Showing papers by "George M. Whitesides published in 2018"
21 Mar 2018
TL;DR: A soft, elastomeric valve that contains a bistable membrane, which acts as a mechanical “switch” to control air flow, enables a gripper to grasp a ball autonomously and autonomous earthworm-like locomotion using an air source of constant pressure.
Abstract: Almost all pneumatic and hydraulic actuators useful for mesoscale functions rely on hard valves for control. This article describes a soft, elastomeric valve that contains a bistable membrane, which acts as a mechanical “switch” to control air flow. A structural instability—often called “snap-through”—enables rapid transition between two stable states of the membrane. The snap-upward pressure, Δ P 1 (kilopascals), of the membrane differs from the snap-downward pressure, Δ P 2 (kilopascals). The values Δ P 1 and Δ P 2 can be designed by changing the geometry and the material of the membrane. The valve does not require power to remain in either “open” or “closed” states (although switching does require energy), can be designed to be bistable, and can remain in either state without further applied pressure. When integrated in a feedback pneumatic circuit, the valve functions as a pneumatic oscillator (between the pressures Δ P 1 and Δ P 2 ), generating periodic motion using air from a single source of constant pressure. The valve, as a component of pneumatic circuits, enables (i) a gripper to grasp a ball autonomously and (ii) autonomous earthworm-like locomotion using an air source of constant pressure. These valves are fabricated using straightforward molding and offer a way of integrating simple control and logic functions directly into soft actuators and robots.
297 citations
TL;DR: The UWED is simple, small in size, assembled from inexpensive components, and completely wireless, it offers new opportunities for the development of affordable diagnostics, sensors, and wearable devices.
Abstract: This paper describes the design and characterization of an open-source “universal wireless electrochemical detector” (UWED). This detector interfaces with a smartphone (or a tablet) using “Bluetooth Low Energy” protocol; the smartphone provides (i) a user interface for receiving the experimental parameters from the user and visualizing the result in real time, and (ii) a proxy for storing, processing, and transmitting the data and experimental protocols. This approach simplifies the design, and decreases both the size and the cost of the hardware; it also makes the UWED adaptable to different types of analyses by simple modification of the software. The UWED can perform the most common electroanalytical techniques of potentiometry, chronoamperometry, cyclic voltammetry, and square wave voltammetry, with results closely comparable to benchtop commercial potentiostats. Although the operating ranges of electrical current and voltage of the UWED (±1.5 V, ±180 μA) are more limited than most benchtop commercial...
238 citations
TL;DR: This review summarizes known sources of H/ S compensation (real and perceived) and lays out a conceptual framework for understanding and dissecting-and, perhaps, avoiding or exploiting-this phenomenon in biophysical systems.
Abstract: Biomolecular recognition can be stubborn; changes in the structures of associating molecules, or the environments in which they associate, often yield compensating changes in enthalpies and entropies of binding and no net change in affinities. This phenomenon-termed enthalpy/entropy (H/S) compensation-hinders efforts in biomolecular design, and its incidence-often a surprise to experimentalists-makes interactions between biomolecules difficult to predict. Although characterizing H/S compensation requires experimental care, it is unquestionably a real phenomenon that has, from an engineering perspective, useful physical origins. Studying H/S compensation can help illuminate the still-murky roles of water and dynamics in biomolecular recognition and self-assembly. This review summarizes known sources of H/ S compensation (real and perceived) and lays out a conceptual framework for understanding and dissecting-and, perhaps, avoiding or exploiting-this phenomenon in biophysical systems.
111 citations
TL;DR: 3D microfluidic paper-based analytical device that can be used to conduct an enzyme-linked immunosorbent assay (ELISA) has the technical characteristics to be employed as a pre-screening tool, when combined with other data such as patient history and clinical signs.
106 citations
TL;DR: A scaffold from variants of poly(glycolic) acid which were braided and coated with an elastomer of poly (glycolide-co-caprolactone) and crosslinked was developed, shown to be highly resorbable following implantation in a porcine femoral artery and biocompatible in an ovine model.
Abstract: Metallic stents have been widely used in coronary angioplasty. Here, the authors develop a resorbable self-expanding stent from polymeric elastomers with high mechanical strength for coronary applications.
96 citations
TL;DR: A new principle for designing soft or 'semisoft' pneumatic actuators: SLiT (for SLit-in-Tube) actuators, which allows sequential actuation by controlling the applied pressure.
Abstract: This article describes a new principle for designing soft or 'semisoft' pneumatic actuators: SLiT (for SLit-in-Tube) actuators. Inflating an elastomeric balloon, when enclosed by an external shell (a material with higher Young's modulus) containing slits of different directions and lengths, produces a variety of motions, including bending, twisting, contraction, and elongation. The requisite pressure for actuation depends on the length of the slits, and this dependence allows sequential actuation by controlling the applied pressure. Different actuators can also be controlled using external "sliders" that act as reprogrammable "on-off" switches. A pneumatic arm and a walker constructed from SLiT actuators demonstrate their ease of fabrication and the range of motions they can achieve.
65 citations
TL;DR: A new method for electrochemical detection of specific sequences of DNA present in trace amounts in serum or blood by combining recombinase polymerase amplification (RPA) with an electroactive mediator enables accurate detection of DNA in the field using a low-cost, portable electrochemical analyzer.
61 citations
TL;DR: In this paper, thread-based ion-selective sensors for point-of-use (POI) measurements of ions were developed using a surfactant-free conductive ink (made of carbon black).
Abstract: Potentiometric sensing of ions with ion-selective electrodes (ISEs) is a powerful technique for selective and sensitive measurement of ions in complex matrices. The application of ISEs is generally limited to laboratory settings, because most commercially available ISEs and reference electrodes are large, delicate, and expensive, and are not suitable for point-of-use or point-of-care measurements. This work utilizes cotton thread as a substrate for fabrication of robust and miniaturized ISEs that are suitable for point-of-care or point-of-use applications. Thread-based ISEs selective for Cl-, K+, Na+, and Ca2+ were developed. The cation-selective ISEs were fabricated by coating the thread with a surfactant-free conductive ink (made of carbon black) and then coating the tip of the conductive thread with the ion-selective membrane. The Cl- ISE was fabricated by coating the thread with an Ag/AgCl ink. These sensors exhibited slopes (of electrical potential vs. log concentration of target ion), close to the theoretically-expected values, over four orders of magnitude in concentrations of ions. Because thread is mechanically strong, the thread-based electrodes can be used in multiple-use applications as well as single-use applications. Multiple thread-based sensors can be easily bundled together to fabricate a customized sensor for multiplexed ion-sensing. These electrodes require volumes of sample as low as 200 μL. The application of thread-based ISEs is demonstrated in the analysis of ions in soil, food, and dietary supplements (Cl- in soil/water slurry, K+ and Na+ in coconut water, and Ca2+ in a calcium supplement), and in detection of physiological electrolytes (K+ and Na+ in blood serum and urine, with sufficient accuracy for clinical diagnostics).
60 citations
TL;DR: The compact design, portability, affordability, and simplicity in use of the "axial MagLev" device will broaden the uses of magnetic methods in analyzing, separating, and manipulating different types of samples in areas such as materials sciences, chemistry, and biochemistry.
Abstract: This work describes the development of magnetic levitation (MagLev) using ring magnets and a configuration (which we call “axial MagLev”) to remove the physical barriers to physical sampling in the magnetic field present in “standard MagLev” and to simplify the procedures used to carry out density-based analyses, separations, and manipulations. The optimized, linear magnetic field generated between the two ring magnets (coaxially aligned and like-poles facing) enables the levitation of diamagnetic (and weakly paramagnetic, e.g., aluminum) materials in a paramagnetic suspending medium and makes density measurements more straightforward. This “axial” configuration enables (i) simple procedures to add samples and paramagnetic medium from an open end and to retrieve samples while levitating in the magnetic field (e.g., a subpopulation of a cluster of small particles); (ii) simple accesses and the abilities to view the samples 360° around the sample container and from the top and bottom; and (iii) convenient d...
54 citations
TL;DR: This system is prototypical of autocatalytic reactions where the formation of a product, which acts as a ligand for a catalytic metal ion, enhances the production and activity of the catalyst.
Abstract: This work describes the autocatalytic copper-catalyzed azide–alkyne cycloaddition (CuAAC) reaction between tripropargylamine and 2-azidoethanol in the presence of Cu(II) salts. The product of this reaction, tris-(hydroxyethyltriazolylmethyl)amine (N(C3N3)3), accelerates the cycloaddition reaction (and thus its own production) by two mechanisms: (i) by coordinating Cu(II) and promoting its reduction to Cu(I) and (ii) by enhancing the catalytic reactivity of Cu(I) in the cycloaddition step. Because of the cooperation of these two processes, a rate enhancement of >400× is observed over the course of the reaction. The kinetic profile of the autocatalysis can be controlled by using different azides and alkynes or ligands (e.g., ammonia) for Cu(II). When carried out in a layer of 1% agarose gel, and initiated by ascorbic acid, this autocatalytic reaction generates an autocatalytic front. This system is prototypical of autocatalytic reactions where the formation of a product, which acts as a ligand for a catalyt...
49 citations
TL;DR: In this article, a poroelastic elastomer film is used to generate tunable surface wettability that can precisely control droplet dynamics from complete pinning, to fast sliding, and even more complex motions such as droplet oscillation, jetting, and mixing.
Abstract: Traditional dynamic adaptive materials rely on an atomic/molecular mechanism of phase transition to induce macroscopic switch of properties, but only a small number of these materials and a limited responsive repertoire are available. Here, liquid as the adaptive component is utilized to realize responsive functions. Paired with a porous matrix that can be put in motion by an actuated dielectric elastomer film, the uncontrolled global flow of liquid is broken down to well-defined reconfigurable localized flow within the pores and conforms to the network deformation. A detailed theoretical and experimental study of such a dynamically actuated liquid-infused poroelastic film is discussed. This system demonstrates its ability to generate tunable surface wettability that can precisely control droplet dynamics from complete pinning, to fast sliding, and even more complex motions such as droplet oscillation, jetting, and mixing. This system also allows for repeated and seamless switch among these different droplet manipulations. These are desired properties in many applications such as reflective display, lab-on-a-chip, optical device, dynamic measurements, energy harvesting, and others.
TL;DR: The high-throughput capacity of this integrated MagLev system will enable new applications in chemistry and biochemistry in a simple and label-free format on the basis of a universal property of all matter, i.e., density.
Abstract: This work describes the development of an integrated analytical system that enables high-throughput density measurements of diamagnetic particles (including cells) using magnetic levitation (MagLev), 96-well plates, and a flatbed scanner. MagLev is a simple and useful technique with which to carry out density-based analysis and separation of a broad range of diamagnetic materials with different physical forms (e.g., liquids, solids, gels, pastes, gums, etc.); one major limitation, however, is the capacity to perform high-throughput density measurements. This work addresses this limitation by (i) re-engineering the shape of the magnetic fields so that the MagLev system is compatible with 96-well plates, and (ii) integrating a flatbed scanner (and simple optical components) to carry out imaging of the samples that levitate in the system. The resulting system is compatible with both biological samples (human erythrocytes) and nonbiological samples (simple liquids and solids, such as 3-chlorotoluene, choleste...
TL;DR: In this paper, the relationship between the rates of charge transport (by tunneling) across self-assembled monolayers (SAMs) in a metal/SAM/Ga2O3/EGaIn junction and the geometric contact area (Ag) between the conical Ga2O 3/EG aIn top-electrode and the bottom-Electrode was described.
Abstract: This paper describes the relationship between the rates of charge transport (by tunneling) across self-assembled monolayers (SAMs) in a metal/SAM//Ga2O3/EGaIn junction and the geometric contact area (Ag) between the conical Ga2O3/EGaIn top-electrode and the bottom-electrode. Measurements of current density, J(V), across SAMs of decanethiolate on silver demonstrate that J(V) increases with Ag when the contact area is small (Ag < 1000 μm2), but reaches a plateau between 1000 and 4000 μm2, where J(0.5 V) ≈ 10–0.52±0.10 A/cm2. The method used to fabricate Ga2O3/EGaIn electrodes generates a tip whose apex is thicker and rougher than its thin, smoother sides. When Ag is small, the Ga2O3/EGaIn electrode contacts the bottom-electrode principally over this rough apex and forms irreproducible areas of electrical contact. When Ag is large, the contact is through the smoother regions peripheral to the apex and is much more reproducible. Measurements of contact pressure between conical EGaIn electrodes and atomic forc...
TL;DR: In this article, an optically transparent membrane is used for active noise cancellation, which consists of a prestretched hydrophobic elastomer, attached to a rigid frame and sandwiched between two hydrogels swollen with an aqueous solution of salt.
Abstract: A method for active noise cancelation that uses an optically transparent membrane is described. The membrane consists of a prestretched hydrophobic elastomer, attached to a rigid frame and sandwiched between two hydrogels swollen with an aqueous solution of salt. The elastomer functions as a dielectric, and the hydrogel functions as an ionic conductor. When the two hydrogels are subjected to a sinusoidal voltage, the membrane generates sound. A linear model for the reflection, transmission, and generation of sound by the membrane in an impedance tube is presented and validated. Active noise cancelation is demonstrated using the linear model and feedforward control. Compared to passive sound absorption, the sound transmission loss across the membrane is improved with active control from an average value of 7 dB to an average value of 16 dB. The transparent membrane may be used to cancel noises through a window, while maintaining its transparency.
TL;DR: This paper describes experiments that are designed to test the influence of terminal groups incorporating carbon-halogen bonds on the current density across self-assembled monolayer (SAM)-based junctions of the form MTS/S(CH2)9NHCOCH nX3- n//Ga2O3/EGaIn.
Abstract: This paper describes experiments that are designed to test the influence of terminal groups incorporating carbon–halogen bonds on the current density (by hole tunneling) across self-assembled monolayer (SAM)-based junctions of the form MTS/S(CH2)9NHCOCHnX3–n//Ga2O3/EGaIn (where M = Ag and Au and X = CH3, F, Cl, Br, I). Within the limits of statistical significance, these rates of tunneling are insensitive to the nature of the terminal group at the interface between the SAM and the Ga2O3. The results are relevant to the origin of an apparent inconsistency in the literature concerning the influence of halogen atoms at the SAM//electrode interface on the tunneling current density.
TL;DR: The field of organic chemistry has been transformed from one state to another, one marked by disciplined, elegant, complexity as discussed by the authors, and the ability to put together molecules bit-by-bit, simple or complex.
Abstract: In 1956 – the year R. B. Woodward’s famous Perspective was published – I was a senior in high school. The next year, when I started college and joined a research group, it was still all the (I thought, hopefully and in anticipation, “we”) organic chemistry graduate students talked about. The vision was so astonishing, and the ambition so grand, that it was transfixing. It clearly marked the transformation of the field of synthesis from one state into something entirely different – one marked by disciplined, elegant, complexity. I never actually met Woodward (other than secondarily, through one of his postdocs, to let me know of his intense displeasure at my use of his IR spectrometers in the middle of the night), but I did go to Woodward group seminars, where I learned humility, as well as new definitions of “endurance” and bladder control (these seminars were – or seemed – very, very long to someone who understood very little of what was going on). Still, it was impossible for me not to share the feeling of the birth of a new field. I did not become a “synthetic organic chemist,” but almost all the research that my colleagues and I have done (and do) involves organic synthesis. The ability to put together molecules – bit-by-bit, simple or complex – is one of chemistry’s great accomplishments, and a source of amazement to those in many other fields of science. More than one physicist has told me that s/he cannot believe that it is possible to manipulate bonds between individual atoms with the skill that organic chemists do. When I look at a complex structure assembled in a beautifully organized campaign, I also am amazed. That said, all fields of science morph with time. The phrase “organic synthesis” has come to mean “synthesis of structurally complex natural products”, or, perhaps, “synthesis of complicated molecules with pharmaceutical activity.” Nature, and relevance to healthcare, define the targets, and provide the utilitarian justification for the effort. Is there (or should there be) more to it than that? Will this style of organic synthesis – a style that emphasizes technical proficiency and complexity rather than simplicity, breadth, and utility – persist? Natural products, and selected, specific types of transformations, provide endless technically interesting problems – in structure, in synthetic design, in development of reagents – but does their solution justify the effort that goes into them? Are there other types of problems that need the skills of experts in synthesis, and other types of opportunity than those that have historically been most exhaustively studied? Aside from the technical focus, there is another issue. Much of complex organic synthesis goes on in universities. In addition to performing research, university research groups have the important obligation to teach students what they need to know for their intended careers. Is the training that students currently receive in organic synthesis the one that best prepares them for their future (and which may possibly be entirely different than their research director’s past)?
TL;DR: Structural-activity relationships drawn from a set of 36 compounds offer a starting point for the design of new compounds targeting the inhibition of histone deacetylases, compatible with the hypothesis that crypts evolved (at least in part), to separate stem cells at the base of crypts from butyrate produced by commensal bacteria.
Abstract: Two biological activities of butyrate in the colon (suppression of proliferation of colonic epithelial stem cells and inflammation) correlate with inhibition of the activity of histone deacetylases. Cellular and biochemical studies of molecules similar in structure to butyrate, but different in molecular details (functional groups, chain-length, deuteration, oxidation level, fluorination, or degree of unsaturation), demonstrated that these activities were sensitive to molecular structure, and were compatible with the hypothesis that butyrate acts by binding to the Zn2+ in the catalytic site of histone deacetylases. Structure–activity relationships drawn from a set of 36 compounds offer a starting point for the design of new compounds targeting the inhibition of histone deacetylases. The observation that butyrate was more potent than other short-chain fatty acids is compatible with the hypothesis that crypts evolved (at least in part), to separate stem cells at the base of crypts from butyrate produced by ...
TL;DR: Using curiosity as the starting point for careful observation of nature and society is a nontrivial skill, and astarting point for new intellectual endeavors and adventures.
Abstract: Using curiosity as the starting point for careful observation of nature and society is a nontrivial skill, and a starting point for new intellectual endeavors and adventures. It is one essential contributor to creativity in science, and a start in forcing new ideas into inflexible professional orthodoxies.
TL;DR: The use of paper scaffolds to create landscapes spatially structured at the scales relevant to bacterial ecology is demonstrated and the bacteria-in-paper platform enables quantitative assessment of bacterial community dynamics in complex environments using everyday materials.
Abstract: Habitat spatial structure has a profound influence on bacterial life, yet there currently are no low-cost equipment-free laboratory techniques to reproduce the intricate structure of natural bacterial habitats. Here, we demonstrate the use of paper scaffolds to create landscapes spatially structured at the scales relevant to bacterial ecology. In paper scaffolds, planktonic bacteria migrate through liquid filled pores, while the paper9s cellulose fibers serve as anchor points for sessile colonies (biofilms). Using this novel approach we explore bacterial colonization dynamics in different landscape topographies, and characterize the community composition of Escherichia coli strains undergoing centimeter-scale range expansions in habitats structured at the micrometer scale. The bacteria-in-paper platform enables quantitative assessment of bacterial community dynamics in complex environments using everyday materials.
TL;DR: Diagnosis of SCD can improve survival, but high costs and complex operational requirements of standard genetic or protein separation mean that standard testing for SCD is not recommended.