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This article describes a process of fabricating highly porous paper from cellulosic fibers and carbon black (CB) with tunable conductivity. By embossing such paper, its porosity decreases while its conductivity increases. Tuning the porosity of composite paper alters the magnitude and trend of conductivity over a spectrum of concentrations of conductive particles. The largest increase in conductivity from 8.38 × 10-6 to 2.5 × 10-3 S/m by a factor of ∼300 occurred at a percolation threshold of 3.8 wt % (or 0.36 vol %) with the composite paper plastically compressed by 410 MPa, which caused a decrease of porosity from 88% to 42% on average. Our composite paper showed stable piezoresistive responses within a broad pressure range from 1 kPa up to 5.5 MPa for 800 cycles. The piezoresistive sensitivities of the composite paper were dependent on concentration and decreased with pressure. Composite paper with 7.5 wt % CB had sensitivities of -0.514 kPa-1 over applied pressures ranging from 1 to 50 kPa and -0.215 kPa-1 from 1 to 250 kPa. This piezoresistive paper with embossed patterns enabled touch sensing and detection of damage from darts and punches. Understanding the percolation behavior of three-phase composites (cellulosic fibers/conductive particles/air) and their response to damage, pressure, and processing conditions has the potential to enable scalable applications in prosthetics and robotics, haptic feedback, or structural health monitoring on expansive surfaces of buildings and vehicles.

Here, we report a novel ammonia : ammonium salt solvent based pretreatment process that can rapidly dissolve crystalline cellulose into solution and eventually produce highly amorphous cellulose under near-ambient conditions. Pre-activating the cellulose I allomorph to its ammonia–cellulose swollen complex (or cellulose III allomorph) at ambient temperatures facilitated rapid dissolution of the pre-activated cellulose in the ammonia-salt solvent (i.e., ammonium thiocyanate salt dissolved in liquid ammonia) at ambient pressures. For the first time in reported literature, we used time-resolved in situ neutron scattering methods to characterize the cellulose polymorphs structural modification and understand the mechanism of crystalline cellulose dissolution into a ‘molecular’ solution in real-time using ammonia-salt solvents. We also used molecular dynamics simulations to provide insight into solvent interactions that non-covalently disrupted the cellulose hydrogen-bonding network and understand how such solvents are able to rapidly and fully dissolve pre-activated cellulose III. Importantly, the regenerated amorphous cellulose recovered after pretreatment was shown to require nearly ∼50-fold lesser cellulolytic enzyme usage compared to native crystalline cellulose I allomorph for achieving near-complete hydrolytic conversion into soluble sugars. Lastly, we provide proof-of-concept results to further showcase how such ammonia-salt solvents can pretreat and fractionate lignocellulosic biomass like corn stover under ambient processing conditions, while selectively co-extracting ∼80–85% of total lignin, to produce a highly digestible polysaccharide-enriched feedstock for biorefinery applications. Unlike conventional ammonia-based pretreatment processes (e.g., Ammonia Fiber Expansion or Extractive Ammonia pretreatments), the proposed ammonia-salt process can operate at near-ambient conditions to greatly reduce the pressure/temperature severity necessary for conducting effective ammonia-based pretreatments on lignocellulose.

As a material, cellulose/paper has attracted significant attention for its fibrous and bendable properties. Paper is a renewable resource with the most common forms coming from trees. This brief article describes efforts to create electronics "on" and "in" paper. Examples of electronics on paper include touch sensors and cold plasma-based sanitizers. The skin-like touch sensors use capacitance and patterned resistive networks for passive, scalable sensing with a reduced number of interconnects. When touched or wetted with water, the interdigitated electrodes in the resistive networks detect significant changes in electrical impedance. The plasma generators with layered and patterned sheets of paper use a simple and flexible format for dielectric barrier discharge to create atmospheric plasma without an applied vacuum. Examples of electronics in paper include sheets with tunable electrical conductivity and piezoresistive force sensors, along with functionalized paper-based electrodes capable of detecting small proteins and clinically relevant biomarkers. These papertronic devices have the potential to supply multi-functionality to new forms of smart bandages, skin-like sensing, food packaging, and robotic sensing and actuation.

Lignocellulosic materials are plant-derived feedstocks, such as crop residues (e.g., corn stover, rice straw, and sugar cane bagasse) and purpose-grown energy crops (e.g., miscanthus, and switchgrass) that are available in large quantities to produce biofuels, biochemicals, and animal feed. Plant polysaccharides (i.e., cellulose, hemicellulose, and pectin) embedded within cell walls are highly recalcitrant towards conversion into useful products. Ammonia fiber expansion (AFEX) is a thermochemical pretreatment that increases accessibility of polysaccharides to enzymes for hydrolysis into fermentable sugars. These released sugars can be converted into fuels and chemicals in a biorefinery. Here, we describe a laboratory-scale batch AFEX process to produce pretreated biomass on the gram-scale without any ammonia recycling. The laboratory-scale process can be used to identify optimal pretreatment conditions (e.g., ammonia loading, water loading, biomass loading, temperature, pressure, residence time, etc.) and generates sufficient quantities of pretreated samples for detailed physicochemical characterization and enzymatic/microbial analysis. The yield of fermentable sugars from enzymatic hydrolysis of corn stover pretreated using the laboratory-scale AFEX process is comparable to pilot-scale AFEX process under similar pretreatment conditions. This paper is intended to provide a detailed standard operating procedure for the safe and consistent operation of laboratory-scale reactors for performing AFEX pretreatment of lignocellulosic biomass.

Flexible devices are particularly important for applications in the bioelectronics arena as materials interface with soft and mechanically compliant surfaces. Polydimethylsiloxane (PDMS) is an elastomer that can form a versatile, inexpensive substrate for electronic components while conferring flexibility, oxygen permeability, and biocompatibility. However, the ability to form microcircuits while maintaining integration of these components to the surfaces without delamination continues to be challenging. Here, we present the development of a benchtop, scalable photolithographic technique that can pattern the conducting polymer PEDOT:PSS on thin photocurable PDMS membranes via a conducting composite ink composed of the polymer and a biofriendly silk protein carrier. The fully aqueous process can result in high resolution microelectrodes that can function as biosensors utilizing both non-specific and specific sensing modalities via entrapped biorecognition molecules. The biosensors display excellent direct detection of dopamine and ascorbic acid with high sensitivity. Also, enzyme loaded sensors can detect glucose in a highly sensitive manner over physiologically relevant glucose concentration range. Owing to the covalent linkage between the ink and the photo-PDMS, the electrodes do no delaminate or lose function under mechanical flexure. The work demonstrates the potential for realization of flexible devices using photoreactive PDMS such as biosensors or electronic skin.

Over the last two decades, silk fibroin has been exploited as a versatile optical material in biological applications due to a combination of unique properties. Recently, protocols have been developed to produce a silk fibroin negative tone resist that is UV crosslinkable, thereby allowing micro and nanoscale patterning of the protein using traditional photolithographic tools. The same protocol has been applied to the silk protein sericin to develop a sericin resist. Despite the immense potential of these biomaterials to develop micro optical patterns on silicon and glass surfaces, as well as self-standing components, their refractive indexes are not well characterized. In this work, optimizing a method to obtain extremely smooth, thin films, the refractive index (RI) of fibroin and sericin proteins and resists were characterized using ellipsometry. The parameters of the Sellmeier and Cauchy dispersion laws have been determined to obtain the RI over a large wavelength range. A complete morphological study of the films has been conducted. In addition, the effect of solvent on the optical properties of silk fibroin and sericin thin films are reported, with differences in values explained by examining the change in the protein secondary structure.

Electrically conductive hydrogels (ECH) which are composites of hydrogels and conducting polymers, exhibit a powerful combination of biocompatibility and conductivity. They combine the high hydration and soft mechanical nature of hydrogel networks, with the electrochemical functionality of conducting components allowing precise control of properties. Interest in these materials has increased recently for applications in tissue engineering, biosensing, and flexible and implantable bioelectronics. Here, we demonstrate a dispersion of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) in a photocurable poly(ethylene glycol)-diacrylate (PEG-DA) matrix to form functional hydrogels via a facile, fully aqueous, photopolymerization process. We report on effect of various compositions of the conducting polymer, tuning of mechanical and electrochemical properties, and the ability to micropattern the composite using photolithography. The electrical properties of the ECH are characterized by cyclic voltammetry, four-point probe, and conductive atomic force microscopy to reveal the competitive properties of the composite, with minimal leaching and stability over time. We further show how minute amounts of graphene dopant can be used to engineer mechanical and electrochemical properties. Overall, the graphene-hydrogel-conducting polymer composite structure enables optimization of various properties by synergistically integrating the electrochemical and mechanical properties of graphene and the PEDOT:PSS, with the biocompatibility and micropatterning of the soft hydrogel matrix.

Improving the performance of electrochemical sensors based on indium tin oxide (ITO) can be achievedvia intrinsically conducting polymers such as poly (3, 4 ethylenedioxythiophene): polystyrene sulfonate(PEDOT:PSS). However micropatterning of PEDOT:PSS to form microelectrodes on such substrates hasbeen challenging. Here we demonstrate a technique for the precise micropatterning of a conductive ink onITO using photolithography to realize a covalently-attached ion-transport matrix for stable biosensing.This micropatterning is accomplished using an all water-based and ambient temperature processing.We present electrochemical characterization of the material composite via electrochemical impedancespectroscopy, cyclic voltammetry and differential pulse voltammetry. A sensitive sensor is fabricated forthe neurotransmitter dopamine, with a linear range from 1 to 50 M. The sensor signal is very stableunder cyclic increase and decrease in the concentration of dopamine. This sensing can be achieved evenin the presence of ascorbic acid at 1000 times higher concentration than dopamine. Further, enzymes canbe immobilized in the conductive matrix to form highly selective sensors. Such robust micropatterningstrategies can greatly expand the use of conducting polymer substrates in biosensing applications., info:eu-repo/semantics/publishedVersion

Non-spherical particles of different shapes have unique properties potentially beneficial in self-assembly, biosensing, therapeutic delivery and optical applications. Forming particles with precisely controlled physical and chemical characteristics, particularly using bioinspired or bio-derived materials can open up applications inaccessible to synthetic polymers. Here, a high throughput fabrication process of different shapes of protein-based particles at high resolution using photolithography is demonstrated. In contrast to synthetic polymers, the particles shown herein are comprised of the two silk proteins – fibroin and sericin. The demonstrated technique of silk protein lithography allows fabrication of monodisperse biopolymer particles with precise geometries ranging from a few to hundreds of microns. Large numbers of particles of controllable aspect ratios can be easily formed, collected and mixed. The particles themselves are mechanically robust and biocompatible, but can be proteolytically degraded over a period of weeks. Owing to the facile fabrication technique that uses benign solvents, bioactive molecules can be encapsulated within these protein matrices. By control of shape, size, thickness and surface properties, particles that may be harvested for optics, delivery or presentation of biologically functional agents, among other applications.

UNLABELLED High-resolution micropatterning of a PEDOT PSS conducting-polymer-silksericin composite is presented using a water-based, benchtop photolithographic process. Conducting microstructures formed on a flexible silk fibroin sheet allow a fully organic, flexible bioelectronic device. Large-area microfabricated devices such as biosensors that are biocompatible and degradable over a controlled period of time can be formed.

Precise spatial patterns and micro and nanostructures of peptides and proteins have widespread applications in tissue engineering, bioelectronics, photonics, and therapeutics. Optical lithography using proteins provides a route to directly fabricate intricate, bio-friendly architectures rapidly and across a range of length scales. The unique mechanical strength, optical properties, biocompatibility and controllable degradation of biomaterials from silkworms offer several advantages in this paradigm. Here, we present the biochemical synthesis and applications of a “protein photoresist” synthesized from the silk proteins, fibroin and sericin. Using light-activated direct-write processes such as photolithography, we show how silk proteins can form high resolution, high fidelity structures in two and three dimensions. Protein features can be precisely patterned at sub-microscale resolution (µm) at the bench-top over macroscale areas (cm), easily and repeatedly with high-throughput. For instance, periodic, microstructured arrays can be patterned over large areas to form structurally induced iridescent patterns and functional opto-electronic structures. We further demonstrate how photocrosslinked protein micro-architectures can function for the spatial guidance of cells without use of cell-adhesive ligands as biocompatible and biodegradable scaffolds. The ease of biochemical functionalization, biocompatibility, as well as favorable mechanical properties and biodegradation of this silk biomaterial provide opportunities for otherwise inaccessible applications as sustainable, bioresorbable protein microdevices.

This work explores the effects of mixing on enzymatic hydrolysis of cellulose to innovate a novel mixing strategy that maximizes glucose and reducing sugar yields for production of cellulosic ethanol while reducing the power required for reactor mixing. Batch experiments of cellulose hydrolysis are performed under aseptic conditions for 72 h at various substrate loading (2–6% wt./vol.), where the reactor mixing is terminated after different intervals of time ranging from 0 to 72 h. We find that initial mixing for a certain ‘optimal mixing time’ followed by no mixing for the rest of the reaction time maximizes glucose and reducing sugar yields. We report a maximum of 26% and 31% increase in glucose and reducing yields, respectively, in case of optimal mixing over continuous mixing for 2% substrate loading. We obtain an algebraic expression that predicts that the optimal mixing time increases exponentially with substrate loading.

Nanofabrication approaches to pattern proteins at the nanoscale are useful in applications ranging from organic bioelectronics to cellular engineering. Specifically, functional materials based on natural polymers offer sustainable and environment-friendly substitutes to synthetic polymers. Silk proteins (fibroin and sericin) have emerged as an important class of biomaterials for next generation applications owing to excellent optical and mechanical properties, inherent biocompatibility, and biodegradability. However, the ability to precisely control their spatial positioning at the nanoscale via high throughput tools continues to remain a challenge. In this study electron beam lithography (EBL) is used to provide nanoscale patterning using methacrylate conjugated silk proteins that are photoreactive 'photoresists' materials. Very low energy electron beam radiation can be used to pattern silk proteins at the nanoscale and over large areas, whereby such nanostructure fabrication can be performed without specialized EBL tools. Significantly, using conducting polymers in conjunction with these silk proteins, the formation of protein nanowires down to 100 nm is shown. These wires can be easily degraded using enzymatic degradation. Thus, proteins can be precisely and scalably patterned and doped with conducting polymers and enzymes to form degradable, organic bioelectronic devices.

Approaches to form flexible biosensors require strategies to tune materials for various biomedical applications. We report a facile approach using photolithography to fabricate poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) sensors on a fully biodegradable and flexible silk protein fibroin support. A benchtop photolithographic setup is used to fabricate high fidelity and high resolution PEDOT:PSS microstructures over a large (cm) area using only water as the solvent. Using the conductive micropatterns as working electrodes, we demonstrate biosensors with excellent electrochemical activity and stability over a number of days. The fabricated biosensors display excellent nonspecific detection of dopamine and ascorbic acid with high sensitivity. These devices are mechanically flexible, optically transparent, electroactive, cytocompatible and biodegradable. The benign fabrication protocol allows the conducting ink to function as a matrix for enzymes as shown by a highly sensitive detection of glucose. These sensors can retain their properties under repeated mechanical deformations, but are completely degradable under enzymatic action. The reported technique is scalable and can be used to develop sensitive, robust, and inexpensive biosensors with controllable biodegradability, leading to applications in transient or implantable bioelectronics and optoelectronics.

The silk protein fibroin is a wondrous biopolymer widely used to form structures that interface with biological entities. In addition to tissue scaffolds, sponges, and films, biochemically modified fibroins can be used in conjunction with techniques such as photolithography and soft lithography to expand their repertoire for micro- and nanofabricated systems. To date, the use of hexafluoro-2-isopropanol (HFIP) has been prevalent as a solvent for fibroin and fibroin “resists.” However, high volatility, toxicity, cost, and need for specialized disposal render the necessity for alternative solvents. Additionally, for applications such as in optics and bioelectronics, smooth, thin (≈100 nm and below) fibroin films are a prerequisite, which are not easily achieved using HFIP. Here, the use of formic acid (FA) as a sustainable solvent is presented for silk fibroin and fibroin “resist” materials, specifically for micro- and nanoscale applications. The reproducible formation and characterization of stable thin films of high homogeneity, smoothness, and optical transparency are demonstrated. Critically, these films can be used for high-resolution photopatterning of proteins using benchtop lithographic techniques. The study indicates that FA is a relatively benign and optimal solvent for forming smooth, thin films, and microscale architectures for the fabrication of next generation silk-based optical devices.

Flexible and thin-film devices are of great interest in epidermal and implantable bioelectronics. The integration of energy storage and delivery devices such as supercapacitors (SCs) with properties such as flexibility, miniaturization, biocompatibility, and degradability are sought for such systems. Reducing e-waste and using sustainable materials and processes are additional desirable qualities. Herein, a silk protein-based biocompatible and degradable thin-film microSC (μSC) is reported. A protein carrier with the conducting polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate and reduced graphene oxide dopant is used as a photopatternable biocomposite ink. Active electrodes are fabricated using photolithography under benign conditions, using only water as the solvent. These electrodes are printed on flexible protein sheets to form degradable, organic devices with a benign agarose–NaCl gel electrolyte. High capacitance, power density, cycling stability over 500 cycles, and the ability to power a light-emitting diode are shown. The device is flexible, can sustain cyclic mechanical stresses over 450 cycles, and retain capacitive properties over several days in liquid. Significantly, the μSCs are cytocompatible and completely degraded over the period of ∼1 month. By precise control of the device configuration, these silk protein-based, all-polymer organic devices can be designed to be tunably transient and provide viable alternatives for powering flexible and implantable bioelectronics., SEM images were obtained in the Nanomaterials Characterization Center at VCU. The assistance of Dr. Ning Zhang and Chenyang Jiang of the VCU Biomedical Engineering Department in cell culture experiments is gratefully acknowledged. SC Kundu presently holds an ERA Chair Full Professor position at the 3B’s Research Group, University of Minho, Portugal supported by the European Union Framework Programme for Research and Innovation Horizon 2020 under grant agreement no 668983 - FoReCaST., info:eu-repo/semantics/publishedVersion