Conductive polymer optimized for wearable biosensors

If you are aiming for stretchy, health monitoring, and skin-like sensor sheets, you need materials with demanding properties. They must be flexible, biocompatible and simultaneously conductive.

The research team at the Max Planck Institute for Polymer Research is working on this complex task. In recent research, scientists present innovative approaches. Using a transfer printing process, the conductive polymer pedo:PSS is modified via a plasticizer that diffuses from the substrate into the polymer membrane. This greatly improves both the electrical conductivity and elasticity of the material.

The findings are published in the Journal Advanced Science.

A deformable patch that measures your heart rate, detects biomarkers in sweat, and feels as soft and flexible as your skin. New materials need to be developed.

To realize such ideas and electronic devices, such as wearables and skin, generally, requires materials with high electrical conductivity and mechanical elasticity.

A team of scientists at the Max Planck Institute for Polymer Research, led by Dr. Ulrike Kraft, is currently working on this challenge. However, stretchability and electrical conductivity are often inconsistent, complicating the development of suitable materials, explains Ulrike Kraft, head of the Organic Bioelectronic Research Group.

In the current study, researchers demonstrate how to overcome these conflicting objectives through targeted migration from substrates to PEDOT:PSS polymer films.

Their approach utilizes a transfer printing process that allows for the rapid, reliable and simple transfer of conductive polymer films to stretchable biodegradable substrates. As a conductive polymer, the particularly promising material PEDOT:PSS is used, combining transparency, flexibility and biocompatibility.

“The plasticizers contained in the substrate diffuse into the conductive polymer, thereby improving both electrical and mechanical properties,” explains Carla Volkert, a doctoral student and first author of the study.

Furthermore, this approach allows for basic insights into the operation of stretchable electronic materials. Combining a variety of analytical methods, including electrical characterization, microscopic imaging, atomic force microscopy, and Raman spectroscopy, researchers were able to gain new insights into the morphological and electronic changes of PEDOT: PSS under strain.

Of particular note is the observed chain alignment of the polymer chains, resulting in an increase in electrical conductivity under mechanical stress.

“Our method simultaneously improves the elasticity and electrical conductivity of PEDOT:PSS. This is an important step towards skin biosensors,” explains Ulrike Kraft, head of the Organic Bioelectronics Research Group.

Therefore, this work represents an important contribution to the fundamental understanding of soft, stretchable conductive materials, as well as opening new perspectives for the development of innovative technologies. This ranges from flexible electrodes in electrical measurement diagrams (ECGs) to stretchable skin biosensors that can detect and monitor analytes such as sweat stress hormones.

The next objective is to apply this new approach to the manufacture and characterization of stretchable biosensors.