Bridging the Gap Between Silicon and Biological Systems: The Age of Flexible, Wireless Sensors

Christian S. Guay, MD

Beverley A. Orser, MD, PhD, FRCPC, FRSC, Chair of the IARS Board of Trustees, opened this year’s Annual Meeting, on Friday, May 17, by acknowledging the diligent work and dedication of the IARS Trustees and staff. She also traced the illustrious history of the IARS and Dr. Thomas Harry Seldon, and underscored the society’s revitalized mission to enhance global anesthesiology research and practice.

Santhanam Suresh, MD, MBA, FASA, IARS Trustee Emeritus, then proceeded to introduce this year’s T.H. Seldon Memorial Lecturer, the esteemed John Rogers, PhD, Simpson/Querrey Professor of Materials Science and Engineering, Biomedical Engineering, and Neurological Surgery at Northwestern University.

Dr. Rogers’ work addresses the inherent limitations of traditional micro- and nanosystems, which are typically planar, rigid, and static, unlike the curved, compliant, and dynamic nature of biological systems. His research aims to bridge these gaps by developing soft, biocompatible, technologies that integrate seamlessly with biological tissues.

Two key principles underly Dr. Rogers’ work on these materials. First, making any material sufficiently thin renders it flexible. Applying this to silicon wafers, his team created extremely thin nanoribbons that, when combined with an elastic framework and buckled, form stretchable silicon circuits. These flexible, stretchable circuits can be applied directly to the epidermis, functioning wirelessly and conforming to curvilinear surfaces. The capabilities of these innovative devices span various domains, including thermal monitoring, electrical measurements (e.g. EEG, ECG, and EMG), fluidic analysis (e.g. sweat and blood flow), mechanical detection (e.g. strain and motion), optical monitoring (e.g. oximetry and plethysmography), and mechano-acoustic auscultation for heart and lung sounds.

Initial applications of these novel devices focused on the pediatric population. Two wireless devices can replace most traditional wired vital sign monitors, tracking ECG, heart rate, photoplethysmography, temperature, pulse oximetry, and respiratory rate. Their wireless functionality enables more maternal-infant skin-to-skin contact and reduces the work burden for nurses. The implications of fully wireless monitoring were not lost on the crowd of keenly attentive anesthesiologists. Ongoing development aims to add noninvasive blood pressure monitoring to these devices. Over 200 patients have enrolled in studies at Lurie Children’s Hospital, with scaled deployments spanning maternal-fetal health in India, Pakistan, Kenya, and Ghana. The company SIBEL Health has deployed over 4,000 sensors across more than 20 countries since 2020.

Expanding to the adult population, Dr. Rogers began collaborating with the Shirley Ryan AbilityLab in Chicago, focusing on poststroke rehabilitation of swallowing and speech functions. Wireless sensors placed at the suprasternal notch are capable of monitoring an astounding array of physiological signals, including swallowing, vocalization, heart rate, heart rate variability, respiratory rate, respiratory sounds, sleep dynamics, motion and body orientation. Although the resulting time-series tracing can appear daunting at first, digital filters can tease out the various biological signals which each have distinct spectral signatures, enabling precise monitoring. A real-time feedback GUI helps retrain patients to swallow at optimal points in the respiratory cycle, during the peaks and troughs of respirations.

The team at Northwestern is also collaborating with neurosurgeons to address a common and potentially lethal complication in patients with hydrocephalus: ventricular shunt failures. Thermal sensors placed above the shunt deliver a small amount of heat to the underlying tissue and shunt. Fluid flow can then be calculated by measuring the skew in temperature readings caused by flow. This novel method has the potential to facilitate shunt function monitoring and save countless CT scans that are traditionally used in this setting.

Dr. Rogers concluded with insights into new, unpublished research on neonatal stress and pain measurements. His group is developing a single, integrated device that is placed on the chest of neonates which can detect body sounds, motion, perfusion, and galvanic skin responses. Considering the inherent limitation that neonates cannot provide a “ground truth” with subjective pain reports, scheduled blood draws are leveraged as nociceptive stimuli to train models in detecting stress and pain markers in neonates.

Dr. John Rogers’ pioneering work in flexible, biocompatible technologies represents a significant leap forward in integrating manufactured electrical systems with biological tissues. His innovations promise to revolutionize medical monitoring and treatment, offering improved outcomes for patients across various fields, from maternal and pediatric health to stroke rehabilitation and neonatal care.