Showing papers by "George M. Whitesides published in 2017"

Soft Mobile Robots with On-Board Chemical Pressure Generation

Abstract: We wish to develop robot systems that are increasingly more elastic, as a step towards bridging the gap between man-made machines and their biological counterparts. To this end, we develop soft actuators fabricated from elastomer films with embedded fluidic channels. These actuators offer safety and adaptability and may potentially be utilized in robotics, wearable tactile interfaces, and active orthoses or prostheses. The expansion of fluidic channels under pressure creates a bending moment on the actuators and their displacement response follows theoretical predictions. Fluidic actuators require a pressure source, which limits their mobility and mainstream usage. This paper considers instances of mechanisms made from distributed elastomer actuators to generate motion using a chemical means of pressure generation. A mechanical feedback loop controls the chemical decomposition of hydrogen peroxide into oxygen gas in a closed container to self-regulate the actuation pressure. This on-demand pressure generator, called the pneumatic battery, bypasses the need for electrical energy by the direct conversion of chemical to mechanical energy. The portable pump can be operated in any orientation and is used to supply pressure to an elastomeric rolling mobile robot as a representative for a family of soft robots.

A Soft Tube-Climbing Robot.

Abstract: This article demonstrates a pneumatically actuated soft robot capable of navigating the inside of a tube. This robot was built using buckling pneumatic actuators (vacuum-actuated muscle-inspired pneumatic structures, or VAMPs). The tube climber can navigate through a tube with turns, inclines, and varying diameters. The robot is also able to remove obstacles (of more than 10 times its own weight) from tubes to perform a clearing function. It maintains climbing and clearing performance in wet conditions and under water. The tube climber is lightweight and completely soft and thus has the potential to be collaborative (i.e., work with humans) and also to interact safely with delicate environments.

Negative-Pressure Soft Linear Actuator with a Mechanical Advantage

Abstract: Dr. D. Yang, Dr. M. S. Verma, E. Lossner, D. Stothers, Prof. G. M. Whitesides Department of Chemistry and Chemical Biology Harvard University 12 Oxford Street, Cambridge, MA 02138, USA E-mail: gwhitesides@gmwgroup.harvard.edu Dr. D. Yang School of Engineering and Applied Sciences Harvard University 29 Oxford Street, Cambridge, MA 02138, USA Prof. G. M. Whitesides Kavli Institute for Bionano Science and Technology Harvard University 29 Oxford Street, Cambridge, MA 02138, USA Prof. G. M. Whitesides Wyss Institute for Biologically Inspired Engineering Harvard University 60 Oxford Street, Cambridge, MA 02138, USA

Electrical Textile Valves for Paper Microfluidics

Abstract: This paper describes electrically-activated fluidic valves that operate based on electrowetting through textiles. The valves are fabricated from electrically conductive, insulated, hydrophobic textiles, but the concept can be extended to other porous materials. When the valve is closed, the liquid cannot pass through the hydrophobic textile. Upon application of a potential (in the range of 100-1000 V) between the textile and the liquid, the valve opens and the liquid penetrates the textile. These valves actuate in less than 1 s, require low energy (≈27 µJ per actuation), and work with a variety of aqueous solutions, including those with low surface tension and those containing bioanalytes. They are bistable in function, and are, in a sense, the electrofluidic analog of thyristors. They can be integrated into paper microfluidic devices to make circuits that are capable of controlling liquid, including autonomous fluidic timers and fluidic logic.

Anomalously Rapid Tunneling: Charge Transport across Self-Assembled Monolayers of Oligo(ethylene glycol)

Abstract: This paper describes charge transport by tunneling across self-assembled monolayers (SAMs) of thiol-terminated derivatives of oligo(ethylene glycol) (HS(CH2CH2O)nCH3; HS(EG)nCH3); these SAMs are positioned between gold bottom electrodes and Ga2O3/EGaIn top electrodes. Comparison of the attenuation factor (β of the simplified Simmons equation) across these SAMs with the corresponding value obtained with length-matched SAMs of oligophenyls (HS(Ph)nH) and n-alkanethiols (HS(CH2)nH) demonstrates that SAMs of oligo(ethylene glycol) have values of β (β(EG)n = 0.29 ± 0.02 natom–1 and β = 0.24 ± 0.01 A–1) indistinguishable from values for SAMs of oligophenyls (β(Ph)n = 0.28 ± 0.03 A–1), and significantly lower than those of SAMs of n-alkanethiolates (β(CH2)n = 0.94 ± 0.02 natom–1 and 0.77 ± 0.03 A–1). There are two possible origins for this low value of β. The more probable involves hole tunneling by superexchange, which rationalizes the weak dependence of the rate of charge transport on the length of the molecul...

Magnetic Levitation To Characterize the Kinetics of Free-Radical Polymerization

Abstract: This work describes the development of magnetic levitation (MagLev) to characterize the kinetics of free-radical polymerization of water-insoluble, low-molecular-weight monomers that show a large change in density upon polymerization. Maglev measures density, and certain classes of monomers show a large change in density when monomers covalently join in polymer chains. MagLev characterized both the thermal polymerization of methacrylate-based monomers and the photopolymerization of methyl methacrylate and made it possible to determine the orders of reaction and the Arrhenius activation energy of polymerization. MagLev also made it possible to monitor polymerization in the presence of solids (aramid fibers, and carbon fibers, and glass fibers). MagLev offers a new analytical technique to materials and polymer scientists that complements other methods (even those based on density, such as dilatometry), and will be useful in investigating polymerizations, evaluating inhibition of polymerizations, and studying polymerization in the presence of included solid materials (e.g., for composite materials).

Water-Restructuring Mutations Can Reverse the Thermodynamic Signature of Ligand Binding to Human Carbonic Anhydrase.

Abstract: This study uses mutants of human carbonic anhydrase (HCAII) to examine how changes in the organization of water within a binding pocket can alter the thermodynamics of protein-ligand association. Results from calorimetric, crystallographic, and theoretical analyses suggest that most mutations strengthen networks of water-mediated hydrogen bonds and reduce binding affinity by increasing the enthalpic cost and, to a lesser extent, the entropic benefit of rearranging those networks during binding. The organization of water within a binding pocket can thus determine whether the hydrophobic interactions in which it engages are enthalpy-driven or entropy-driven. Our findings highlight a possible asymmetry in protein-ligand association by suggesting that, within the confines of the binding pocket of HCAII, binding events associated with enthalpically favorable rearrangements of water are stronger than those associated with entropically favorable ones.

Fabrication of Paper‐Templated Structures of Noble Metals

Abstract: This manuscript describes a simple and rapid method for fabricating free-standing structures composed primarily (>94% w/w, and 55–80 at%) of noble metals (e.g., gold, silver, platinum, etc.) and having physical morphologies that resemble paper, thread, or fabric. In this method, templates (i.e., pieces of paper, or cotton fabric) are loaded with aqueous solutions of salts of noble metals, and then the cellulosic component is burned off in a furnace held at high temperatures (i.e., from 550 °C to 800 °C, depending on the procedure, in air). Even though the environment in a furnace is ostensibly oxidizing (e.g., hot air), the metal ions are reduced to elemental metal and form paper-templated or fabric-templated structures that have morphologies similar to that of the material from which they were derived (i.e., paper or fabric). Paper-templated structures are fibrous, permeable to gases and liquides, electrically conductive, and in some cases (e.g., paper-templated gold and paper-templated platinum structures), their surfaces are electroactive. The surface areas of paper-templated structures are more than 20 times higher than their projected areas. Paper-templated structures thus have properties that make them potentially useful in catalysis, sensing, and electroanalysis.

Method for culturing and patterning cells

Abstract: A cell scaffold includes a string having a diameter of less than 500 μm; a hydrogel matrix supported on the string; and cells seeded onto the hydrogel matrix The scaffold is used to cultivate cells, and to evaluate cell viability or cell metabolic activity

Image based photometry

Abstract: An image based photometer includes a light source adapted to hold a well plate having multiple wells for testing samples, the light source providing a source of broadband white light for transmission through the multiple wells. A sensing surface is positioned opposite the light source to receive light transmitted through the multiple wells and shield ambient light from transmission through the wells.

Co-fabrication of paper electronics and microfluidics

Abstract: In an aspect, a device includes a substrate including a cellulose matrix that provides an interconnected porous structure, a hydrophobic barrier disposed through the thickness of the substrate to define at least one porous channel within the volume of the cellulose matrix, and an electrically conducting material. The electrically conducting material is disposed within the volume of the porous channel to coat at least a portion of the cellulose matrix therein. A method of making and using actuators, electrochemical sensors, and batteries based on the device are also disclosed.