Transcutaneous Electrical Nerve Stimulation (TENS) is a promising technique for eliciting referred tactile sensations in patients with limb amputation. Although several studies show the validity of this technique, its application in daily life and away from laboratories is limited by the need for more portable instrumentation that guarantees the necessary voltage and current requirements for proper sensory stimulation. This study proposes a low-cost, wearable high-voltage compliant current stimulator with four independent channels based on Components-Off-The-Shelf (COTS). This microcontroller-based system implements a voltage-current converter controllable through a digital-to-analog converter that delivers up to 25 mA to load up to 3.6 kΩ. The high-voltage compliance enables the system to adapt to variations in electrode-skin impedance, allowing it to stimulate loads over 10 kΩ with currents of 5 mA. The system was realized on a four-layer PCB (115.9 mm × 61 mm, 52 g). The functionality of the device was tested on resistive loads and on an equivalent skin-like RC circuit. Moreover, the possibility of implementing an amplitude modulation was demonstrated.

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.

The adoption of upper limb myoelectric prosthesis is limited by the lack of closed control loop systems. Although the efferent control has already been integrated into these devices, the sensory feedback restoration in the afferent channel still remains an open challenge. Transcutaneous electrical nerve stimulation (TENS) is a promising method for generating somatotopic sensory feedback, allowing the closure of the control loop system. The application of this technique is limited by cumbersome and grid-powered electrical stimulators, making them unsuitable for everyday life, whereas most portable stimulators available on the market are designed for other purposes (e.g., muscular stimulation or pain therapy) and present limited stimulation wave customization. The stimulation devices employed in the literature often produce not fully suitable stimulation parameters and are frequently validated through procedures that do not fully clarify their practical application for sensory feedback restoration. The research aims to present a novel wearable TENS stimulation device (46 g, 62 × 49 × 20 mm) suitable for sensory feedback application. The validation was achieved through a benchtop test and a preliminary analysis on 10 healthy participants comparing the qualities, intensities, and stimulated areas of the sensations elicited by the proposed device and a reference stimulator. The proposed device is capable of delivering charge-balanced stimulation waves over skin-like resistive load and eliciting tingling and vibration sensations with similar intensities compared to the adopted reference.

Neuroprostheses capable of providing Somatotopic Sensory Feedback (SSF) enables the restoration of tactile sensations in amputees, thereby enhancing prosthesis embodiment, object manipulation, balance and walking stability. Transcutaneous Electrical Nerve Stimulation (TENS) represents a primary non-invasive technique for eliciting somatotopic sensations. Devices commonly used to evaluate the effectiveness of TENS stimulation are often bulky and main powered. However, current portable TENS devices frequently fall short of key functional requirements, particularly in terms of stimulation parameter ranges that are insufficient to reliably evoke somatotopic sensations in either upper and lower limb applications. Moreover, they typically do not support real-time independent channels programming and wireless communication. This work introduces a compact, wearable stimulator, including its external casing, with a total weight of 64 g and dimensions of 70 ${\boldsymbol{\times}}$ 40 ${\boldsymbol{\times}}$ 35 mm, designed to deliver SSF in both upper and lower limb applications. The device was validated through bench testing and human trials involving 20 healthy participants, by comparing the intensity, qualitative characteristics, and referred area of the elicited sensations with those produced by a benchmark. The stimulator reliably delivered the required parameters on a skin-like capacitive-resistive load and elicited somatotopic sensations consistent with the benchmark device and prior somatotopic feedback studies. The proposed stimulator provides non-invasive somatotopic sensory feedback for both upper and lower limbs. Its portability and modular design address key limitations of current commercial and research-grade TENS systems, enabling future studies on the functional benefits of sensory feedback in prosthetic control.

Transcutaneous Electrical Nerve Stimulation (TENS) has been widely adopted as a non-invasive method for delivering somatotopic sensory feedback (SSF) in ne