69)(70). While restoring natural touch information with non-invasive electrical stimulation remains an unresolved challenge (27,29,30,35,71), these paresthetic sensations can still be subconsciously integrated in the sensory motor scheme (40). Despite not eliciting natural sensation, non-invasive stimulation technologies, still have many advantages, namely that they do not require a surgical procedure, avoiding extensive post-surgery care and complications (35). ...
Peripheral neuropathy (PN) is the most common complication of diabetes. It is characterized by sensory loss which often causes major health consequences including foot ulceration, chronic pain, poor mobility and increased risk of falls. However, present treatments do not counteract the cause of the disease, namely lack of sensory feedback, but rather aim at partial and temporal symptoms relief (e.g. analgesics for pain or creams for ulcers healing). Electrical stimulation is a promising solution for sensory restoration, but it is yet unknown if it can elicit perceivable sensations in PN damaged nerves and whether it could lead to any health or functional benefits. To this aim, we designed a wearable sensory neuroprosthesis providing targeted neurostimulation at the ankle level (NeuroStep) restoring feet lost sensations. We tested it in 14 participants with PN, evaluating its effects on functional outcomes and pain, and the cortical activation related to the restored sensations. Our system was able to restore lost sensations in all participants. The nerves of PN participants resulted significantly less excitable and sensitive than healthy individuals (N=22). Thanks to the neurostimulation, participants improved cadence and functional gait, with even stronger improvements in individuals with higher risk of falls. A full day of NeuroStep use led to a clinically significant reduction of 30.4% ± 9.2% in neuropathic pain. Restored sensations activated cortical patterns, as measured via fMRI, similar to the naturally located foot sensations, thus not requiring training by the user. NeuroStep restores intuitive sensations in PN participants, improving mobility and decreasing pain, possibly replacing multiple inefficient treatments. It holds potential to drastically improve patients quality of life thanks to functional and health benefits, while paving the way to new effective neuromodulation treatments.
... This study sought to develop and assess the use of antimicrobial nanomaterials as an alternative to antibiotics to curb antibiotic spillover into the environment. Numerous natural antimicrobial materials have been previously used for this purpose [15][16][17]. However, their application has been limited by high costs, labor intensiveness, and the bioincompatibility of their extraction and nanoformulation processes [18][19][20]. ...
Antimicrobial resistance has recently been considered an emerging catastrophe globally. The public health and environmental threats were aggravated by the injudicious use of antibiotics in animal farming, aquaculture, and croup fields, etc. Consequently, failure of antibiotic therapies is common because of the emergence of multidrug-resistant (MDR) bacteria in the environment. Thus, the reduction in antibiotic spillage in the environment could be an important step for overcoming this situation. Bear in mind, this research was focused on the green synthesis of chitosan nanoparticles (ChiNPs) using Citrus lemon (Assam lemon) extract as a cross-linker and application in controlling MDR bacteria to reduce the antibiotic spillage in that sector. For evaluating antibacterial activity, Staphylococcus aureus and Escherichia coli were isolated from environmental specimens, and their multidrug-resistant pa ern were identified both phenotypically by disk diffusion and genotypically by detecting methicillin-(mecA), penicillin-(blaZ), and streptomycin (aadA1)-resistance encoding genes. The inhibitory zone's diameter was employed as a parameter for determining the antibacterial effect against MDR bacteria revealing 30 ± 0.4 mm, 34 ± 0.2 mm, and 36 ± 0.8 mm zones of inhibition against methicillin-(mecA) and penicillin (blaZ)-resistant S. aureus, and streptomycin (aadA1)-resistant E. coli, respectively. The minimum inhibitory concentration at 0.31 mg/mL and minimum bactericidal concentration at 0.62 mg/mL of yielded ChiNPs were used as the broad-spectrum application against MDR bacteria. Finally, the biocompatibility of ChiNPs was confirmed by showing a negligible decrease in BHK-21 cell viability at doses less than 2 MIC, suggesting their potential for future application in antibiotic-free farming practices.
... So, for external stimulation (i.e., TENS), it is mandatory to have a higher voltage compliance, which is achieved by adding the third board. Additionally, the quantity of stimulation channels required for external applications is less than that required for PNS; as reported in the literature, TENS was already used for sensory feedback with a number of stimulating channels ranging between 2 and 4 [40][41][42][43]. For this reason, the third board was developed with a lower number of active channels. ...
... Regarding the wearable version, it is necessary to add the third board to increase the voltage compliance of the system, making it suitable for TENS, and maintaining control of the current stimulation via the current mirrors. All this, however, resulted in a reduction in the stimulation channels from 30 to 8, which are still suitable for TENS [40][41][42][43]. To summarize, the stimulator is a modular system, composed of two or three boards based on the application scenario. ...
... Regarding the wearable version, it is necessary to add the third board to increase the voltage compliance of the system, making it suitable for TENS, and maintaining control of the current stimulation via the current mirrors. All this, however, resulted in a reduction in the stimulation channels from 30 to 8, which are still suitable for TENS [40][41][42][43]. ...
The restoration of sensory feedback is one of the current challenges in the field of prosthetics. This work, following the analysis of the various types of sensory feedback, aims to present a prototype device that could be used both for implantable applications to perform PNS and for wearable applications, performing TENS, to restore sensory feedback. The two systems are composed of three electronic boards that are presented in detail, as well as the bench tests carried out. To the authors’ best knowledge, this work presents the first device that can be used in a dual scenario for restoring sensory feedback. Both the implantable and wearable versions respected the expected values regarding the stimulation parameters. In its implantable version, the proposed system allows simultaneous and independent stimulation of 30 channels. Furthermore, the capacity of the wearable version to elicit somatic sensations was evaluated on healthy participants demonstrating performance comparable with commercial solutions.
... After each stimulus, the virtual hand was shown on the screen in front of them, and they were instructed to draw using a computer mouse the outline of the area where they perceived the stimulus. As usual (D'Anna et al. 2017;Fifer et al. 2022;Marasco et al. 2011;Shaballout et al. 2019;Tan et al. 2015), the size of the virtual hand was always the same (not scaled to the participant). Importantly, the participants could edit the drawing as much as they wanted to minimize the errors due to poor drawing skills. ...
... An open question about the drawing test is how well the participants can draw what they feel. Nevertheless, this approach is routinely used across studies (D'Anna et al. 2017;Fifer et al. 2022;Marasco et al. 2011;Shaballout et al. 2019;Tan et al. 2015), and we have made an effort to minimize subjective bias, as explained in Methods. ...
Electrotactile stimulation through matrix electrodes is a promising technology to restore high-resolution tactile feedback in extended reality applications. One of the fundamental tactile effects that should be simulated is the change in the size of the contact between the finger and a virtual object. The present study investigated how participants perceive the increase of stimulation area when stimulating the index finger using static or dynamic (moving) stimuli produced by activating 1 to 6 electrode pads. To assess the ability to interpret the stimulation from the natural cues (natural decoding), without any prior training, the participants were instructed to draw the size of the stimulated area and identify the size difference when comparing two consecutive stimulations. To investigate if other “non-natural” cues can improve the size estimation, the participants were asked to enumerate the number of active pads following a training protocol. The results demonstrated that participants could perceive the change in size without prior training (e.g., the estimated area correlated with the stimulated area, p < 0.001; ≥ two-pad difference recognized with > 80% success rate). However, natural decoding was also challenging, as the response area changed gradually and sometimes in complex patterns when increasing the number of active pads (e.g., four extra pads needed for the statistically significant difference). Nevertheless, by training the participants to utilize additional cues the limitations of natural perception could be compensated. After the training, the mismatch in the activated and estimated number of pads was less than one pad regardless of the stimulus size. Finally, introducing the movement of the stimulus substantially improved discrimination (e.g., 100% median success rate to recognize ≥ one-pad difference). The present study, therefore, provides insights into stimulation size perception, and practical guidelines on how to modulate pad activation to change the perceived size in static and dynamic scenarios.
