Li Mengfei, Matouš Karel, Nerenberg Robert
Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, Indiana, USA.
Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, Indiana, USA.
Biotechnol Bioeng. 2022 May;119(5):1301-1313. doi: 10.1002/bit.28056. Epub 2022 Feb 14.
Biofilms are typically heterogeneous in morphology, structure, and composition, resulting in nonuniform mechanical properties. The distribution of mechanical properties, in turn, determines the biofilm behavior, such as deformation and detachment. Most biofilm models neglect biofilm heterogeneity, especially at the microscale. In this study, an image-based modeling approach was developed to transform two-dimensional optical coherence tomography (OCT) biofilm images to a pixel-scale non-Newtonian viscosity map of the biofilm. The map was calibrated using the bulk viscosity data from rheometer tests, based on assumed maximum and minimum viscosities and a relationship between OCT image intensity signals and non-Newtonian viscosity. While not quantitatively measuring biofilm viscosity for each pixel, it allows a rational spatial allocation of viscosities within the biofilm: areas with lower cell density, for example, voids, are assigned lower viscosities, and areas with high cell densities are assigned higher viscosities. The spatial distribution of non-Newtonian viscosity was applied in an established Oldroyd-B constitutive model and implemented using the phase-field continuum approach for the deformation and stress analysis. The heterogeneous model was able to predict deformations more accurately than a homogenous one. Stress distribution in the heterogeneous biofilm displayed better characteristics than that in the homogeneous one, because it is highly dependent on the viscosity distribution. This study, using a pixel-scale, image-based approach to map the mechanical heterogeneity of biofilms for computational deformation and stress analysis, provides a novel modeling approach that allows the consideration of biofilm structural and mechanical heterogeneity. Future research should better characterize the relationship between OCT signal and viscosity, and consider other constitutive models for biofilm mechanical behavior.
生物膜在形态、结构和组成上通常是异质的，导致其力学性能不均匀。力学性能的分布反过来又决定了生物膜的行为，如变形和脱离。大多数生物膜模型忽略了生物膜的异质性，尤其是在微观尺度上。在本研究中，开发了一种基于图像的建模方法，将二维光学相干断层扫描（OCT）生物膜图像转换为生物膜的像素尺度非牛顿粘度图。该图是根据流变仪测试的体粘度数据进行校准的，基于假定的最大和最小粘度以及OCT图像强度信号与非牛顿粘度之间的关系。虽然没有对每个像素进行生物膜粘度的定量测量，但它允许在生物膜内合理地进行粘度的空间分配：例如，细胞密度较低的区域，如空隙，被赋予较低的粘度，而细胞密度高的区域被赋予较高的粘度。非牛顿粘度的空间分布应用于已建立的Oldroyd-B本构模型中，并使用相场连续介质方法进行变形和应力分析。与均匀模型相比，非均匀模型能够更准确地预测变形。非均匀生物膜中的应力分布比均匀生物膜中的应力分布表现出更好的特性，因为它高度依赖于粘度分布。本研究使用基于像素尺度、基于图像的方法来绘制生物膜的力学非均匀性，以进行计算变形和应力分析，提供了一种新颖的建模方法，允许考虑生物膜的结构和力学非均匀性。未来的研究应该更好地表征OCT信号与粘度之间的关系，并考虑用于生物膜力学行为的其他本构模型。
