Capabilities and limitations of 3D printed microserpentines and integrated 3D electrodes for stretchable and conformable biosensor applications

Charles Didier,Swaminathan Rajaraman,Avra Kundu

doi:10.1038/s41378-019-0129-3

Charles Didier, Swaminathan Rajaraman + Show 1 more

Open Access

https://doi.org/10.1038/s41378-019-0129-3

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Journal: Microsystems & Nanoengineering	Publication Date: Apr 20, 2020
Citations: 32	License type: open-access

Affiliation: University of Central Florida

Abstract

We explore the capabilities and limitations of 3D printed microserpentines (µserpentines) and utilize these structures to develop dynamic 3D microelectrodes for potential applications in in vitro, wearable, and implantable microelectrode arrays (MEAs). The device incorporates optimized 3D printed µserpentine designs with out-of-plane microelectrode structures, integrated on to a flexible Kapton® package with micromolded PDMS insulation. The flexibility of the optimized, printed µserpentine design was calculated through effective stiffness and effective strain equations, so as to allow for analysis of various designs for enhanced flexibility. The optimized, down selected µserpentine design was further sputter coated with 7–70 nm-thick gold and the performance of these coatings was studied for maintenance of conductivity during uniaxial strain application. Bending/conforming analysis of the final devices (3D MEAs with a Kapton® package and PDMS insulation) were performed to qualitatively assess the robustness of the finished device toward dynamic MEA applications. 3D microelectrode impedance measurements varied from 4.2 to 5.2 kΩ during the bending process demonstrating a small change and an example application with artificial agarose skin composite model to assess feasibility for basic transdermal electrical recording was further demonstrated.

Highlights

1234567890():,; 1234567890():,; 1234567890():,; 1234567890():,; Introduction Stretchable electronics and microsensors have begun to be applied to several consumer and biomedical areas, including wearables for personal health monitoring[1,2], surgical robotics[3], implantable devices[4], tactile sensors[5], and devices for power harvesting and storage[6]
The μserpentine base structures used were optimized according to two key compound equations for the effective stiffness and maximum U-bend strain
The final optimized μserpentines had an l/R ratio of 2, and an α of 10°, creating a μserpentines that could stretch up to 155% its resting length. This optimized μserpentine was subsequently characterized with varying conformal gold coating thicknesses, to find the optimal thickness to retain resistance values during strain

Summary

Introduction

Stretchable electronics and microsensors have begun to be applied to several consumer and biomedical areas, including wearables for personal health monitoring[1,2], surgical robotics[3], implantable devices[4], tactile sensors[5], and devices for power harvesting and storage[6]. Inorganic materials used in the microfabrication of stretchable microsensors such as silicon[7] and aluminum[8] are very stiff and deform to an extent where electrical failure occurs at small amounts of tensile strain[9]. In order to alleviate this problem, a common strategy for a device design with such materials, is to replace “straight wire” features[10] fabricated out of these materials with shapes engineered to be stretchable and flexible including “Archimedean spiral”11, “μserpentines,” and other geometries[6,12]. In addition to the aforementioned standard materials, there are numerous material sets and combinations currently in use for the fabrication of stretchable electronics, with polydimethylsiloxane (PDMS) being a widely used substrate and packaging material[14,15]

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