Introducing non-covalent crosslinking moieties to polymer semiconductors produces a stretchable and healable material suitable for wearable electronics. There is great interest and potential in the development of skin-inspired flexible and wearable electronic devices. Such devices require materials that twist, fold and bend with no loss in electronic—or material—properties. Zhenan Bao and colleagues report a conjugated polymer that also incorporates non-covalent interactions between adjacent chains, enabling the material to accommodate up to 100% strain whilst maintaining high charge-carrier mobility. In this proof-of-principle study the authors use the polymers to fabricate flexible and stretchable organic transistors that combine robustness with good electronic properties. Thin-film field-effect transistors are essential elements of stretchable electronic devices for wearable electronics1,2. All of the materials and components of such transistors need to be stretchable and mechanically robust3,4. Although there has been recent progress towards stretchable conductors5,6,7,8, the realization of stretchable semiconductors has focused mainly on strain-accommodating engineering of materials, or blending of nanofibres or nanowires into elastomers9,10,11. An alternative approach relies on using semiconductors that are intrinsically stretchable, so that they can be fabricated using standard processing methods12. Molecular stretchability can be enhanced when conjugated polymers, containing modified side-chains and segmented backbones, are infused with more flexible molecular building blocks13,14. Here we present a design concept for stretchable semiconducting polymers, which involves introducing chemical moieties to promote dynamic non-covalent crosslinking of the conjugated polymers. These non-covalent crosslinking moieties are able to undergo an energy dissipation mechanism through breakage of bonds when strain is applied, while retaining high charge transport abilities. As a result, our polymer is able to recover its high field-effect mobility performance (more than 1 square centimetre per volt per second) even after a hundred cycles at 100 per cent applied strain. Organic thin-film field-effect transistors fabricated from these materials exhibited mobility as high as 1.3 square centimetres per volt per second and a high on/off current ratio exceeding a million. The field-effect mobility remained as high as 1.12 square centimetres per volt per second at 100 per cent strain along the direction perpendicular to the strain. The field-effect mobility of damaged devices can be almost fully recovered after a solvent and thermal healing treatment. Finally, we successfully fabricated a skin-inspired stretchable organic transistor operating under deformations that might be expected in a wearable device.

/pdf/intrinsically-stretchable-and-healable-semiconducting-32oe4skn60.pdf

Intrinsically stretchable and healable semiconducting polymer for organic transistors

Recent progress in electronic skin or e-skin research is broadly reviewed, focusing on technologies needed in three main applications: skin-attachable electronics, robotics, and prosthetics. First, since e-skin will be exposed to prolonged stresses of various kinds and needs to be conformally adhered to irregularly shaped surfaces, materials with intrinsic stretchability and self-healing properties are of great importance. Second, tactile sensing capability such as the detection of pressure, strain, slip, force vector, and temperature are important for health monitoring in skin attachable devices, and to enable object manipulation and detection of surrounding environment for robotics and prosthetics. For skin attachable devices, chemical and electrophysiological sensing and wireless signal communication are of high significance to fully gauge the state of health of users and to ensure user comfort. For robotics and prosthetics, large-area integration on 3D surfaces in a facile and scalable manner is critical. Furthermore, new signal processing strategies using neuromorphic devices are needed to efficiently process tactile information in a parallel and low power manner. For prosthetics, neural interfacing electrodes are of high importance. These topics are discussed, focusing on progress, current challenges, and future prospects.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201904765

Electronic Skin: Recent Progress and Future Prospects for Skin‐Attachable Devices for Health Monitoring, Robotics, and Prosthetics

Soft and conformable wearable electronics require stretchable semiconductors, but existing ones typically sacrifice charge transport mobility to achieve stretchability. We explore a concept based on the nanoconfinement of polymers to substantially improve the stretchability of polymer semiconductors, without affecting charge transport mobility. The increased polymer chain dynamics under nanoconfinement significantly reduces the modulus of the conjugated polymer and largely delays the onset of crack formation under strain. As a result, our fabricated semiconducting film can be stretched up to 100% strain without affecting mobility, retaining values comparable to that of amorphous silicon. The fully stretchable transistors exhibit high biaxial stretchability with minimal change in on current even when poked with a sharp object. We demonstrate a skinlike finger-wearable driver for a light-emitting diode.

/pdf/highly-stretchable-polymer-semiconductor-films-through-the-2tm94kx0ke.pdf

Highly stretchable polymer semiconductor films through the nanoconfinement effect

With much advancement in the field of nanotechnology, bioengineering, and synthetic biology over the past decade, microscales and nanoscales devices are becoming a reality. Yet the problem of engineering a reliable communication system between tiny devices is still an open problem. At the same time, despite the prevalence of radio communication, there are still areas where traditional electromagnetic waves find it difficult or expensive to reach. Points of interest in industry, cities, and medical applications often lie in embedded and entrenched areas, accessible only by ventricles at scales too small for conventional radio waves and microwaves, or they are located in such a way that directional high frequency systems are ineffective. Inspired by nature, one solution to these problems is molecular communication (MC), where chemical signals are used to transfer information. Although biologists have studied MC for decades, it has only been researched for roughly 10 year from a communication engineering lens. Significant number of papers have been published to date, but owing to the need for interdisciplinary work, much of the results are preliminary. In this survey, the recent advancements in the field of MC engineering are highlighted. First, the biological, chemical, and physical processes used by an MC system are discussed. This includes different components of the MC transmitter and receiver, as well as the propagation and transport mechanisms. Then, a comprehensive survey of some of the recent works on MC through a communication engineering lens is provided. The survey ends with a technology readiness analysis of MC and future research directions.

/pdf/a-comprehensive-survey-of-recent-advancements-in-molecular-2pjzig1xwb.pdf

A Comprehensive Survey of Recent Advancements in Molecular Communication

This review discusses one-dimensional supramolecular polymers that form in aqueous media. First, naturally occurring supramolecular polymers are described, in particular, amyloid fibrils, actin filaments, and microtubules. Their structural, thermodynamic, kinetic, and nanomechanical properties are highlighted, as well as their importance for the advancement of biologically inspired supramolecular polymer materials. Second, five classes of synthetic supramolecular polymers are described: systems based on (1) hydrogen-bond motifs, (2) large π-conjugated surfaces, (3) host–guest interactions, (4) peptides, and (5) DNA. We focus on recent studies that address key challenges in the field, providing mechanistic understanding, rational polymer design, important functionality, robustness, or unusual thermodynamic and kinetic properties.

Supramolecular Polymers in Aqueous Media

A stretchable polymer channel layer for organic field-effect transistors is obtained by spin-coating a blend solution of polythiophene and rubber polymer. A network of the polythiophene nanofibril bundles surface-embedded in the rubber matrix allows large stretchability of the polythiophene film layer.

Polythiophene nanofibril bundles surface-embedded in elastomer: a route to a highly stretchable active channel layer.

Motor proteins generate motions in a biological system by converting the chemical energy of adenosine triphosphate (ATP) into mechanical energy. Actin filament/myosin (actomyosin) is a well-studied example, and it performs essential functions in biological systems, such as muscle contraction, organelle transport, and cell motility. A common experimental scheme tostudymotorproteins is aglidingassayonglass substrates,where themotionsof actin filaments are analyzedon randomly distributed myosin on two-dimensional (2D) substrates. In this case, the actin filaments exhibited rather disordered motions close to a 2D random walk, which is somewhat different to that in vivo systems. In muscle cells, myosin goes through one-dimensional (1D) motion on straight actin filaments. Many researchers have tried to build narrow myosin patterns or guiding channels to imitate 1D in vivo systems. However, previous strategies have often suffered fromvarious limitations.Forexample, theguidingbarriers used to confine actin filaments in 1D trajectories can disturb the natural motion of actomyosin. Without guiding barriers, actin filaments can easily leave the narrow myosin patterns. On the other hand, motor proteins have been actively investigated for protein-based nanomechanical systems due to their high fuel efficiencyand large forcegeneration.For suchapplications, one

Functionalization of silicon nanowires with actomyosin motor protein for bioinspired nanomechanical applications.

We report a new strategy to selectively localize and control microtubule translocation via electrical control of microtubules using a microfabricated channel on a functionalized-graphene electrode with high transparency and conductivity. A patterned SU-8 film acts as an insulation layer which shields the electrical field generated by the graphene underneath while the localized electric field on the exposed graphene surface guides the negatively charged microtubules. This is the first report showing that functionalized graphene can support and control microtubule motility.

https://iopscience.iop.org/article/10.1088/0957-4484/24/19/195102/pdf

Electrical control of kinesin-microtubule motility using a transparent functionalized-graphene substrate.

Provided is a method of forming graphene. The method of forming graphene includes treating a surface of a substrate placed in a reaction chamber with plasma while applying a bias to the substrate, and growing graphene on the surface of the substrate by plasma enhanced chemical vapor deposition (PECVD).

Kyung Eun Byun

Papers

Polythiophene nanofibril bundles surface-embedded in elastomer: a route to a highly stretchable active channel layer.

Functionalization of silicon nanowires with actomyosin motor protein for bioinspired nanomechanical applications.

Electrical control of kinesin-microtubule motility using a transparent functionalized-graphene substrate.

Method of forming graphene

Surface-programmed assembly for nanomanufacturing