Conducting polymers are often employed as coatings on smooth metal electrodes to improve the electrode performance with respect to the signal-to-noise ratio for neural recording, charge-injection capacity for neural stimulation, and inducement of neural growth for electrode-tissue integration. However, adhesion of conducting polymer coatings on metal electrodes is poor, making the coating less durable and the electrical property of the electrode less stable. Moreover, conventional conducting polymers have relative low conductance, preventing their direct use as the electrode and lead material; and they are brittle, making it difficult for flexible neural electrodes to incorporate conducting polymer coatings. We have developed a new polypyrrole/polyol-borate composite film with concurrent excellent electrical and mechanical properties. We further developed a method to fabricate a stretchable multielectrode array using this new material as the sole conductor for both electrodes and leads, in contrast with the conventional approach of incorporating conducting polymers only through coating on non-stretchable metal electrodes. The resulting stretchable polymeric multielectrode array (SPMEA) was stretchable up to 23% uniaxial tensile strain with minimal losses in electrical conductivity. Electrochemical testing revealed the SPMEA’s impressive advantage for recording local field neural potentials and for epimysial stimulation of denervated skeletal muscles. As a neural interface engineer, I would also like to compare the compliant neural interfacing technology to other technologies, such as optogenetics, radiogenetics, and even a living neural interface that is currently under development in our lab.

We report on the results of culturing SH-SY5Y neuron-like cells on PEDOT:PSS wrinkled surfaces fabricated by thermally-induced shrinking of commercial polystyrene sheets. Such smart biointerfaces combine the functional properties of conducting polymers with the topographic patterning at the micro- and sub-microscale, as a result of surface wrinkling. By imposing mechanical constraints during shrinking, anisotropic topographic features are formed, with a spatial periodicity in the range 0.7 - 1.2 μm, tunable by varying the thickness of the PEDOT:PSS thin film. The effectiveness of wrinkled surfaces in enhancing and orientating the outgrowth of neurites is demonstrated by a 42% increase in length and by the 85% of neurites aligned along wrinkles direction (angle 0 < θ < 15°), after 5 days of differentiation. Furthermore, the conductive properties of the PEDOT:PSS film are retained after the surface wrinkling, opening the way for the exploitation of these smart biointerfaces for the electrical stimulation of cells.

We present a novel logic family alternative to classic CMOS logic and its experimental demonstration for digital application of organic electronics. The proposed logic family is a modified version of the complementary pass-transistor logic (mCPL), which allows use of a stronger transistor (in our case the p-FET) to provide more of the current required to switch the capacitance in the device. We report the integration and characterization of this new class of gates and compare them with the equivalent CMOS structures. The characterization of inverters shows improved tolerance to process variation, up to 2.5× better delay, and 1.7× smaller area for the mCPL devices. Comparison of NOR and NAND gates shows 1.8× and 4.1× reduced gate delay. A 3× reduced energy consumption per operation is also simulated. The improved performance of the mCPL design makes it an alternative architecture for logic application of organic electronics.

The development of highly conductive, robust edible hydrogels was investigated using a combination of the biopolymers gellan gum and gelatin, a common salt (NaCl) and plant-derived cross-linker (genipin). Robust strain gauge/pressure sensors were developed using edible materials to demonstrate the potential of these hydrogels. The hydrogels exhibited gauge factor and pressure sensitivity values of 7.6 ± 0.1 and 400 ± 7 μΩ/Pa for loads up to 3 kPa, respectively. Furthermore, these devices were able to operate under larger loads with gauge factor and pressure sensitivity values of 0.308 ± 0.002 and 7.17 ± 0.05 μΩ/Pa, respectively, for loads between 9 kPa and 280 kPa.

Ultrasensitive biosensors based on bottom gate organic field-effect transistors can be developed by depositing a functional biological (protein) interlayer directly on the silicon oxide gate dielectric and underneath the organic semiconductor film. However, the deposition methods for assembling the protein biological recognition layer can affect the biosensor analytical performances for the target analyte detection. Here, spin-coating and layer-by-layer techniques were considered as different approaches for streptavidin protein deposition. X-ray photoelectron spectroscopy (XPS) was systematically used in the non-destructive parallel angle resolved mode to characterize the multilayer device at each step of its assembly to gain information on elemental depth profiles. Scanning electron and scanning Helium ion microscopies gave information about stacked layer structure and morphology corroborating XPS results.

In this work, Polyaniline (PANI) was used as a sensing film for pH measures due to its characteristic of switching protonation states under acid and alkaline solutions. Equally produced films had their sensitivity (electric response versus pH) measured before and after being under the influence of a constant electric potential (from 3.5 to 6 V, one for each film) for the analysis on how the electric potential influenced the sensitivity. Then, the protonation caused by the application of the first potential was reversed by applying a constant 5 V reverse potential and the sensitivity was then evaluated again. The results show, on average, a constant relation between intensity of protonation and the potential applied and that the process of protonation is reversible by applying a higher opposite potential then the protonation one.