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1. Statistics of noisy growth with mechanical feedback in elastic tissues

   https://doi.org/10.1073/pnas.1816100116  

   Damavandi, Ojan Khatib ; Lubensky, David K. ( February 2019 , Proceedings of the National Academy of Sciences)

   Tissue growth is a fundamental aspect of development and is intrinsically noisy. Stochasticity has important implications for morphogenesis, precise control of organ size, and regulation of tissue composition and heterogeneity. However, the basic statistical properties of growing tissues, particularly when growth induces mechanical stresses that can in turn affect growth rates, have received little attention. Here, we study the noisy growth of elastic sheets subject to mechanical feedback. Considering both isotropic and anisotropic growth, we find that the density–density correlation function shows power law scaling. We also consider the dynamics of marked, neutral clones of cells. We find that the areas (but not the shapes) of two clones are always statistically independent, even when they are adjacent. For anisotropic growth, we show that clone size variance scales like the average area squared and that the mode amplitudes characterizing clone shape show a slow$1/n$decay, where n is the mode index. This is in stark contrast to the isotropic case, where relative variations in clone size and shape vanish at long times. The high variability in clone statistics observed in anisotropic growth is due to the presence of two soft modes—growth modes that generate no stress. Our results lay the groundwork for more in-depth explorations of the properties of noisy tissue growth in specific biological contexts.

    

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2. Growth of tumor emboli within a vessel model reveals dependence on the magnitude of mechanical constraint

   https://doi.org/10.1093/intbio/zyaa024  

   Kulwatno, Jonathan ; Gearhart, Jamie ; Gong, Xiangyu ; Herzog, Nora ; Getzin, Matthew ; Skobe, Mihaela ; Mills, Kristen L ( January 2021 , Integrative Biology)

   null (Ed.)

   ABSTRACT Tumor emboli—aggregates of tumor cells within vessels—pose a clinical challenge as they are associated with increased metastasis and tumor recurrence. When growing within a vessel, tumor emboli are subject to a unique mechanical constraint provided by the tubular geometry of the vessel. Current models of tumor emboli use unconstrained multicellular tumor spheroids, which neglect this mechanical interplay. Here, we modeled a lymphatic vessel as a 200 μm-diameter channel in either a stiff or soft, bioinert agarose matrix to create a vessel-like constraint model (VLCM), and we modeled colon or breast cancer tumor emboli with aggregates of HCT116 or SUM149PT cells, respectively. The stiff matrix VLCM constrained the tumor emboli to the cylindrical channel, which led to continuous growth of the emboli, in contrast to the growth rate reduction that unconstrained spheroids exhibit. Emboli morphology in the soft matrix VLCM, however, was dependent on the magnitude of mechanical mismatch between the matrix and the cell aggregates. In general, when the elastic modulus of the matrix of the VLCM was greater than the emboli (EVLCM/Eemb > 1), the emboli were constrained to grow within the channel, and when the elastic modulus of the matrix was less than the emboli (0 < EVLCM/Eemb < 1), the emboli bulged into the matrix. Due to a large difference in myosin II expression between the cell lines, we hypothesized that tumor cell aggregate stiffness is an indicator of cellular force-generating capability. Inhibitors of myosin-related force generation decreased the elastic modulus and/or increased the stress relaxation of the tumor cell aggregates, effectively increasing the mechanical mismatch. The increased mechanical mismatch after drug treatment was correlated with increased confinement of tumor emboli growth along the channel, which may translate to increased tumor burden due to the increased tumor volume within the diffusion distance of nutrients and oxygen. 

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3. Impact of tumor-parenchyma biomechanics on liver metastatic progression: a multi-model approach

   https://doi.org/10.1038/s41598-020-78780-7  

   Wang, Yafei ; Brodin, Erik ; Nishii, Kenichiro ; Frieboes, Hermann B. ; Mumenthaler, Shannon M. ; Sparks, Jessica L. ; Macklin, Paul ( January 2021 , Scientific Reports)

   Colorectal cancer and other cancers often metastasize to the liver in later stages of the disease, contributing significantly to patient death. While the biomechanical properties of the liver parenchyma (normal liver tissue) are known to affect tumor cell behavior in primary and metastatic tumors, the role of these properties in driving or inhibiting metastatic inception remains poorly understood, as are the longer-term multicellular dynamics. This study adopts a multi-model approach to study the dynamics of tumor-parenchyma biomechanical interactions during metastatic seeding and growth. We employ a detailed poroviscoelastic model of a liver lobule to study how micrometastases disrupt flow and pressure on short time scales. Results from short-time simulations in detailed single hepatic lobules motivate constitutive relations and biological hypotheses for a minimal agent-based model of metastatic growth in centimeter-scale tissue over months-long time scales. After a parameter space investigation, we find that the balance of basic tumor-parenchyma biomechanical interactions on shorter time scales (adhesion, repulsion, and elastic tissue deformation over minutes) and longer time scales (plastic tissue relaxation over hours) can explain a broad range of behaviors of micrometastases, without the need for complex molecular-scale signaling. These interactions may arrest the growth of micrometastases in a dormant state and prevent newly arriving cancer cells from establishing successful metastatic foci. Moreover, the simulations indicate ways in which dormant tumors could “reawaken” after changes in parenchymal tissue mechanical properties, as may arise during aging or following acute liver illness or injury. We conclude that the proposed modeling approach yields insight into the role of tumor-parenchyma biomechanics in promoting liver metastatic growth, and advances the longer term goal of identifying conditions to clinically arrest and reverse the course of late-stage cancer.

    

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4. Continuum interpretation of mechano-adaptation in micropatterned epithelia informed by in vitro experiments

   https://doi.org/10.1093/intbio/zyad009  

   Cook, Bernard L. ; Alford, Patrick W. ( August 2023 , Integrative Biology)

   Epithelial tissues adapt their form and function following mechanical perturbations, or mechano-adapt, and these changes often result in reactive forces that oppose the direction of the applied change. Tissues subjected to ectopic tensions, for example, employ behaviors that lower tension, such as increasing proliferation or actomyosin turnover. This oppositional behavior suggests that the tissue has a mechanical homeostasis. Whether attributed to maintenance of cellular area, cell density, or cell and tissue tensions, epithelial mechanical homeostasis has been implicated in coordinating embryonic morphogenesis, wound healing, and maintenance of adult tissues. Despite advances toward understanding the feedback between mechanical state and tissue response in epithelia, more work remains to be done to examine how tissues regulate mechanical homeostasis using epithelial sheets with defined micropatterned shapes. Here, we used cellular microbiaxial stretching (CμBS) to investigate mechano-adaptation in micropatterned tissues of different shape consisting of Madin–Darby canine kidney cells. Using the CμBS platform, tissues were subjected to a 30% stretch that was held for 24 h. We found that, following stretch, tissue stresses immediately increased then slowly evolved over time, approaching their pre-stretch values by 24 h. Organization of the actin cytoskeletal was found to play a role in this process: anisotropic ally structured tissues exhibited anisotropic stress patterns, and the cytoskeletal became more aligned following stretch and reorganized over time. Interestingly, in unstretched tissues, stresses also decreased, which was found to be driven by proliferation-induced cellular confinement and change in tissue thickness. We modeled these behaviors with a continuum-based model of epithelial growth that accounted for stress-induced actin remodeling and proliferation, and found this model to strongly capture experimental behavior. Ultimately, this combined experimental-modeling approach suggests that epithelial mechano-adaptation depends on cellular architecture and proliferation, which can be modeled with a field-averaged approach applicable to more specific contexts in which change is driven by epithelial mechanical homeostasis.

   Insight box Epithelial tissues adapt their form and function following mechanical perturbation, and it is thought that this ‘mechano-adaptation’ plays an important role in driving processes like embryonic morphogenesis, wound healing, and adult tissue maintenance. Here, we use cellular microbiaxial stretching to probe this process in vitro in small epithelial tissues whose geometries were both controlled and varied. By using a highly precise stretching device and a continuum mechanics modeling framework, we revealed that tissue mechanical state changes following stretch and over time, and that this behavior can be explained by stress-dependent changes in actin fibers and proliferation. Integration of these approaches enabled a systematic approach to empirically and precisely measure these phenomena.

    

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5. Development and Optimization of a Novel Centrifugal Bioreactor with a Real-Time Monitoring Sensor for T Cell Exhaustion with Applications in Cancer Immunotherapy

   Brenden Fraser-Hevlin, Kitana M. ( November 2021 , Annual meeting American Institute of Chemical Engineers)

   Cancer has been one of the most significant and critical challenges in the field of medicine. It is a leading cause of death both in the United States and worldwide. Common cancer treatments such as radiation and chemotherapy can be effective in destroying cancerous tissue but cause many detrimental side effects. Thus, recent years have seen new treatment methods that do not harm healthy tissue, including immunotherapy. Adoptive cell therapy (ACT) is one form of immunotherapy in which patients’ immune cells are modified to target cancer cells and then reintroduced into the body. ACT is promising, but most current treatments are inefficient and costly. Widespread implementation of ACT has been a difficult task due to the high treatment cost and inefficient methods currently used to expand the cells. Additionally, if the manufacturing process is not carefully controlled, it can result in the cells losing their cancer-killing ability after expansion. To address the need for an economically feasible culture process to expand immune cells for immunotherapy, our laboratory has designed a centrifugal bioreactor (CBR) expansion system. The CBR uses a balance of centrifugal forces and fluid forces, as shown in Figure 1, to quickly expand infected CD8+ T-cells from a bovine model up to high population densities. With other applications, the CBR has achieved cell densities as high as 1.8 x 108 cells/mL over 7 days in an 11.4-mL chamber. For this study, our goal is to begin validating the CBR by optimizing the growth of CEM (human lymphoblastic leukemia) cells, which are similar cell to cytotoxic T lymphocytes (CTLs). This can be accomplished by measuring kinetic growth parameters based on the concentrations of glucose and inhibitory metabolites in the culture. We hypothesize that by designing a kinetic model from static culture experiments, we can predict the parameters necessary to achieve peak CEM and eventually CTL growth in the CBR. We will report on kinetic growth studies in which different glucose concentrations are tested, and a maximum specific growth rate and Monod constant determined, as well as studies where varying levels of the inhibitory growth byproducts, lactate and ammonium, are added to the culture and critical inhibitor concentrations are determined. Another recent conceptual development for the design of the CBR is a real-time monitoring and feedback control system to regulate the cellular environment, based on levels of surface co-receptors and mRNA signaling within the culture. Prior studies have pinpointed T cell exhaustion as a significant issue in achieving successful immunotherapy, particularly in treatments for solid tumors; T cell exhaustion occurs during a period of chronic antigen stimulation when the cells lose their ability to target and kill cancer cells, currently theorized to be associated with particular inhibitory receptors and cytokines in the immune system. Designing a system with a fiber optic sensor that can monitor the cell state and use feedback control to regulate the pathways involved in producing these receptors will ensure the cells maintain cytotoxic properties during the expansion process within a Centrifugal Fluidized Expansion we call the CentriFLEX. In this presentation, we will also report on early results from development of this exhaustion monitoring system. In brief, achieving optimal kinetic models for the CBR system and methods to prevent T cell exhaustion has the potential to significantly enhance culture efficiency and availability of immunotherapy treatments. 

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