Graduate student Wichita State University, United States
Introduction:: Inkjet printing is widely used as an alternative of MEMS techniques in fabricating electronics due to its low-cost, additive patterning, maskless approach, low material consumption, and environmentally friendly manufacturing [1, 2]. Despite the numerous advantages, little research has been carried out on developing stretchable electronics using inkjet printing. One of biggest obstacles to the realization of inkjet-printed stretchable electronics is the limit in printing resolution [3]. Here, we propose to develop ultrathin, stretchable skin-like electrodes via fundamental understanding of inkjet-printing technologies, solid-liquid interactions, stretchable mechanics, and materials for reliable and user-friendly biopotential monitoring. The proposed development and characterization of the inkjet-printed skin-like electrodes present the first step toward low-cost, rapid manufacturing of smart multifunctional, bio-integrated systems by inkjet printing technology that can be used for real-time non-invasive health monitoring, human-machine interfaces, wearable biosensors, and electronic skins.
Materials and Methods:: To develop inkjet-printed stretchable skin-like electrodes, computational and experimental studies were applied to optimize inkjet printing parameters including jetting voltages and waveforms. Contact angle measurements were performed to understand solid-liquid interactions on CF4 treated polyimide substrates, and cyclic biaxial stretching tests were performed to understand stretchable mechanism of inkjet-printed electrodes.
Results, Conclusions, and Discussions:: Results and Discussion: The objectives of this study were 1) providing proof of concept for the inkjet printing parameters for silver nanoparticle (AgNP) inks, 2) understanding the relationship between the dynamics of inkjet-printed patterns and surface energies of the substrate, 3) demonstrating inkjet printing skin-like electrodes with a fine resolution, and finally 4) demonstrating biopotential measurements with inkjet-printed skin-like electrodes. During experiments, the hydrophobicities of polyimide (PI) coated substrates were manipulated by applying CF4 plasma for different durations, and their effects on inkjet printing were measured by the means of contact angle measurements (Fig. 1a) and ink drop size and line width measurements (Fig. 1b and c). The effects of the printing parameters including jetting voltages, waveforms, and drop spacings of the AgNP inks via the drop size and line width measurements were also explored. Our results indicated that 1) the drop sizes increase as jetting voltages increase, 2) the line widths decrease with increasing drop spacings, and 3) the CF4 plasma increases the hydrophobicity of the surface. Based on those data, we were able to achieve the line width of 39.32 ± 1.21 µm and successfully demonstrated inkjet printing of skin-like electrodes whose feature size was 60 µm. The next steps will be mechanical characterizations and demonstrations of biopotential monitoring of inkjet-printed skin-like electrodes. Conclusion: Overall, inkjet-printed ultrathin skin-like electrodes will demonstrate reliable and user-friendly biopotential monitoring with high stretchability. Compared to other manufacturing techniques, inkjet printing technique will offer low-cost and time efficient manufacturing of flexible and stretchable electronics.
Acknowledgements (Optional): : This work was supported by NIH (NIA R15AG077210 and NICHD R15HD107526) and the Kansas INBRE (P20 GM103418).
References (Optional): : 1. Singh, M.; Haverinen, H. M.; Dhagat, P.; Jabbour, G. E., Inkjet Printing—Process and Its Applications. Advanced Materials 2010, 22, (6), 673-685.
2. Gao, M.; Li, L.; Song, Y., Inkjet printing wearable electronic devices. Journal of Materials Chemistry C 2017, 5, (12), 2971-2993.
3. Liu, W. C.; Watt, A. A. R., Solvodynamic Printing As A High Resolution Printing Method. Scientific Reports 2019, 9, (1), 10766.
