Significant limitations still exist for brain and neural interface technologies. Desirable tools and technologies for people suffering from neuromuscular deficits are currently not sufficiently accessible. Non-invasive neural interface technologies, such as EEG or EMG are inherently unidirectional and of limited capacity. On the other hand, although more invasive interfaces (e. g. implanted nerve electrodes) allow bidirectionality and better performance, still depend on surgical procedures and complex signal processing.

Since early 2018, partners in the EU joint project "EXTEND" have been developing a novel concept of Bidirectional Hyper-connected Neural Systems (BHNS) to expand the capabilities of neural interfaces with minimally invasive communication links between multiple nerves in the body and multiple external devices. EXTEND aims to realize BHNS by developing a disruptive wireless neuromuscular (injectable) interface technology that enables distributed stimulation, acquisition, processing, and analysis of neuromuscular activity that ultimately represents the neural code of movement.

Tremor management and exoskeletons for spinal cord injury assistance demonstrate benefits

The benefits of the new BHNS are demonstrated in two applications. The first is tremor management in essential tremor (ET) and Parkinson's disease (PD). ET is estimated to affect 4–5% of the population above 65 years old, while PD is estimated to affect around 1% of the population above 60 years old. The second application field is in neural-interfaced assistive exoskeletons (wearable robots) for spinal cord injury (SCI). EXTEND is also working towards a community hub that will bring stakeholders together to create an innovation ecosystem that can foster the rapid development of neural interfaces around the new concept.

The BHNS creates communication channels between different sensory and motor nerves that enable a synthetic action-response chain of sensorimotor activity. Muscle activity or sensory perception is modulated by neuromuscular stimulation based not only on measured local information (e. g. voluntary activation, reflex activation), but also on activity measured in other parts of the body. In addition, external devices (e. g. wearable robots) can be controlled by neuromuscular activity in real time at multiple sites on the body. These external devices are then used as a closed loop to modify sensorimotor behavior to correct movement disorders (e. g. electrical stimulation in pathological tremor suppression and EMG-based control of exoskeletons for SCI rehabilitation).

As a first implementation of the BHNS approach, the EXTEND researchers tested intramuscular electrical stimulation below motor threshold to reduce tremor in essential tremor patients. Results showed acute and prolonged (24 h) tremor reduction, which might open the possibility of an alternative therapeutic approach for tremor patients. In the paper published online, titled “Intramuscular stimulation of muscle afferents attains prolonged tremor reduction in essential tremor patients”, these promising research results are described. The paper will appear in spring in the journal IEEE Transactions on Biomedical Engineering. The early access version is available via the EXTEND webpage listed below.

The EXTEND consortium brings together nine partners from five different countries (Germany, Iceland, Spain, UK and USA) on the basis of multi-disciplinary expertise and transnationality required to achieve the ambitious goals and to ensure an appropriate exploitation of the results, mainly in technological and scientific terms, but with an innovation perspective.

Fraunhofer IBMT expertise in sensing and actuation neural interfaces and implants

The Fraunhofer Institute for Biomedical Engineering IBMT profitably contributes its many years of experience and technologies in the field of neuromuscular interfaces for sensing and actuation purposes to the project. Three successive approaches with increasing integration density and miniaturization will be designed, engineered and built by Fraunhofer IBMT in close cooperation with the EXTEND partners. The first system developed for the tremor management study consists of an intramuscular thin-film electrode structure including both an actuating stimulation electrode and a sensory electromyography (EMG) recording electrode for closed-loop control. To make this possible, Fraunhofer IBMT combines its expertise and skills in micromachining of highly flexible and thin, high-channel polyimide interfaces with its expertise in system integration and implant technology under consideration of biocompatibility and biostability requirements.

Further implementation studies of the EXTEND researchers are planned for the coming months. Corresponding publications can be accessed via the project website and the Neuro Interface Hub.

Duration: 01.01.2018 - 31.12.2021

Project website:
https://extend-project.eu/
https://neurointerfacehub.extend-project.eu/

Coordinator:
Spanish National Research Council (CSIC)
Neural Rehabilitation Group, Cajal Institute, Dr. Filipe Barroso, Spain

Project partners:
Imperial College London (ICL), United Kingdom
Pompeu Fabra University (UPF), Spain
Fraunhofer Institute for Biomedical Engineering IBMT, Germany
Madrilenian Health Service (SERMAS), Spain
Ossur HF (OSSUR), Iceland
Regional Health Service of Castilla La Mancha, (SESCAM), Spain
Institute of Philosophy (CSIC), Spain
Shirley Ryan AbilityLab, USA
Technaid, S.L. - Leading Motion, Spain