Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session D05: Morphogenesis IFocus Recordings Available
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Sponsoring Units: DBIO GSNP DSOFT Chair: Andrej Kosmrlj, Princeton Room: McCormick Place W-178A |
Monday, March 14, 2022 3:00PM - 3:36PM |
D05.00001: Bottom-up synthetic embryology for understanding early human development Invited Speaker: Jianping Fu Early human development remains mysterious and very difficult to study. Recent advances in mammalian embryology, stem cell biology, organoid technology, and bioengineering have contributed to a significant interest in bottom-up, synthetic stem cell-derived models of human development (or embryoids). The controllability and reproducibility of human embryoids coupled with the ease of genetically modifying stem cell lines, the ability to manipulate culture conditions and the simplicity of live imaging make them robust and attractive systems to disentangle cellular behaviors and signaling interactions that drive human embryogenesis. In this talk, I will describe our effort in using human pluripotent stem cells (hPSCs) to develop tractable experimental models of the peri-implantation embryonic development and neurulation. The peri-implantation human embryoids developed by us recapitulate key early post-implantation developmental landmarks successively, including pro-amniotic cavity formation, amniotic ectoderm-epiblast patterning, primordial germ cell specification, and development of the primitive streak with controlled anteroposterior polarity. I will further discuss an hPSC-based neuroectoderm patterning model to recapitulate the formation of the neural plate and another more recently developed, patterned neural tube model with fully defined anterior-posterior and dorsal-ventral axes. |
Monday, March 14, 2022 3:36PM - 3:48PM |
D05.00002: Large-scale cortex-core structure formation in brain organoids Ahmad Borzou, J. M Schwarz, J. M Schwarz Brain organoids recapitulate a number of brain properties, including neuronal |
Monday, March 14, 2022 3:48PM - 4:00PM |
D05.00003: A morphogenetic action principle for thin tissues and the origins of anisotropic growth Dillon J Cislo, Boris I Shraiman How does growth encode form in developing organisms? Many different spatiotemporal growth profiles may sculpt 2D epithelial sheets into the same target 3D shapes, but only specific growth patterns are observed in animal and plant development. The criteria that select for these stereotypic growth patterns and the ubiquity of anisotropic growth remain poorly understood. We propose that nature settles on the 'simplest' growth patterns. Using the geometric formalism of quasiconformal transformations, we demonstrate that growth pattern selection can be formulated as an optimization problem and solved for the trajectories that minimize spatiotemporal variation in areal growth rates and deformation anisotropy. The result is a complete prediction for the growth of the surface, including not only a set of intermediate shapes, but also a prediction for how cells flow along those surfaces. Optimization of growth trajectories for both idealized surfaces and experimentally acquired data show that relative growth rates can be uniformized at the cost of introducing anisotropy. Minimizing complexity can therefore be viewed as a generic mechanism for growth pattern selection and may help to understand the prevalence of anisotropy in developmental programs. |
Monday, March 14, 2022 4:00PM - 4:12PM |
D05.00004: Epithelial tissue as a self-sculpting, viscoelastic slab XinXin Du, Michael J Shelley Epithelial tissues are cell monolayers composed of adhering columnar cells. During embryonic development, in a process called morphogenesis, epithelia actively alter their shape to create various body parts of the animal, making epithelia one of the most active and critical structures in early animal development. Even though epithelial cells exist and move in three dimensions, mathematical models frequently describe them as two-dimensional. With the importance of the third dimension in mind, we have developed a self-sculpting, three-dimensional model of epithelia whose dynamics are driven by active forces on its surface. Our model describes mechanical properties such as viscoelasticity, biologically relevant tissue geometry, fluid surroundings, and active forces that come from the localization of molecular motors to cell surfaces. We represent epithelial tissue as a thick slab, a 3D continuum comprised of a Stokes fluid with extra viscoelastic stress. Employing this model, we can make quantitative predictions about cell shapes, cell dynamics, and the tissue's response to force in a three-dimensional setting, allowing for physics-based studies of animal morphogenesis. |
Monday, March 14, 2022 4:12PM - 4:24PM |
D05.00005: Butterfly scale morphogenesis: Wrinkling on the micron scale Jan F Totz, Anthony McDougal, Mathias Kolle Micron-scale surface modulations such as wrinkles or folds underly a number of modern engineering applications, such as photonic structures in photovoltaics and flexible metasurfaces. Controlled and precise fabrication of these modulations is a challenge for human manufacturing techniques. In stark contrast, biological systems robustly utilize morphological changes in their developmental program to create multi-germ bodies, hairs and scales on spatial scales which would be costly to replicate with human manufacturing. In this talk I will present recent measurements of in-vivo butterfly scale development exhibiting wrinkling. The observations are rationalized with a parsimonious continuum mechanics model. |
Monday, March 14, 2022 4:24PM - 4:36PM |
D05.00006: Active nematic defects and epithelial morphogenesis Farzan Vafa, L Mahadevan Inspired by recent experiments that highlight the role of nematic defects in the morphogenesis of epithelial tissues, we develop a minimal framework to study the dynamics of an active curved surface driven by its nematic texture. Allowing the surface to evolve via relaxational dynamics leads to a theory linking nematic defect dynamics, cellular division rates, and Gaussian curvature. Regions of large positive (negative) curvature and positive (negative) growth are co-localized with the presence of positive (negative) defects. In an ex-vivo setting of cultured murine neural progenitor cells, we show that our framework is consistent with the observed cell accumulation at positive defects and depletion at negative defects. In an in-vivo setting, we show that activity stabilizes a bound +1 defect state by creating an incipient tentacle, while a bound +1 defect state surrounded by two -1/2 defects can create a stationary ring configuration of tentacles, consistent with observations of a basal marine invertebrate Hydra. |
Monday, March 14, 2022 4:36PM - 4:48PM |
D05.00007: Physical limits on size precision in growing organs and cells Daniel McCusker, David K Lubensky Developing organs maintain robust size control in a noisy environment. Measurements of fluctuating asymmetry (FA) in adult Drosophila wings and adult human arms indicate a developmental precision of about 1% in final organ size. This observation invites the question of what sets the 1% level. To address this question theoretically, we investigate fundamental physical limits on setting the size of growing organs. An important feature of these systems is that the organ must decide when to stop growing based on a necessarily noisy estimate of its own size. We use a first-passage formalism to investigate the termination of growth and find that a Kalman filter that minimizes the estimate's dynamical tracking error also comes close to minimizing the organ's final size variance in most parameter regimes. For a simple model in which the concentration of a diluted chemical species is used to measure organ size, the calculated minimum variance works out to be an order of magnitude smaller than the experimental constraint. This suggests either that other downstream noise sources are important or that other considerations impose a noisier mechanism of size measurement. We can also apply our formalism to investigate variance in single cell sizes at division. |
Monday, March 14, 2022 4:48PM - 5:00PM |
D05.00008: Improved Solid Mechanic Model of Aortic Dissection Sanjeev S Dhara, Nabeel Rasheed, Kameel Khabaz, Nhung Nguyen, Kathleen Cao, Cheong Jun Lee, Ross Milner, Luka Pocivavsek Aortic dissections form through a tear in the inner layer of the blood vessel wall, such that a dynamic flap separates two lumens of blood flow. This phenomenon can be modelled as a mechanical fracture problem. The evolution of dissection geometry is influenced by the pressure differential between these two lumens as well as the changing stiffness of the dissection flap. However, current finite element analysis (FEA) models of aortic dissection rarely incorporate either of these characteristics and often use idealized rather than patient-specific geometries. We create a more realistic model of aortic dissection progression via a semiautomatic segmentation and meshing workflow, followed by separation of the complex surfaces of the true and false lumens as well as the flap geometry. This allows us to create FEA models of aortic dissections that incorporate differential pressurization of the true and false lumens while varying the flap's material properties. Through studying the impact of varying these parameters on dissections, we hope to better elucidate why certain aortic geometries are more prone to dissection, thereby improving future clinical decision making. |
Monday, March 14, 2022 5:00PM - 5:12PM |
D05.00009: A Growth-Based Computational Model of Aortic Dissection Morphogenesis Kameel Khabaz, Luka Pocivavsek, Nhung Nguyen, Janet Kang, Seth Sankary, Kathleen Cao, Gordon Kindlmann, Ross Milner Aortic dissections originate with a tear in the inner layer of the aortic wall, compromising its integrity and creating a mechanically unstable system. As the human body’s largest pressurized vessel, the aorta is a complex structure composed of hyperbolic and cylindrical sections. This geometric complexity influences dissection evolution as well as suitability for different modalities of clinical treatment. Concurrently, progression of aortic dissection is marked by dynamic shape changes over time. As such, predicting this deformation is a challenge with major implications in treatment of aortic diseases. We used a finite element analysis (FEA) computational model of the aorta’s complex geometry and anisotropic fiber composition (with the Ogden-Gasser-Holzapfel constitutive model) that incorporates pressurization and growth to predict shape change of aortic dissections over time. We modeled deformation of an aorta from a dissection patient with initial minimal pressurization followed by isotropic growth in the longitudinal and circumferential directions. We observed that the resulting geometry predicted by the FEA model closely replicates the patient’s true dissection evolution.Further refining our computational model may help improve treatment for aortic diseases. |
Monday, March 14, 2022 5:12PM - 5:24PM |
D05.00010: Surface Geometry Analysis of Pathological Aortas for Endovascular Aortic Repair Junsung Kim, Alyssa Varsanik, Blessing Nnate, Kameel Khabaz, Nhung Nguyen, Luka Pocivavsek Endovascular repair (EVAR) is a surgical method to remodel abdominal aortic aneurysms (AAA) by restricting blood flow into the aneurysm sac by inserting a cylindrical stent. However, when the biomechanical stability between the proximal seal zone of the cylindrical stent and ill-defined geometry of the AAA is compromised, Type 1A endoleaks occur, which is persistent perigraft blood flow between the endograft and aortic wall. The complexities of Type IA endoleaks indicate a lack of understanding of the biomechanical interface and geometric compatibility between the two surfaces. The goal of this project is to compare the surface geometry, specifically the curvedness and shape index of aortas that demonstrated successful remodeling after EVAR and aortas with persistent Type 1A endoleaks. We plot the changes of the mean shape index vs. curvedness of the AAAs pre-op and post-op and observed that there is a clear distinction in the trajectories of the surface geometry changes between the two cohorts. By further understanding the 3D geometry of these two cohorts, we hypothesize that we will be able to predict the remodeling potential of AAA. |
Monday, March 14, 2022 5:24PM - 5:36PM |
D05.00011: A Case Study to Predict Endoleaks with Aortic Geometry Blessing Nnate Funding by the University of Chicago Jeff Metcalf Fellowship Grant and the National Institutes of Health (NIH 1R01HL159205-01) |
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