Von Willlebrand Adhesion to Surfaces at High Shear Rates Is Controlled by Long-Lived Bonds

Von Willebrand factor (vWF) adsorbs and immobilizes platelets at sites of injury under high-shear-rate conditions. It has been recently demonstrated that single vWF molecules only adsorb significantly to collagen above a threshold shear, and here we explain such counterintuitive behavior using a coarse-grained simulation and a phenomenological theory. We find that shear-induced adsorption only occurs if the vWF-surface bonds are slip-resistant such that force-induced unbinding is suppressed, which occurs in many biological bonds (i.e., catch bonds). Our results quantitatively match experimental observations and may be important to understand the activation and mechanical regulation of vWF activity during blood clotting

Polymer Fiber Probes Enable Optical Control of Spinal Cord and Muscle Function In Vivo

Restoration of motor and sensory functions in paralyzed patients requires the development of tools for simultaneous recording and stimulation of neural activity in the spinal cord. In addition to its complex neurophysiology, the spinal cord presents technical challenges stemming from its flexible fibrous structure and repeated elastic deformation during normal motion. To address these engineering constraints, we developed highly flexible fiber probes, consisting entirely of polymers, for combined optical stimulation and recording of neural activity. The fabricated fiber probes exhibit low-loss light transmission even under repeated extreme bending deformations. Using our fiber probes, we demonstrate simultaneous recording and optogenetic stimulation of neural activity in the spinal cord of transgenic mice expressing the light sensitive protein channelrhodopsin 2 (ChR2). Furthermore, optical stimulation of the spinal cord with the polymer fiber probes induces on-demand limb movements that correlate with electromyographical (EMG) activity.National Science Foundation (U.S.) (EEC-1028725)National Science Foundation (U.S.) (Career Award)National Science Foundation (U.S.) (DMR-0819762)McGovern Institute for Brain Research at MIT (Neurotechnology Grant)Massachusetts Institute of Technology. Simons Center for the Social Brai

Electrically pumped continuous wave quantum dot lasers epitaxially grown on patterned, on-axis (001) Si

High performance III-V lasers at datacom and telecom wavelengths on on-axis (001) Si are needed for scalable datacenter interconnect technologies. We demonstrate electrically injected quantum dot lasers grown on on-axis (001) Si patterned with {111} v-grooves lying in the [110] direction. No additional Ge buffers or substrate miscut was used. The active region consists of five InAs/InGaAs dot-in-a-well layers. We achieve continuous wave lasing with thresholds as low as 36 mA and operation up to 80°C

Characterization and connectorization of optoelectronic neural probes

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.Cataloged from PDF version of thesis.Includes bibliographical references (pages 45-46).Reliability of interfaces between the nervous system and the neuroprosthetics can be significantly improved through the use of flexible polymer and polymer composite neural stimulation and recording systems. Furthermore, recent advances in optical neural stimulation methods would benefit from seamless integration of optical waveguides into neural probes. In this thesis, we describe electronic and optical characterization of polymer-based probes produced through thermal drawing process. Our results indicate that polymer-based fiber-probes maintain low-loss optical transmission even in the presence of 90-270* bending deformation with radii of curvature as low as 500 pim over multiple deformation cycles. These probes were robust enough to chronically function in the brain of freely moving mice. Furthermore, these flexible devices enabled direct optical stimulation in the spinal cord, which for the first time allowed for direct spinal optical control of lower limb muscles. In addition to optical characterization, we have developed a method for high-throughput connectorization of the fiber-probes with microscale features to external electronics. This required the development of custom printed circuit boards and involved a multi-step lithographic process. Finally, in a three-months long study we have demonstrated that probes characterized in this thesis yield significantly reduced tissue response in the brain as compared to the steel microwires traditionally used by neuroscientists.by Jennifer Selvidge.S.B