Similarly, the metallization of such 3D printed structures has not been fully characterized or understood. This work has adapted and expanded on the mathematical background on printed µserpentine structures that was recently developed 24. In this work, considerations and limitations for using standard and commercially available clear resin 23 to produce a stretchable and flexible engineered design that can incorporate robust 3D structures through additive micro-stereolithographic (µSLA) 3D printing is explored.
While prior work demonstrating the development of 2D and 3D MEAs in static cell culture settings has been reported 22 (including from our group), to date understanding the capabilities and limitations of 3D printed geometries and their application to stretchable and dynamic 3D microelectrodes is missing. Owing to the commercial availability of various 3D printing systems and the innovations of makerspace environments, the development of 3D printed devices has increasingly expanded and continues to show promise in innovation 21. Recently, the ease of microfabrication of complex shapes such as µserpentines and base structures for 2D and 3D MEAs has been achieved through rapid and cost-effective additive manufacturing methods like 3D printing 1. Such two-dimensional (2D) and three-dimensional (3D) microelectrode arrays (MEAs) have become ubiquitous in in vitro, cell-based biosensing 17, wearable 18, implantable 19, and environmental sensing applications 20. 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.Ī common structure in a stretchable electronics system is microelectrode, which consists of a substrate (with an additional package or the package defined on the substrate) atop which a grid or line of metal traces and an insulation layer are defined 16. Specifically in flexible electronics devices, “serpentine” designs have resulted in enhanced strain performance 13. 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. 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. A basic requirement in the micro-structuring of such devices is the design and development of the components of the system that are able to mechanically deform without losing their ability to electrically function successfully. 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.
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. 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. 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. 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 device incorporates optimized 3D printed µserpentine designs with out-of-plane microelectrode structures, integrated on to a flexible Kapton® package with micromolded PDMS insulation. 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).