WFU Physics Colloquium

TITLE: Characterizing the micro-scale mechanical properties of hydrogels and cancer cells

SPEAKER: Xinyi Guo

TIME: Thursday April 23, 2015 at 9:00 AM

PLACE: Room 204 ZSR Library

Tissue engineering strategies nowadays require attention to not only cells, but also to the mechanical properties of the extracellular matrix (ECM). We studied the elasticity of hydrogels formulations frequently used in cell and tissue culturing. A variety of concentrations in a variety of biomaterials, including agarose, alginate, the collagens, fibrin, hyaluronic acid, kerateine, laminin, Matrigel, and polyethylene glycol diacrylate (PEGDA), were tested with atomic force microscopy (AFM). We also determined the Young’s modulus (E) of hydrogels with different concentrations. E tended to increase with increased concentration.

The stiffness (Young’s modulus) of bone marrow stromal cells (BMSCs) co-cultured with multiple myeloma (MM) cells were measured. In our study, we found that both M-BMSCs (BMSCs from MM patient) and MGUS (Monoclonal gammopathy of undetermined significance) cells are stiffer than N-BMSCs (BMSCs from healthy volunteers). Also co-culturing with myeloma cells increased the stiffness of M-BMSCs. On the other hand, co-culturing with the cancerous counterparts did not increase the stiffness of N-BMSCs or MGUS cells. The results also showed that it is CD138- (syndecan-1 negative expressed), instead of CD138+ (syndecan-1 positive expressed), that regulates the stiffness of BMSCs. Western blotting experiments suggested that SDF-1 (Stromal Cell-Derived Factor 1) was expressed more in CD138-. Inhibiting SDF-1 using AMD 3100 or knocking-down CXCR4 in M-BMSCs would decrease the stiffness of M-BMSCs induced by CD138-. Meanwhile, inhibition of AKT (Protein Kinase B) also resulted in decreasing stiffness of M-BMSC when co-cultured with CD138-.

By employing an AFM with 5.3μm diameter spherical probe, we measured the Young’s muduli of individual human mammary epithelial cells. Measurements were taken both on cytoplasmic and nuclear regions. The stiffness of cells in different microenvironments was obtained to show the influence of cell-cell interactions on single cell stiffness. Cells were sorted into 3 categories: isolated cells; cells residing on the periphery of a contiguous cell monolayer; and cells on the inside of a contiguous cell monolayer. Generally, cells become softer as they advance to the tumorigenic phase. However, metastatic cells are stiffer than tumorigenic cells. Moreover, we found normal cells are sensitive to their microenvironment. That is, normal cells inside the monolayer are stiffer than isolated cells. But the stiffness of tumorigenic cells did not show significant differences between different microenvironment.