Liquid crystals are phases of matter intermediate between the liquid and the solid phase. They are fluids made by components that spontaneously align with each other. When this spontaneous alignment is impossible, topological defects form. We study topological defects in various settings in liquid crystals. 

Topological defects in cells. Many cell types align just like liquid crystals do, and form topological defects. In particular, the types of defects formed by monolayers of cells closely resemble those formed by nematic liquid crystals in 2 dimensions. There is increasing evidence that cells near topological defects experience a different level of stress than the other cells. With the use of topographic patterns, we investigate the similarities and differences between these two systems in order to understand more about the self-organization of cells in analogy with self-organization in liquid crystals (main contact: Kirsten Endresen, Aniruddh Murali). 

In our research, we discovered that some cells accumulate near some type of topological defects. In collaboration with Brian Camley's group, we found that cells tend to divide more frequently near these defects. This suggests that defects help regulate not only dynamics, but also division within a cell layer.

Here is a link to our paper: K.D. Endresen, M.S. Kim, M. Pittman, Y. Chen, F. Serra, "Topological defects of integer charge in cell monolayers", Soft Matter 2021,  10.1039/D1SM00100K  

Check our new preprint: www.biorxiv.org/content/10.1101/2022.12.22.521493v1 

Topological defects at the phase transition. The control of topological defects in "traditional" liquid crystals is still a challenge in many case. In particular, topological defects change dramatically when liquid crystals undergo a transition to a different type of liquid crystal phase. We have explored various phenomena where we observe either the formation of new types of defects at the phase transition, or we can transform a defect into a different one preserving its location (main contacts: Zhaofei Zheng, Sean Hare). 

Here is a link to our papers: S. Hare, B. Lunsford-Poe, M.S. Kim, F. Serra, "Chiral liquid crystal lenses confined in micro-channels". Materials 13, 3761, 2020 ; J. X.Velez, Z. Zheng, D.A. Beller, F. Serra, "Emergence and stabilization of transient twisted defect structures in confined achiral liquid crystals at a phase transition" Soft Matter 17, 3848, 2021

Control of topological defect lines. How can we create an arbitrary pattern of defect lines in nematic liquid crystals? We tried to answer this question in collaboration with Hillel Aharoni's group (Weizmann institute). We found that we can think of defect lines as current lines in a magnetic field - with some differences! With a set of simple rules, we patterned defect lines to draw a heart that "beats" with temperature changes (main contact: Alvin Modin). 

Our recently published paper is here:  https://www.pnas.org/doi/10.1073/pnas.2300833120

Arrays of topological defects. One of the more useful properties of defects is their capability to self-assemble into regular arrays without need for external manipulation. They can be used to create tunable gratings and other optical components. We have created arrays of the so-called “umbilical defects”, which can be used as diffraction gratings tunable with an external electric field. Thanks to a combination of electric field and an array of polymeric micro-pillars we can make the array regular over large areas (main contact: MinSu Kim, now Research Professor @ Department of Nano Convergence Engineering, Jeonbuk National University, Korea).

Here are the links to our publications: M.S. Kim, F. Serra, Crystals 2020: https://www.mdpi.com/2073-4352/10/4/314/htm ; M.S. Kim, F. Serra, Adv. Opt. Mater. https://doi.org/10.1002/adom.201900991; M.S.Kim, F. Serra, RSC Adv. 2018 https://pubs.rsc.org/en/Content/ArticleLanding/RA/2018/C8RA08251K#!divAbstract