Softening implantable bioelectronics: Material designs, applications, and future directions

Immunomodulatory bioadhesive technologies

Bioadhesives have found significant use in medicine and engineering, particularly for wound care, tissue engineering, and surgical applications. Compared to traditional wound closure methods such as sutures and staples, bioadhesives offer advantages, including reduced tissue damage, enhanced healing, and ease of implementation. Recent progress highlights the synergy of bioadhesives and immunoengineering strategies, leading to immunomodulatory bioadhesives capable of modulating immune responses at local sites where bioadhesives are applied. They foster favorable therapeutic outcomes such as reduced inflammation in wounds and implants or enhanced local immune responses to improve cancer therapy efficacy. The dual functionalities of bioadhesion and immunomodulation benefit wound management, tissue regeneration, implantable medical devices, and post-surgical cancer management. This review delves into the interplay between bioadhesion and immunomodulation, highlighting the mechanobiological coupling involved. Key areas of focus include the modulation of immune responses through chemical and physical strategies, as well as the application of these bioadhesives in wound healing and cancer treatment. Discussed are remaining challenges such as achieving long-term stability and effectiveness, necessitating further research to fully harness the clinical potential of immunomodulatory bioadhesives.

Phase-change metal ink with pH-controlled chemical sintering for versatile and scalable fabrication of variable stiffness electronics

Variable stiffness electronics represent the forefront of adaptive technology, integrating rigid and soft electronics in a single system through dynamic mechanical modulation. While gallium's high modulus tuning ratio and rapid phase transitions make it ideal for transformative electronic systems (TES), its liquid-state instability, high surface tension, and unintended phase transitions during processing pose substantial challenges. Here, we introduce STiffness-Adjustable temperature-Responsive ink (STAR ink), a chemically sinterable gallium composite electronic ink designed to overcome these obstacles. STAR ink enables high-resolution (~50 micrometers) circuit patterning, large-scale batch fabrication, and three-dimensional structure coating at room temperature. Through pH-controlled chemical sintering, STAR ink-based TES exhibits exceptional mechanical tunability (tuning ratio: 1465) and electrical conductivity (2.27 × 106 siemens per meter). Demonstrated applications-from multilayered variable stiffness printed circuit boards (PCBs) matching standard PCBs' complexity to body-temperature responsive neural probe-underscore STAR ink's potential for reconfigurable electronics across consumer electronics and biomedical devices.

PEDOT:PSS-based bioelectronics for brain monitoring and modulation

The growing demand for advanced neural interfaces that enable precise brain monitoring and modulation has catalyzed significant research into flexible, biocompatible, and highly conductive materials. PEDOT:PSS-based bioelectronic materials exhibit high conductivity, mechanical flexibility, and biocompatibility, making them particularly suitable for integration into neural devices for brain science research. These materials facilitate high-resolution neural activity monitoring and provide precise electrical stimulation across diverse modalities. This review comprehensively examines recent advances in the development of PEDOT:PSS-based bioelectrodes for brain monitoring and modulation, with a focus on strategies to enhance their conductivity, biocompatibility, and long-term stability. Furthermore, it highlights the integration of multifunctional neural interfaces that enable synchronous stimulation-recording architectures, hybrid electro-optical stimulation modalities, and multimodal brain activity monitoring. These integrations enable fundamentally advancing the precision and clinical translatability of brain-computer interfaces. By addressing critical challenges related to efficacy, integration, safety, and clinical translation, this review identifies key opportunities for advancing next-generation neural devices. The insights presented are vital for guiding future research directions in the field and fostering the development of cutting-edge bioelectronic technologies for neuroscience and clinical applications.

Functional Hydrogels for Implantable Bioelectronic Devices

In recent years, with the rapid development of flexible electronics, implantable electronic devices have received increasing attention, and they provide new solutions for medical diagnosis and treatment. To ensure the long-term and stable operation of electronic devices in the internal environment, materials with conductivity, flexibility, biocompatibility, and other properties are in high demand. Hydrogels are polymers with three-dimensional network structures that not only have physical and chemical properties similar to those of biological tissues but can be also modulated by introducing functional groups to regulate the conductivity, adhesion, self-healing, and other functions. Therefore, hydrogel-based implantable bioelectronic devices are considered to be a candidate development direction in the future of the biomedical field. Here, this paper reviews the research progress in the molecular design and performance modulation of functionalized hydrogels based on four key properties of hydrogels: conductivity, self-healing, adhesion, and toughness. The latest progress in the use of functionalized hydrogels in implantable bioelectronic device applications is summarized below. Finally, discussions are given on the challenges and opportunities of hydrogels for implantable bioelectronic devices.

Flexible silicon for high-performance photovoltaics, photodetectors and bio-interfaced electronics

Silicon (Si) is currently the most mature and reliable semiconductor material in the industry, playing a pivotal role in the development of modern microelectronics, renewable energy, and bio-electronic technologies. In recent years, widespread research attention has been devoted to the development of advanced flexible electronics, photovoltaics, and bio-interfaced sensors/detectors, boosting their emerging applications in distributed energy sources, healthcare, environmental monitoring, and brain-computer interfaces (BCIs). Despite the rigid and brittle nature of Si, a series of new fabrication technologies and integration strategies have been developed to enable a wide range of c-Si-based high-performance flexible photovoltaics and electronics, which were previously only achievable with intrinsically soft organic and polymer semiconductors. More interestingly, programmable geometric engineering of crystalline silicon (c-Si) units and logic circuits has been explored to enable the fabrication of various highly flexible nanoprobes for intracellular sensing and the deployment of soft BCI matrices to record and understand brain neural activities for the development of advanced neuroprosthetics. This review will systematically examine the latest progress in the fabrication of Si-based flexible solar cells, photodetectors, and biological probing interfaces over the past decade, identifying key design principles, mechanisms, and technological milestones achieved through novel geometry, morphology, and composition control. These advancements, when combined, will not only promote the practical applications of sustainable energy and wearable electronics but also spur new breakthroughs in emerging human-machine interfaces (HMIs) and artificial intelligence applications, which hold significant implications for understanding neural activities, implementing more efficient artificial Intelligence (AI) algorithms, and developing new therapies or treatments. Finally, we will summarize and provide an outlook on the current challenges and future opportunities of Si-based electronics, flexible optoelectronics, and bio-sensing.

Clinical challenges and opportunities related to the biological responses experienced by indwelling and implantable bioelectronic medical devices

Implantable electrodes have been utilized for decades to stimulate, sense, or monitor a broad range of biological processes, with examples ranging from glucose monitoring devices to cochlear implants. While the underlying science related to the application of electrodes is a mature field, preclinical and clinical studies have demonstrated that there are still significant challenges in vivo associated with a lack of control over tissue-material interfacial interactions, especially over longer time frames. Herein we discuss the current challenges and opportunities for implantable electrodes and the associated bioelectronic interfaces across the clinical landscape with a focus on emerging technologies and the obstacles of biofouling, microbial colonization, and the foreign body response. Overcoming these challenges is predicted to open the door for a new generation of implantable medical devices and significant associated clinical impact. STATEMENT OF SIGNIFICANCE: Implantable electrodes have been utilised for decades to stimulate, sense, or monitor a broad range of biological processes, with examples ranging from glucose monitoring devices to cochlear implants. Next-generation bioelectronic implantable medical devices promise an explosion of new applications that have until this point in time been impossible to achieve. However, there are several persistent biological challenges hindering the realisation of these new applications. We present a clinical perspective on how these biological challenges have shaped the device market and clinical trial landscape. Specifically, we present statistical breakdowns of current device applications and discuss biofouling, the foreign body response, and microbial colonisation as the main factors that need to be addressed before a new generation of devices can be explored.

The Liquid Metal Age: A Transition From Hg to Ga

This review offers an illuminating journey through the historical evolution and modern-day applications of liquid metals, presenting a comprehensive view of their significance in diverse fields. Tracing the trajectory from mercury applications to contemporary innovations, the paper explores their pivotal role in industry and research. The analysis spans electrical switches, mechanical applications, electrodes, chemical synthesis, energy storage, thermal transport, electronics, and biomedicine. Each section examines the intricacies of liquid metal integration, elucidating their contributions to technological advancements and societal progress. Moreover, the review critically appraises the challenges and prospects inherent in liquid metal applications, addressing issues of recycling, corrosion management, device stability, economic feasibility, translational hurdles, and market dynamics. By delving into these complexities, the paper advances scholarly understanding and offers actionable insights for researchers, engineers, and policymakers. It aims to catalyze innovation, foster interdisciplinary collaboration, and promote liquid metal-enabled solutions for societal needs. Through its comprehensive analysis and forward-looking perspective, this review serves as a guide for navigating the landscape of liquid metal applications, bridging historical legacies with contemporary challenges, and highlighting the transformative potential of liquid metals in shaping future technologies.

Tissue/Organ Adaptable Bioelectronic Silk-Based Implants

Implantable bioelectronic devices, designed for both monitoring and modulating living organisms, require functional and biological adaptability. Pure silk is innovatively employed, which is known for its excellent biocompatibility, to engineer water-triggered, geometrically reconfigurable membranes, on which functions can be integrated by Micro Electro Mechanical System (MEMS) techniques and specially functionalized silk. These devices can undergo programmed shape deformations within 10 min once triggered by water, and thus establishing stable bioelectronic interfaces with natively fitted geometries. As a testament to the applicability of this approach, a twining peripheral nerve electrode is designed, fabricated, and rigorously tested, demonstrating its efficacy in nerve modulation while ensuring biocompatibility for successful implantation.