Framework structure with nanoscopic insulation enables components for soft robotics

The schematic illustration shows how the basic structure of the material is compressed without being destroyed. Credit: Igor Barg et. al, Adv. Funct. Mater. 2023, 2212688 (CC BY 4.0)

Classical robots are known for their ability to lift heavy loads and carry out automated processes with precision. However, their rigid and bulky nature makes them unsuitable for delicate work and interaction with humans. The field of soft robotics focuses on developing robots made of soft, organic materials and flexible technical components that can perform fluid and fine movements and adapt to their environment. Soft robots require elastic electrical conductors for communication between their sensors and actuators. Materials researchers at Kiel University have developed a novel soft conductive material that shows remarkably stable electrical properties even upon deformation. This article delves into the details of this soft conductive material and its potential applications.

The Challenge with Conventional Conductors

Conventional conductors made of metal are rigid and unsuitable for flexible components. They change their electrical resistance upon deformation, rendering them unsuitable for use in soft robotics. Soft robotics requires elastic electrical conductors that can maintain a constant electrical resistance even upon deformation.

The Development of the Novel Soft Conductive Material

Materials researchers at Kiel University developed a novel soft conductive material that can maintain a constant electrical resistance even upon deformation. The material is made of fine wires that resemble a dark sponge. The wires are made of interconnected microtubes made of an electrically conductive polymer, which makes the material ultra-light and extremely elastic.

Mechanical compression tests show how the coating (left) improves the elasticity compared to the same material without the coating (right). (Scale in blue: 6mm.). Credit: Igor Barg et. al, Adv. Funct. Mater. 2023, 2212688 (CC BY 4.0)

Nanoscopic Insulation Film to Protect Electrical Properties

The research team coated the soft conductive material with a nanoscopic thin film of Polytetrafluorethylene (PTFE) to protect its electrical properties from external influences such as moisture. The coating prevents the wires from coming into direct contact with each other during compression, thus avoiding the piezoresistive effect, which changes the resistance of the material upon deformation. The insulation also improves the mechanical stability of the wires.

The Technique of Initiating Chemical Vapor Deposition (iCVD)

To coat the highly porous framework structure of the soft conductive material, the research team used the technique of initiating chemical vapor deposition (iCVD). This technique allows for the even coating of materials with complex structures and surfaces conformally. The process involves bringing together different gases in a reactor, triggering a chemical reaction, and causing a thin polymer film to grow on the material to be coated. Since the coating is only a few nanometers thin, the wires remain elastic, and the total weight of the material hardly increases.

Potential Applications in Medical Technology and Energy Storage

The research team believes that their soft conductive material has potential applications in various fields, including medical technology and energy storage. The material's stability and flexibility make it suitable for use in medical devices, such as wearable sensors and prosthetics. Additionally, the material's elasticity and electrical conductivity make it suitable for energy storage applications, such as in stretchable batteries.

Journal Information: Igor Barg et al, Strain‐Invariant, Highly Water Stable All‐Organic Soft Conductors Based on Ultralight Multi‐Layered Foam‐Like Framework Structures, Advanced Functional Materials (2023). DOI: 10.1002/adfm.202212688