Direct Wiring of Liquid Metal on an Ultrasoft Substrate Using a Polyvinyl Alcohol Lift-off Method

Area of Science:

• Materials Science
• Biotechnology
• Electrical Engineering

Background:

• Ultrasoft materials like biological tissues and hydrogels are crucial for advanced wearable devices, implantable devices, and soft robotics.
• Gallium-based liquid metals (LMs) offer biocompatibility and ultrasoftness, ideal for electrodes on soft substrates.
• Conventional soft substrates are more wettable to LMs than biological tissues and gels, posing a challenge for direct wiring.

Purpose of the Study:

• To demonstrate a novel method for transferring liquid metal paste onto ultrasoft substrates, including biological tissues and gels.
• To overcome the wettability challenges of ultrasoft materials for precise liquid metal wiring.
• To enable the integration of electrical systems onto soft and biological materials.

Main Methods:

• Development of a liquid metal (LM) paste using Ga-based LM and Ni nanoparticles.
• Utilization of sacrificial polyvinyl alcohol (PVA) films for transferring LM paste patterns onto ultrasoft substrates.
• Fabrication of microscale wiring and 3D structures on gel fibers and biological tissues.

Main Results:

• Successful transfer of LM paste onto biological tissue and gels with a minimum line width of approximately 165 μm.
• Demonstration of 3D wiring capabilities, including helical structures on gel fibers.
• Successful application in vagus nerve stimulation in rats and integration of a temperature measurement system onto a gel substrate.

Conclusions:

• The sacrificial PVA film method effectively enables the transfer of LM paste onto challenging ultrasoft substrates.
• This technique facilitates the development of advanced electrical devices, including implantable sensors and stimulators, for biological applications.
• The study provides a foundational approach for wiring fabrication and system integration on ultrasoft materials.