Implantable neural interfaces are important tools to accelerate neuroscience research and translate clinical neurotechnologies. The promise of a bidirectional communication link between the nervous system of humans and computers is compelling, yet important materials challenges must be first addressed to improve the reliability of implantable neural interfaces. This perspective highlights recent progress and challenges related to arguably two of the most common failure modes for implantable neural interfaces: (1) compromised barrier layers and packaging leading to failure of electronic components; (2) encapsulation and rejection of the implant due to injurious tissue–biomaterials interactions, which erode the quality and bandwidth of signals across the biology–technology interface. Innovative materials and device design concepts could address these failure modes to improve device performance and broaden the translational prospects of neural interfaces. A brief overview of contemporary neural interfaces is presented and followed by recent progress in chemistry, materials, and fabrication techniques to improve in vivo reliability, including novel barrier materials and harmonizing the various incongruences of the tissue–device interface. Challenges and opportunities related to the clinical translation of neural interfaces are also discussed.

The main goal of the field of neuromorphic computing is to build machines that emulate aspects of the brain in its ability to perform complex tasks in parallel and with great energy efficiency. Thanks to new computing architectures, these machines could revolutionize high-performance computing and find applications to perform local, low-energy computing for sensors and robots. The use of organic and soft materials in neuromorphic computing is appealing in many respects, for instance, because it allows better integration with living matter to seamlessly meld sensing with signal processing, and ultimately, stimulation in a closed-feedback loop. Indeed, not only can the mechanical properties of organic materials match those of tissue, but also, the working mechanisms of these devices involving ions, in addition to electrons, are compatible with human physiology. Another advantage of organic materials is the potential to introduce novel fabrication techniques relying on additive manufacturing amenable to one-of-a-kind form factors. This field is still nascent, therefore many concepts are still being proposed, without a clear winner. Furthermore, the field of application of organic neuromorphics, where bioinspiration and biointegration are extremely appealing, calls for a co-design approach from materials to systems.

This work demonstrated the possibility to integrate electrochemical molecularly imprinted polymers (e-MIPs) on microelectrodes to detect organic pollutants. e-MIPs are a cross-linked polymer with specific target binding cavities with a redox tracer inside. e-MIPs were obtained by precipitation copolymerization of ferrocenylmethyl methacrylate as a functional monomer and a redox tracer with ethylene glycol dimethacrylate as a cross-linker and bisphenol A as a target molecule. FTIR and elemental analysis confirmed the presence of ferrocene inside the polymers. Nitrogen adsorption/desorption experiments and binding isotherms demonstrated the presence of binding cavities inside the e-MIP. The electrochemical properties of the e-MIP were characterized in organic/aqueous media before their patterned on microelectrode.

Biologic neural networks are immersed in common electrolyte environment, and homeoplasticity or global factors of this environment are forcing specific normalization functions that regulate the overall network behavior. In this work, a common electrolyte is used to gate a grid of organic electrochemical devices. The electrolyte functions as a global parameter that controls collectively the device grid. Statistical analysis of the grid and the subsequent definition of global metrics reveal that the grid behaves similarly to a single device. This global control modulates the gain of the device grid, a phenomenon analog to multiplicative scaling in biologic networks. This work demonstrates the potential use of electrolytes as homeostatic media in neuromorphic device architectures.

In vitro electrophysiology using microelectrode arrays (MEAs) plays an important role in understanding fundamental biologic processes, screening potential drugs and assessing the toxicity of chemicals. Low electrode impedance and ability to sustain viable cultures are the key technology requirements. We show that MEAs consisting of poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) and coated with poly-L-lysine satisfy these requirements. Hippocampal cell cultures, maintained for 3–6 weeks on these MEAs, give high quality recordings of neural activity. This enables the observation of drug-induced activity changes, which paves the way for using these devices in in vitro drug screening and toxicology applications.

Screen-printed organic electrochemical transistors (OECTs) were tested as glucose and lactate sensors. The intrinsic amplification of the device allowed it to detect metabolites in low molecular range and validation tests were made on real human sweat. The development of an organically modified sol–gel solid electrolyte paves the way for all printed OECT-based biosensors.

Interfacing organic electrochemical transistors (OECTs) with biological systems holds considerable promise for building-sensitive biosensors and diagnostic tools. We present a simple model that describes the performance of biosensors in which an OECT is integrated with a biological barrier layer. Using experimentally derived parameters we explore the limits of sensitivity and find that it is dependent on the resistance of the barrier layer. This work provides guidelines on how to optimize biosensors in which OECTs transduce changes in the impedance of biological layers, including lipid bilayer membranes and confluent cell layers.

In biological applications, conjugated polymers offer many advantages compared to inorganic semiconductors, due to their favorable electrical properties and their biocompatibility. Many different parameters affect the cell-substrate interaction and in this work we focus our attention on the role played by the oxidation state and surface morphology of conducting polymer substrates. We realized cell culture substrates using a thin film of a biocompatible conducting polymer widely employed in organic electronics, poly(3,4-ethylene dioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS). The oxidation state of the samples was electrochemically modified through the application of a fixed potential, and they were subsequently characterized by atomic force microscopy and optical spectroscopy. Using these techniques we have been able to measure the oxidation state of the polymer films, and to asses that its surface roughness does not depend on its oxidation state. Furthermore, human dermal fibroblast (hDF) were grown on PEDOT:PSS films with different oxidation state, in order to test their efficacy as cell culture substrates and their biocompatibility.

Record-brightness infrared LEDs based on colloidal quantum-dots have been achieved through control of the spacing between adjacent quantum-dots. By tuning the size of quantum-dots, the emission wavelengths can be tuned between 900nm and 1650nm.

The emergence of organic electronics represents one of the most dramatic technological developments of the past two decades. Perhaps the most important frontier of this field involves the interface with biology. The “soft” nature of organics offers better mechanical compatibility with tissue than traditional electronic materials, while their natural compatibility with mechanically flexible substrates suits the nonplanar form factors often required for implants. More importantly, the ability of organics to conduct ions in addition to electrons and holes opens up a new communication channel with biology. In this article, we consider a few examples that illustrate the coupling between organic electronics and biology and highlight new directions of research.

Simplicity of construction and operation are advantages of iTMC (ionic transition metal complex) OLEDs compared with multi-layer OLED devices. Unfortunately, lifetimes do not compare favorably with the best multi-layer devices. We have previously shown for Ru(bpy)3(PF6)2 based iTMC OLEDs that electrical drive produces emission-quenching dimers of the active species. We report evidence here that a chemical process may also be implicated in degradation of devices based on Ir(ppy)2(dtb-bpy)PF6 albeit by a very different mechanism. It appears that degradation of operating devices made with this Ir-based complex is related to current-induced heating of the organic layer, resulting in loss of the dtb-bpy ligand. (The dtb-bpy ligand is labile compared with the cyclometallated ppy ligands.) Morphological changes observed in electrically driven Ir(ppy)2(dtb-bpy)PF6 OLEDs provide evidence of substantial heating during device operation. Evidence from UV-vis spectra in the presence of an electric field as well as MALDI-TOF mass spectra of the OLED materials before and after electrical drive add support for this model of the degradation process.

The Women in Materials (WIM) program is an on-going collaboration between Simmons College and the Cornell Center for Materials Research (CCMR). Beginning in 2001, during the initial four years of the project, materials-related curricula were developed, a new joint research project was begun, and nearly 1/2 of Simmons College science majors participated in materials-related research during their first two years as undergraduates. We have previously reported the student outcomes as a result of this initial stage of the project, demonstrating a successful partnership between a primarily undergraduate women's college and a federally funded Materials Research Science and Engineering Center. Here, we report the evolution and impact of this project over the last three years, subsequent to the initial seed funding from the National Science Foundation. The Women in Materials project is now a key feature of the undergraduate science program at Simmons College and has developed into an organizing structure for materials-related research at the College. Initially, three faculty members were involved and now eight faculty members from all three laboratory science departments participate (biology, chemistry, and physics). The program now involves research related to optoelectronics, polymer synthesis, biomaterials, and green chemistry, and each semester about 80% of the students who participate in these projects are 1st and 2nd year science majors. This structure has led to enhanced funding within the sciences, shared instrumentation facilities, a new minor in materials science, and a spirit of collaboration among science faculty and departments. It has also spawned a new, innovative curricular initiative, the Undergraduate Laboratory Renaissance, now in its second year of implementation, involving all three laboratory science departments in incorporating actual, on-going research projects into introductory and intermediate science laboratories. Most importantly, the Women in Materials program has embedded materials-related research into our science curriculum and has deepened and broadened the educational experience for our students; the student outcomes speak to the program's success. Approximately 70% of our science majors go on to graduate school within two years of completing their undergraduate degree. Our students also have a high acceptance rate at highly competitive summer research programs, such as Research Experience for Undergraduates (REU) programs funded by the National Science Foundation.

The processes underlying degradation of organic light emitting diodes (OLEDs) are gradually becoming understood. In ruthenium-based ionic transition metal complex (iTMC) OLEDs, a dimeric species forms during device operation that quenches light emission [1]. Water has been implicated in this degradation process [2]. We report recent studies on degradation of OLEDs fabricated with Ir(ppy)2(dtb-bpy)PF6 [ppy = 2-phenylpyridine, dtb-bpy = 4,4'-di-tert-butyl 2,2'-bipyridine [3]. We have found that applying a thicker-than-usual metal electrode results in shorter turn-on times and higher light emission, though little improvement in lifetime. It appears that the degradation of these devices occurs by a different mechanism from that of the ruthenium-based devices and may involve local heating leading to chemical decomposition of the organic material.

Observation of recurring but often transient dark-colored substances in both the Ru(bpy)3(PF6)2 and Ir(ppy)2(dtb-bpy)PF6 systems, seen both in the solid state and in solution samples, may also be indicative of decomposition.

We have studied the effect of substrate atomic steps on the azimuthal alignment of vapor-deposited pentacene crystals. Si(111) substrates with a low miscut angle were annealed at high temperature in ultra-high vacuum before the pentacene deposition; this produced surfaces with atomically flat terraces and arrays of parallel atomic steps. AFM analysis shows that pentacene deposited on these heated samples, at a low deposition rate, results in significant alignment of the pentacene crystals along the atomic steps.

The Women in Materials (WIM) program, supported by the National Science Foundation, is a collaboration between Simmons College, a predominately undergraduate women’s college, and the Cornell Center for Materials Research (CCMR). For the past four years, this program has provided unusual curricular and research opportunities for undergraduate women at Simmons College. This program demonstrates a successful model for enhancing undergraduate science and technology preparation through collaboration between primarily undergraduate institutions (PUIs) and NSF-supported Materials Research Science and Engineering Centers.

Analysis of the possible mechanisms of degradation of Ru(bpy)32+-based OLEDs has led to the idea of quencher formation in the metalloorganic area close to the cathode. It has been suggested that the quencher results from an electrochemical process where one of the bipyridine (bpy) groups is replaced with two water molecules [1] or from reduction of Ru(bpy)32+ to Ru(bpy)30 [2]. We have tested these and other degradation ideas for Ru(bpy)32+-based OLEDs, both prepared and tested with considerable exposure to the ambient environment and using materials and procedures that emphasize cost of preparation rather than overall efficiency. In order to understand the mechanisms involved in these particular devices, we have correlated changes in the devices' electrical and optical properties with MALDI-TOF mass spectra and UV-vis absorption and fluorescence spectra.

Qualitatively, the basic principles behind the operation of OLEDs are well established. In order to optimize device parameters such as power efficiency and operating voltage, to explore the limits of performance and to understand changes in the electrical properties as diodes age, it is necessary to develop a quantitative understanding of each of the relevant processes: injection of electrons and holes at the cathode and anode, charge transport, recombination and exciton formation, and emission. In this paper, we summarize our experimental, theoretical and numerical studies to address these issues.