Breast tumors are typically surrounded by extracellular matrix (ECM) that is heterogeneous, not just structurally but also mechanically. Conventional rheometry is inadequate for describing cell-size-level spatial differences in ECM mechanics that are evident at micrometer scales. Optical tweezers and passive microrheometry provide a microscale resolution for the purpose but are incapable of measuring ECM viscoelasticity (the liquid-like viscous and solid-like elastic characteristics) at stiffness levels as found in breast-tumor biopsies. Magnetic microrheometry records data on varying microscale viscoelasticity within 3D ECM-mimicking materials up to the biopsy-relevant stiffness. However, the measurement-probe-based microrheometry data has limitations in spatial resolution. Here, we present a probabilistic modeling method-providing analysis of sparse, probe-based spatial information on microscale viscoelasticity in ECM obtained from magnetic microrheometry-in two parts. First, we validated the method's applicability for analysis of a controlled stiffness difference, based on two collagen type 1 concentrations in one sample, showing a detectable stiffness gradient in the interface of the changing concentrations. Second, we used the method to quantify and visualize differences in viscoelasticity within 3D cell cultures containing breast-cancer-associated fibroblasts, and collagen type 1 (both typically present in the tumor ECM). The fibroblasts' presence stiffens the collagen material, which aligns with previous research. Importantly, we provided probabilistic quantification of related spatial-heterogeneity differences in viscoelasticity recorded by magnetic microrheometry, for the first time. The fibroblasts culturing leads to an initially higher spatial heterogeneity in the collagen stiffness. In summary, this method reports on enhanced spatial mapping of viscoelasticity in breast-cancer 3D cultures, with the future potential for matching of spatial viscoelasticity distribution in the 3D cultures with the one in biopsies.

中文翻译：

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使用磁性微流变法对 3D 细胞培养中的空间粘弹性线索进行概率分析。


乳腺肿瘤通常被细胞外基质 （ECM） 包围，这些基质不仅在结构上而且在机械上都是异质的。传统的流变学不足以描述 ECM 力学中细胞大小水平的空间差异，这些差异在微米尺度上很明显。光镊和被动微流变测量为此目的提供了微米级分辨率，但无法测量乳腺肿瘤活检中发现的刚度水平的 ECM 粘弹性（液体状粘性和固体状弹性特性）。磁性微流变测量法记录 3D ECM 模拟材料中不同微尺度粘弹性的数据，直至活检相关刚度。然而，基于测量探针的微流变测量数据在空间分辨率方面存在局限性。在这里，我们提出了一种概率建模方法，对磁性微流变法获得的 ECM 中微尺度粘弹性的稀疏、基于探针的空间信息进行了分析，分为两部分。首先，我们验证了该方法对分析受控刚度差异的适用性，基于一个样品中的两种 1 型胶原蛋白浓度，在浓度变化的界面中显示出可检测的刚度梯度。其次，我们使用该方法量化和可视化含有乳腺癌相关成纤维细胞和 1 型胶原蛋白（通常存在于肿瘤 ECM 中）的 3D 细胞培养物中粘弹性的差异。成纤维细胞的存在使胶原蛋白材料变硬，这与之前的研究一致。重要的是，我们首次提供了磁性微流变仪记录的粘弹性相关空间异质性差异的概率量化。 成纤维细胞培养导致胶原刚度最初较高的空间异质性。总之，该方法报告了乳腺癌 3D 培养物中粘弹性的增强空间映射，未来有可能将 3D 培养物中的空间粘弹性分布与活检中的空间粘弹性分布相匹配。