High-Frequency, Conformable Organic Amplifiers.

Large-bandwidth, low-operation-voltage, and uniform organic amplifiers are fabricated on ultrathin foils. By the integration of short-channel OTFTs and AlOx capacitors, organic amplifiers with a bandwidth of 25 kHz are realized, demonstrating the highest gain-bandwidth product (GBWP) reported to date. Owing to material and process advancements, closed-loop architectures operate at frequencies of several kilohertz with an area smaller than 30 mm(2) .

A transparent bending-insensitive pressure sensor.

Measuring small normal pressures is essential to accurately evaluate external stimuli in curvilinear and dynamic surfaces such as natural tissues. Usually, sensitive and spatially accurate pressure sensors are achieved through conformal contact with the surface; however, this also makes them sensitive to mechanical deformation (bending). Indeed, when a soft object is pressed by another soft object, the normal pressure cannot be measured independently from the mechanical stress. Here, we show a pressure sensor that measures only the normal pressure, even under extreme bending conditions. To reduce the bending sensitivity, we use composite nanofibres of carbon nanotubes and graphene. Our simulations show that these fibres change their relative alignment to accommodate bending deformation, thus reducing the strain in individual fibres. Pressure sensitivity is maintained down to a bending radius of 80 µm. To test the suitability of our sensor for soft robotics and medical applications, we fabricated an integrated sensor matrix that is only 2 µm thick. We show real-time (response time of ∼20 ms), large-area, normal pressure monitoring under different, complex bending conditions.

Vacuum Ultraviolet Treatment of Self-Assembled Monolayers: A Tool for Understanding Growth and Tuning Charge Transport in Organic Field-Effect Transistors.

Vacuum ultraviolet irradiation is used as a tool to systematically study the morphology, growth, and performance of small-molecule organic field-effect transistors. The surface energy can be carefully and precisely tuned by varying the dose of irradiation, allowing for the systematic study of the growth of an emerging organic semiconductor. This technique helps to methodically control the morphology and performance of organic semiconductors.

A strain-absorbing design for tissue-machine interfaces using a tunable adhesive gel.

To measure electrophysiological signals from the human body, it is essential to establish stable, gentle and nonallergic contacts between the targeted biological tissue and the electrical probes. However, it is difficult to form a stable interface between the two for long periods, especially when the surface of the biological tissue is wet and/or the tissue exhibits motion. Here we resolve this difficulty by designing and fabricating smart, stress-absorbing electronic devices that can adhere to wet and complex tissue surfaces and allow for reliable, long-term measurements of vital signals. We demonstrate a multielectrode array, which can be attached to the surface of a rat heart, resulting in good conformal contact for more than 3 h. Furthermore, we demonstrate arrays of highly sensitive, stretchable strain sensors using a similar design. Ultra-flexible electronics with enhanced adhesion to tissue could enable future applications in chronic in vivo monitoring of biological signals.

An MRI-compatible, ultra-thin, flexible stimulator array for functional neuroimaging by direct stimulation of the rat brain.

We developed an MRI-compatible, ultra-thin, flexible stimulator array for the rat brain and performed functional MRI (fMRI) acquisition during direct electrical stimulation of the brain. This technique measured brain activity evoked by direct stimulation of the motor and the somatosensory cortex. In order to avoid MR signal loss due to interferences with the main static field and RF field in the MRI system, the stimulator array was made from a non-magnetic gold electrode of 100-nm thickness on a 2-um-thick parylene substrate. By using this stimulator array, MR images without signal loss around conducting electrode pads were acquired, and fMRI acquisition during concurrent electrical stimulation of the cerebral cortex was achieved. Neuronal activity propagated to distant brain areas from the stimulated motor cortex. Positive blood oxygenation level dependent (BOLD) signals were observed with direct stimulation of the motor cortex, while negative BOLD signals were observed with direct stimulation of the somatosensory cortex. Interestingly, the pattern of brain activity evoked by direct stimulation of the somatosensory cortex was different from that evoked by electrical stimulation of the forepaw.