Cheong Hoon Kwon

High-power biofuel cell textiles from woven biscrolled carbon nanotube yarns

Biofuel cells that generate electricity from glucose in blood are promising for powering implantable biomedical devices. Immobilizing interconnected enzyme and redox mediator in a highly conducting, porous electrode maximizes their interaction with the electrolyte and minimizes diffusion distances for fuel and oxidant, thereby enhancing power density. Here we report that our separator-free carbon nanotube yarn biofuel cells provide an open-circuit voltage of 0.70 V, and a maximum areal power density of 2.18 mW cm(-2) that is three times higher than for previous carbon nanotube yarn biofuel cells. Biofuel cell operation in human serum provides high areal power output, as well as markedly increased lifetime (83% remained after 24 h), compared with previous unprotected biofuel cells. Our biscrolled yarn biofuel cells are woven into textiles having the mechanical robustness needed for implantation for glucose energy harvesting.

Hybrid carbon nanotube yarn artificial muscle inspired by spider dragline silk

Torsional artificial muscles generating fast, large-angle rotation have been recently demonstrated, which exploit the helical configuration of twist-spun carbon nanotube yarns. These wax-infiltrated, electrothermally powered artificial muscles are torsionally underdamped, thereby experiencing dynamic oscillations that complicate positional control. Here, using the strategy spiders deploy to eliminate uncontrolled spinning at the end of dragline silk, we have developed ultrafast hybrid carbon nanotube yarn muscles that generated a 9,800 r.p.m. rotation without noticeable oscillation. A high-loss viscoelastic material, comprising paraffin wax and polystyrene-poly(ethylene-butylene)-polystyrene copolymer, was used as yarn guest to give an overdamped dynamic response. Using more than 10-fold decrease in mechanical stabilization time, compared with previous nanotube yarn torsional muscles, dynamic mirror positioning that is both fast and accurate is demonstrated. Scalability to provide constant volumetric torsional work capacity is demonstrated over a 10-fold change in yarn cross-sectional area, which is important for upscaled applications.

Carbon Nanotube Yarn-Based Glucose Sensing Artificial Muscle

Boronic acid (BA), known to be a reversible glucose-sensing material, is conjugated to a nanogel (NG) derived from hyaluronic acid biopolymer and used as a guest material for a carbon multiwalled nanotube (MWNT) yarn. By exploiting the swelling/deswelling of the NG that originates from the internal anionic charge changes resulting from BA binding to glucose, a NG MWNT yarn artificial muscle is obtained that provides reversible torsional actuation that can be used for glucose sensing. This actuator shows a short response time and high sensitivity (in the 5-100 × 10(-3) m range) for monitoring changes in glucose concentration in physiological buffer, without using any additional auxiliary substances or an electrical power source. It may be possible to apply the glucose-sensing MWNT yarn muscles as implantable glucose sensors that automatically release drugs when needed or as an artificial pancreas.

Bio-inspired, moisture-powered hybrid carbon nanotube yarn muscles

Hygromorph artificial muscles are attractive as self-powered actuators driven by moisture from the ambient environment. Previously reported hygromorph muscles have been largely limited to bending or torsional motions or as tensile actuators with low work and energy densities. Herein, we developed a hybrid yarn artificial muscle with a unique coiled and wrinkled structure, which can be actuated by either changing relative humidity or contact with water. The muscle provides a large tensile stroke (up to 78%) and a high maximum gravimetric work capacity during contraction (2.17 kJ kg−1), which is over 50 times that of the same weight human muscle and 5.5 times higher than for the same weight spider silk, which is the previous record holder for a moisture driven muscle. We demonstrate an automatic ventilation system that is operated by the tensile actuation of the hybrid muscles caused by dew condensing on the hybrid yarn. This self-powered humidity-controlled ventilation system could be adapted to automatically control the desired relative humidity of an enclosed space.

Bio-inspired Hybrid Carbon Nanotube Muscles.

There has been continuous progress in the development for biomedical engineering systems of hybrid muscle generated by combining skeletal muscle and artificial structure. The main factor affecting the actuation performance of hybrid muscle relies on the compatibility between living cells and their muscle scaffolds during cell culture. Here, we developed a hybrid muscle powered by C2C12 skeletal muscle cells based on the functionalized multi-walled carbon nanotubes (MWCNT) sheets coated with poly(3,4-ethylenedioxythiophene) (PEDOT) to achieve biomimetic actuation. This hydrophilic hybrid muscle is physically durable in solution and responds to electric field stimulation with flexible movement. Furthermore, the biomimetic actuation when controlled by electric field stimulation results in movement similar to that of the hornworm by patterned cell culture method. The contraction and relaxation behavior of the PEDOT/MWCNT-based hybrid muscle is similar to that of the single myotube movement, but has faster relaxation kinetics because of the shape-maintenance properties of the freestanding PEDOT/MWCNT sheets in solution. Our development provides the potential possibility for substantial innovation in the next generation of cell-based biohybrid microsystems.

Mediator-free carbon nanotube yarn biofuel cell

Enzymatic biofuel cells are the most promising energy sources for implanted biomedical devices. However, direct implantation of biofuel cells has been limited by toxicity from metal-based redox mediators, and by a short operation time because of their instability, especially in physiological conditions. Here we introduce a yarn-type enzymatic biofuel cell for direct electron transfer using surface tension induced self-assembly of aligned multi-walled carbon nanotubes. This biofuel cell offers a maximum power density of 236 μW cm−2, and an open circuit voltage of 0.61 V in 30 mM glucose-containing phosphate-buffered saline, without any mediators or chemical cross-linkers. Furthermore, the proposed self-assembled carbon nanotube-based structure provides enhanced stability for biofuel cells: 84% of the initial power output was consistently maintained after 20 days of continuous operation. Our biocompatible, microsized yarn biofuel cell electrode could be applied easily as needle or catheter shapes in various biomedical fields.

Tensile actuators of carbon nanotube coiled yarn based on polydiacetylene–pluronic copolymers as temperature indicators

Most polydiacetylenes (PDAs) have been studied as chromatic sensors or temperature indicators because of their phase transition that is accompanied by a color change from blue to red. Here, we focus on the structural change based on the polydiacetylene phase transition for a temperature-responsive tensile actuator at low temperature using a copolymer composed of PDA and pluronic in a multi-walled carbon nanotube (MWCNT) coiled yarn. In this paper, we do not focus on the general color change phenomenon of PDA. We demonstrate that the volume change of PDA in the MWCNT coiled yarn provides ~180% tensile strain at low temperature (~53 °C). Insertion of the pluronic copolymer into the coiled yarn composed of PDA and MWCNT caused the tensile actuation temperature to decrease by ~6 °C (with tensile actuation of ~230%) compared to an actuator without pluronic copolymer. Furthermore, we could verify that the large tensile actuation was also predominantly affected by the melting of the nonpolymerized diacetylene (DA) monomer and the pluronic copolymer. MWCNT coiled yarn actuators with PDA-pluronic copolymer can be easily prepared, have a large tensile actuation, and are actuated at low temperature. It could be used as temperature indicators in the food, drugs, and medical fields.

Artificial Muscle: Carbon Nanotube Yarn-Based Glucose Sensing Artificial Muscle (Small 15/2016)

On page 2085, S. J. Kim and co-workers introduce a reversibly rotatable and highly glucose-sensitive carbon multiwalled nanotube (MWNT) yarn artificial muscle. This yarn is created using a boronic acid-conjugated hyaluronic acid/cholesterol nanogel (HC-BA NG) deposited on a two-end-tethered structural actuator. By exploiting the swelling/de-swelling of HC-BA NG, the MWNT yarn actuator shows a reversible torsional actuation with short response time and high sensitivity for monitoring changes in glucose concentration with 5-100 mM range. This actuator can be utilized for an implantable glucose monitoring sensor.