Stretchable electronics, also known as elastic electronics or elastic circuits, is a group of technologies for building electronic circuits by depositing or embedding electronic devices and circuits onto stretchable substrates such as silicones or

polyurethane Polyurethane (; often abbreviated PUR and PU) refers to a class of polymers composed of organic chemistry, organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethan ...

s, to make a completed circuit that can experience large strains without failure. In the simplest case, stretchable electronics can be made by using the same components used for rigid printed circuit boards, with the rigid substrate cut (typically in a serpentine pattern) to enable in-plane stretchability. However, many researchers have also sought intrinsically stretchable conductors, such as

liquid metal A liquid metal is a metal or a metal alloy which is liquid at or near room temperature. The only stable liquid elemental metal at room temperature is mercury (Hg), which is molten above −38.8 °C (234.3 K, −37.9 °F). Three more ...

s. One of the major challenges in this domain is designing the substrate and the interconnections to be stretchable, rather than flexible (see

Flexible electronics Flexible electronics, also known as ''flex circuits'', is a technology for assembling electronic circuits by mounting electronic devices on flexible plastic substrates, such as polyimide, PEEK or transparent conductive polyester film. Additio ...

) or rigid (

Printed Circuit Board A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a laminated sandwich str ...

s). Typically,

polymer A polymer (; Greek ''poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic and ...

s are chosen as substrates or material to embed. When bending the substrate, the outermost radius of the bend will stretch (see Strain in an Euler–Bernoulli beam, subjecting the interconnects to high mechanical strain. Stretchable electronics often attempts biomimicry of

human skin The human skin is the outer covering of the body and is the largest organ of the integumentary system. The skin has up to seven layers of ectodermal tissue guarding muscles, bones, ligaments and internal organs. Human skin is similar to m ...

and

flesh Flesh is any aggregation of soft tissues of an organism. Various multicellular organisms have soft tissues that may be called "flesh". In mammals, including humans, ''flesh'' encompasses muscles, fats and other loose connective tissues, but ...

, in being stretchable, whilst retaining full functionality. The design space for products is opened up with stretchable electronics, including sensitive electronic skin for robotic devices and

in vivo Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, and ...

implantable sponge-like electronics.

Applications

Energy

Several stretchable energy storage devices and supercapacitors are made using carbon-based materials such as single-walled

carbon nanotubes A scanning tunneling microscopy image of a single-walled carbon nanotube Rotating single-walled zigzag carbon nanotube A carbon nanotube (CNT) is a tube made of carbon with diameters typically measured in nanometers. ''Single-wall carbon nan ...

(SWCNTs). A study by Li et al. showed a stretchable supercapacitor (composed of buckled SWCNTs macrofilm and elastomeric separators on an elastic PDMS substrate), that performed dynamic charging and discharging. The key drawback of this stretchable energy storage technology is the low specific capacitance and energy density, although this can potentially be improved by the incorporation of redox materials, for example the SWNT/MnO2 electrode. Another approach to creating a stretchable energy storage device is the use of Origami folding principles. The resulting origami battery achieved significant linear and areal deformability, large twistability and bendability.

Medicine

Stretchable electronics could be integrated into smart garments to interact seamlessly with the human body and detect diseases or collect patient data in a non-invasive manner. For example, researchers from Seoul National University an
MC10
(a flexible-electronics company) have developed a patch that is able to detect glucose levels in sweat and can deliver the medicine needed on demand (insulin or metformin). The patch consists of graphene riddled with gold particles and contains sensors that are able to detect temperature, pH level, glucose, and humidity. Stretchable electronics also permit developers to create soft robots, to implement minimally invasive surgeries in hospitals. Especially when it comes to surgeries of the brain and every millimeter is important, such robots may have a more precise scope of action than a human.

Tactile Sensing

Rigid electronics doesn't typically conform well to soft, biological organisms and tissue. Since stretchable electronics is not limited by this, some researchers try to implement it as sensors for touch, or tactile sensing. One way of achieving this is to make an array of conductive OFET (Organic Field Effect Transistors) forming a network that can detect local changes in capacitance, which gives the user information about where the contact occurred. This could have potential use in robotics and virtual reality applications.

References

External links