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Ultrasound peripheral interface and in-vitro model of human somatosensory system and muscles for motor decoding and restoration of somatic sensations in amputees

Periodic Reporting for period 1 - SOMA (Ultrasound peripheral interface and in-vitro model of human somatosensory system and muscles for motor decoding and restoration of somatic sensations in amputees)

Reporting period: 2020-09-01 to 2021-08-31

Worldwide, the number of people suffering from an arm amputation is estimated to 3 million, but there is a limited regular prosthetic use due also to lack of functionality. The potential of the development of closed-loop neuroprostheses can let SOMA significantly improve the quality of life of people who have suffered from an amputation. The SOMA project wants to develop a completely novel low invasive peripheral interface for restoring natural and multimodal tactile sensations in amputee subjects, with high selectivity and discrimination capabilities. The project wants to investigate whether multiple somatic and close-to-natural sensations can be delivered in amputees via focused US. The development of a bio-inspired sensory system, of bio-inspired control strategies and of encoding algorithms for peripheral stimulation aim at significantly improve manipulation capability and user acceptability of the prostheses.
SOMA will profoundly improve the knowledge of the sensory afferent pathway providing for the first time an in-vitro model of the somatosensory system and muscle. The capability of this artificial skin in producing neural signals consistent with the afferent signals of a real in-vivo counterpart will be verified.
The SOMA US multiprobe low-invasive bidirectional peripheral interface will be used both for afferent stimulation and efferent recording, thus enabling the establishment of a radically new neural interface and of motor unit identification from ultrafast ultrasound with high depth and spatial discrimination capabilities.
The mechanical design of the positioning system for the experimental studies on animals was accomplished. The relevant frequency range in the broad spectral range was also defined. A 32 channel portable electronic system for investigational use allowing acquiring pulse-echo data from up to 32 individual transducers has been arranged. A 32 element “transducer bracelet” consisting of individual 1 MHz transducers has been developed. Simulations were conducted for optimizing the US probe configuration for recording. A subsystem for inductive power transmission and regulation has been developing. Power and wireless data transmission methods have been investigated.
The work within SOMA has so far provided the first steps for a new generation of motor unit identification from UF US with high depth and spatial discrimination capabilities. The use of a probe with 32 US transducers capable of producing B mode images and HD sEMG grids synchronized with a motion capture system can predict the joint angles using only the US signal, thus acting as a portable gesture recognition device.
The characteristics of the somatosensory system to be integrated in the prosthetic hand were defined and the design of an instrumented fingertip embedding commercial force and temperature sensors was proposed. The information provided by the sensors has been adopted as input to i) a new force-slippage-temperature control strategy able to guarantee an online reaction of the hand to external stimuli; ii) new encoding algorithms of mechanical, thermal and painful sensations. The neurophysiological models of the somatosensory receptors on the skin have been studied and new encoding algorithms for restoring mechanical and thermal sensations are being developed.
Two human innervated tissues were developed: innervated skin and neuromuscular tissue. Both tissues were developed in vitro using primary human cells. A mechatronic testbed able to produce force and thermal (and also consequently pain-related) stimuli on both the in-vivo and in-vitro models has been developed.
Coordination and management were oriented to accomplish the objectives established in the CA.
Both internal and external dissemination activities have been performed.
Existing implantable systems for ultrasound recording are for imaging such as intravascular ultrasound imaging. Ultrasound recording of muscular signals are currently performed with bulky probes. There is a huge opportunity to push beyond the state of the art in this area by developing integrated circuits for miniaturised ultrasound recording of muscular signals.
Existing systems for ultrasound stimulation are bulky and conceived for stimulating the central nervous system. An implantable (or wearable but of small dimension) system remains to be explored and presents many design challenges and room for innovation.
The implementation of a Ultra Fast Ultrasound (UF US) platform capable of identifying single motor unit activity in voluntary contractions has achieved breakthrough novel results. Currently, very few studies have been published on this topic and, as far as we are aware, our method is the first one to combine HD sEMG decomposition and UF US for motor unit identification. With this framework, our experimental data collection and analysis are providing novel insights into muscle contraction and neural control of movements.
The application of B-mode ultrasound for gesture recognition has so far been applied for the classification of different gestures and contractions. Our studies have shown two novelties with respect to the state of the art: i) we used a portable B-mode US system instead of a larger medical grade US; ii) we developed a regression approach, instead of a classification, with the inclusion of a motion capture system demonstrating that the US-based regression is superior to the more established sEMG models.
A somatosensory system able to reproduce the human hand physiological characteristics and to to replicate the huge variety of sensations felt by humans in the prosthetic system is still missing in the literature. There is also a lack of models describing how to combine stimuli of different nature, and how to return this integrated information to the amputee through appropriate peripheral stimulation.
. The information retrieved by a somatosensory system embedded in the prosthesis could be fundamental to ameliorate manipulation performance in several tasks and to restore multimodal somatic sensations, by means of new encoding approaches, with a significant impact on the user’s satisfaction.
The full validation of an artificial innervated skin and muscle biohybrid model based on three different types of stimulation tests (physical, TENS-based and FUS-based) is a novelty that will demonstrate its reliability and the consequent possibility of using it as an artificial testbed as alternative to a living animal.
Our innervated skin represents a unique model in which all components of extracellular matrix are endogenous and not synthetic materials present in the final tissue. This feature improves the possibility to obtain a physiological interaction between the peripheral sensory neural network and skin tissue in vitro, into a completely native and human environment. The integration of a fully innervated bio-hybrid model with CMOS-MEA system will lead to replicate skin sensory function and muscle activity by recording and decoding the spontaneous electrical signal or evoked by complex stimulations such as thermal, mechanical, nociceptive and FUS.
Small animal experimental neurostimulation setup