Showing papers by "George M. Whitesides published in 2020"

Magnetic Levitation in Chemistry, Materials Science, and Biochemistry.

Abstract: All matter has density. The recorded uses of density to characterize matter date back to as early as ca. 250 BC, when Archimedes was believed to have solved "The Puzzle of The King's Crown" using density.[1] Today, measurements of density are used to separate and characterize a range of materials (including cells and organisms), and their chemical and/or physical changes in time and space. This Review describes a density-based technique-magnetic levitation (which we call "MagLev" for simplicity)-developed and used to solve problems in the fields of chemistry, materials science, and biochemistry. MagLev has two principal characteristics-simplicity, and applicability to a wide range of materials-that make it useful for a number of applications (for example, characterization of materials, quality control of manufactured plastic parts, self-assembly of objects in 3D, separation of different types of biological cells, and bioanalyses). Its simplicity and breadth of applications also enable its use in low-resource settings (for example-in economically developing regions-in evaluating water/food quality, and in diagnosing disease).

Smart Thermally Actuating Textiles

Abstract: Biologically inspired actuators made from soft materials are innately compliant, adaptable to their environment, and able to perform biomimetic motions;[1–4] as such, they are ideal for devices that interact with humans, including wearable robots.[5–7] The majority of current soft robots rely on a pressurized fluid delivered via tether and require hardware (e.g., pumps and valves) to supply the fluid and control its flow. This hardware, which can often be heavy, noisy, and bulky,[1,2] prevents the realization of lightweight and portable wearable devices, especially for applications requiring multiple actuator arrays because the number of valves and pneumatic lines scales with the number of actuators. This can pose a challenge for the development of soft robotic devices that require multiple controlled actuators, such as wearable robots to assist multiple-degree-of-freedom limb movement for assistance[7] or rehabilitation[6] or active pressure modulation devices for prevention of pressure sores or mechanotherapy applications.[8] To remove the need for a pressurized fluid supply, researchers have developed alternative electrically and thermally activated soft actuator technologies including shape memory polymers,[9,10] piezopolymers,[11] electrostatic actuators,[12,13] chargeinjection electrohydrodynamic devices,[14] electrolysis-based actuators,[15] and encapsulated electromagnetic systems.[16] Building upon this work, researchers have translated untethered soft actuator designs to textiles when considering wearable applications, motivated by the prevalence of textiles as the base material for the vast majority of soft goods and clothing. Every day we intimately interact with textiles because they are lightweight, conformal (compared to molded and printed elastomeric systems), and robust to repeated, sometimes violent, stresses and abrasions encountered during use (compared to polymer films). The hierarchical nature of textiles provides the opportunity to create soft robotic systems for wearable devices through the integration of smart fibers that can sense or actuate by electrical or chemical means.[17,18] Textile systems that can apply force, change shape, or modulate stiffness have been achieved through the integration of shape-memory alloys (SMAs) as fibers into the textile structure.[19,20] Other textile actuation approaches include thermally actuated coiled Soft robots have attracted attention for biomedical and consumer devices. However, most of these robots are pneumatically actuated, requiring a tether and thus limiting wearable applications that require multiple controlled actuators. By pairing liquid-vapor phase change actuation with a textile-based laminated manufacturing method, smart thermally actuating textiles (STATs) eliminate the need for a pneumatic tether. STATs are lightweight and unobtrusive for wearable applications and exploit a facile manufacturing approach that supports arbitrary customization of the form factor and easy creation of connected arrays of individual robotic modules. Through integrated sensing and heating elements, STATs demonstrate closed-loop feedback that enables dynamic pressure control in the presence of environmental temperature fluctuations.

Analysis of Powders Containing Illicit Drugs Using Magnetic Levitation

Abstract: Magneto-Archimedes levitation (MagLev) enables the separation of powdered mixtures of illicit drugs (cocaine, methamphetamine, heroin, fentanyl, and its analogues), adulterants, and diluents based on density, and allows the presumptive identification of individual components. Small samples (mass <50 mg), with low concentrations of illicit drugs, present a particular challenge to analysis for forensic chemists. The MagLev device, a cuvette containing a solution of paramagnetic gadolinium(III) chelate in a non-polar solvent, placed between two like-poles-facing NdFeB magnets, allowed separation of seven relevant compounds simultaneously. In particular, initial separation with MagLev, followed by characterization by FTIR-ATR, enabled identification of fentanyl in a sample of fentanyl-laced heroin (1.3 wt % fentanyl, 2.6 wt % heroin, and 96.1 wt % lactose). MagLev allows identification of unknown powders in mixtures and enables confirmatory identification based on structure-specific techniques.

Soft Non-Volatile Memory for Non-Electronic Information Storage in Soft Robots

Abstract: Pneumatically operated soft robots require complex infrastructure for their operation: microcontrollers must control hard pneumatic valves via power electronics. Although soft digital logic gates based on soft valves have been demonstrated as a replacement for electronic control, the development of memory from logic gates is cumbersome (three logic gates with mono-stable membranes for the development of a single S-R latch), and such memory is only capable of holding, but not storing, information; after a power reset, the membranes relax to their idle states, and the information is lost. In this work, we introduce a soft memory device with a bistable membrane that allows the permanent storage of binary information in soft materials, and we demonstrate its writing and erasing operations. We also introduce a new type of pneumatically-driven soft display, the soft bubble display. We connect the display to our soft memory device to visualize the information that is held in the memory. Our work highlights the importance of material-based memory and its future use for programming soft robots.

Variation and selection in axon navigation through microtubule-dependent stepwise growth cone advance

Abstract: Myosin II (MII) activity is required for elongating mammalian sensory axons to change speed and direction in response to Nerve Growth Factor (NGF) and laminin-1 (LN). NGF signaling induces faster outgrowth on LN through regulation of actomyosin restraint of microtubule advance into the growth cone periphery. It remains unclear whether growth cone turning on LN works through the same mechanism and, if it does, how the mechanism produces directed advance. Using a novel method for substrate patterning, we tested how directed advance occurs on LN by creating a gap immediately in front of a growth cone advancing on a narrow LN path. The growth cone stopped until an actin-rich protrusion extended over the gap, adhered to LN, and became stabilized. Stepwise advance over the gap was triggered by microtubule +tip entry up to the adhesion site of the protrusion and was independent of traction force pulling. We found that the probability of microtubule entry is regulated at the level of the individual protrusion and is sensitive to the rate of microtubule polymerization and the rate of rearward actin flow as controlled by adhesion-cytoskeletal coupling and MII. We conclude that growth cone navigation is an iterative process of variation and selection. Growth cones extend leading edge actin-rich protrusions that adhere transiently (variation). Microtubule entry up to an adhesion site stabilizes a protrusion (selection) leading to engorgement, consolidation, protrusive activity distal to the adhesion site, and stepwise growth cone advance. The orientation of the protrusion determines the direction of advance.

Système de lévitation magnétique

Abstract: L'invention concerne un systeme de levitation magnetique, lequel systeme comprend un premier et un second aimants ayant des surfaces de leurs poles identiques qui se font face ; et un recipient dispose entre les premier et second poles du type magnetique et contenant une solution comprenant un complexe paramagnetique dans un solvant non aqueux, le complexe paramagnetique comprenant un metal paramagnetique et au moins un ligand qui se coordonne au metal paramagnetique par l'intermediaire d'un don d'electrons. L'invention concerne egalement des procedes de separation d'un melange de composes solides, et/ou d'identification, de confirmation et/ou de prevision de la composition du melange.

Magnetic levitation system

Abstract: A magnetic levitation system is described, including a first and second magnets having surfaces of their like-poles facing each other; and a container disposed between the first and second magnets' like poles and containing a solution including a paramagnetic complex in a non-aqueous solvent, where the paramagnetic complex includes a paramagnetic metal and at least one ligand that coordinates to the paramagnetic metal via electron donation. Methods of separating a mixture of solid compounds, and/or identifying, confirming, and/or predicting the composition of the mixture, are also described.

Thread-based potentiometric ion-sensing

Abstract: Fabrication of a low-cost and miniaturized solid-contact thread-based ion sensing electrode (ISE) that is suitable for point-of-care applications is described. The fabrication process is simple and scalable. Different types of threads and a variety of different conductive ion-to-electron transducer inks can be used to fabricate the thread-based ISEs with Nernstian responses. Multiple thread-based sensors can be easily bundled with the reference electrode to fabricate a customized sensor for multiplexed ion-sensing in small sample volumes. The thread-based electrodes can be used in both single-use and reusable fashion. The thread-based multiplexed ion-sensor is used for detection of a wide array of ions in many different types of aqueous solutions.