Research projects

Overview

My research involves the experimental and theoretical investigation of smart and shape-morphing soft bio-inspired composite systems. I probe the fundamentals of nonlinear elasticity and linear viscoelasticity to develop and simulate smart multi-material bio-mimetic systems. Part of my research led to the development of high performance biomimetic soft robots and reconfigurable structures using shape memory alloy springs as the actuation mechanism. These systems have potential applications in marine, space, energy, electronics, and medicine to replace traditional actuation and delivery methods. My doctoral research also addresses the cellular and molecular origins of the mechano-chemo-transduction mechanisms in the heart through which each cardiac cell autoregulates its contraction in response to changes in mechanical load. In collaboration with researchers at the University of California, Davis, I established a viscoelastic Eshelby inclusion model to provide more accurate predictions of the 3D time-dependent mechanical strains and stresses inside cardiac cells in the in vitro Cell-in-Gel system. In another part of my Ph.D. research, I developed an experimental and theoretical framework for axisymmetric and asymmetric inflation of rubber membranes with variable geometric and material properties. In particular, I explored several designs with applications in civil, automotive, and aerospace structures for which a membrane would map to different 3D shapes upon pressurization. Finally, the last research experience during my doctoral studies involves the development of a fully autonomous optical fiber-based self-healing shape memory polymers with broad applications especially as structural members in safety-critical fields such as aeronautics and civil engineering.

Robotic Jellyfish

We demonstrate a new approach to the design of a synthetic jellysh that imitates the morphology and kinematics of the actual animal. Since jellysh usually move at low speeds, the locomotion can be mimicked using shape memory alloy (SMA) springs as articial muscles. Compared to previous attempts at biomimetic underwater robots, the current research aims to simplify the design, generate larger stroke, and lower the actuation cycle for propulsion. The robot consists of a soft silicone rubber disk with an embedded pre-stretched SMA spring along its circumference, which when heated contracts to initiate large shape changes in the structure. Our approach harnesses the buckling instability of the main body to create a relatively quick motion that produces a pulsed jet of water to generate thrust. The rubber disk is also equipped with several flaps that contribute to the swimming motion by displacing the surrounding water through a rowing-like mechanism.

Viscoelastic Mechanical Modeling of Cardiomyocyte Contraction

The whole heart pumps blood by the contraction of cardiac muscle cells, and increased blood flow is supplied by autonomous compensating mechanisms (Frank-Starling and Anrep effects) in response to increased activity of the body. Recent experiments on single cells indicate that each cardiomyocyte has biochemical signals that autoregulate cell contraction in response to changes in mechanical load. To investigate the cellular and molecular origins of these mechano-chemo transduction (MCT) mechanisms, we developed (in collaboration with a group of researchers at UC Davis) the in vitro Cell-in-Gel system, where isolated cardiac cells are embedded in a hydrogel matrix and stimulated to contract. The hydrogel stiffness acts as a surrogate for the mechanical resistance of the surrounding extracellular matrix and systolic blood pressure in vivo.In this project, we present a mathematical model to quantify all mechanical fields, as a companion tool to help guide the ongoing Cell-in-Gel experiments and to interpret the experimental data. The model is based on the classical Eshelby problem of an ellipsoidal inclusion embedded in an elastic matrix, which is extended here to account for the viscoelasticity of the cardiomyocyte (inclusion) and the hydrogel (matrix). Accurate mechanical analysis of the 3D stresses in the cardiomyocyte provided by this model sets the physical foundation to understand how the cell senses multiaxial stresses, activates mechano-sensors at various locations, transduces the stresses to biochemical signals, and autoregulates contractile force in adaptive response to load changes.

Inflatables

Inflatable structures have gained a considerable attention recently due to the growing demand for lightweight and low-cost structures. These structures possess an exceptionally high mechanical packaging efficiency and very small stowage volume, which gives them a wide scope of applicability ranging from space deployable structures, such as antenna reflectors, solar arrays, inflatable rovers, and human habitats, to implementations in automotive and civil engineering industries. Of particular interest, is to achieve a desired shape upon inflation in order to meet certain criteria or perform a specific task. Multiple tests were performed to mechanically characterize and fit the constitutive behavior of silicone rubber materials with an appropriate hyperelastic strain energy density function assuming isotropy and incompressibility. These constitutive tests include (1) uniaxial tension, (2) planar tension, and (3) equi-biaxial tension.

Self-healing Shape Memory Polymers

Structural health monitoring (SHM) has received significant interest over the past decade and has led to the development of a wide variety of sensors and signal processing techniques to determine the presence of changes or damage in a structural system. The topic has attracted significant attention due to the safety and performance enhancing benefits as well as the potential lifesaving capabilities offered by the technology. While the resulting systems are capable of sensing their surrounding structural and environmental conditions, few methods exist for using the information to autonomously react and repair or protect the system. One of the major challenges in the future implementation of SHM systems is their coupling with materials that can react to the damage to heal themselves and return to normal function. The coupling of self-healing materials with SHM has the potential to significantly prolong the lifetime of structural systems and extend the required inspection intervals. In this study, we developed an optical fiber based self-healing system composed of mendable polyurethanes based on the thermally reversible Diels–Alder (DA) reaction.

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