Liquid-crystal elastomers (LCEs) uniquely combine molecular ordering with entropic elasticity. The result is a class of anisotropic elastomers with remarkable properties spanning stimuli responsive actuation to exceptional dissipation of mechanical energy.
Our group has recently developed a range of photopolymerizable LCE resins and inks which we 3D print using direct ink writing (DIW) and digital light processing (DLP) technologies. The combination of our chemistries and these 3D printing technologies allows facile production of some of the largest LCE devices ever produced - on a scale finally suitable for real-world applications such as spinal implants and football helmets.
In this webinar, we will briefly introduce LCEs and our 3D printing methods. Next, we will demonstrate our methods and instrumentation that have enabled our fundamental characterization of these exceptional materials. To measure the rate-dependence of DLP-printed LCE lattices, we used compression testing with strain rates ranging from 0.21 to 220 % s-1 and compared the changes in strain energy density and peak stresses with lattices printed from traditional elastomers. With anisotropic DIW-printed LCE devices we studied the dependence of quasi-static (modulus, strain energy density) and dynamic (dynamic modulus and tan delta between 0.1 - 100 Hz) mechanical properties on loading direction. Additionally, using dynamic testing we studied the long-term performance of a semi-crystalling LCE 3D printed spinal device. By subjecting prototype devices to 1 M compressive cycles under physiological conditions we measured the change in mechanical properties and demonstrated our device’s fatigue resistance.
Overall, this webinar covers a range of quasi-static and dynamic mechanical testing methods which we perform using the ElectroForce 3200 instrument to characterize these highly complex and fascinating materials.
About the Speakers
Dr. Chris Yakacki
Dr. Chris Yakacki received his Ph.D. in mechanical engineering at the University of Colorado Boulder in 2007. During his graduate studies, he helped co-found Medshape, Inc. - a university-based startup focused on developing novel shape-memory devices. Dr. Yakacki worked as the principal scientist at Medshape from 2007-2011, during which time he helped clear the first shape-memory polymer devices through the USFDA. This includes the morphix suture anchor and exoshape anterior cruciate ligament (ACL) fixation device. He returned to academia in 2012 and joined the faculty at the University of Colorado Denver. He received the prestigious NSF Career Award to investigate liquid-crystal elastomers for biomedical applications. He has published over 50 peer-reviewed publications and raised over $2M in federally funded research. He is dedicated to once again translating his research from the university into the marketplace with Impressio - another university-based startup now focused on commercializing liquid-crystal elastomers.
Dr. Devesh Mistry
My interests lie in the fundamental physics behind the mechanical properties of anisotropic and functionalised polymers. I completed my PhD in 2018 in the School of Physics and Astronomy at the University of Leeds, UK. Supervised by Professor Helen Gleeson, my PhD focused on unresolved inconsistencies in our knowledge of LCE mechanical behaviours. In this process I discovered the inherent negative Poisson’s ratio (auxetic) behaviour of LCEs.
Following my PhD, I joined Prof. Chris Yakacki’s group at the University of Colorado Denver as a postdoctoral fellow - supported by a Lindemann Trust Fellowship. Here my research has focused on using 3D printing to understand the role of order and disorder in the exceptional dissipative properties of LCEs.
To date I have published nine peer-reviewed papers and I hold one patent. From March 2021 I will be commencing a Leverhulme Trust Early Career Fellowship at the University of Leeds, UK.
I am a PhD candidate in Mechanical Engineering at the University of Colorado Denver under the tutelage of Prof. Chris Yakacki. My research focuses on how to tailor bulk liquid crystal elastomer (LCE) structures across different length scales (e.g. meso, micro, and macro) to better dissipate mechanical energy. In the course of my research, I have discovered several different molding and manufacturing techniques through the use of additive manufacturing as well as helping to improve synthetic methods for the thiol-acrylate LCE chemistry. One of my greatest achievements to date includes creating a scalable and tailorable method to use digital light processing to 3D print LCE structures that would otherwise be difficult to impossible to fabricate.
In my downtime on campus from researching LCEs, I am often tinkering with 3D printers. My knowledge and abilities with 3D printing led to an opportunity to work as a consultant for 3D printing PEEK, and I have success with 3D printing other engineering polymers such as PPSU.
I currently have six peer-reviewed papers, including a recent publication in Advanced Materials for DLP printing LCEs.
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