Nozzle Clogging Investigation of Silver Nanoparticle Ink for Improved Printing Performance of Flexible, Wearable Medical Devices

Wearable, flexible 3D electronic devices encompass a significant potential for healthcare applications, demonstrated by their ability to conduct real-time, point-of-care patient monitoring while ensuring user comfort and convenience. However, the fabrication of these devices remains challenging, primarily due to the complexities involved with integrating multiple materials and the intricate mechanical property requirements [1, 2]. Powder-based inkjet 3D printing is a feasible fabrication technique with the ability to simultaneously process multiple materials. The 3D printing process involves depositing conductive silver nanoparticle ink onto thermoplastic powder, resulting in 3D structures with embedded conductive silver channels. While inkjet 3D printing is promising for 3D flexible electronics, nozzle clogging remains a crucial factor that hinders reliable printing. Typically, silver ink is designed for 2D printing at room temperature. In contrast, using silver ink in the powder-based inkjet 3D printer exposes it to temperatures above 100°C [3]. This is due to the major difference between inkjet 3D printing and its 2D counterpart – the need for powder fusion during the 3D printing process that involves heat and a longer nozzle non-jetting duration.

Therefore, we identified printing temperature and nozzle non-jetting duration as the key parameters for systematic investigation of silver ink nozzle clogging. Silver ink nozzles were subjected to temperatures ranging from room temperature to 140°C – the target temperature for powder fusion – after non-jetting intervals of 1.5, 5, or 8.5 minutes. The progression of nozzle clogging was monitored through scanning electron microscopy (SEM) and laser profilometry techniques for the analysis of jetted silver ink morphology and deposition characteristics. Digital microscopy was also utilized to directly examine the nozzle condition over time. We discovered that the temperature had a minimal effect on nozzle clogging for the non-jetting duration of 1.5 minutes at 25°C and 140°C. In contrast, the non-jetting duration of 8.5 minutes resulted in jetted ink volume variation of 7.7% and 133.9% for temperatures 25°C and 140°C respectively. Hence, we determined that the combination of a long non-jetting duration (>5 minutes) with high temperature (>100°C) resulted in the most prominent nozzle clogging for silver ink. The proposed nozzle clogging analyses provided insight into the clogging mechanisms which is critical for implementation of anti-clogging strategies for enhanced printing reliability of silver ink.

[1] H. Hu et al., "Elasto-plastic design of ultrathin interlayer for enhancing strain tolerance of flexible electronics," Acs Nano, vol. 17, no. 4, pp. 3921-3930, 2023, doi: 10.1021/acsnano.2c12269.
[2] Y.-Y. Hsu et al., "Design for reliability of multi-layer stretchable interconnects," Journal of Micromechanics and Microengineering, vol. 24, no. 9, 2014, doi: 10.1088/0960-1317/24/9/095014.
[3] K. Ráz, Z. Chval, and S. Thomann, "Minimizing Deformations during HP MJF 3D Printing," Materials, vol. 16, no. 23, doi: 10.3390/ma16237389.