The dielectric elastomer, a particularly attractive type of electroactive polymer, uses commercial polymers such as acrylic and silicone elastomers. The technology has been limited in application by perceived lifetime issues. By addressing several lifetime issues, lifetimes of more than one million cycles, and in some cases beyond ten million cycles, were achieved with a variety of transducer configurations (including operation in generator mode) under a variety of operating conditions (including high humidity). Dielectric elastomers can produce maximum actuation strains of more than 100% and specific energy density exceeding that of known electric-field induced technology. Performance testing for dielectric elastomer actuators has typically been for peak-performance or “over-driven” conditions with short operational lifetimes (typically 100s or 1000s of cycles), particularly under conditions such as high humidity. By minimizing electric field and mechanical strain concentration factors, long lifetimes (>1 million cycles) with acrylic transducers were achieved with actuation strains as great as 40% areal strain (and up to 100% areal strain in generator mode). Actuators in a dry environment had an almost 20x increase in lifetime over actuators at ambient humidity (about 50% RH) at the same driving field conditions. Long actuation lifetimes were also achieved in a 100% RH environment and when fully submerged in salt water at reduced operating strain and field. In 100% RH, lifetimes of several million cycles were achieved at 4% strain. In underwater operation, 6 out of 11 actuators survived for >10 million cycles with an electric field limited to 32 MV/m and approximately 2% strain. The demonstrated lifecycle improvements are applicable to a variety of uses of dielectric elastomers, including haptic interface devices, pumps (implantable and external), optical positioners, and “artificial muscles” to replace small damaged muscles. Continued improvements in materials, actuator design, and packaging, combined with management of operational conditions as described here, should support new practical application of this promising technology.

Electronics in “wearable systems” or “smart textiles” are nowadays mainly realized on traditional interconnection substrates, like rigid Printed Circuit Boards (PCB) or mechanically flexible substrates. The electronic modules are detachable to allow cleaning and washing of the textile. In order to achieve a higher degree of integration and user comfort, IMEC-UGent/CMST developed a technology for flexible and stretchable electronic circuits. The electronic system is completely embedded in an elastomer material like PDMS (silicone), resulting in soft and stretchable electronic modules. The technology uses standard packaged components (IC's) and meander shaped copper tracks, so that stretchable systems with complex functionality can be achieved. Testing methods for washability were selected and developed. First tests are showing promising results, leveling the path to washable electronics in textiles. In order to show the possibilities of the technology in the field of textile applications a 7x8 single color stretchable LED-matrix was designed and integrated in textile. This LED-matrix can be applied for example in wearable signage applications.

In this paper, we present a stretchable electrode array for studying cell behavior subjected to mechanical strain. The electrode array consists of four gold nail-head pins (250μm tip diameter and 1.75mm spacing) or tungsten microwires (25.4μm in diameter) inserted into a polydimethylsiloxane (PDMS) platform (25.4×25.4mm2). Fusible indium alloy (liquid at room temperature) filled microchannels were used to connect the electrodes to the outside, thus providing the required stretchability. The electrodes were able to withstand strains of up to 40%. Repeated strain tests of several hundred cycles did not reveal any failure, illustrating the robustness of the platform. Mice cardiomyocytes and chick neurons were successfully cultured onto the platform.

A novel technology for stretchable electronics is presented which can be used for the realization of wearable textile electronics and biomedical implants. It consists of rigid or flexible component islands interconnected with stretchable meander-shaped copper conductors embedded in a stretchable polymer, e.g. PDMS. The technology uses standard PCB manufacturing steps and liquid injection molding techniques to achieve a robust and reliable product. Due to the stretchable feature of the device, conductors and component islands should be able to withstand a certain degree of stress to guarantee the functionality of the system. Although the copper conductors are meander-shaped in order to minimize the local plastic strain, the lifetime of the system is still limited by the occurrence of crack propagation through the copper, compromising the connectivity between the functional islands. In order to improve the lifetime of the conductors, the most important feature of the presented technology is the use of spin-on polyimide as a mechanical support for the stretchable interconnections and the functional flexible islands. In this way, every stretchable copper connection is supported by a 20μm layer of polyimide being shaped in the same manner as the above laying conductor. The grouped SMD components and straight copper tracks on the functional islands are also supported by a complete 20 μm polyimide layer. By use of the polyimide, the reliability of the stretchable interconnections, the straight interconnections on the flexible islands and the transitions between the stretchable and non-stretchable parts is improved. This approach results in a significant increase of the lifetime of the stretchable interconnections as it is doubled. In this contribution, the different process steps and materials of the technology will be highlighted. Initial reliability results will be discussed and the realization of some functional demonstrators containing a whole range of different components will further illustrate the feasibility of this technology. The advantages and disadvantages in terms of processability, cost and mechanical strength of the photo-definable polyimide will be covered.

Stretchable electronic circuits have the potential to the fields where electronics have to be conformable, deformable and stretchable into three dimensional surfaces. In this work, an “interlaced” structure is developed for multidirectional stretchable circuit. The shape of the conductor is loop-like configuration. A knitted structure is employed for the elastic substrate due to its flexibility, high stretchability, low cost and simple fabrication. The electro-mechanical behavior of the interlaced circuit is investigated in three different directions, i.e., 0-degree, 45-degree, and 90-degree, respectively. A significant improvement in stretchability is achieved in 0-degree direction. Then, a preliminary theoretical analysis is made in the electro-mechanical mechanism of the interlaced circuit. From the experimental investigation and theoretical analysis, it is found that the interlaced structure gives the conductor more freedom to move in the substrate, decreasing the stress concentration in the crest and trough parts of the loop when it is stretched.