Skin Interface Design

 A core challenge for noninvasive neuroimaging is interfacing sensors with the skin. This is particularly important in field recordings, such as in this flight test at the University of Iowa. But it is also important for laboratory studies using electrical source imaging, in which even small levels of uncontrolled artifactual noise may impair precision of the source solutions. EGI has organized an ongoing R&D effort, supported by SBIR awards and US and international patents, to develop advanced skin interface technologies for electrical, optical, and acoustic signals. 

Minimize Infection Risk 

The traditional laboratory practice of breaking the skin to make a low-impedance electrode contact, such as used with elastic caps, increases the risk of infection, particularly to the participant, but also to the experimenter (AES Infections Diseases Committee Report, 1984; CDC, 1991). This infection may be serious, indeed life-threatening, with blood-borne pathogens such as HIV, prions, or Hepatitis C. With these pathogens, the infection is insidious because the disease may not be symptomatic for months or years after the infection is introduced.  Electrode caps which break the skin cannot be sterilized and present a serious infection risk. The Geodesic Sensor Net was introduced in the1980s with new ideals: using saline solution and small sponges to allow an effective conductive contact, while avoiding breaking the skin. All EGI and GeoMedica products maintain this priority on minimizing infection risk. Our rule is never break the skin with any skin interface technology.
Ferree, T. C., Luu, P., Russell, G. S., & Tucker, D. M. (2001). Scalp electrode impedance, infection risk, and EEG data quality. Clinical Neurophysiology, 112, 536-544.
American Electroencephalographic Society Infectious Diseases Committee report (1984).  J Clin Neurophysiol, 1(4), 437-441.
Center for Disease Control (1991). Recommendations for Preventing Transmission of Human Immunodeficiency Virus and Hepatitis B Virus to Patients During Exposure-Prone Invasive Procedures.

Designer Polymers for HydroCel Nets 

The HydroCel Geodesic Sensor Net includes a soft pedestal foot that creates a small chamber or cell against the scalp or skin. In this cell, the electrolyte (saline or hydrogel) is kept from evaporating, which hydrates skin and lowers the electrode-skin impedance to acceptable levels.
Recent research with hydrogel polymers has provided flexible technologies for designing skin interface materials.  
From consulting with experts in polymer chemistry and related fields, EGI scientists have been able to design hydrogels that bond without causing skin irritation even to sensitive skin, and that provide specific properties for optimal transmission of electrical signals.