ECM macromolecules: height-mapping and nano-mechanics using atomic force microscopy

Characterization of early extracellular matrix secretions in a three-dimensional thixotropic cell culture system

The extracellular matrix (ECM) provides both molecular and physical cues that affect cell phenotype and function, and hence both normal and abnormal tissue development. The evolution of ECM mechanical properties with time is thus of great importance for cell culture. We have developed a thixotropic polymer-silica nanocomposite gel that may be used to characterize the ECM secretions of cells cultured in a three-dimensional environment. This thixotropic gel can be characterized by its liquefaction stress (τ(y)), defined as the minimum shear stress required to liquefy the gel. When cells were cultivated within these gels, τ(y) was observed to change in a predictable fashion according to the cell type and quantity of ECM secreted. A general trend was observed for different cell lines, where τ(y) increased with increasing ECM concentration when cells were cultivated in gels of lower stiffness, and decreased with increasing ECM concentration when cells were cultivated in gels of higher stiffness. A particular gel stiffness could be identified where increasing the ECM concentration did not change the τ(y) of the gels. We have defined the τ(y) at this point as τ(ECM), which is characteristic for the ECM produced by a specific cell type cultured in the thixotropic gel.

Detection of cancerous cervical cells using physical adhesion of fluorescent silica particles and centripetal force

Here we describe a non-traditional method to identify cancerous human cervical epithelial cells in a culture dish based on physical adhesion between silica beads and cells. It is a simple optical fluorescence-based technique which detects the relative difference in the amount of fluorescent silica beads physically adherent to surfaces of cancerous and normal cervical cells. The method utilizes the centripetal force gradient that occurs in a rotating culture dish. Due to the variation in the balance between adhesion and centripetal forces, cancerous and normal cells demonstrate clearly distinctive distributions of the fluorescent particles adherent to the cell surface over the culture dish. The method demonstrates higher adhesion of silica particles to normal cells compared to cancerous cells. The difference in adhesion was initially observed by atomic force microscopy (AFM). The AFM data were used to design the parameters of the rotational dish experiment. The optical method that we describe is much faster and technically simpler than AFM. This work provides proof of the concept that physical interactions can be used to accurately discriminate normal and cancer cells.