@article{schroeder_aizenberg_2022, title={Patterned crystal growth and heat wave generation in hydrogels}, url={https://doi.org/10.1038/s41467-021-27505-z}, DOI={10.1038/s41467-021-27505-z}, abstractNote={Abstract The crystallization of metastable liquid phase change materials releases stored energy as latent heat upon nucleation and may therefore provide a triggerable means of activating downstream processes that respond to changes in temperature. In this work, we describe a strategy for controlling the fast, exothermic crystallization of sodium acetate from a metastable aqueous solution into trihydrate crystals within a polyacrylamide hydrogel whose polymerization state has been patterned using photomasks. A comprehensive experimental study of crystal shapes, crystal growth front velocities and evolving thermal profiles showed that rapid growth of long needle-like crystals through unpolymerized solutions produced peak temperatures of up to 45˚C, while slower-crystallizing polymerized solutions produced polycrystalline composites and peaked at 30˚C due to lower rates of heat release relative to dissipation in these regions. This temperature difference in the propagating heat waves, which we describe using a proposed analytical model, enables the use of this strategy to selectively activate thermoresponsive processes in predefined areas.}, journal={Nature Communications}, author={Schroeder, Thomas B. H. and Aizenberg, Joanna}, year={2022}, month={Jan} }
 @article{guha_kalkus_schroeder_willis_rader_ianiro_mayer_2021, title={Powering Electronic Devices from Salt Gradients in AA‐Battery‐Sized Stacks of Hydrogel‐Infused Paper}, volume={6}, url={http://dx.doi.org/10.1002/adma.202101757}, DOI={10.1002/adma.202101757}, abstractNote={Strongly electric fish use gradients of ions within their bodies to generate stunning external electrical discharges; the most powerful of these organisms, the Atlantic torpedo ray, can produce pulses of over 1 kW from its electric organs. Despite extensive study of this phenomenon in nature, the development of artificial power generation schemes based on ion gradients for portable, wearable, or implantable human use has remained out of reach. Previously, an artificial electric organ inspired by the electric eel demonstrated that electricity generated from ion gradients within stacked hydrogels can exceed 100 V. The current of this power source, however, was too low to power standard electronics. Here, an artificial electric organ inspired by the unique morphologies of torpedo rays for maximal current output is introduced. This power source uses a hybrid material of hydrogel‐infused paper to create, organize, and reconfigure stacks of thin, arbitrarily large gel films in series and in parallel. The resulting increase in electrical power by almost two orders of magnitude compared to the original eel‐inspired design makes it possible to power electronic devices and establishes that biology's mechanism of generating significant electrical power can now be realized from benign and soft materials in a portable size.}, journal={Advanced Materials}, publisher={Wiley}, author={Guha, Anirvan and Kalkus, Trevor J. and Schroeder, Thomas B. H. and Willis, Oliver G. and Rader, Chris and Ianiro, Alessandro and Mayer, Michael}, year={2021}, month={Jun}, pages={2101757} }
 @article{meeks_lerch_schroeder_shastri_aizenberg_2021, title={Spiropyran Photoisomerization Dynamics in Multiresponsive Hydrogels}, volume={12}, url={http://dx.doi.org/10.1021/jacs.1c08778}, DOI={10.1021/jacs.1c08778}, abstractNote={Light-responsive, spiropyran-functionalized hydrogels have been used to create reversibly photoactuated structures for applications ranging from microfluidics to nonlinear optics. Tailoring a spiropyran-functionalized hydrogel system for a particular application requires an understanding of how co-monomer composition affects the switching dynamics of the spiropyran chromophore. Such gels are frequently designed to be responsive to different stimuli such as light, temperature, and pH. The coupling of these influences can significantly alter spiropyran behavior in ways not currently well understood. To better understand the influence of responsive co-monomers on the spiropyran isomerization dynamics, we use UV-vis spectroscopy and time-dependent fluorescence intensity measurements to study spiropyran-modified hydrogels polymerized from four common hydrogel precursors of different pH and temperature responsivity: acrylamide, acrylic acid, N-isopropylacrylamide, and 2-(dimethylamino)ethyl methacrylate. In acidic and neutral gels, we observe unusual nonmonotonic, triexponential fluorescence dynamics under 405 nm irradiation that cannot be explicated by either the established spiropyran-merocyanine interconversion model or hydrolysis. To explain these results, we introduce an analytical model of spiropyran interconversions that includes H-aggregated merocyanine and its light-triggered disaggregation under 405 nm irradiation. This model provides an excellent fit to the observed fluorescence dynamics and elucidates exactly how creating an acidic internal gel environment promotes the fast and complete conversion of the hydrophilic merocyanine speciesto the hydrophobic spiropyran form, which is desired in most light-sensitive hydrogel actuators. This can be achieved by incorporating acrylic acid monomers and by minimizing the aggregate concentration. Beyond spiropyran-functionalized gel actuators, these conclusions are particularly critical for nonlinear optical computing applications.}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Meeks, Amos and Lerch, Michael M. and Schroeder, Thomas B. H. and Shastri, Ankita and Aizenberg, Joanna}, year={2021}, month={Dec} }
 @article{fluid surface coatings for solid-state nanopores: comparison of phospholipid bilayers and archaea-inspired lipid monolayers_2019, url={http://dx.doi.org/10.1088/1361-6528/ab19e6}, DOI={10.1088/1361-6528/ab19e6}, abstractNote={In the context of sensing and characterizing single proteins with synthetic nanopores, lipid bilayer coatings provide at least four benefits: first, they minimize unwanted protein adhesion to the pore walls by exposing a zwitterionic, fluid surface. Second, they can slow down protein translocation and rotation by the opportunity to tether proteins with a lipid anchor to the fluid bilayer coating. Third, they provide the possibility to impart analyte specificity by including lipid anchors with a specific receptor or ligand in the coating. Fourth, they offer a method for tuning nanopore diameters by choice of the length of the lipid’s acyl chains. The work presented here compares four properties of various lipid compositions with regard to their suitability as nanopore coatings for protein sensing experiments: (1) electrical noise during current recordings through solid-state nanopores before and after lipid coating, (2) long-term stability of the recorded current baseline and, by inference, of the coating, (3) viscosity of the coating as quantified by the lateral diffusion coefficient of lipids in the coating, and (4) the success rate of generating a suitable coating for quantitative nanopore-based resistive pulse recordings. We surveyed lipid coatings prepared from bolaamphiphilic, monolayer-forming lipids inspired by extremophile archaea and compared them to typical bilayer-forming phosphatidylcholine lipids containing various fractions of curvature-inducing lipids or cholesterol. We found that coatings from archaea-inspired lipids provide several advantages compared to conventional phospholipids; the stable, low noise baseline qualities and high viscosity make these membranes especially suitable for analysis that estimates physical protein parameters such as the net charge of proteins as they enable translocation events with sufficiently long duration to time-resolve dwell time distributions completely. The work presented here reveals that the ease or difficulty of coating a nanopore with lipid membranes did not depend significantly on the composition of the lipid mixture, but rather on the geometry and surface chemistry of the nanopore in the solid state substrate. In particular, annealing substrates containing the nanopore increased the success rate of generating stable lipid coatings.}, journal={Nanotechnology}, year={2019}, month={Apr} }
 @article{schroeder_houghtaling_wilts_mayer_2018, title={It's Not a Bug, It's a Feature: Functional Materials in Insects}, url={https://doi.org/10.1002/adma.201705322}, DOI={10.1002/adma.201705322}, abstractNote={Over the course of their wildly successful proliferation across the earth, the insects as a taxon have evolved enviable adaptations to their diverse habitats, which include adhesives, locomotor systems, hydrophobic surfaces, and sensors and actuators that transduce mechanical, acoustic, optical, thermal, and chemical signals. Insect‐inspired designs currently appear in a range of contexts, including antireflective coatings, optical displays, and computing algorithms. However, as over one million distinct and highly specialized species of insects have colonized nearly all habitable regions on the planet, they still provide a largely untapped pool of unique problem‐solving strategies. With the intent of providing materials scientists and engineers with a muse for the next generation of bioinspired materials, here, a selection of some of the most spectacular adaptations that insects have evolved is assembled and organized by function. The insects presented display dazzling optical properties as a result of natural photonic crystals, precise hierarchical patterns that span length scales from nanometers to millimeters, and formidable defense mechanisms that deploy an arsenal of chemical weaponry. Successful mimicry of these adaptations may facilitate technological solutions to as wide a range of problems as they solve in the insects that originated them.}, journal={Advanced Materials}, author={Schroeder, Thomas B. H. and Houghtaling, Jared and Wilts, Bodo D. and Mayer, Michael}, year={2018}, month={May} }
 @article{an electric-eel-inspired soft power source from stacked hydrogels_2017, url={https://www.nature.com/articles/nature24670}, DOI={10.1038/nature24670}, abstractNote={Progress towards the integration of technology into living organisms requires electrical power sources that are biocompatible, mechanically flexible, and able to harness the chemical energy available inside biological systems. Conventional batteries were not designed with these criteria in mind. The electric organ of the knifefish Electrophorus electricus (commonly known as the electric eel) is, however, an example of an electrical power source that operates within biological constraints while featuring power characteristics that include peak potential differences of 600 volts and currents of 1 ampere. Here we introduce an electric-eel-inspired power concept that uses gradients of ions between miniature polyacrylamide hydrogel compartments bounded by a repeating sequence of cation- and anion-selective hydrogel membranes. The system uses a scalable stacking or folding geometry that generates 110 volts at open circuit or 27 milliwatts per square metre per gel cell upon simultaneous, self-registered mechanical contact activation of thousands of gel compartments in series while circumventing power dissipation before contact. Unlike typical batteries, these systems are soft, flexible, transparent, and potentially biocompatible. These characteristics suggest that artificial electric organs could be used to power next-generation implant materials such as pacemakers, implantable sensors, or prosthetic devices in hybrids of living and non-living systems.}, journal={Nature}, year={2017}, month={Dec} }
 @article{fennouri_mayer_schroeder_mayer_2017, title={Single channel planar lipid bilayer recordings of the melittin variant MelP5}, DOI={10.1016/j.bbamem.2017.07.005}, abstractNote={MelP5 is a 26 amino acid peptide derived from melittin, the main active constituent of bee venom, with five amino acid replacements. The pore-forming activity of MelP5 in lipid membranes is attracting attention because MelP5 forms larger pores and induces dye leakage through liposome membranes at a lower concentration than melittin. Studies of MelP5 have so far focused on ensemble measurements of membrane leakage and impedance; here we extend this characterization with an electrophysiological comparison between MelP5 and melittin using planar lipid bilayer recordings. These experiments reveal that MelP5 pores in lipid membranes composed of 3:1 phosphatidylcholine:cholesterol consist of an average of 10 to 12 monomers compared to an average of 3 to 9 monomers for melittin. Both peptides form transient pores with dynamically varying conductance values similar to previous findings for melittin, but MelP5 occasionally also forms stable, well-defined pores with single channel conductance values that vary greatly and range from 50 to 3000pS in an electrolyte solution containing 100mM KCl.}, journal={Biochimica et Biophysica Acta (BBA)-Biomembranes}, publisher={Elsevier}, author={Fennouri, Aziz and Mayer, Simon Finn and Schroeder, Thomas BH and Mayer, Michael}, year={2017} }
 @article{schroeder_leriche_koyanagi_johnson_haengel_eggenberger_wang_kim_diraviyam_sept_et al._2016, title={Effects of Lipid Tethering in Extremophile-Inspired Membranes on H+/OH- Flux at Room Temperature}, volume={110}, DOI={10.1016/j.bpj.2016.04.044}, abstractNote={This work explores the proton/hydroxide permeability (PH+/OH-) of membranes that were made of synthetic extremophile-inspired phospholipids with systematically varied structural elements. A fluorescence-based permeability assay was optimized to determine the effects on the PH+/OH- through liposome membranes with variations in the following lipid attributes: transmembrane tethering, tether length, and the presence of isoprenoid methyl groups on one or both lipid tails. All permeability assays were performed in the presence of a low concentration of valinomycin (10 nM) to prevent buildup of a membrane potential without artificially increasing the measured PH+/OH-. Surprisingly, the presence of a transmembrane tether did not impact PH+/OH- at room temperature. Among tethered lipid monolayers, PH+/OH- increased with increasing tether length if the number of carbons in the untethered acyl tail was constant. Untethered lipids with two isoprenoid methyl tails led to lower PH+/OH- values than lipids with only one or no isoprenoid tails. Molecular dynamics simulations revealed a strong positive correlation between the probability of observing water molecules in the hydrophobic core of these lipid membranes and their proton permeability. We propose that water penetration as revealed by molecular dynamics may provide a general strategy for predicting proton permeability through various lipid membranes without the need for experimentation.}, number={11}, journal={Biophysical journal}, publisher={Cell Press}, author={Schroeder, Thomas BH and Leriche, Geoffray and Koyanagi, Takaoki and Johnson, Mitchell A and Haengel, Kathryn N and Eggenberger, Olivia M and Wang, Claire L and Kim, Young Hun and Diraviyam, Karthik and Sept, David and et al.}, year={2016}, pages={2430–2440} }
 @article{bruhn_schroeder_li_billeh_wang_mayer_2014, title={Osmosis-based pressure generation: dynamics and application}, volume={9}, DOI={10.1371/journal.pone.0091350}, abstractNote={This paper describes osmotically-driven pressure generation in a membrane-bound compartment while taking into account volume expansion, solute dilution, surface area to volume ratio, membrane hydraulic permeability, and changes in osmotic gradient, bulk modulus, and degree of membrane fouling. The emphasis lies on the dynamics of pressure generation; these dynamics have not previously been described in detail. Experimental results are compared to and supported by numerical simulations, which we make accessible as an open source tool. This approach reveals unintuitive results about the quantitative dependence of the speed of pressure generation on the relevant and interdependent parameters that will be encountered in most osmotically-driven pressure generators. For instance, restricting the volume expansion of a compartment allows it to generate its first 5 kPa of pressure seven times faster than without a restraint. In addition, this dynamics study shows that plants are near-ideal osmotic pressure generators, as they are composed of many small compartments with large surface area to volume ratios and strong cell wall reinforcements. Finally, we demonstrate two applications of an osmosis-based pressure generator: actuation of a soft robot and continuous volume delivery over long periods of time. Both applications do not need an external power source but rather take advantage of the energy released upon watering the pressure generators.}, number={3}, journal={PloS one}, publisher={Public Library of Science}, author={Bruhn, Brandon R and Schroeder, Thomas BH and Li, Suyi and Billeh, Yazan N and Wang, KW and Mayer, Michael}, year={2014}, pages={e91350} }
 @article{dugal-tessier_o’bryan_schroeder_cohen_scheidt_2012, title={An N-Heterocyclic Carbene/Lewis Acid Strategy for the Stereoselective Synthesis of Spirooxindole Lactones}, volume={51}, DOI={10.1002/anie.201201643}, abstractNote={A cooperative catalysis approach for the enantioselective formal [3+2] addition of α,β-unsaturated aldehydes to isatins has been developed. Homoenolate annulations of β-aryl enals catalyzed by an N-heterocyclic carbene (NHC) require the addition of lithium chloride for high levels of enantioselectivity. This NHC-catalyzed annulation has been used for the total synthesis of maremycin B.}, number={20}, journal={Angewandte Chemie International Edition}, publisher={Wiley Online Library}, author={Dugal-Tessier, Julien and O’Bryan, Elizabeth A and Schroeder, Thomas BH and Cohen, Daniel T and Scheidt, Karl A}, year={2012}, pages={4963–4967} }