Symposium EP03—Materials Strategies and Device Fabrication for Biofriendly Electronics

Fabrication approaches to biodegradable and biocompatible microelectromechanical (MEMS) devices suitable for implantation in the body will be discussed. Three topical areas will be touched upon: biodegradable wireless pressure sensors; biodegradable batteries; and MEMS fabricated from protein materials.

Biodegradable Wireless Pressure Sensors: A wireless pressure sensor made entirely of biodegradable materials will be discussed. Such biodegradable sensors may be appropriate for short-term, acute medical implantation applications as they potentially eliminate the need for implant extraction when sensing is no longer required. Metallic bilayers with controllable corrosion characteristics are utilized as conductors, and biodegradable polymers poly-L-lactide (PLLA) and polycaprolactone are used as dielectric and structural materials. The fabricated sensor is based on a resonant variable capacitance technique and was wirelessly tested in both air and 0.9% saline. The sensor exhibited a linear resonant frequency response to external applied pressure, over the physiologically-relevant 0-20 kPa applied pressure range. Sensors remained stable and functional for approximately 86 hours in saline solution.

Biodegradable Batteries: Implantable and biodegradable batteries play an important role in the fully degradable medical systems; however, in such systems compactness and energy density are of great importance. Harnessing liquid from the body to serve as the battery electrolyte may, therefore, be desirable; however, for stable operation, maintaining a constant environment inside the electrochemical cell is required even in the presence of changing body conditions. A biodegradable battery featuring a solid electrolyte of sodium chloride and polycaprolactone will be discussed. This approach harnesses the body fluid that diffuses into the cell as an element of the electrolyte; however, the large excess of sodium chloride suspended in the polycaprolactone holds ionic conditions inside the battery relatively constant. A constant discharge profile can then be achieved even in the presence of varying external aqueous conditions, enabling compact, stable-performing cells.

Protein MEMS: The use of extracellular matrix (ECM) protein materials in the fabrication of MEMS offer the possibility of MEMS-based devices that are more easily integrated with the body, are better tolerated by the immune system, and/or which have mechanical properties that are well-matched to potential biological applications. However, the incorporation of these relatively delicate materials into standard MEMS processes can result in significant fabrication challenges. Suitable fabrication approaches to Protein MEMS will be discussed, and their use will be illustrated in a collagen-based cortical neural electrode, which has demonstrated reduced inflammation and superior persistence of functionality in in vivo models when compared to similarly-sized MEMS electrodes fabricated from conventional materials.

Biodegradable transient devices is an emerging type of electronics that could play an essential role in medical therapeutic/diagnostic processes, such as wound healing, tissue regeneration, etc. The associated biodegradable power sources, however, remain as a major challenge towards future clinical applications, as the demonstrated electrical stimulation and sensing functions are limited by wired external power or wireless energy harvesters via near-field coupling. We propose novel materials strategies and fabrication schemes that enable a high-performance fully biodegradable magnesium-molybdenum trioxide battery as an alternative approach for in vivo on-board power supply. The battery can deliver a stable high output voltage as well as prolonged lifetime that could satisfy requirements of representative implantable electronics. The battery is fully biodegradable, and demonstrates desirable biocompatibility. The battery system provides a promising solution to advanced energy harvesters for self-powered transient bioresorbable implants as well as eco-friendly electronics.

Nanoscale thin-film technology has opened an era of soft, flexible and stretchable electronics and has also changed the timescale of dissolution of materials. Silicon nanomembranes of 10-100 nm thickness have dissolution behavior on the order of days to months. This feature lets us construct Si electronics for water-soluble and bioresorbable performance using unusual fabrication processes and combining soft/biodegradable polymers. Here we introduce two representative examples of bioresorbable Si electronic devices useful in monitoring and modulating the nervous system. First, a bioresorbable pressure sensor using piezoresistive Si strain gauge and 3D microstructured diaphragm was demonstrated to provide accurate measurement of intracranial pressure during the incubation period of traumatic injury. Wireless interfaces made of polymer-coated bioresorbable metal strips offer stable and continuous pressure monitoring. In-vivo functional and immunochemical demonstrations in a rat model suggests the potential validation of bioresorbable sensors in the clinical stage. In the other example, bioresorbable wireless electrical stimulator interfacing the peripheral nerve was demonstrated as a therapeutic modulator. An integrated circuit of Si diode, capacitor, and inductor with all-biodegradable metal, semiconductor and dielectric materials generate therapeutic electrical pulses by near-field inductive energy transfer. The accelerated functional recovery of transected nerve with electrical stimulation suggests the capability of bioresorbable stimulator to promote and/or modulate the nervous system in the treatment and rehabilitation stage.

Electrofluorochromic devices (EFCD) receive increasing attention in investigation in the past years, because they offer the possibilities for various optical devices. Besides that, the little power consumption, the low voltage requirement and simple device architecture (i.e. electrochemical cell) provide the opportunity for low-cost display devices. To provide a cost-effective method with the freedom of design necessary for smart windows and display applications, inkjet printing can be used as a suitable method with high through-put, low-material waste and up-scaling capabilities to industrial fabrication. These exceptional properties can be extended with the use of biocompatible and biodegradable materials for their use in medical applications or to reduce the waste after usage to a minimum.
Here, we report on inkjet-printed electro(fluoro)chromic devices consisting of biocompatible and biodegradable components on biodegradable deformable gelatin substrates. To simplify the device architecture for the inkjet printing process we chose a parallel electrode configuration with PEDOT:PSS as electrode material. We used two different solid polymer electrolytes, one on the basis of gelatin coated from water and the other on the basis of Poly(D,L-lactide-co-glycolide) (PLGA) from a Dimethyl sulfoxide (DMSO) solution, whereby all of these polymers and solvents are biodegradable and biofriendly. As ionic species we used tetrabutylammonium bis-oxalato borate (TBABOB) which was developed as a non-fluorinated biodegradable salt. The electro(fluoro)chromic layers were made out of two different polymer derivatives consisting triarylamine, namely polyindenofluorene-8-triarylamine (PIF8-TAA) and polytriarylamine (PTAA). The fabricated devices exhibit a sufficient contrast, efficiency and lifetime to be used in deploy-and-forget or short-lifecycle applications with potential use in disposable consumer and health care biofriendly disposable applications.

Flexible organic electronics have attracted considerable attention over the past decade. Stretchable electronics represent another type of optoelectronic devices that are intrinsically elastic, that is they are foldable, twistable, and stretchable while maintaining performance, integrity and durability. Incorporated into devices, properly designed stretchable materials may result in more robust devices under bending and strain compared to flexible but not stretchable materials. For intrinsically stretchable electronics, it is desirable to have intrinsically stretchable materials, ranging from stretchable conductors, stretchable dielectric to stretchable semiconductors. In this talk, I will present various molecular design concepts for realizing stretchable electronic polymers without compromising electronic properties. Their applications in bioelectronics will also be presented.

Wearable bioelectronic devices rely on oxidoreductase enzymes and have already demonstrated considerable promise for on-body applications ranging from highly selective non-invasive biomarker monitoring to epidermal energy harvesting. Critical to such progress is the judicious design of the enzyme-electronic interface, along with flexible platforms with mechanical properties similar to those of biological tissues. Such devices require special attention to the enzyme-electronic interface and to several considerations related to wearable applications, such as mechanical properties (flexibility and stretchability), operational stability in different biofluids and under changing conditions (e.g., pH, temperature), biofouling, selectivity, and low target concentrations. Keeping these requirements in mind, our group has pioneered a variety of wearable biocatalytic sensors and biofuel cells devices. By leveraging the advantages of biocatalysis, electrochemistry, and flexible electronics, and addressing key challenges, wearable bioelectronic devices could have a tremendous impact on diverse biomedical, fitness and defense fields.

Among various pressure sensors, transduction mechanisms, piezoresistive, capacitive, triboelectric, and piezoelectric effects are generally considered for converting tactile stimuli into electrical signals.^1,2 Owing to the fast response time and higher sensitivity, piezoelectric pressure sensors (PEPS) are the most useful for the detection of full-range human activities. It has been found that pressure sensor based artificial electronic skin (e-skin) can mimic the human skin and detects subtle pressure (1 Pa–1 kPa). A broad range of applications is expected to be implemented such as wearable health care systems, human–machine interfacing devices, artificial intelligence and prosthetic skin. Nevertheless, piezoelectric materials with adequate flexibility, light weight, ease of large-area processing, low cost and environmental safety are attractive but several issues are remaining for next-generation pressure/force sensors and mechanical energy harvesters. Recent advances on PEPS development is primarily focused on varies types of inorganic and semiconducting piezoelectric materials such as, barium titanate (BaTiO₃), zinc oxide (ZnO), zinc sulfide (ZnS) and lead zirconate titanate (PZT).² In spite of their superior electromechanical responses, the brittleness and toxic properties limit their implementation in wide range of biomedical and flexible electronics applications. On the other hand, natural piezoelectric materials are not yet extensively investigated as an e-skin for measuring and quantifying human physiological signal.²
In this context, we have developed human skin interactive self-powered piezoelectric biomaterials based e-skin (Bio-e-skin) which can detect and discriminate acute human physiological signals such as low frequency as subtle as wrist pulse and even intra-body pressures such as intraocular and intracranial pressure, to relatively high frequency dynamic human motions such as movements of synovial joints of wrist, elbow, knee and finger bending. Natural bio-polymers such as, collagen, chitin, gelatin and cellulose were found to possesses superior mechanosensitivity which was sufficient to fabricate self-powered wearable bio-e-skin that can mimic spatiotemporal human perception and monitors real-time human physiological signals in non-invasive rational strategy. In addition, the bio-skins are found to generate superior output power density which is sufficient to operate the commercial consumer electronics. These observations suggest that fabricated bio-e-skins could eventually find a wide range of applications in autonomous epidermal electronics, implantable medical device, surgery, e-healthcare monitoring, in vitro and in vivo diagnostics apart from its broad range applications in the field of self-powered personal portable electronic devices.^3-5
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Recently emerging classes of battery free, ultrasmall¹, fully implantable devices for optogenetic neuromodulation² eliminate physical tethers associated with bulky head-stages and batteries in alternative wireless technologies and conventional setups by leveraging cellular scale light emitting diodes on flexible injectable filaments as light sources³. These highly miniaturized systems enable untethered, operation for behavioral studies that eliminate motion constraints and enable new experimental paradigms in a range of complex 3D environments and contexts (e.g. social interactions) that cannot be explored with conventional technologies. These devices are, however, purely passive in their design, thereby precluding any form of active control or programmability, resulting in limitations when investigating circuit dynamics where independent operation of multiple light sources with precise active control is needed. Here we present a series of important concepts that enable controlled device operation, independent of position and angle relative to the experimental arena, with advanced wireless power harvesting capabilities and full user-programmability over multiple devices. This level of functionality is demonstrated in integrated platforms that are compatible with noninvasive imaging technologies such as computed tomography and magnetic resonance imaging and have sizes and weights not significantly larger than those of previous, passive systems. The resulting devices qualitatively expand options in brain tissue illumination for optogenetic neuromodulation and multimodal operation, with broad potential applications in neuroscience research, with specific advances in precise dissection of neural circuit function during unconstrained behavioral studies.


1 V. K. Samineni, J. Yoon, K. E. Crawford, Y. R. Jeong, K. C. McKenzie, G. Shin, Z. Xie, S. S. Sundaram, Y. Li, M. Y. Yang, J. Kim, D. Wu, Y. Xue, X. Feng, Y. Huang, A. D. Mickle, A. Banks, J. S. Ha, J. P. Golden, J. A. Rogers, and R. W. I. Gereau, PAIN 158,2017).
2 G. Shin, A. M. Gomez, R. Al-Hasani, Y. R. Jeong, J. Kim, Z. Q. Xie, A. Banks, S. M. Lee, S. Y. Han, C. J. Yoo, J. L. Lee, S. H. Lee, J. Kurniawan, J. Tureb, Z. Z. Guo, J. Yoon, S. I. Park, S. Y. Bang, Y. Nam, M. C. Walicki, V. K. Samineni, A. D. Mickle, K. Lee, S. Y. Heo, J. G. McCall, T. S. Pan, L. Wang, X. Feng, T. I. Kim, J. K. Kim, Y. H. Li, Y. G. Huang, R. W. Gereau, J. S. Ha, M. R. Bruchas, and J. A. Rogers, Neuron 93,2017).
3 T. I. Kim, J. G. McCall, Y. H. Jung, X. Huang, E. R. Siuda, Y. Li, J. Song, Y. M. Song, H. A. Pao, R. H. Kim, C. Lu, S. D. Lee, I. S. Song, G. Shin, R. Al-Hasani, S. Kim, M. P. Tan, Y. Huang, F. G. Omenetto, J. A. Rogers, and M. R. Bruchas, Science 340,2013).

On-skin sensors have attractive much attention as the next-generation wearable devices, because the conformal contact on human skin enables accurate and continuous detection of physiological signals. One of the most important technologies to improve usability of on-skin sensors is a power source to continuously supply electricity to health-monitoring systems. In this talk, we will report on recent progresses of ultraflexible organic photovoltaic cells for applications to wearable sensors. First, ultraflexible organic power sources that can be wrapped around an object have been developed with mechanical and thermal stability in long-term operation. Then, the integration of these power sources with functional electric devices including sensors has been achieved.

Recent studies have demonstrated that in addition to biochemical and genetic interactions, cellular systems also respond to biophysical cues, such as electrical, thermal, and mechanical signals. However, we only have limited tools that can introduce localized physical stimuli and/or sense cellular responses with high spatiotemporal resolution. Inorganic semiconductors display a spectrum of physical properties and offer the possibility of numerous device applications. My group integrates material science with biophysics to study several semiconductor-based biointerfaces. In this talk, I will first pinpoint domains where semiconductor properties can be leveraged for biointerface studies, providing a sample of numbers in semiconductor-based biointerfaces. Next, I will present a few recent studies from our lab and highlight key biophysical mechanisms underlying the non-genetic optical modulation interfaces. In particular, I will present a biology-guided two-step design principle for establishing tight intra-, inter-, and extracellular silicon-based interfaces in which silicon and the biological targets have matched mechanical properties and efficient signal transduction. Finally, I will discuss new materials and biological targets that could catalyze future advances.

Organic electronic devices, apart from consumer applications, are presently paving the path for key applications at the interface between electronics and biology. In such applications, organic polymers are very attractive candidates, due to their distinct properties of mechanical flexibility, self-healing and mixed conduction.
My group investigated the processing conditions leading to high electrical conductivity, long-term stability in aqueous media as well as robust mechanical properties of the conducting polymer poly(3,4-ethylenedioxythiophene) doped with polystyrenesulfonate (PEDOT:PSS) [1-3].We have demonstrated that stretchable PEDOT:PSS films can be achieved by adding a fluorosurfactant to the film processing mixture and by pre-stretching the substrate during film deposition. We have achieved patterning of organic materials on a wide range of substrates, using orthogonal lithography and pattern transfer [4-5]. Recently we have discovered that PEDOT:PSS films can be rapidly healed with water drops after being damaged with a sharp blade [6] or show autonomous self-healing if processed in presence of certain additives.
My talk will deal with processing, characterization and patterning of conducting polymer films and devices for flexible, stretchable and healable electronics. I will particularly focus on the strategies to achieve films with optimized electrical conductivity and mechanical properties, on unconventional micro patterning on flexible and stretchable substrates, on the different routes to achieve films stretchability and self-healing.

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Transient materials/electronics is an emerging class of functional devices that are capable of undergoing rapid degradation at prescribed time and controlled rate once transiency is triggered. Application of these materials in circuit boards and environmental sensors eliminates the need for their retrieval, thus minimizing electronic waste production.
Transiency rate in solvent-triggered devices is strongly dependent on the chemical composition of the constituents, as well as their interactions with the solvent, upon exposure. Such chemical interactions are typically slow, passive, and diffusion-driven. In this study, we present integration of gas forming reactions into transient materials/electronics to achieve selective, expedited, controlled, and active transiency. Integration of more complex chemical reaction paths to transiency, not only increases selectivity of the process, but also enhances pre-transiency chemical stability of the system while under operation. A proof-of-concept transient electronic device, utilizing sodium-bicarbonate/citric-acid pair as gas forming agents is studied vs. control devices, consisting of polymeric substrate and metal colloid as electronic component, in the absence of gas forming agents. While exhibiting enhanced transiency behavior, substrates with gas forming agents also proved sufficient to be applied as substrates, concerning pre-transiency mechanical properties and physical stability.

Polythiophenes have been widely investigated for use in a variety of applications including photovoltaics, sensors and electrochromic displays. However, they have been of particular interest to the biomedical community because of their simultaneous electronic and ionic conductivity. They also are mechanically softer than inorganic materials, making it possible for them to be more compatible with living wet tissues. Poly(3,4-ethylenedioxythophene) (PEDOT) and its copolymers, including the polymer formed from the carboxyl-substituted monomer P(EDOTacid), have been of specific attention because of their chemical stability and excellent charge transport properties. Despite the continued interest in PEDOT, there are still many unknown questions about the details of its polymerization process. One of the major challenges is that PEDOT polymers are relatively insoluble, making an accurate analysis of the degree of polymerization during the reaction difficult.
We have been investigating the use of vibrational spectroscopy techniques along with Gaussian molecular simulations to get a better understanding of the electropolymerization process. The experiments have used microfocused Raman and Fourier Transform Infrared (FTIR) techniques, and compliment ongoing research in our laboratory using in-situ Transmission Electron Microscopy (TEM) and hot stage optical microscopy (OM).
We have identified critical peaks associated with the reactive hydrogens on the thiophene ring that allow us to monitor the process of polymerization. We studied the vibrational modes associated with the reactive proton and conjugation of the thiophene network. The 3110 cm^-1 thiophene C-H stretch peaks is of particular interest to us, since it decreases with intensity as the molecules react. In addition, we are monitoring the peak at 1422 cm^-1 associated with the C=C stretch and the peaks at 835-1184 cm^-1 associated with the conjugation in PEDOT. The peaks at 1540 cm^-1 and 1573 cm^-1 are associated with the quinoidal structure of the PEDOT. These clues provide insight about the changes occurring during the polymerization reaction. By correlating these spectroscopic results with data using microscopy, we are developing a deeper understanding of the thiophene electropolymerization reaction.

In this work, natural organic honey as gate dielectric in organic thin-film transistor has been systematically investigated. In recent years, organic materials for electronic applications have gained wide research interests due to their advantages such as environmentally friendly, biodegradable, bioresorbable, biocompatible, and do not require chemical synthesis. Thin-film transistor using organic materials as semiconductors (C60, pentacene, etc.), dielectrics (Aloe vera, chicken albumen, benzocyclobutene), and substrates (Silk, PLGA, etc.) have been developed and investigated. This work reports the usage of honey as a gate dielectric layer in a C60-based thin-film transistor. Different curing temperature and duration for honey solidification were applied. Honey film thicknesses under different spin rates and water ratio were measured and compared. MOS capacitors and transistors were fabricated with standard microfabrication processes including photolithography and metal deposition. Effects of solidification conditions of honey including drying temperature and duration on the quality of the honey film such as electrical breakdown, leakage current, hydrophobicity, smoothness, etc. were examined. The results with optimized process parameters and device properties will be reported in the paper and presentation.

The effectiveness of using oxygen plasma to clean the organic residue from biomineralized nanoporous valves of marine diatoms (Coscinodiscus wailesii) was investigated. Two plasma processes were employed, one using a commercial 13.6 MHz oxygen plasma cleaner with a maximum plasma power of 30 Watts, the other using a microwave oven with a 2.4 GHz microwave output power of 900 Watts. A reference experiment using photoresist-coated silicon wafers was conducted to determine the etch rate for a planar organic film. While the planar organic layers were being etched in either plasma process, optical microscopy on the actual diatom nanopore frustules showed organic residue (chloroplasts) remaining even for the longest plasma treatment times. This reduced etch rate can be attributed to the shape of the frustules themselves, with the nanopore membrane encapsulating the chloroplast, limiting the diffusion of the reacting species through the nanopores.

Bioplastics are indispensable for establishment of green-sustainable society. Conventional bioplastics were composed of aliphatic polymers like poly(lactic acid)s having not very high softening temperature and no specific functions. In order to open the world of high-performance bioplastics, we have prepared aromatic biopolymers derived from exotic amino acid. Here we used 4-aminocinnamic acid (4ACA) which was bioavailable by a microorganismal genetic-engineering. The photodimer of 4ACA was successively prepared as a bio-derived aromatic diamine via [2+2] cycloaddition in the solid state with a perfect conversion degree. The biodianilines were polymerized with tetraacid dianhydrides to produce aromatic polyimides. Especially the aromatic polyimides derived from the biodianiline with cyclobutanetetracarboxylic dianhydrides, which is also a photodimer of bio-available fumaric acid, showed a good thermomechanical performance as well as low density around 1.05-1.28 g/cm³, and additionally showed a high transparency and a breakdown voltage as high as conventional polyimide. Additionally, we hybridized the biopolyimides with silica by sol-gel methods to get the increased inslulating performanced with keeping high transparency. The transparent biomaterials can be used for next-generation transparent and flexible materials.

Electronics have become indispensable in our daily routine. A great part of the electronic equipment that surrounds us belongs to what is known as conventional electronics, based on inorganic materials such as silicon and gallium arsenide. However, with the life of the electric and electronic equipment becoming shorter and shorter, two major issues arise for both the scientific community and municipalities: the increasing amount of Waste of Electrical and Electronic Equipment (WEEE) and the depletion of natural resources. Taking into account the definition of sustainability provided by the United Nations (the ability of satisfying one generation’s needs without compromising the possibility of future generations to satisfy), those two issues point to the lack of sustainability in the electronics field of the current generation, at least so far. Consequently, great attention has been given to green (sustainable) electronics in the last years, having as core values (i) the use of abundant and low-cost precursors, leveraging on processing routes that (ii) lack toxic solvents as well as toxic waste and (iii) are low cost and (iv) involve biodegradable materials. In this contribution, we will present our preliminary results on the biodegradability and compostability of organic electronic materials of interest for electronics and energy storage devices, focusing on the case of study of melanin biopigments used in transistors, batteries and supercapacitors.

Implantable medical devices provide an effective therapeutic approach for neurological and cardiovascular diseases. With the development of transient electronics, a new power source with biocompatibility, controllability, and bioabsorbability becomes an urgent demand for medical sciences. Here, various fully bioabsorbable natural-materials-based triboelectric nanogenerators (BN-TENGs), in vivo, are developed. The “triboelectric series” of five natural materials is first ranked, it provides a basic knowledge for materials selection and device design of the TENGs and other energy harvesters. Various triboelectric outputs of these natural materials are achieved by a single material and their pairwise combinations. The maximum voltage, current, and power density reach up to 55 V, 0.6 µA, and 21.6 mW m⁻² , respectively. The modification of silk fibroin encapsulation film makes the operation time of the BN-TENG tunable from days to weeks. After completing its function, the BN-TENG can be fully degraded and resorbed in Sprague– Dawley rats, which avoids a second operation and other side effects. Using the proposed BN-TENG as a voltage source, the beating rates of dysfunctional cardiomyocyte clusters are accelerated and the consistency of cell contraction is improved. This provides a new and valid solution to treat some heart diseases such as bradycardia and arrhythmia.

Achieving biodegradability in optoelectronic devices, such as light-emitting electrochemical cells (LECs), requires assessing every component for its degradability in a biologic environment. The substrate makes up the vast majority of the device’s mass, thus governs its biodegradability and mechanical behavior. While biodegradable thermoplastic foils provide mechanical flexibility by bending, they don’t offer any elastic stretchability. However, replacing biodegradable thermoplastics with elastomers would extend the range of potential applications in packaging and medicine. Silicone-based elastomers are frequently used as stretchable substrates but are merely biocompatible, not biodegradable.
We present four different biodegradable options as elastic substrates for LECs with different processing concepts: A commercially available compostable thermoplastic elastomer (Terratek Flex), two synthesized poly(glycerol-sebacate) elastomers being either photo- or thermally cross-linked and a gelatin-blend from commercial ingredients. Their suitability as substrates is investigated by the optoelectronic performance of LECs. These are composed of biodegradable and biocompatible materials and fully printed via inkjet printing and doctor blading.¹ Their charge transport and light-emission is characterized under increasing isotropic strain of the elastic substrate. The combination of stretchable biomaterials with up-scalable manufacturing techniques will enable the fabrication of transient and disposable electronic products ranging from biodegradable smart packaging via soft robotics to skin-adhered wearable healthcare applications, without adding to the global plastic carpet.

(1) J. Zimmermann, L. Porcarelli, T. Rödlmeier, A. Sanchez-Sanchez, D. Mecerreyes, G. Hernandez-Sosa; Adv. Funct. Mater. 2017, 1830, 1705795.

The growing demand for implementing wearable and implantable devices that can sense and harvest energy from human motion and biomechanical vibrations, is motivated to build next-generation smart sensors, flexible circuits, and artificial electronic skin devices. Recently, triboelectric nanogenerator devices based on electrostatic induction have been demonstrated to scavenge mechanical vibrations. For the seamless interface between the devices and human tissue, it is required that the devices are composed of soft, flexible, and biocompatible materials. In addition, obtaining conductive electrodes for the bio-devices is still challenging due to the tradeoff between the flexibility and conductivity. Attractive properties of silk protein such as biocompatibility, flexibility in thin film form, compatibility with the aqueous solution, and highly optical transparency have made it to be a promising candidate for realizing wearable and implantable electronic energy devices.
Herein, we present the fabrication of flexible, transparent, and biocompatible single-electrode silk bio-triboelectric nanogenerators (SBTENG) to sense and harvest energy from biomechanical vibrations. We constructed a SBTENG using a 0.12 mm thick silk film with the grating structure of periodicity of 1.5 μm and the buried silver nanowires (Ag-NWs) network with a sheet resistance of 35 Ω sq^-1. The fabricated SBTENG devices offer biocompatibility, flexibility and transparency (average transmittance of 85% in the visible region), which are essential for bioelectronics. The SBTENG is capable of outputting an open circuit voltage of 90 V (V_max = 110 V), a short circuit current of 0.06 μA (I_max = 0.1 μA) and the maximum power density of 2 mW/m² on a load of 1 MΩ under light finger tapping, which can drive five commercial green light emitting diodes instantaneously. The mechanism of SBTENG is based on the tribo-charge generation on the surface of silk upon tapping it with human finger. Owing to the transparency of the SBTENG devices, they can be attached to electronic devices (commercial cell phone and electrical mouse) to harvest the biomechanical energy with an output power of 1 μW. The low cost, ease of fabrication, biocompatibility, flexibility and transparency of SBTENG devices enable their potential usage in applications including human-machine interface, touch sensor, and biomechanical energy harvesting.

Flexible electronic devices underpin many biomedical technologies that record and stimulate neuronal activity from organs in the central and peripheral nervous systems. Reliable and stable chronic recording from excitable tissues using implantable multielectrode arrays has been elusive to date due, in part, to host tissue interactions that contribute to device failure. Local tissue damage and device failure is worsened by the mechanical mismatch between materials used to fabricated rigid silicon-based microfabricated multielectrode arrays (E_MEA ~ 100 GPa) and tissues in the nervous system (E_PNS ~ 10 kPa). Hydrogel-based electronics could reduce the mechanical mismatch across the tissue-device interface and enhance performance. Furthermore, adhesive ultracompliant hydrogel-based electrodes have potential applications in wearable devices ranging from EEG electrodes to consumer electronics. Here we present materials and companion fabrication strategies to create ultracompliant electronic devices for use in peripheral nerve interfaces. Integrated strategies for polymer synthesis, processing, and microfabrication are described. Details regarding the in vitro and in vivo performance of these devices will also be presented.

Organic materials offer attractive properties for solid-state lasers, including large oscillator strength, high exciton binding energy, spectral tunability, and compatibility with low-cost fabrication processes. However, despite impressive proof-of-principle demonstrations and dramatic improvements in performance, important fundamental limitations remain. Particular challenges are concentration quenching and bi-molecular exciton recombination which limit the available gain under practical pumping conditions.

Here, I will summarize key results from a number of studies that we performed on a rather unconventional class of organic materials, the biologically produced fluorescent proteins. The nano-scale barrel-like molecular structure of fluorescent proteins like GFP prevents concentration-induced quenching of fluorescence and drastically reduces singlet-singlet annihilation at high exciton densities. This facilitates low-threshold lasing in various configurations and has recently enabled the realization of the first organic polariton laser that can be pumped in a quasi-continuous ns-regime.

Implantable triboelectric nanogenerators (iTENGs) are promising to work as sustainable power source for implanted healthcare electronic devices. In this study, we fabricated a serial of biodegradable (BD) iTENGs and effectively tuned their degradation process in vivo by employing Au nanorods (AuNRs), which responded to the near-infrared (NIR) light sensitively. The implanted BD-iTENG worked well for more than 28 days in vivo, without NIR treatment. When NIR treatment was applied, the output of AuNRs-BD-iTENG rapidly reduced to 0 within 24 h and the device was mostly degraded in 14 days. This showed that the in vivo degradation of our BDiTENG could be triggered and come into effect very quickly with rational manipulation. The peak value of in vitro and in vivo output voltage generated by the AuNRs-BD-iTENG were 28 V and 2 V, respectively. Moreover, the in vivo output voltage was applied on fibroblast cells and demonstrated a significant acceleration for cell migration across the scratch, which was very beneficial to wound healing process. In addition, we discovered that the alternating BD-iTENG output was as efficient as direct current (DC) stimuli. The mechanisms were investigated. Our work has demonstrated the feasibility of building a photothermally tunable BD-iTENG as a transient power source for biomedical healthcare electronics.

Microelectronic devices placed in the nervous system present tremendous potentials for investigating neural circuits and treating neurological disorders. Currently, these devices often experience failures in part due to the electrical, mechanical, and biochemical, mismatch between the artificial device and neural tissue. Quantitative histology and 2 photon imaging have revealed neuronal damage and degeneration, inflammatory gliosis, blood brain barrier leakage and oxidative stress as a result of implantation. Several biomaterial strategies have been investigated to minimize the mismatches and achieve seamless and stable device-tissue interface. First, various conducting polymer based nanocomposites have been investigated as electrode coatings and facilitate the signal transduction/charge transfer between ionically conductive tissue and electrical device. Secondly, to minimize the mechanical mismatch at the device-brain tissue interface, novel soft and elastomeric electrode materials have been developed with Young’s modulus approaching that of neural tissue (less than 1 MPa). Soft implants demonstrated reduced inflammatory tissue response in both CNS and PNS compared to stiff implants of similar geometry and surface chemistry. Thirdly, bioactive approaches are being developed to modulate the biological responses. One approach is to decorate the implant surface with biomolecules derived from the brain or synthetic biomolecule mimics. Surface immobilization with these bioactive molecules significantly improved neuronal health and inhibited the inflammatory tissue response around the implants. Another approach is to deliver therapeutics that control inflammation, neurodegeneration and oxidative stress. These bioactive approaches have demonstrated significant benefit in neural recording quality and longevity. The ultimate solution to a seamless device/tissue interface may be a combinatorial approach that takes advantage of multiple biomimetic strategies discussed above and beyond.

Rapid developments of smart electronics, flexible and wearable e-skin sensors are attracting a great deal of attention due to their smart sensing applications in next-generation device. Interestingly, it can eventually measure and quantify electrical output signals generated by various human activities.^[1-5] However, the flexibility, biocompatibility, sensing capability, cost-effectiveness and packaging are the main concerns, which immensely drive to carry out this present work.^[2] In this framework, organic piezoelectric materials such as poly(vinylidene fluoride) (PVDF) and its copolymers are of particular interest towards device integration, having adequate advantages over inorganic materials.^[3,4] In addition, it should be mentioned that the choice of electrodes and their compatibility with organic and hydrophobic surfaces of PVDF remain challenging tasks, particularly when device performance, durability and implant ability are considered.
The brittleness, toxicity and high cost of inorganic materials have prohibited its use as a conducting electrode; in addition, direct adherence on electrospun nanofibers (NFs) surface is one of the major challenges to build the permanent electrodes in device structures. In contrast, organic conducting polymers are being presented as a viable alternative for organic electronic device, particularly if one can achieve adequate coating on the electrospun polymer fibers.^[4]
Here we present an all-organic piezoelectric e-skin sensor (AOPESS) based on highly aligned poly(vinylidene fluoride) (PVDF) NF arrays and conducting polymer i.e. polyaniline (PANI) coated PVDF NFs mat as electrode; for energy harvesting from various types of mechanical motions and self-powered human physiological signal sensing. The electrospinning technique in combination with vapor phase polymerization (VPP) enables such aligned structure followed by successive coating of PANI upon PVDF NFs surface. The Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy and Field emission scanning electron microscope (FE-SEM) clearly indicate the successful coating of PANI upon the PVDF NFs surface. The electrical performances were clarified by measuring the current-voltage (I-V) characteristic under the application of external pressure. Owing to highly aligned structure with superior piezoelectric β-phase contained (~98%) and excellent electrode contact-adherence, AOPESS exhibits an effective conversion of mechanical energy of human finger movements into electrical energy (~10 V). The coating of PANI upon PVDF NFs opens the use of organic electrode in various applications especially for e-skin devices solving the so called electrode issues. Recently, human physiological signal monitoring is an effective approach for the assessment of various human health problems. So, we can monitor our physiological signals such as body temperature and heartbeat rates.^[5] More importantly AOPESS can show ultra-sensitivity towards various human movements such as wrist bending, neck stretching, arm compressions, throat movement, and phonation recognition to name a few. Thus it will play an essential role in future wearable electronics and shed light on multiple advancements like electronic skins to human–machine interfaces.
References:
[1] Wang et al. Science 2006, 312, 242.
[2] Kim et al., Science 2011, 333, 838
[3] Maity et al., Energy Technol. 2017, 5, 234.
[4] Maity et al., ACS Appl. Mater. Interfaces 2018, 10, 18257
[5] Amjadi et al. Adv. Funct. Mater. 2016, 26, 1678.

The combination of conformable and organic bioelectronics can enable a full range of unprecedented applications, from unperceivable personal monitoring systems -to be used in healthcare and sport, especially in skin contact applications- to bio-friendly and edible electronics.
To this aim we chose Temporary Tattoo paper as an unconventional substrate for developing ultrathin and transferrable devices which are able to conform to surfaces with complex topography. Such a layered material is composed of (1) a support paper, (2) a water-soluble starch/dextrin sacrificial layer, and (3) a releasable ethylcellulose nanosheet (thickness ~ 500 nm). It is commercially available in the form of large area sheets or rolls at very low cost.
In a first part of this talk I will report about a robust, low cost and safe strategy for producing disposable ultraconformable electrodes for skin-contact electrophysiology recordings. Temporary Tattoo Electrodes (TTE) and multielectrode arrays (TTMEA) based on conducting polymer PEDOT:PSS are fabricated by ink-jet printing, laser cutting/engraving and lamination. Thanks to this choice, several different configurations of arrays can be customized for different applications. They can be transferred on skin as temporary transfer tattoos and the overall thickness of such electrodes is < 1 μm. We demonstrated their successful performances as stable, dry electrodes for several electrophysiological recordings: skin impedance, surface electromyography (sEMG) on limbs and face, electrocardiography (ECG), and the most challenging electroencephalography (EEG). TTEs demonstrated stable adhesion and operation on skin. Long-term recording was assessed which favorably compares with state of art Ag/AgCl electrodes. Moreover myographic control of a robotic hand through TTE was demonstrated paving the way to novel applications as unperceivable sensors in human and brain machine interfaces.
Temporary Tattoo-paper is furthermore proposed as a simple and versatile platform for the integration of electronics onto food and pharmaceutical capsules. In particular, the fabrication of all-printed organic field-effect transistors on untreated commercial tattoo-paper, and their subsequent transfer and operation on edible substrates with a complex nonplanar geometry is demonstrated.

References
1) Zucca, A.; Cipriani, C.; Sudha; Tarantino, S.; Ricci, D.; Mattoli, V.; Greco, F. Advanced Healthcare Materials 2015, 4 (7), 983-990.
2) Ferrari, L.; Sudha, S.; Tarantino, S.; Esposti, R.; Bolzoni, F.; Cavallari, P.; Cipriani, C.; Mattoli, V.; Greco, F. Advanced Science 2018, 5, 1700771.
3) Piva, N.; Greco, F.: Garbugli, M.; Iacchetti, A.; Mattoli, V.; Caironi, M. Advanced Electronic Materials 2017, 1700325.
4) Bonacchini, G. E.; Bossio, C.; Greco, F.; Mattoli, V.; Kim, Y.H.; Lanzani, G.; Caironi, M. Advanced Materials 2018, 30, 1706091.

As wearable devices gain traction, inexpensive and simple sensors that can connect with an internet of things platform are promising devices for continuous wellness data monitoring. One approach to making such sensors is using stimulus-responsive (i.e. smart) materials. Inspired by nature, smart materials sense a stimulus in their surroundings and undergo a measurable change in property. Smart materials based on nanoparticle- polymer composites can be designed to sense various stimuli and exhibit changes in color, resistance, capacitance, etc. In our composite systems, conducting nanoparticles (carbon-based materials) impart electrical conductivity to the composite, while the bio-compatible and bio-derived polymer matrix provides mechanical stability. Either the polymer or the nanofiller (or both) may act as the sensing element, undergoing changes in electronic properties in response to an external stimulus.
In this presentation, a negative temperature coefficient (NTC) temperature-responsive composite is reported (where the NTC is defined as (R-R₀)/(R₀△T)). Our materials consist of a high melting point biopolymer (polyhydroxybutyrate (PHB)) and graphenic nanomaterial (reduced graphene oxide (rGO)). At a given temperature, the electronic properties of the composites are strongly dependent on the concentration of rGO within the polymer matrix. Upon heating, these materials exhibit large and reversible changes in resistivity (NTC of - 0.008 /°C) and fast response time (less than 70 ms for a 3 wt% rGO composite). This response results from the semiconducting properties of the rGO, where the number of charge carriers in the conduction band increases with temperature, thereby reducing the overall resistivity of the composites.
These responsive conductive composites are good candidate for low-cost sensing devices. The composites are solution processible and thus are compatible with many printing techniques such as direct printing. Devices are capable of measuring dynamic change of temperature subjects with curved surfaces and of thermomaping a large area. Devices are further connected to the wireless system to monitor wellness data in a time-controlled manner.

Quantitative assessment involving non-contact electrical methods without the involvement of microscopy can enable a remote user to monitor the cell growth and development at different stages. We introduce and demonstrate a facile approach to probe the ensemble of cells and the role of environment and substrates in the growth and functions. Specifically, cell lines which are of neuronal like and primary explant from chick-embryo retina are studied closely using this novel monitoring method along with conventional from multielectrode array (MEA) type electrical recording approaches. The studies using this technique of the cells at different stages of growth and the changes introduced upon differentiation point to the versatility of the approach. The environment of the cells are varied by choice of different substrates including a variety of non-rigid substrates with different degrees of electrical properties. Optoelectronic substrates with the ability to absorb light and change the surface potential to trigger stimulated responses from the cells and blind-retina explants are also demonstrated. A specially designed microfluidic setup which eliminates air bubbles and is integrated to the measurement assembly was developed to carry out long-term recordings. A systematic development studies of chick retina from the blind-stage (day 12) to a fully mature state (day 21) was carried out. We utilize this chick-model system to study the signal transduction mechanism and pathways upon introducing artificial photoreceptors.

Ion generation in bacteria cells is a central component in their life cycle. Ion generation helps us understand bacterial responses to stimuli, as well as the mechanisms by which ion transport is regulated. Recent attention has been given to ion-based communication within and between bacteria colonies [1]. Two methods of detecting bacterial ions are fluorescent and electronic detection. Fluorescent dyes provide a view of ion concentrations spatially, allowing detection of ion movement and position both within and outside cells. Electronic measurements are limited to extracellular ion concentrations and are typically performed using ion selective electrodes (ISEs) or ion-selective FETs (ISFET) to measure specific ion concentrations or changes in pH.
We report on the use of organic electrochemical transistors (OECTs) to sense ion concentrations in bacteria growth media. OECTs high transconductance, bio-compatibility, low cost, and small size have made them a popular sensor for detection and characterization of whole cells [2]. OECT switching is driven by ions from either a liquid or solid source. Understanding changes in OECT behavior for different solid and liquid ion sources is needed to fully optimize device for specific applications. These changes can come from ion concentration and species (or other particulates) and significantly affect device operation.
Cells captured or cultured onto OECTs can induce a change in effective gate voltage, or a change in transconductance due to their effect on medium pH. While the OECT response to the presence of various cells has been reported, the effect of the culture medium has not been reported. Characterization of the driving electrolyte, or culture medium, is needed to optimize OECT performance and sensitivity for whole cell detection.
We have tested transconductance, ON/OFF ratio, and peak transconductance gate voltage of PEDOT:PSS based OECTs operating in several media: KCl, NaCl, PBS, LB broth, YT broth, and water solutions. Our results show peak device transconductance utilizing 0.1M KCl, which is in line with literature [3]. A decrease of 37.7 µS (57%) and 55.1 µS (84%) is shown for LB and YT culture media compared to the 0.1M KCl solution. An increase in ON/OFF ratio of LB and YT broth of 300% and 224% is obtained, compared to 0.1M KCl solution. Interestingly, a reduction in peak transconductance gate voltage from ~0.6V to ~0.3V was measured for both broth solutions compared to pure electrolyte solutions (KCl, NaCl, etc.). This is beneficial for operating under low OECT power conditions. Overall, these results indicate that cell culture media play an important role in OECT-cell interactions.

1. Prindle, A., et al., Ion channels enable electrical communication in bacterial communities. Nature, 2015. 527: p. 59.
2. Ahmed, A., et al., Biosensors for whole-cell bacterial detection. Clinical Microbiology Reviews, 2014. 27(3): p. 631-646.
3. Lin, P., F. Yan, and H.L. Chan, Ion-sensitive properties of organic electrochemical transistors. ACS Applied Materials & Interfaces, 2010. 2(6): p. 1637-1641.

In vitro models of biological systems are essential for our understanding of biological systems. In many cases where animal models have failed to translate to useful data for human diseases, physiologically relevant in vitro models can bridge the gap. Many difficulties exist in interfacing complex, 3D models with sensing technology adapted for monitoring function of cells within these models. Polymeric electroactive materials and devices can bridge the gap between hard inflexible materials used for physical transducers and soft, compliant biological tissues. An additional advantage of these electronic materials is their flexibility for processing and fabrication in a wide range of formats. In this presentation, I will discuss our recent progress in adapting conducting polymer devices, including simple electrodes and transistors, to integrate with 3D cell models. We go further, by generating 3D electroactive scaffolds capable of hosting and monitoring cells.
In some cases, it is useful to zoom in on interactions occurring at the molecular level, to read out events happening at the level of the cell membrane. In addition to monitoring properties of cells and tissues, electrical monitoring is a powerful tool to monitor transmembrane protein function. I will highlight recent research using biomimetic models of cell membranes interfaced with organic electronic devices for drug discovery.

Solution-processed, carbon based electrolyte-gated transistors represent an ideal ionic/electronic hybrid device that bridges biology and electronics. These devices are being investigated for a wide range of applications, from drug delivery to neuromodulation and highly sensitive biosensing. Cell-based elecrical bio-sensors are of particular interest because they can enable a high level of automation and parallelisation in real-time in vitro monitoring of cells cultures, highly desirable for dianostigs and toxicology tests. While typical sensing platforms rely on impendace measurements, we propose here an electrolyte-gated transitor for cell viability monitoring, based on a network of solution-processed, polymer-wrapped semiconducting carbon-nonotubes. Our sensors display extended stability to water-gating and allow an easy signal read-out, without requiring complex modeling and/or parameters fitting, as this corresponds to variations in the static transistor channel current. We demostrate successful cell-proliferation monitoring in excess of 70 h of three different cell models.

Photosynthetic microorganisms can be envisaged as sources of active materials for bioelectronic devices for photoconversion or light-induced processes.¹
In particular, photosynthetic Reaction Centers (RCs) are enzymes capable to convert solar energy into charge separated states with efficiency close to 100%.² We have demonstrated the use of the RC from the photosynthetic bacterium Rhodobacter sphaeroides in bioelectronic and electrochemical devices.³
We have first reported the highly selective covalent functionalization of the bacterial RC with several classes of tailored molecular fluorophores which act as antennas to enhance its light harvesting capability.⁴ The resulting hybrid systems outperform the native protein in the photogeneration of charges and in the photoenzymatic activity.⁵ We have also built up smart supramolecular architectures combining multiple enzymes assembled with tailored linkers, which are able to perform manifold functions. Finally, we have developed protocols for addressing the RC on thin films of molecular or polymeric semiconductors deposited onto metal electrodes by covalent or weak collective interactions, obtaining RC-sensitized electronic⁶ and electrochemical devices. Biomimetic polymers, such as polydopamine mimics of melanin, have also been investigated as efficient electronic interfaces of RC with electrodes in photoelectrochemical cells.
Our study discloses new concepts for the generation of bio-hybrid materials for sunlight photoconversion and for light-triggered bioelectronics, by combination of tailored functional molecules with highly efficient photo-active natural structures optimized in billions of years of evolution.

References
[1] Milano, F.; Punzi, A.; Ragni, R.; Trotta, M.; Farinola, G.M. Adv. Funct. Mater. accepted, DOI: 10.1002/adfm.201803732.
[2] Tangorra, R. R.; Antonucci, A.; Milano, F.; la Gatta, S.; Farinola, G. M.; Agostiano, A.; Ragni, R.; Trotta, M. Hybrid Interfaces for Electron and Energy Transfer Based on Photosynthetic Proteins. In Handbook of Photosynthesis, Third Edition, Pessarakli, M., Ed. CRC Press: 2016; pp 201-220.
[3] Operamolla, A.; Ragni, R.; Milano, F.; Tangorra, R.R.; Antonucci, A.; Agostiano, A.; Trotta, M.; Farinola G.M. J. Mater. Chem. C, 2015, 3, 6471.
[4] Milano, F.; Tangorra, R. R.; Hassan Omar, O.; Ragni, R.; Operamolla, A.; Agostiano, A.; Farinola, G. M.; Trotta, M. Angew. Chem. Int. Ed. 2012, 51, 11019.
[5] Hassan Omar O.; la Gatta, S.; Tangorra, R. R.; Milano, F.; Ragni, R.; Operamolla, A.; Argazzi R.; Chiorboli, C.; Agostiano, A.; Trotta, M.; Farinola, G. M. Bioconjugate Chem. 2016, 27, 1614.
[6] Glowacki, E. D.; Tangorra, R. R.; Coskun, H.; Farka, D.; Operamolla, A.; Kanbur, Y.; Milano, F.; Giotta, L.; Farinola, G. M.; Sariciftci, N. S. J. Mater. Chem. C, 2015, 3, 6554.

Using proteins as active device components is of particular interest for the fabrication of next-generation electronic devices. Proteins provide soft, biocompatible and genetically tunable scaffolds that can be rationally engineered to participate in charge transport processes. In addition, proteins can retain biological functions, to produce multifunctional bioelectronics materials that could be applied to a variety of bio-sensing and bio-energy applications.

Here, we report the fabrication of conductive protein gels and films with novel opto-electronic properties. We fabricated these protein-based materials using genetically engineered amyloid proteins as building blocks and introduced desired functionalities via synthetic biology. Using bio-inspired and bio-derived syntheses, we have developed strategies to produce and isolate macroscopic quantities of functional protein materials. We have explored the synthesis of electronically conductive protein fibers and films, by introducing aromatic residues within the core of the self-assembling amyloid proteins. We have characterized the electrical properties of these proteins, and examined factors that influence the conductivity in such protein systems. In addition, we are investigating the potential of engineered proteins to participate in light harvesting in bio-hybrid energy devices. Our scalable biosynthesis process allows us to produce engineered protein materials in sufficient quantities to integrate them, in the future, in bio-hybrid functional devices.

Organometallic halide perovskites are fast grown photoactive material in the field of solar cell technology due to high absorption coefficient, almost 100 % internal quantum efficiency, high diffusion length, and broader absorption wavelength (visible to near IR spectrum) [1,2]. Their advantageous optical properties provide high potential to use perovskites as biointerface. But, low stability in aqueous environments and the presence of toxic lead content in commonly used perovskite semiconductors make it difficult to use in the biological environment. Although there is significant focus on lead-free perovskites, their performance remained far from the lead-based perovskites. In order to use perovskites as photoelectrode for neuronal prostheses, three important conditions including stability in water, biocompatibility, and generation of safe photostimulation need to be satisfied.
The present work demonstrates the first use of perovskite for neural interfaces. The photoelectrode consist of a perovskite photoactive layer sandwiched between transparent conducting oxide (ITO-Indium tin oxide) and biocompatible PDMS (dimethylpolysiloxane, a silicon-based organic polymer):P3HT (Poly(3-hexylthiophene), a semiconducting polymer) hybrid layer. The coverage of PDMS layer over perovskite thin film blocks the direct contact of neuron cells with toxic perovskite for biocompatibility. It also functions as an encapsulant against water that lead to enhanced stability in aqueous medium. Furthermore, we observed that the thickness of the perovskite layer is critical to generate safe capacitive photostimulation. We studied the perovskite biointerface with ShSy-5Y neuronal cells using whole-cell patch clamping and observed depolarization of the cells.

References
1. T. C. Sum, N. Mathews, Energy & Environmental Science 2014, 7, 2518
2. D. B. Mitzi, Progress in Inorganic Chemistry, Volume 48 2007, 1.

We report on an organic semiconductor nanoscale device optimized for neuronal stimulation: the organic electrolytic photocapacitor. The devices consist of a trilayer of metal and p and n semiconductors. When illuminated in physiological solution, these metal-semiconductor devices charge up, transducing light pulses into localized displacement currents that are strong enough to stimulate cells. The devices are freestanding, requiring no wiring or external bias, and are stable in physiological conditions. We have systematically evaluated the ability of photocapacitor devices to alter the cell membrane potential of single nonexcitable cells, generate action potentials in neuronal cell cultures, and stimulate explanted light-insensitive embryonic retinas.

Blood is the most intensely studied human biofluid and is used as the main indicator (so-called “gold standard”) of the health status of the individual. Blood is a biologically renewing fluid with ~ 1 million red blood cells (RBCs) injected every second from the bone marrow into the blood stream (equivalent to ~ 10¹¹ RBCs being created every day) of an adult human body and a similar number cleared or recycled. Blood is a very complex fluid, containing a multiplicity of components, including cells and cell fragments (red and white blood cells, platelets), proteins, and many other organic molecules and ions. Laboratory-based blood analysis is a well-established procedure that provides a wealth of information about the concentrations of key blood components and enables medical personnel to establish diagnoses and treatments. It is typically performed in hospital or laboratory settings using a variety of methods and equipment, with the emphasis on accuracy and measurement automation. To date, options for point-of-care blood analysis are limited and very low-cost options even more so. One analytical platform that contains the promise to fill this need utilizes cellulose-based microfluidic devices. Cellulose, the most abundant naturally occurring organic compound (polysaccharide), is the main constituent of cell walls in plants and is available in many practical forms, including conventional paper. Paper microfluidics utilizes the self-wicking ability of paper by capillary action to implement simple device that do need external pressure to transport fluids. This has opened the door to simple paper-based point-of-care (PoC) or point-of-use (PoU) devices for monitoring various medical conditions (e.g. pregnancy testing, virus assays, etc.). This research area has exhibited significant growth in the past few years, primarily because of its simplicity, fundamental low cost, and versatility. This presentation provides a review¹ of the convergence of these two materials – blood and paper - into an exciting new field for PoC/PoU diagnostics using whole blood. The starting point is a brief overview of the properties of blood and of cellulose, followed by methods and instrumentation for conventional and novel blood sampling. The main part of the presentation is a review of several important applications, including blood grouping, glucose and coagulation monitoring, biomarker detection. The presentation concludes with a discussion of current challenges of paper-based blood diagnostics and a look forward to future prospects.

¹H. Li and A. J. Steckl, ACS Analytical Chemistry, 2018, 10.1021/acs.analchem.8b03636.

With the advent of wearables in biomedical, consumer health and safety applications a whole new class of electronics products is emerging with a high potential for further application in robotics, but also sports and fashion. While this is still a comparingly small market there is the chance of mass application in the mid-term future. Inevitably this will result in major challenges for sustainability. By now, there is very limited research on environmental impacts of smart textiles and more specifically wearables, and even less consideration of sustainability aspects when it comes to related product development.
This presentation is supposed to facilitate the understanding of potential environmental implications of wearables, related material choices and design decisions. From a life cycle perspective raw material choices, manufacturing technologies, use phase (including maintenance, repair, smart textile care), and end-of-life have to be considered and a thorough understanding of what happens to materials throughout product lifecycles is required. For this, existing guidelines for eco-design have to be adapted to the specific case of wearable electronics. This does not only mean to reflect from an environmental perspective on flexible and stretchable electronics and bio-compatibility. Heterogeneous parameters such as performance, reliability and robustness requirements, target application markets, business-to-business vs. consumer markets, intended single or multiple use, and possible use scenarios in general all define what might count as “green wearables”.
This presentation is meant to stimulate an early reflection on material developments for wearables to help material scientists and product developers alike to consider sustainability implications of their research, innovation and development. The more such wearable electronics enter the market, the more these composite products will emerge as an ecological problem, unless appropriate counter-measures are taken right now.
Given that there is an evolving environmental product regulation in the European Union, which does not cover wearables comprehensively yet, an outlook will be given, where recent trends in wearables might run into conflicts with upcoming product policies.

Developing aqueous electrolyte compatible, redox-active polymers that can be processed from environmentally sustainable solvents is desirable because these traits will effectively reduce environmental impact and human health hazards during processing procedures and in the final device architecture. Additionally, the ability to dope and dedope conjugated polymers in aqueous media may allow for conjugated polymers to find applicability in biological systems. In an effort to address these criteria, we have synthesized two ester-functionalized 3,4-propylenedioxy-thiophene polymers that are sufficiently soluble in environmentally sustainable (2-methyltetrahydrofuran) and benign (ethyl and propyl acetate) solvents to be processed as thin, electroactive films. Furthermore, as the ester-functionality on the side chains is increased, the polymer films are able to be reversibly switched in aqueous electrolytes. The polymers were studied as electrochromic films as a case study and it was revealed that optical, electrochemical, and morphological properties showed slight variations depending on the casting solvent. However, properties such as switching time and contrast were unaffected. Our work highlights a simple design strategy to synthesize aqueous electrolyte compatible electrochromic polymers processable from sustainable solvents without post-polymerization modifications, which will ultimately reduce the environmental impact of electrochromic device fabrication and testing.

Silk fibroin produced by Bombyx mori silkworm, a fibrous protein-based biopolymer, has been used as a material for high-quality clothing since ancient times due to its superior textile properties such as lightness, fineness, and a unique luster. Moreover, because of its excellent strength and attractive biological properties, regenerated silk fibroin has been widely studied as a biomaterial over the past decades. Recently, silk fibroin has been considered as a promising candidate for biocompatible and green electronics due to its interesting resistive switching behavior. However, while prior works demonstrated promising proof-of-concept resistive switching, the high programming voltage, subpar on/off ratio, and limited endurance have hindered the development for silk-based resistive memory devices.
In this work, we present a comprehensive study to investigate how we may improve the electrical switching properties of silk memory devices by tuning its crystalline structure. Silk fibroin is mainly composed of two kinds of amino acids, glycine (Gly) and alanine (Ala). The high contents of these two amino acids result in highly conserved amino acid repeat units such as poly-(Gly-Ala) and poly-Ala domains in the primary sequence, which provides an advantage in the arrangement and local conformation of protein chains, referred to as the secondary structure such as α-helices, β-sheets, turns, and loops. The α-helix structure coiled around an axis like a spring by intra-chain hydrogen, whereas β-sheet is fully extended and stabilized by inter-chain hydrogen bonds between the protein chains aligned in an opposite direction. By promoting the molecular interactions in silk fibroins through selective heating in a water vapor treatment, we developed helix-rich silk fibroin films that may be more suitable for resistive switching applications as α-helix structures can facilitate the ion migration process that may be responsible for the resistive switching in fibroins.
We fabricated crossbar arrays of silk-based memory devices, where 200-nm thick silk fibroin thin films (both helix-rich and amorphous fibroins) are sandwiched by the top (Ag 100 nm) and bottom (Au 50 nm) electrodes. We observed that memory devices based on helix-rich fibroin showed lower average set voltages (V_set) at ~1.8 V compared to that in the amorphous fibroin devices (2.7 V). This partly supports our hypothesis that α-helix structure may facilitate the cation ion migration process within the fibroin and hence allowing a conductive pathway to be formed at a lower electric field. In addition, we also observed higher on/off ratio (an average of 10⁸ out of 20+ devices) for helix-rich fibroins compared to that of the amorphous fibroins based devices (~10⁶). The helix-rich fibroin based memory devices also demonstrated a reasonable endurance performance at 160 cycles compared to <30 cycles in previous studies.
In summary, we study how the composition of structures in the silk fibroin may affect its resistive switching behaviors. We demonstrate significant improvement in terms of low programming voltage, large on/off ratio, and better cycling lifetimes in silk memories based on helix-rich fibroins. This approach of tailoring the electronic properties of silk fibroin by tuning its molecular structures opens up exciting opportunities for silk-based biocompatible and green electronic applications.

Natural systems utilize multifunctional biocomposites by a bottom-up self-assembly of nanomaterials for creating multiscale, hierarchical, and multiphasic structures. While conventional man-made synthetic composites increase one functionality by sacrificing the others, the biocomposites often synergistically utilize their multi-functionalities. Here, by molecularly organized layer-by-layer assembly as well as thermodynamically driven orientation, we introduce multifunctional nanocomposites, recently developed from our laboratory, from natural biomaterials including high crystalline cellulose nanofibers and conductive melanin nanoparticles. High crystalline cellulose nanofibers, extracted from tunicates, have shown almost perfect crystallinity, straight fibrous shape, and liquid crystalline alignments. Thus, their nanocomposites showed uniquely oriented structures as well as excellent optical, mechanical, and barrier properties. On the other hand, naturally derived melanin nanoparticles are molecularly structured to possess finely tunable electrochemical conductivities, optical reflectivity, and casting shape stability with inherent biocompatibility. These composites can be used as key functional materials in the emerging applications such as biotic-abiotic smart interfaces, implantable electronics, and eco-electronics.

Organic semiconductors are of interest for optoelectronic applications due to their low cost, solution processability, and tunable properties. Recently, natural product-derived organic pigments attracted attention due to their extraordinary environmental stability and unexpectedly good optoelectronic performance, in spite of only partially conjugated molecular structure. We present a study of the optical and electronic properties of several fungi-derived pigments and of their use in organic (opto)electronic devices. Fungi-derived pigments are a naturally sourced, sustainable class of materials that are yet to be explored as organic semiconductor materials. Examples of such pigments under study are a blue-green pigment xylindein, which is secreted by the wood-staining fungi Chlorociboria (C.) aeruginosa and C. aeruginascens, red pigment draconin derived from Scytalidium cuboideum, and a yellow pigment derived from Scytalidium ganodermophthorum.

Photophysics of pigments is explored using absorption and photoluminescence (PL) spectroscopy combined with density functional theory calculations. In xylindein and the red pigment (a novel naphtoquinone derivative), our studies reveal contributions of several tautomers to the optical properties and solvent-dependent pigment aggregation and crystallization. Molecular packing-dependent properties of aggregates and crystals were studied using polarization- and temperature-dependent absorption and PL and related to film or crystal structure and morphology obtained from the SEM and XRD. Photostability and thermal stability of pigments was also quantified.

(Opto)electronic properties of pristine pigments and their blends with synthetic polymers and naturally derived biopolymers, developed to improve film morphology and processability, were explored in several device structures. Charge carrier mobilities were obtained from space-charge limited currents and from measurements of thin film transistor characteristics and related to film structure and morphology. Some blends such as xylindein:PMMA revealed ambipolar charge transport with charge carrier mobilities of up to ~0.01 cm²/Vs. Photoresponse was observed throughout the pigment absorption range, and photocurrent spectroscopy was carried out to obtain wavelength-dependent charge generation efficiencies. Charge and energy transfer in donor-acceptor combinations of pigments with several benchmark donors such as P3HT and PTB7-Th and acceptors such as PCBM were also investigated to determine the feasibility of using pigments under study in bulk heterojunction solar cells.

Digital Microfluidic (DMF) devices have been developed recently as its promising ability to replace conventional laboratory processes. Small sample consumption and high controllability make the device suitable for electrochemical or biochemical applications. However, the fabrication of current DMF device is limited to rigid substrates, which confine its potential on flexible, fabric substrates for further applications.
Here, we present DMF devices fabricated through additive manufacturing method with integrated on-chip ion-selective test function. The DMF electrodes are printed directly with conductive silver ink, followed by spin coating and spray coating of dielectric and hydrophobic layers. The overall fabrication procedure is easy and fast, which can be applied to various substrates. In addition, a capacitance monitoring system has been added to the device to obtain the droplet position and speed data in real-time for providing feedback signals. The ion-selective function is tested with a layer of ion-selective membrane on one of DMF electrodes. Fabricated DMF device demonstrated droplet manipulation functions including moving, mixing, and testing sequence. The on-chip membrane shows targeted ion selectivity from the droplet containing mixed interference ions.

Electromechanically active materials change their shape under external electrical stimulation or generate electrical signal upon mechanical stimulus. These materials are in the focus of intense research as bioinspired devices need replacement for traditional actuators.

The present study aims to development of biofriendly ionic electromechanically active polymer actuators (IEAPs). A typical IEAP is a soft thin laminate composed of a microporous ion-permeable polymer membrane containing electrolyte (for example ionic liquid (IL)) placed between electrodes with a high specific surface area (for example conductive polymers). IEAPs can work as actuators and sensors transducing between electric current and mechanical deformation. In addition, IEAPs can sense temperature, humidity and chemical composition of the environment. Migration of ions in response to electrical stimulation enables controlled release. Combining all these functionalities leads to smart devices, which sense surroundings and react accordingly. Potential applications for IEAPs include implantable or disposable biomedical devices, smart prosthesis, soft haptic devices and wearable electronics. Mentioned applications require biocompatible materials, which has still remained challenging during decades of research in the field.

Our approach towards biofriendly of IEAPs was to use biocompatible materials for different parts of IEAPs without compromising in performance. A key component hereby was low-toxicity IL as electrolyte. For electrode material polypyrrole (PPy) was chosen due to proven biocompatibility: PPy is a suitable substrate for cell growth, implantable and can be functionalized to be biodegradable. Medically approved synthetic polymer PVdF and inherently biofriendly and biodegradable gelatin were applied and compared as membrane materials. So far mostly the conventional imidazolium based ILs had been used as electrolytes in IEAPs despite the well-known toxicological issues of these salts and a large variety of alternative ILs available. In the present study low-toxicity choline based ILs were applied instead.

In the presentation preparation, characterization, and electrochemomechanical performance of the developed biocompatible IEAPs will be discussed. Significant differences in actuation were found in case of different ILs as electrolytes although the actuators were found to be cation active and all of the ILs contained the same choline cation. Experimental results were explained using computational methods: formation of ionic clusters was studied with molecular dynamics (MD) simulations and with density functional theory (DFT) calculations.

Owing to the burgeoning waste electrical and electronic equipment is the effort to recycle the printed circuit board (PCB), which if improperly disposed of results in health hazards and environmental pollution. This study describes a new PCB substrate that would vanish in water leaving the metals on it for re-use. A preliminary substrate made from water, gelatin, and poly vinyl alcohol was coated with polyurethane for the purpose of preservation under humid conditions and a voltage divider circuit was attached. Dynamic mechanical analysis and thermomechanical analysis were performed to characterize the PCB for its physical characteristics, while Fourier transformed infrared spectroscopy was used for chemical characterization. It was demonstrated that the metal components including solder, copper, and electronic components can be fully recovered without generation of any toxic byproducts or negative impact on the environment.

Sustainability assessment is an important approach for emerging technologies, as it can shed light on their potential environmental impacts and benefits when deployed at large scales, identify possible unintended consequences, and expose specific technology characteristics which can be optimized during the innovation and deployment phases to maximize future societal benefits.
While there have been many life-cycle assessments (LCA) of bio-based fuels and products, applications of LCA to emerging biofriendly electronics have been much more limited. Moreover, because biofriendly electronics are a rapidly emerging class of technologies, any sustainability analysis must move beyond retrospective LCAs and be largely prospective in nature (because empirical technology and market data are scarce/nonexistent), requiring special care with respect to uncertainty analysis and scenario design for meaningful feedback on potential impacts and benefits. Finally, in a future requiring deep decarbonization of all economic sectors, there may be competition with prospective applications of limited global sustainable biomass resources, notably for biofuels in the transport sector, bio-feedstocks in the chemicals sector, and bioenergy with carbon capture and sequestration (BECCS) in the power sector; this competition may affect the sources and quality of biomass available for biofriendly electronics applications. As such the integration of LCA with dynamic energy and resource systems modeling and scenario analysis will also be necessary.
Therefore, to be useful, sustainability assessment of biofriendly electronics demands a dynamic, prospective, integrated, and life-cycle systems modeling approach. This presentation will explore the development of such a best-practice assessment approach to meet this analytical vision, by reviewing strengths and weaknesses of existing modeling methods (e.g., LCA) and data sources, known data gaps and possibilities for filling them, exploring the role of lab-analysis partnerships to accelerate data availability and conduct R&D-relevant scenario analyses, and propose a research roadmap for building a sustainability assessment community of practice for biofriendly electronic applications. While such a framework is just a first step toward developing the needed framework and research capacities, it can be an important one for giving direction and building community to ensure the development and deployment of biofriendly electronics follows pathways that maximize future social benefits.

E-waste is one of the fastest growing waste streams in the world in terms of volume and its subsequent environmental impact on the planet. The global growth rate for the e-waste stream is 3–5% (Cucchiella et al., 2015) and expected to reach 50 million tonnes worldwide by the end of 2018 (Balde 2015). This e-waste stream provides an economic opportunity of 40 billion Euros (Balde 2015) and an environmental opportunity if recycled correctly. This is due to the presence of valuable metals such as copper, silver, gold, and palladium but also the presence of hazardous chemicals. There are many challenges associated with the recovery of metals and non-metal fractions from e-waste due to the composite nature of these materials. The recovery of metals is the main economic driver for e-waste recycling and downstream reprocessing. The existing technologies for metal recovery from e-waste are mostly designed to capture metals. When hydrometallurgical methods are used to extract metals, fine grinding is usually required and all components are ground to very fine particle sizes. Very corrosive chemicals are commonly used to extract metals of interest, and as a result, hydrometallurgical techniques are very energy intensive and toxic residue is left after processing. Pyrrometallurgical methods are also quite often used to recover metals by smelting. Both hydrometallurgical and pyrrometallurgical methods are energy intensive and destructive, particularly if the focus is to only to recover metals. The physical separation and step-by-step preceding final end processing allows for recovery of metals at much coarser sizes and the other non-metal materials like plastic, fiber glass, and resins to be recovered in a form that could be reused as a secondary raw material in the manufacturing of new products. This will provide an opportunity to design processes that will focus on minimizing the final residue after the recycling and end reprocessing of e-waste. The presentation will discuss current research on the step-by-step recovery of metal and non-metal fractions from e-waste.