Biocompatibility Testing of Liquid Metal as an Interconnection Material for Flexible Implant Technology

Diels-Alder Network Blends as Self-Healing Encapsulants for Liquid Metal-Based Stretchable Electronics

Two dynamic covalent networks based on the Diels-Alder reaction were blended to exploit the properties of the dissimilar polymer backbones. Furan-functionalized polyether amines based on poly(propylene oxide) (PPO) FD4000 and polydimethylsiloxane (PDMS) FS5000 were mixed in a common solvent and reversibly cross-linked with the same bismaleimide DPBM. The morphology of the phase-separated blends is primarily controlled by the concentration of backbones. Increasing the PDMS content of the blends results in a dilute droplet morphology at 25 wt %, with a growing size and concentration of droplets and the formation of two separate PPO- and PDMS-rich layers at 50 wt %. Further increasing the PDMS content to 75 wt % leads to larger droplets and a thicker layer of the secondary phase. The hydrophobic PDMS phase creates a barrier against water, while the more hydrophilic PPO phase enhances the resistance against oxygen diffusion. Lowering the maleimide-to-furan stoichiometric ratio resulted in a decrease in cross-link density and thus more flexible and stretchable encapsulants. Changes in the stoichiometric ratio also affected the phase morphology due to resulting changes in phase separation and network formation kinetics. Lowering the stoichiometric ratio also resulted in enhanced self-healing properties of 96% at room temperature as a consequence of the increased chain mobility in the blended networks. The self-healing blends were used to encapsulate liquid metal circuits to create stretchable strain sensors with a linear electro-mechanical response without much drift or hysteresis, which could be efficiently recovered by 90% after the damage-healing cycles.

Resorbable conductive materials for optimally interfacing medical devices with the living

Implantable and wearable bioelectronic systems are arising growing interest in the medical field. Linking the microelectronic (electronic conductivity) and biological (ionic conductivity) worlds, the biocompatible conductive materials at the electrode/tissue interface are key components in these systems. We herein focus more particularly on resorbable bioelectronic systems, which can safely degrade in the biological environment once they have completed their purpose, namely, stimulating or sensing biological activity in the tissues. Resorbable conductive materials are also explored in the fields of tissue engineering and 3D cell culture. After a short description of polymer-based substrates and scaffolds, and resorbable electrical conductors, we review how they can be combined to design resorbable conductive materials. Although these materials are still emerging, various medical and biomedical applications are already taking shape that can profoundly modify post-operative and wound healing follow-up. Future challenges and perspectives in the field are proposed.

Liquid metal-hydrogel composites for flexible electronics

As an emerging functional material, liquid metal-hydrogel composites exhibit excellent biosafety, high electrical conductivity, tunable mechanical properties and good adhesion, thus providing a unique platform for a wide range of flexible electronics applications such as wearable devices, medical devices, actuators, and energy conversion devices. Through different composite methods, liquid metals can be integrated into hydrogel matrices to form multifunctional composite material systems, which further expands the application range of hydrogels. In this paper, we provide a brief overview of the two materials: hydrogels and liquid metals, and discuss the synthesis method of liquid metal-hydrogel composites, focusing on the improvement of the performance of hydrogel materials by liquid metals. In addition, we summarize the research progress of liquid metal-hydrogel composites in the field of flexible electronics, pointing out the current challenges and future prospects of this material.

Liquid Metal-Based Flexible Bioelectrodes for Management of In-Stent-Restenosis: Potential Application

Although vascular stents have been widely used in clinical practice, there is still a risk of in-stent restenosis after their implantation. Combining conventional vascular stents with liquid metal-based electrodes with impedance detection, irreversible electroporation, and blood pressure detection provides a new direction to completely solve the restenosis problem. Compared with conventional rigid electrodes, liquid metal-based electrodes combine high conductivity and stretchability, and are more compliant with the implantation process of vascular stents and remain in the vasculature for a long period of time. This perspective reviews the types and development of conventional vascular stents and proposes a novel stent that integrates liquid metal-based electrodes on conventional vascular stents. This vascular stent has three major functions of prediction, detection and treatment, and is expected to be a new generation of cardiovascular implant with intelligent sensing and real-time monitoring.

Liquid Metal Patterning and Unique Properties for Next-Generation Soft Electronics

Room-temperature liquid metal (LM)-based electronics is expected to bring advancements in future soft electronics owing to its conductivity, conformability, stretchability, and biocompatibility. However, various difficulties arise when patterning LM because of its rheological features such as fluidity and surface tension. Numerous attempts are made to overcome these difficulties, resulting in various LM-patterning methods. An appropriate choice of patterning method based on comprehensive understanding is necessary to fully utilize the unique properties. Therefore, the authors aim to provide thorough knowledge about patterning methods and unique properties for LM-based future soft electronics. First, essential considerations for LM-patterning are investigated. Then, LM-patterning methods-serial-patterning, parallel-patterning, intermetallic bond-assisted patterning, and molding/microfluidic injection-are categorized and investigated. Finally, perspectives on LM-based soft electronics with unique properties are provided. They include outstanding features of LM such as conformability, biocompatibility, permeability, restorability, and recyclability. Also, they include perspectives on future LM-based soft electronics in various areas such as radio frequency electronics, soft robots, and heterogeneous catalyst. LM-based soft devices are expected to permeate the daily lives if patterning methods and the aforementioned features are analyzed and utilized.

Responsive Liquid Metal Droplets: From Bulk to Nano

Droplets exist widely in nature and play an extremely important role in a broad variety of industrial processes. Typical droplets, including water and oil droplets, have received extensive attention and research, however their single properties still cannot meet diverse needs. Fortunately, liquid metal droplets emerging in recent years possess outstanding properties, including large surface tension, excellent electrical and thermal conductivity, convenient chemical processing, easy transition between liquid and solid phase state, and large-scale deformability, etc. More interestingly, liquid metal droplets with unique features can respond to external factors, including the electronic field, magnetic field, acoustic field, chemical field, temperature, and light, exhibiting extraordinary intelligent response characteristics. Their development over the past decade has brought substantial breakthroughs and progress. To better promote the advancement of this field, the present article is devoted to systematically summarizing and analyzing the recent fundamental progress of responsive liquid metal droplets, not only involving droplet characteristics and preparation methods, but also focusing on their diverse response behaviors and mechanisms. On this basis, the challenges and prospects related to the following development of liquid metal droplets are also proposed. In the future, responsive liquid metal droplets with a rapid development trend are expected to play a key role in soft robots, biomedicine, smart matter, and a variety of other fields.