Showing papers by "Sheng Xu published in 2017"

Soft, stretchable, high power density electronic skin-based biofuel cells for scavenging energy from human sweat

Abstract: This article describes the fabrication, characterization, and real-life application of a soft, stretchable electronic-skin-based biofuel cell (E-BFC) that exhibits an open circuit voltage of 0.5 V and a power density of nearly 1.2 mW cm−2 at 0.2 V, representing the highest power density recorded by a wearable biofuel cell to date. High power density is achieved via a unique combination of lithographically-patterned stretchable electronic framework together with screen-printed, densely-packed three-dimensional carbon-nanotube-based bioanode and cathode array arranged in a stretchable “island-bridge” configuration. The E-BFC maintains its performance even under repeated strains of 50%, and is stable for two days. When applied directly to the skin of human subjects, the E-BFC generates ∼1 mW during exercise. The E-BFC is able to power conventional electronic devices, such as a light emitting diode and a Bluetooth Low Energy (BLE) radio. This is the first example of powering a BLE radio by a wearable biofuel cell. Successful generation of high power density under practical conditions and powering of conventional energy-intense electronic devices represents a major step forward in the field of soft, stretchable, wearable energy harvesting devices.

Self-assembled three dimensional network designs for soft electronics

Abstract: Low modulus, compliant systems of sensors, circuits and radios designed to intimately interface with the soft tissues of the human body are of growing interest, due to their emerging applications in continuous, clinical-quality health monitors and advanced, bioelectronic therapeutics. Although recent research establishes various materials and mechanics concepts for such technologies, all existing approaches involve simple, two-dimensional (2D) layouts in the constituent micro-components and interconnects. Here we introduce concepts in three-dimensional (3D) architectures that bypass important engineering constraints and performance limitations set by traditional, 2D designs. Specifically, open-mesh, 3D interconnect networks of helical microcoils formed by deterministic compressive buckling establish the basis for systems that can offer exceptional low modulus, elastic mechanics, in compact geometries, with active components and sophisticated levels of functionality. Coupled mechanical and electrical design approaches enable layout optimization, assembly processes and encapsulation schemes to yield 3D configurations that satisfy requirements in demanding, complex systems, such as wireless, skin-compatible electronic sensors.

Merging of Thin- and Thick-Film Fabrication Technologies: Toward Soft Stretchable “Island–Bridge” Devices

Abstract: DOI: 10.1002/admt.201600284 fabrication of such materials onto deterministically stretchable designs thus requires reliance on other fabrication techniques. The key focus of the present work was to develop a strategy for combining lithography (thin-film) and screen-printing (thick-film) techniques to realize deterministic, high-performance stretchable devices. Screen printing has been widely used toward large-scale, cost-effective incorporation of a myriad of materials onto numerous substrates for various applications.[19,20] However, most of the printable inks form either rigid or flexible films. Developing stretch-enduring inks is challenging as only a handful of elastomeric binders and functional materials can be homogeneously dispersed to achieve highperformance stretchable inks. While lithographic and printing techniques have been the primary methods used for fabricating wearable devices, their distinct and complementary advantages and characteristics have not been combined. The described new hybrid fabrication process, combining the printing of functional ink materials onto lithographically stretchable deterministic patterns, represents an attractive route that can address the challenges of each individual technique. For example, while lithography has been exploited for realizing complex stretchable systems, they are limited to thin films (<10 μm), which are not suitable for devices requiring high loading of active materials (e.g., energy harvesting and storage devices). In addition, there are limited choices of materials that can be vacuum deposited and solution etched. On the other hand, screen printing enables sufficient loading of a variety of active materials into thick (20–50 μm) films, but it suffers from meeting required layout resolutions and performance. In the hybrid system, the thick film resides over rigid isolated islands interconnected with free-standing stretchable serpentine bridges. The device can thus afford to include a wide range of rigid and lithographically incompatible materials without concern of device failure, since most of the strain is accommodated by the serpentine structures while leaving the thick-film islands unharmed. The hybrid system thus combines the best of two worlds. The hybrid pattern has been realized by first lithographically fabricating the entire “island–bridge” layout of the device in gold onto an elastomeric substrate, followed by printing the ink layer on the islands (Figure 1A). Briefly, a polyimide-coated copper film was bonded to a polydimethylsiloxane-covered glass slide. Thereafter, copper electrodes were patterned via standard lithographic technique. Subsequently, gold electrodes were patterned onto the copper design. Later, a top layer of polyimide was patterned to define the active electrode area and finally transferred to an EcoFlex layer. Subsequently, the device was transferred to the printer where electrodes were screen printed with inks. The detailed fabrication process is described in the Biointegrated soft electronic devices are expected to play crucial roles in consumer electronics,[1] healthcare,[2] and energy[3] domains to significantly transform our lifestyle. However, mating of conventional rigid electronic devices with soft biological tissues leads to significant compromise in performance.[4] The rapidly emerging field of soft, stretchable electronics has the potential to address this issue by ensuring conformal contact between wearable devices and the human body.[5] Researchers have mainly focused on using two approaches for realizing stretchable devices: deterministic[6] and random[7] composites. The deterministic composite route, also known as the “island–bridge” approach, involves lithographic fabrication of the device components onto rigid islands connected by serpentine bridges and ultimately bonding the device to a soft, stretchable elastomeric substrate.[8] When subjected to external strain, the underlying elastomeric substrate and the serpentine structures accommodate most of the stress, thus leaving the crucial device components unharmed.[5,9] On the other hand, random composite-based stretchability relies on the random incorporation of functional material within or on the elastomeric matrix to develop stretchable systems.[10] Deterministically stretchable devices have an edge over their random composite counterparts since the performance of random composite devices diminishes by incorporating the functional components within/on elastomeric substrates.[11] In contrast, deterministic systems allow fabrication of complex, stretchable devices with performance similar to conventional rigid devices.[12] Additionally, lithographically fabricated deterministic stretchable systems can possess features with a few micrometer and even sub-micrometer dimensions, thus leading to compact, multifunctional devices. However, widespread applications of such devices are hindered since there are several materials that are incompatible with the lithographic fabrication route. For example, many devices rely on nanomaterials,[13] polymer composites,[14] carbonaceous,[15] biological,[16] lowtemperature,[17] and solvent-sensitive[18] materials. Integrating these materials in microstructured forms on elastomeric substrates, for intimate contact with biological tissues, will open up new paradigms for wearable devices. High-precision scalable www.advmattechnol.de

Electroplating lithium transition metal oxides

Abstract: Materials synthesis often provides opportunities for innovation. We demonstrate a general low-temperature (260°C) molten salt electrodeposition approach to directly electroplate the important lithium-ion (Li-ion) battery cathode materials LiCoO2, LiMn2O4, and Al-doped LiCoO2. The crystallinities and electrochemical capacities of the electroplated oxides are comparable to those of the powders synthesized at much higher temperatures (700° to 1000°C). This new growth method significantly broadens the scope of battery form factors and functionalities, enabling a variety of highly desirable battery properties, including high energy, high power, and unprecedented electrode flexibility.

Deterministic Integration of Biological and Soft Materials onto 3D Microscale Cellular Frameworks

Abstract: Complex 3D organizations of materials represent ubiquitous structural motifs found in the most sophisticated forms of matter, the most notable of which are in life-sustaining hierarchical structures found in biology, but where simpler examples also exist as dense multilayered constructs in high-performance electronics. Each class of system evinces specific enabling forms of assembly to establish their functional organization at length scales not dissimilar to tissue-level constructs. This study describes materials and means of assembly that extend and join these disparate systems—schemes for the functional integration of soft and biological materials with synthetic 3D microscale, open frameworks that can leverage the most advanced forms of multilayer electronic technologies, including device-grade semiconductors such as monocrystalline silicon. Cellular migration behaviors, temporal dependencies of their growth, and contact guidance cues provided by the nonplanarity of these frameworks illustrate design criteria useful for their functional integration with living matter (e.g., NIH 3T3 fibroblast and primary rat dorsal root ganglion cell cultures).