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1. Dry Printing Fully Functional Eco-Friendly and Disposable Transient Papertronics

   https://doi.org/10.1088/2058-8585/ad70c5  

   Taba, Adib; Patel, Aarsh; Mahjouri-Samani, Masoud (August 2024, Flexible and Printed Electronics)

   Abstract The demand for flexible printed electronics is growing fast, especially with the move toward the Internet of Things (IoT). These printed electrons are usually designed for short-term use, after which they are disposed of. The polymeric substrates used in printed electronics comprise the biggest portion of their non-biodegradable E-waste after their disposal. This paper demonstrates the feasibility of printing fully functional transient electronics on flexible, water-soluble, and biodegradable paper substrates using the dry printing approach. The in-situ generation and real-time sintering of silver nanoparticles at room temperature enables the fabrication of complex circuits on such water-soluble papers. A layout similar to an Arduino pro mini board is printed on both sides of a paper substrate with electrical interconnects. Various electrical components are then directly mounted to fabricate a complete, working paper Arduino circuit. Cyclic bending tests demonstrate the mechanical durability and reliability of printed paper circuits under repeated bending stress. The process uniquely achieves robust and complex printed electronics without thermal damage, and the water solubility tests successfully show rapid dissolution of the paper devices in water. Furthermore, the components detached during dissolution are collected and reused, demonstrating the recyclability of the process. Overall, this transformative manufacturing method establishes key technical capabilities to produce next-generation sustainable, green electronics and sensors using renewable materials. 

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2. Dry Printing and Additive Nanomanufacturing of Flexible Hybrid Electronics and Sensors

   https://doi.org/10.1002/admi.202102569  

   Ahmadi, Zabihollah; Lee, Seungjong; Patel, Aarsh; Unocic, Raymond_R; Shamsaei, Nima; Mahjouri‐Samani, Masoud (February 2022, Advanced Materials Interfaces)

   Abstract The growing demand for flexible and wearable hybrid electronics has triggered the need for advanced manufacturing techniques with versatile printing capabilities. Complex ink formulations, use of surfactants/contaminants, limited source materials, and the need for high‐temperature heat treatments for sintering are major issues facing the current inkjet and aerosol printing methods. Here, the nanomanufacturing of flexible hybrid electronics (FHE) by dry printing silver and indium tin oxide on flexible substrates using a novel laser‐based additive nanomanufacturing process is reported. The electrical resistance of the printed lines is tailored during the print process by tuning the geometry and structure of the printed samples. Different FHE designs are fabricated and tested to check the performance of the devices. Mechanical reliability tests including cycling, bending, and stretching confirm the expected performance of the printed samples under different strain levels. This transformative liquid‐free process allows the on‐demand formation and in situ laser crystallization of nanoparticles for printing pure materials for future flexible and wearable electronics and sensors. 

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3. In-situ tension investigation of additively manufactured silver lines on flexible substrates

   https://doi.org/10.1016/j.addlet.2023.100171  

   Lee, Seungjong; Ahmadi, Zabihollah; Paul, Mikyle; Mahjouri-Samani, Masoud; Shao, Shuai; Shamsaei, Nima (December 2023, Additive Manufacturing Letters)

   The reliability of additively manufactured flexible electronics or so-called printed electronics is defined as mean time to failure under service conditions, which often involve mechanical loads. It is thus important to understand the mechanical behavior of the printed materials under such conditions to ensure their applicational reliability in, for example, sensors, biomedical devices, battery and storage, and flexible hybrid electronics. In this article, a testing protocol to examine the print quality of additively nanomanufactured electronics is presented. The print quality is assessed by both tensile and electrical resistivity responses during in-situ tension tests. A laser based additive nanomanufacturing method is used to print conductive silver lines on polyimide substrates, which is then tested in-situ under tension inside a scanning electron microscope (SEM). The surface morphology of the printed lines is continuously monitored via the SEM until failure. In addition, the real-time electrical resistance variations of the printed silver lines are measured in-situ with a multimeter during tensile tests conducted outside of the SEM. The protocol is shown to be effective in assessing print quality and aiding process tuning. Finally, it is revealed that samples appearing identical under the SEM can have significant different tendencies to delaminate. 

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4. Laser-assisted dry printing eco-friendly paper-based humidity and temperature sensors

   https://doi.org/10.2351/7.0001652  

   Jaiswal, Suman; Taba, Adib; Patel, Aarsh; Mahjouri-Samani, Masoud (February 2025, Journal of Laser Applications)

   Monitoring humidity and temperature is critical for many applications, including enhancing food production in greenhouses and open farms. This demands for environmentally friendly, cost-effective, and biocompatible sensors. Paper-based sensors meet these requirements as they are cost-effective, eco-friendly, and adaptable to varying agricultural conditions due to their affordability, biodegradability, and flexibility. This research developed printed capacitance-based humidity and resistance-based temperature sensors using a dry additive nanomanufacturing technique on four distinct types of commercially available uncoated paper substrates. Based on the principles of a capacitor and resistor, humidity and temperature sensors were fabricated by printing silver interdigitated electrodes on papers with varying solubility and thicknesses to measure the humidity absorption capability and the printed silver electrode’s response to temperature change. The sensors successfully detected the changes in relative humidity levels from 20 to 90% and temperature variations from 25 to 50 °C. The humidity and temperature sensors developed in this study have strong implications for use in smart agricultural applications, food supply, food storage, and preservation. Since these sensors are affordable, biodegradable, and environmentally friendly, they can be intended for one- or two-time applications and safely disposed of after use. 

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5. Electrohydrodynamic printing of silver nanowires for flexible and stretchable electronics

   https://doi.org/10.1039/C7NR09570H  

   Cui, Zheng; Han, Yiwei; Huang, Qijin; Dong, Jingyan; Zhu, Yong (January 2018, Nanoscale)

   A silver nanowire (AgNW) based conductor is a promising component for flexible and stretchable electronics. A wide range of flexible/stretchable devices using AgNW conductors has been demonstrated recently. High-resolution, high-throughput printing of AgNWs remains a critical challenge. Electrohydrodynamic (EHD) printing has been developed as a promising technique to print different materials on a variety of substrates with high resolution. Here, AgNW ink was developed for EHD printing. The printed features can be controlled by several parameters including AgNW concentration, ink viscosity, printing speed, stand-off distance, etc . With this method, AgNW patterns can be printed on a range of substrates, e.g. paper, polyethylene terephthalate (PET), glass, polydimethylsiloxane (PDMS), etc. First, AgNW samples on PDMS were characterized under bending and stretching. Then AgNW heaters and electrocardiogram (ECG) electrodes were fabricated to demonstrate the potential of this printing technique for AgNW-based flexible and stretchable devices. 

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