Arterial Pulse Localization with Varying Electrode Sizes and Spacings in Wrist-Worn Bioimpedance Sensing.

Bioimpedance has emerged as a promising modality to continuously monitor hemodynamic and respiratory physiological parameters through a non-invasive skin-contact approach. Bioimpedance sensors placed at the radial zone of the volar wrist provide sensitive operation to the blood flow of the underlying radial artery. The translation of bioimpedance systems into medical-grade settings for continuous hemodynamic monitoring, however, presents challenges when constraining the necessary sensing components to a minimal form factor while maintaining sufficient accuracy and precision of measurements. Thus, it is important to understand the effects of electrode configuration on bioimpedance signals when reducing them to a wearable form factor. Previous work regarding electrode configurations in bioimpedance does not address wearable constraints, nor do they focus on electrodes viable for wearable applications. In this study, we present empirical evidence of the effects of dry silver electrode sizes and spacings on the specificity and sensitivity of a wrist-worn bioimpedance sensor array. We found that wrist-worn bioimpedance systems for hemodynamic monitoring would benefit from reduced injection electrode spacings (up to a 392% increase in signal amplitude with a 50% decrease in spacing), increased sensing electrode spacings, and decreased electrode surface areas. Clinical Relevance - The work directly contributes towards the development of cuffless continuous blood pressure monitors with applications in clinical and ambulatory settings.

Microfabricated and 3-D printed electroconductive hydrogels of PEDOT:PSS and their application in bioelectronics.

Biofabrication techniques such as microlithography and 3-D bioprinting have emerged in recent years as technologies capable of rendering complex, biocompatible constructs for biosensors, tissue and regenerative engineering and bioelectronics. While instruments and processes have been the subject of immense advancement, multifunctional bioinks have received less attention. A novel photocrosslinkable, hybrid bioactive and inherently conductive bioink formed from poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) nanomaterials within poly(2-hydroxyethyl methacrylate-co-polyethyleneglycol methacrylate) p(HEMA-co-EGMA) was used to render complex hydrogel constructs through microlithographic fabrication and 3-D printing. Constructs were directly compared through established metrics of acuity and fidelity, using side-by-side comparison of microarray grids, triangles incorporating angles 15-90°, and a multi-ink hydrogel disk array. Compositional variation from 0.01 to 1.00 wt% PEDOT:PSS produced hydrogels of varying and tunable electrical and electrochemical properties, while maintaining similar rheological properties (up to 0.50 wt% PEDOT:PSS). Furthermore, hydrogel membrane resistances extracted from equivalent circuit modeling of electrical impedance spectroscopy data varied only according to the included wt% of PEDOT:PSS and were agnostic of fabrication method. An in-silico variable frequency active low-pass filter was developed using a microlithographically fabricated Individually Addressable Microband Electrode (IAME) as the filtering capacitor, wherein 3-D printed lines of varying wt% of PEDOT:PSS hydrogels were shown to alter the cutoff frequency of the analog filter, indicating a potential use as tunable 3-D printed organic electronic analog filtering elements for biosensors. Bioinks of different PEDOT:PSS (0.0, 0.1, and 0.5 wt%) manufactured into hydrogel disks using the two methods were shown to yield similarly cytocompatible substrates for attachment and differentiation of PC-12 neural progenitor cells.