Functional Fiber Materials to Smart Fiber Devices.

The development of fiber materials has accompanied the evolution of human civilization for centuries. Recent advances in materials science and chemistry offered fibers new applications with various functions, including energy harvesting, energy storing, displaying, health monitoring and treating, and computing. The unique one-dimensional shape of fiber devices endows them advantages to work as human-interfaced electronics due to the small size, lightweight, flexibility, and feasibility for integration into large-scale textile systems. In this review, we first present a discussion of the basics of fiber materials and the design principles of fiber devices, followed by a comprehensive analysis on recently developed fiber devices. Finally, we provide the current challenges facing this field and give an outlook on future research directions. With novel fiber devices and new applications continuing to be discovered after two decades of research, we envision that new fiber devices could have an important impact on our life in the near future.

A Biodegradable Fiber Calcium Ion Sensor by Covalently Bonding Ionophores on Bioinert Nanoparticles.

Implantable sensors, especially ion sensors, facilitate the progress of scientific research and personalized healthcare. However, the permanent retention of implants induces health risks after sensors fulfill their mission of chronic sensing. Biodegradation is highly anticipated; while; biodegradable chemical sensors are rare due to concerns about the leakage of harmful active molecules after degradation, such as ionophores. Here, a novel biodegradable fiber calcium ion sensor is introduced, wherein ionophores are covalently bonded with bioinert nanoparticles to replace the classical ion-selective membrane. The fiber sensor demonstrates comparable sensing performance to classical ion sensors and good flexibility. It can monitor the fluctuations of Ca2+ in a 4-day lifespan in vivo and biodegrade in 4 weeks. Benefiting from the stable bonding between ionophores and nanoparticles, the biodegradable sensor exhibits a good biocompatibility after degradation. Moreover, this approach of bonding active molecules on bioinert nanoparticles can serve as an effective methodology for minimizing health concerns about biodegradable chemical sensors.

Technology Roadmap for Flexible Sensors.

Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of flexible sensors remains limited. To ease and to expedite their deployment, here, we identify bottlenecks hindering the maturation of flexible sensors and propose promising solutions. We first analyze challenges in achieving satisfactory sensing performance for real-world applications and then summarize issues in compatible sensor-biology interfaces, followed by brief discussions on powering and connecting sensor networks. Issues en route to commercialization and for sustainable growth of the sector are also analyzed, highlighting environmental concerns and emphasizing nontechnical issues such as business, regulatory, and ethical considerations. Additionally, we look at future intelligent flexible sensors. In proposing a comprehensive roadmap, we hope to steer research efforts towards common goals and to guide coordinated development strategies from disparate communities. Through such collaborative efforts, scientific breakthroughs can be made sooner and capitalized for the betterment of humanity.

An Anti-Biofouling Flexible Fiber Biofuel Cell Working in the Brain.

Biofuel cell (BFC) that transfers chemical energy into electricity is a promising candidate as an energy-harvesting device for implantable electronics. However, there still remain major challenges for implantable BFCs, including bulky and rigid device structure mismatching with soft tissues such as the brain, and the power output decreases due to the fouling process in a biological environment. Here, a flexible and anti-biofouling fiber BFC working in the brain chronically is developed. The fiber BFC is based on a carbon nanotube fiber electrode to possess small size and flexibility. A hydrophilic zwitterionic anti-biofouling polydopamine-2-methacryloyloxyethyl phosphorylcholine layer is designed on the surface of fiber BFC to resist the nonspecific protein adsorption in a complex biological environment. After implantation, the fiber BFC can achieve a stable device/tissue interface, along with a negligible immune response. The fiber BFC has first realized power generation in the mouse brain for over a month, exhibiting its promising prospect as an energy-harvesting device in vivo.

A fiber-shaped neural probe with alterable elastic moduli for direct implantation and stable electronic-brain interfaces.

Researchers developing implantable neural probes face a dilemma. Rigid neural probes facilitate direct implantation, but the brain tissue suffers from a vulnerable interface and a strong neuroinflammatory response due to mechanical mismatch between the probe and the brain tissue. Flexible neural probes offer stable interfaces and eliminate neuroinflammatory responses but require auxiliary implantation. Here, we have created a new kind of micro fiber-shaped neural probe with alterable elastic moduli before and after implantation. Carbon nanotube fibers and calcium crosslinked sodium alginate functioned as the core electrode and sheath layer, respectively. The response of calcium crosslinked sodium alginate to water will alter the probe elastic moduli from ∼10 GPa to ∼10 kPa post implantation, which is close to the elastic modulus of brain tissue. The micro fiber probes were directly implanted into mouse brains without any additional materials. After implantation, they became soft and offered dynamically adaptable interfaces with a reduced inflammatory response, benefiting long-term monitoring of neuron signals. Continuous four week monitoring of neuron signals was achieved. The simplicity of the strategy makes it suitable for versatile neuron techniques in neuron recording and modulation.

Phosphine-Free Synthesis of Metal Chalcogenide Quantum Dots by Directly Dissolving Chalcogen Dioxides in Alkylthiol as the Precursor.

Semiconductor quantum dots (QDs) are competitive emitting materials in developing new-generation light-emitting diodes (LEDs) with high color rendering and broad color gamut. However, the use of highly toxic alkylphosphines cannot be fully avoided in the synthesis of metal selenide and telluride QDs because they are requisite reducing agents and solvents for preparing chalcogen precursors. In this work, we demonstrate the phosphine-free preparation of selenium (Se) and tellurium (Te) precursors by directly dissolving chalcogen dioxides in the alkylthiol under the mild condition. The chalcogen dioxides are reduced to elemental chalcogen clusters, while the alkylthiol is oxidized to disulfides. The chalcogen clusters further combine with the disulfides, generating dispersible chalcogen precursors. The resulting chalcogen precursors are suitable for synthesizing various metal chalcogenide QDs, including CdSe, CdTe, Cu2Te, Ag2Te, PbTe, HgTe, and so forth. In addition, the precursors are of high reactivity, which permits a shorter QD synthesis process at lower temperature. Owing to the high quantum yield (QYs) and easy tunability of the photoluminescence (PL), the as-synthesized QDs are further employed as down-conversion materials to fabricate monochrome and white LEDs.