Research Interest: functional architected materials, mechanical metamaterials, multiscale mechanics, additive manufacturing, soft robotics

Develop multi-stable structures and metamaterials with programmable morphing

Morphable Metamaterials: Metamaterials obtain their effective properties mainly by structure rather than composition. Mechanical metamaterials, in particular, have been designed to show superior mechanical properties, such as ultrahigh strength-to-weight ratio, or unusual properties, such as a negative coefficient of thermal expansion (CTE). However, once fabricated, structural modifications are generally difficult, making it rare to find metamaterials that can be reconfigured beyond their original design. Recent efforts have produced metamaterials with morphing functionalities by mimicking the snap-through mechanism of Venus Flytrap in nature (Fig. a). For example, multi-stable metamaterials have two or more different stable stages that can be switched reversibly among each other via snap-through buckling caused by mechanical loading (Fig. b). Morphing metamaterials can provide unprecedented performance for multiple sectors, such as aerospace, medical devices, and soft robotics.

Develop actuators and sensors for soft robotics

Thermal sensors and actuators: Morphable metamaterials that are integrated with time-dependent, highly deformable responses to environmental stimuli have allowed deployable mechanisms and soft robots to move or adapt their shape to their surroundings, as well as acquire novel features such as stretchability, growth, morphing, self-reconfigurability, self-healing, and edibility. Our research group will develop metamaterials that self-conforms around an object of interest as a physical route for computing and reporting the object’s shape.

Develop functional structures and metamaterials for aerospace applications

Metamaterials with tunable thermal expansion: In extreme thermal environments, sensitive applications that require very fine precision call for materials with zero thermal expansion. They can thus avoid undesired thermal deformation. For example, thermal expansion of the supporting struts can change the distance between the sub-reflector and the antenna. Thus the signal cannot be received accurately. To suppress such failures, materials with a zero Coefficient of thermal expansion (CTE) over a wide range of temperatures are desired. The developed structural efficient metamaterials with near-zero thermal expansion have been engineered for a satellite antenna of the MDA Corp. to avoid undesired thermal distortion in extreme environments.

Develop meta-crystal lattices with phase transformation induced plasticity

Analogous to the rapid decreases in stress associated with dislocation slip in metallic single crystals, localized bands in metamaterials cause post-yielding collapse problems. However, in TRIP steels, the phase transformation between FCC and BCC structure induced outstanding plasticity. In our research, hardening mechanisms found in crystalline alloys are integrated into mechanical metamaterials to obtain the desired combination of outstanding strength and ductility.

Develop medical balloon catheters for Atrial Fibrillation (AFib) Treatment

Atrial fibrillation is the most common heart rhythm disturbance. It is caused by abnormal areas of the heart, causing disruption to the normal electrical beats in the heart. These areas can be treated by ‘ablation’ – a procedure in which parts of the heart are cauterised. To find these areas, we need to collect electrical signals directly from the surface of the heart. This needs many electrical wires to touch the surface of the heart wall at the same time (Fig. a). However, the signals are variable in the shape of electrical wires. The large nonlinear deformation of the current balloon catheter (Fig. b) is hard to be precisely predicted and controlled, making the signal collection difficult. The precisely controlled catheter tips can increase signal accuracy, save surgical time, improve the surgical success rate, and decrease medical costs. In this project, novel morphing metamaterials are proposed to provide precise motions, hence improving the accuracy of signal collection.

Develop metamaterial with structural hierarchy

As mechanical properties are highly coupled, there is a lack of design methodologies that can demonstrate one superior property without a trade-off in others. For example, most existing design methods achieve desired thermal actuation while penalizing elastic stiffness and vice versa. In this work, I present hierarchical bi-material lattices that are stiff and can be designed to attain a theoretically unbounded range of thermal expansion without (i) impact on elastic moduli and (ii) severe penalty in specific stiffness.

Routes to program metamaterials

Opportunities to tailor thermal expansion in architected materials exist, but design options that are stiff and provide full directional authority on thermal expansion are currently limited by the structural characteristics of existing concepts. In this work, we report routes to systematically engineer thermally responsive lattice materials that are built from dual-material tetrahedral units that are stiff and strong. Drawing from concepts of vector analysis, crystallography, and tessellation, a scheme is presented for three-dimensional lattices to program desired magnitude and spatial directionality, such as unidirectional, transverse isotropic, or isotropic, of thermal expansion.