Large contraction conducting polymer molecular actuators

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, February 2005.Vita. Leaf 239 blank.Includes bibliographical references.The development of powerful and efficient artificial muscles that mimic Nature will profoundly affect engineering sciences including robotics and prosthetics, propulsion systems, and microelectromechanical systems (MEMS). Biological systems driven by muscle out-perform human-engineered systems in many key aspects. For example, muscle endows animals with a level of dexterity and speed that has yet to be emulated by even the most complex robotic system to date. Conducting polymers were chosen for research as actuators, based on a review of the relevant properties of all known actuators and active materials. Key features of conducting polymer actuators include low drive voltages (1 - 2 V) and high active strength (10 - 40 MPa) but moderate active strains (2 %). Active strains of 20 %, which human skeletal muscle is capable of, are desirable for applications in life-like robotics, artificial prostheses or medical devices. This thesis focuses on two approaches to create large contraction in conducting polymer actuators. The first strategy utilizes polypyrrole (PPy), a conducting polymer actuator material that contracts and expands based on a bulk ion swelling mechanism. Optimization of the polymer activation environment via room temperature ionic liquids enables PPy actuators to generate large contractions (16.3 % recoverable strain at 2.5 MPa, 21 % max) at slow speeds (0.4 %/s). In addition, cycle life can reach 10⁵ cycles without significant polymer degradation. This thesis presents an in-depth characterization of the behavior of polypyrrole actuators in room temperature 1-butyl-3-methyl imidazolium tetrafluoroborate liquid salt electrolyte.(cont.) The characterization includes the assessment of passive and electroactive mechanical properties as well as electrical and morphological properties. Using Nature's actin-myosin molecular engine as a source of inspiration, the second approach uses molecular mechanisms to create motion. In this bottom-up approach molecules are rationally designed from the molecular level for specific actuation properties. Such active molecular building blocks include shape changing, load bearing, passively deformable or hinge-like molecular elements. Several novel materials based on contractile molecular design were synthesized and their active properties characterized.by Patrick A.T. Anquetil.Ph.D

Independent control of polar and azimuthal anchoring

Monte Carlo simulation, experiment and continuum theory are used to examine the anchoring exhibited by a nematic liquid crystal at a patterned substrate comprising a periodic array of rectangles that, respectively, promote vertical and planar alignment. It is shown that the easy axis and effective anchoring energy promoted by such surfaces can be readily controlled by adjusting the design of the pattern. The calculations reveal rich behavior: for strong anchoring, as exhibited by the simulated system, for rectangle ratios $\geq 2$ the nematic aligns in the direction of the long edge of the rectangles, the azimuthal anchoring coefficient changing with pattern shape. In weak anchoring scenarios, however, including our experimental systems, preferential anchoring is degenerate between the two rectangle diagonals. Bistability between diagonally-aligned and edge-aligned arrangement is predicted for intermediate combinations of anchoring coefficient and system length-scale.Comment: 12 pages, 12 figure

Neural-network approach to modeling liquid crystals in complex confinement

Finding the structure of a confined liquid crystal is a difficult task since both the density and order parameter profiles are non-uniform. Starting from a microscopic model and density-functional theory, one has to either (i) solve a non-linear, integral Euler-Lagrange equation, or (ii) perform a direct multi-dimensional free energy minimisation. The traditional implementations of both approaches are computationally expensive and plagued with convergence problems. Here, as an alternative, we introduce an unsupervised variant of the Multi-Layer Perceptron (MLP) artificial neural network for minimising the free energy of a fluid of hard non-spherical particles confined between planar substrates of variable penetrability. We then test our algorithm by comparing its results for the structure (density-orientation profiles) and equilibrium free energy with those obtained by standard iterative solution of the Euler-Lagrange equations and with Monte Carlo simulation results. Very good agreement is found and the MLP method proves competitively fast, flexible and refinable. Furthermore, it can be readily generalised to the richer experimental patterned-substrate geometries that are now experimentally realisable but very problematic to conventional theoretical treatments

Nematic liquid crystal alignment on chemical patterns

Patterned Self-Assembled Monolayers (SAMs) promoting both homeotropic and planar degenerate alignment of 6CB and 9CB in their nematic phase, were created using microcontact printing of functionalised organothiols on gold films. The effects of a range of different pattern geometries and sizes were investigated, including stripes, circles and checkerboards. EvanescentWave Ellipsometry was used to study the orientation of the liquid crystal (LC) on these patterned surfaces during the isotropic-nematic phase transition. Pretransitional growth of a homeotropic layer was observed on 1 ¹m homeotropic aligning stripes, followed by a homeotropic mono-domain state prior to the bulk phase transition. Accompanying Monte-Carlo simulations of LCs aligned on nano-patterned surfaces were also performed. These simulations also showed the presence of the homeotropic mono-domain state prior to the transition.</p

Impact of PI3K (Phosphoinositide 3-Kinase Alpha) Inhibition on Hemostasis and Thrombosis

Objective— PI3Kα (phosphoinositide 3-kinase alpha) is a therapeutic target in oncology, but its role in platelets and thrombosis remains ill characterized. In this study, we have analyzed the role of PI3Kα in vitro, ex vivo, and in vivo in 2 models of arterial thrombosis. Approach and Results— Using mice selectively deficient in p110α in the megakaryocyte lineage and isoform-selective inhibitors, we confirm that PI3Kα is not mandatory but participates to thrombus growth over a collagen matrix at arterial shear rate. Our data uncover a role for PI3Kα in low-level activation of the GP (glycoprotein) VI-collagen receptor by contributing to ADP secretion and in turn full activation of PI3Kβ and Akt/PKB (protein kinase B). This effect was no longer observed at high level of GP VI agonist concentration. Our study also reveals that over a vWF (von Willebrand factor) matrix, PI3Kα regulates platelet stationary adhesion contacts under arterial flow through its involvement in the outside-in signaling of vWF-engaged αIIbβ3 integrin. In vivo, absence or inhibition of PI3Kα resulted in a modest but significant decrease in thrombus size after superficial injuries of mouse mesenteric arteries and an increased time to arterial occlusion after carotid lesion, without modification in the tail bleeding time. Considering the more discrete and nonredundant role of PI3Kα compared with PI3Kβ, selective PI3Kα inhibitors are unlikely to increase the bleeding risk at least in the absence of combination with antiplatelet drugs or thrombopenia. Conclusions— This study provides mechanistic insight into the role of PI3Kα in platelet activation and arterial thrombosis

Simulation Modifies Prehension: Evidence for a Conjoined Representation of the Graspable Features of an Object and the Action of Grasping It

Movement formulas, engrams, kinesthetic images and internal models of the body in action are notions derived mostly from clinical observations of brain-damaged subjects. They also suggest that the prehensile geometry of an object is integrated in the neural circuits and includes the object's graspable characteristics as well as its semantic properties. In order to determine whether there is a conjoined representation of the graspable characteristics of an object in relation to the actual grasping, it is necessary to separate the graspable (low-level) from the semantic (high-level) properties of the object. Right-handed subjects were asked to grasp and lift a smooth 300-g cylinder with one hand, before and after judging the level of difficulty of a “grasping for pouring” action, involving a smaller cylinder and using the opposite hand. The results showed that simulated grasps with the right hand exert a direct influence on actual motor acts with the left hand. These observations add to the evidence that there is a conjoined representation of the graspable characteristics of the object and the biomechanical constraints of the arm

Coxsackie-adenovirus receptor expression is enhanced in pancreas from patients with type 1 diabetes

Objectives: One of the theories connecting enterovirus (EV) infection of human islets with type 1 diabetes (T1D) is the development of a fertile field in the islets. This implies induction of appropriate proteins for the viral replication such as the coxsackie–adenovirus receptor (CAR). The aim of this study was to investigate to what extent CAR is expressed in human islets of Langerhans, and what conditions that would change the expression. Design: Immunohistochemistry for CAR was performed on paraffin-embedded pancreatic tissue from patients with T1D (n=9 recent onset T1D, n=4 long-standing T1D), islet autoantibody-positive individuals (n=14) and non-diabetic controls (n=24) individuals. The expression of CAR was also examined by reverse transcription PCR on microdissected islets (n=5), exocrine tissue (n=5) and on explanted islets infected with EV or exposed to chemokines produced by EV-infected islet cells. Results: An increased frequency of patients with T1D and autoantibody-positive individuals expressed CAR in the pancreas (p<0.039). CAR staining was detected more frequently in pancreatic islets from patients with T1D and autoantibody-positive subjects (15/27) compared with (6/24) non-diabetic controls (p<0.033). Also in explanted islets cultured in UV-treated culture medium from coxsackievirus B (CBV)-1-infected islets, the expression of the CAR gene was increased compared with controls. Laser microdissection of pancreatic tissue revealed that CAR expression was 10-fold higher in endocrine compared with exocrine cells of the pancreas. CAR was also expressed in explanted islets and the expression level decreased with time in culture. CBV-1 infection of explanted islets clearly decreased the expression of CAR (p<0.05). In contrast, infection with echovirus 6 did not affect the expression of CAR. Conclusions: CAR is expressed in pancreatic islets of patients with T1D and the expression level of CAR is increased in explanted islets exposed to proinflammatory cytokines/chemokines produced by infected islets. T1D is associated with increased levels of certain chemokines/cytokines in the islets and this might be the mechanism behind the increased expression of CAR in TID islets

Bayesian Action–Perception Computational Model: Interaction of Production and Recognition of Cursive Letters

In this paper, we study the collaboration of perception and action representations involved in cursive letter recognition and production. We propose a mathematical formulation for the whole perception–action loop, based on probabilistic modeling and Bayesian inference, which we call the Bayesian Action–Perception (BAP) model. Being a model of both perception and action processes, the purpose of this model is to study the interaction of these processes. More precisely, the model includes a feedback loop from motor production, which implements an internal simulation of movement. Motor knowledge can therefore be involved during perception tasks. In this paper, we formally define the BAP model and show how it solves the following six varied cognitive tasks using Bayesian inference: i) letter recognition (purely sensory), ii) writer recognition, iii) letter production (with different effectors), iv) copying of trajectories, v) copying of letters, and vi) letter recognition (with internal simulation of movements). We present computer simulations of each of these cognitive tasks, and discuss experimental predictions and theoretical developments

Relations between C9orf72 expansion size in blood, age at onset, age at collection and transmission across generations in patients and presymptomatic carriers

A (GGGGCC) n repeat expansion in C9orf72 gene is the major cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). The relations between the repeats size and the age at disease onset (AO) or the clinical phenotype (FTD vs. ALS) were investigated in 125 FTD, ALS, and presymptomatic carriers. Positive correlations were found between repeats number and the AO (p &lt; 10 e−4 ) but our results suggested that the association was mainly driven by age at collection (p &lt; 10 e−4 ). A weaker association was observed with clinical presentation (p = 0.02), which became nonsignificant after adjustment for the age at collection in each group. Importantly, repeats number variably expanded or contracted over time in carriers with multiple blood samples, as well as through generations in parent-offspring pairs, conversely to what occurs in several expansion diseases with anticipation at the molecular level. Finally, this study establishes that measure of repeats number in lymphocytes is not a reliable biomarker predictive of the AO or disease outcome in C9orf72 long expansion carriers