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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.

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.

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.