In recent advancements in bioelectronic technology, researchers have developed a groundbreaking approach involving stretchable and conductive nanocomposites. These innovations are instrumental in creating more effective wearable devices, such as skin-like electronics, and enhancing the capabilities of implantable bioelectronics and soft robots.

Traditional design approaches in this field have struggled to integrate brittle electrode materials with stretchable polymers. The core issue lies in the mechanical mismatch between these components, a significant barrier to achieving seamless integration in ultra-thin, stretchable conductive nanocomposites.

Laser-induced graphene (LIG), generated through laser irradiation of polyimide (PI), has emerged as a promising material in this context due to its digital patterning capabilities, adaptability in physical and chemical properties, and suitability for creating various wearable sensors. However, existing methods of integrating LIG into devices have been limited by mechanical constraints, primarily due to the brittle nature of LIG and its compatibility with only certain types of substrates.

Addressing these limitations, researchers have introduced an innovative ultrathin LIG-hydrogel-based nanocomposite. This novel material is designed for multifunctional applications as an on-skin sensor and implantable bioelectronics. The breakthrough involves a unique cryogenic transfer technique, where LIG is transferred to a hydrogel film at a cryogenic temperature of 77 Kelvin (approximately -196°C). This process overcomes the mechanical mismatch by using the hydrogel as an interface for energy dissipation and electrical conduction.

One of the critical achievements of this method is the significant enhancement of the intrinsic stretchability of the LIG. The process induces continuously deflected cracks in the LIG, which improves its stretchability by more than five times. This advancement opens up new possibilities for constructing carbon-hydrogel-based stretchable nanocomposites that are ultra-thin yet robust, paving the way for integrated sensor systems in wearable and implantable bioelectronics.

Kaichen Xu, the leading researcher in this study, highlighted the limitations of conventional LIG transfer methods, which necessitated thicker substrates for adequate transfer, thereby restricting their application in bioelectronics. Xu's team overcame these limitations with the cryogenic transfer approach, employing an ultrathin and adhesive polyvinyl alcohol/phytic acid/honey (PPH) hydrogel.

The study also reveals insights from molecular dynamics calculations, which show an enhanced interfacial binding energy between the graphene and the crystallised water in the hydrogel at the cryogenic temperature. This finding was corroborated by a peeling test, which demonstrated a substantial increase in the peeling force at 77 Kelvin.

Moreover, the universality of this transfer technology was confirmed by successfully transferring LIG onto various types of hydrogels. However, it was noted that only adhesive hydrogels could form a stable mechanical binding interface under tensile strain.

The practical applications of this technology are vast. The researchers have successfully integrated multimodal sensor components into a multifunctional wearable sensor sheet designed for on-skin in vitro monitoring. This integration was achieved using the laser direct writing and cryogenic transfer technique. Additionally, the ultrathin and biocompatible nature of the micropatterned LIG-based nanocomposites allows them to interface with living tissues seamlessly. In a notable application, the researchers demonstrated this by tracking cardiac signals in Sprague Dawley (SD) rats, showcasing the potential for real-time, in situ monitoring of vital biological processes.

This breakthrough in stretchable graphene-hydrogel interfaces marks a significant stride in bioelectronic technology. This research opens up new avenues for developing advanced wearable and implantable bioelectronics by addressing the longstanding issue of mechanical mismatch in conductive nanocomposites. Such devices promise to revolutionise how we interact with and monitor biological systems, offering potential advancements in medical diagnostics, personalised healthcare, and human-machine interfaces.

The research led by Kaichen Xu and his team not only provides a viable strategy for constructing ultrathin, stretchable nanocomposites but also sets the stage for future innovations in the field of bioelectronics. Their work underscores the importance of interdisciplinary approaches in overcoming technical challenges and advancing the frontiers of technology for better human health and well-being.

COMPANIES TO WATCH:

Macklin Biochemical Technology, Reade Advanced Materials, Graphene One LLC

Author:

Arnold Kristoff

Content Producer and Writer

Nano Magazine | The Breakthrough 

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