LAURA LEAY: Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on the hot topics in materials research. My name is Laura Leay. Additive manufacturing offers some excellent advantages when it comes to customizing the production of materials. For some applications, developments in the technology can lead to easier, cheaper, and more accessible production of materials and electronic components. Semiconductors are manufactured in a clean room, often taking days or weeks to produce. Multi-material printing could take manufacture out of the clean room, if the resolution of additive manufacturing can be improved. This challenge has been one focus for a particular research group. They have developed a new method for multi-material printing that uses light to cure the ink, allowing for finer structures to be printed and so obtaining a higher resolution than other printing methods. The ink includes a polymer that has applications in bioelectronics.
ANTONIO DOMINGUEZ-ALFARO: We have formulated for the first time a conducting ink made of PEDOT:PSS with good resolution. Then we have combined that in a multi-material approach modulating some of the properties of the device and then we have proved somehow that the mixed ionic-electronic conductor combined with an ionic conductor as a gel for electrodes for EMG has good performance – good signal-to-noise ratio – and good stability.
LAURA LEAY: That was Dr. Antonio Dominguez-Alfaro, a research associate in the bioelectronics laboratory led by George G. Malliaras at Cambridge University in the UK. Antonio has developed a printing method that achieves a resolution of less than 100 microns. This low resolution allows for neuron activity in the body to be determined since these biological structures can have a diameter of 100 microns or less. The team created two inks. One ink is a polymeric deep eutectic solvent – polyDES – made by combining and heating two salts to form a deep eutectic monomer and adding a photo-initiator to allow the ink to be cured. This ink is an ionic conductor so can capture signals from neurons inside a biological system. The other ink was based on the polymer PEDOT:PSS which is commonly used in bioelectronics as a mixed electronic and ionic conductor. The polymer was combined with a crosslinking polymer, photo-initiators, an acrylate and ethylene glycol to achieve an optimal balance between printability and high resolution of this ink. Its ability to act as an electronic conductor means that ionic activity can be converted to an electronic signal.
ANTONIO DOMINGUEZ-ALFARO: It was, at the end, a concept of a mixture of a mixed ionic and electronic conductor encapsulated on an ionic conductor.
LAURA LEAY: The inks were printed onto a flexible substrate so that they could be attached to the human body. The PEDOT:PSS was printed into mushroom shapes, forming electrodes surrounded by the polyDES which, as well as offering ionic conductivity, provided adhesion. The research team overcame quite a few challenges to design a working device.
ANTONIO DOMINGUEZ-ALFARO: It was particularly difficult to find a formulation where the PEDOT:PSS was stable, and also to find a way to make it adhesive to the skin without losing the performance and the conformation to the skin.
LAURA LEAY: The inks were mixed by hand and Antonio is keen to develop a method to make ink mixing autonomous. The 3D-printed mixed-material device was used to evaluate the electrical activity produced by muscles in a person’s forearm. Currently, methods of performing this evaluation in clinical settings – known as electromyography or EMG – can involve inserting small needles through the skin. The device was also shown to be stable, showing no loss of performance when used 90 days after it was printed. This research addresses many challenges of applying additive manufacturing in the field of bioelectronics.
ANTONIO DOMINGUEZ-ALFARO: We have addressed many problems that were in the literature up to now. And I think with the paper we have got most of them resolved: multi-material, stability, mixed conditions, a good or an interesting application and also adhesion.
LAURA LEAY: This work was published in a recent issue of Advanced Science. My name is Laura Leay from the Materials Research Society. For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on twitter, @MRSBulletin. Don’t miss the next episode of MRS Bulletin Materials News – subscribe now. Thank you for listening.