Everything Is a Materials Problem
Our group studies the interplay between mechanics and architecture at the nanoscale to create new classes of nanoarchitected materials with unprecedented mechanical properties. Our goal is to utilize the exceptional behaviors of nanomaterials — like ultrahigh strength and toughness, radiation damage tolerance, and enhanced ductility — using a range of micro- and nanoscale fabrication and testing methods. We have shown that nanoarchitected materials can attain remarkable properties. Examples include ceramics that are able to bounce back after compression to over 50% strain and fractal-like architectures that can localize failure to tune the mechanical response.
Our work is often bioinspired in nature, as the techniques we use can approach and replicate the length scale and complexity of natural materials. We are currently interested in the general areas of materials for extreme environments (irradiation, high temperature, ballistic impact, etc), multifunctional materials with combined mechanical, electrical and thermal performance, and biocompatible materials for operation in medical devices.
We use two approaches in conducting our research:
Materials from the bottom up
We use a suite of advanced 3D micro- and nanofabrication techniques to create new materials with features that are controllable on ~10nm length scales. We apply these nano-“building blocks” to make architectures starting at fundamental material length scales and investigate how this can bring about novel behaviors at micro-, meso- and bulk scales. Our research utilizes the Washington Nanofabrication Facility (WNF) and Molecular Analysis Facility (MAF) at UW along with a set of custom-built equipment. This topic encompasses work on nanolattices, tough nanoarchitectures and metamaterials.
Materials from the top down
The properties of natural and engineering materials are governed by a complex interaction of materials and architecture starting at the nanoscale and moving up. Unraveling the nature of these multi-scale interactions is a fundamental problem in material science. Our work studies the mechanics of materials starting from their nanoscale constituents and investigates how their structure (or architecture) at nano-, micro- and meso-scales affects their large-scale properties. This topic encompasses work on carbon fiber composites, biomaterials and artificial tissues.
Nanoscale Tensegrity-Based Metamaterials
Tensegrity (tension + integrity) structures are deeply embedded in nature, arising in cell cytoskeletons, spider silk, musculoskeletal systems, and many other areas where strength and versatility are required. Tensegrities demonstrate exceptional load carrying efficiency and deformability but have only been created at the macro scale. Our group is pushing the materials envelope by using tensegrity architectures at the microscale to create metamaterials with novel properties. These are created using a 2-photon lithography 3D printing system, which allows us to fabricate the complex architectures needed to replicate tensegrity morphologies. By using nanomechanical testing tools, we can measure the properties of these novel materials and better optimize their performance.
Parameterization of Pyrolysis
Two-photon lithography can be used to create 3D polymeric structures with control of features at the nanoscale. Pyrolyzing these polymer structures converts them into pure carbon and causes them to undergo as much as 80% shrinkage. This process not only decreases weight and improves feature sizes, but it allows for nanoarchitectures to be made from ultrahigh strength nano-carbon. We are investigating how to better control this process to differently affect shrinkage and enhance mechanical properties. These efforts directly tie into other work on the design of new engineered-materials with previously unachievable strength-density ratios and ultralight weights through pyrolysis-induced pretensioning.
Investigating Toughening Mechanisms in Bioinspired Nanoarchitected Materials
Biological materials exhibit remarkable strength and toughness, achieved by a strategic combination of weak interface, hierarchical architectures and fundamental building blocks at the nano-micro scale. We are studying the underlying toughening mechanisms in these materials at the micro-nano scales to understand the role of each building block and the associated material size effects. By utilizing novel fabrication techniques like 2D photon lithography and post processing techniques like pyrolysis and plasma etching, we create complex architectures with precisely controlled sub-micron geometry. In-situ nanoindentation of these dense architectures then enables understanding the fracture mechanics of these materials at length scales not explored before.
Nanoarchitected Metamaterials with Engineered Recovery
The remarkable properties of natural materials like shell and bone can be attributed to the unique cellular architecture spanning over multiple length scales, which results in a unique combination of strong, stiff and lightweight materials. For instance, a typically brittle material like alumina Al2O3, that undergoes a small amount of strain before failure could instead behave viscoelastic, reaching 50% strain and still recovering because of its architecture. Although many people are researching these types of metamaterials for application purposes, few are examining the underlying mechanics of the metamaterial design as a means to control recovery. My work aims to understand and design deformable metamaterials on the nanoscale. By using unique fabrication and post processing techniques like Direct Laser Writing, Atomic Layer Deposition, and Plasma Etching, I can fabricate complex shell structures that use instabilities as mechanisms for recoverable deformation. These lightweight materials have many applications, not limited to, shock absorption, sensing, and highly compressible piezoelectrics.
Modeling of Biopsy Device for In-Situ Endoscopic Tissue Sampling
Biliary biopsy procedure is a process conducted to obtain cell/ tissue samples from the inside of the bile duct to predict the presence of malignant tissues. The sample obtained is analyzed to decide whether the tissue is cancerous in nature. This biopsy process is performed conventionally by two main procedures, brush cytology and needle with or without forceps. Both these procedures have proven to have either one or more of the three problems which are that they are either not able to produce the required tissue yield, have low sensitivity or are very invasive in nature. We have therefore come up with a novel design which at the microscale is a thin walled cylindrical tool with an aspect ratio of 3:8. Through numerical simulations (FEM) and experimental analysis of the scaled up prototype, the method and magnitude of actuation in terms of displacement and cutting force withstanding ability have been found out. Further work will involve actual fabrication of the biopsy tool by either micro- laser machining or microscale Electrical Discharge Machining (EDM). This final tool will be tested in an artificial bile duct phantom.
Nanoarchitected Interfaces and Ceramic Layer for the Creation of Thin and Durable Thermal Barrier Coatings
Thermal barrier coatings are used on combustion lines, blades and other hot sections of gas turbines allowing them to operate at temperatures above the melting temperature of the superalloy. The insulating ceramic layer is subjected to a combination of mechanical, chemical, and thermal stresses causing delamination at the metal-ceramic interface and premature cracking of the ceramic layer. We aim to improve the toughness of the interface through the introduction of hierarchical nano-sutures to promote adhesion through interlocking, improve flaw tolerance by engineering crack propagation pathways and prevent macroscopic buckling by limiting crack growth below the critical flaw size. The ceramic layer is nano architected to have a spinodal structure(Figure) with high thermal shock resistance, ultra-low thermal conductivity, and tailorable mechanical properties to prevent premature spalling.
Modeling of a CFRP Support Tube to house the ATLAS Inner Detector
The Large Hadron Collider(LHC) is being upgraded to the High-Luminosity Large Hadron Collider(HL-LHC), increasing the luminosity of the particle accelerator by a factor of 10. This will increase the number of collisions that occur in a given amount of time, allowing the experiments to gather more data and observe rare new phenomena. The largest experiment at the LHC is the ATLAS particle detector. The aim of this project is to design, and through numerical simulations, model a CFRP(Carbon Fiber Reinforced Polymer) tube. This support tube will house the Inner Detector of the ATLAS experiment, the Inner Detector being the first part of ATLAS to see the decay products of the particle collisions. Abaqus/CAE will be used to construct a numerical model of the tube and Python scripts will be written to run multiple simulations and perform parametric studies. These parametric studies will help decide important specifications for the tube, such as the laminate stacking sequence to be used for its construction.
Nano-origami Shape Memory Hydrogels
The goal of this project is to design and fabricate unique metamaterials with architectures based on the waterbomb Origami structure. Hydrogels exhibiting shape memory will be used for the fabrication using two-photon nanolithography. These hydrogels exhibit shape memory through reversible cross-links that are sensitive to stimuli like heat, light, pH etc. The origami structures that we are trying to design switch between two stable configurations upon the application or release of a compressive force. This can be reproduced in shape memory hydrogels through their stimuli-responsive shape change. Successful replication of this behaviour would enable us to use this technology in stimuli-triggered actuation, drug delivery, production of membranes with variable permeability etc. My work with the group predominantly lies in the design of the waterbomb tessellations and finding ways to achieve the aforementioned goals.