Simultaneous real-time viscoelasticity, mass and cell cycle monitoring for single adherent cancer cells

Cancer is a complex disease caused by the combined effects of genetic and environmental factors. Evidently, there exists a correlation between the surrounding environment of a cell, its biophysical properties and health. Information gained from biomechanics has led to an improved understanding of the way diseases evolve and their progression cycle, providing methods targeted towards curing these diseases. Countless studies have been carried out on the mechanisms underlying cell cycle progression. More particularly, these studies on the mechanics of individual cells have pointed to their coordination, which helps us understand cellular metabolic and physiological process better. Development of more precise, versatile and reliable measurement tools and techniques will provide a greater understanding of cellular behavior and biophysical properties. Micromechanical systems (MEMS) technology can provide these tools – for analyzing single cells and providing important and useful information of their biophysical properties. In modern research, the ability to reliably investigate and understand these cellular properties requires measurement devices that provide high sensitivity, high throughput, and adaptability to include multiple on-chip functionalities. Many MEMS-based resonant sensors have been extensively studied and used as biological and chemical sensors. However, previous works have shown that there are several technology limitations that inhibit application of various MEMS-sensors to mechanical measurement and analysis, including insufficient cell capture efficiency, media perfusion for long term growth, cell adhesion and cell movement/spreading and cell-sensor modelling. Cellular mechanics and viscoelastic properties are known to play a role in biological processes such as cell growth, stem cell differentiation, cell crawling, wound healing, protein regulation, cell malignancy and even apoptosis (programmed cell death). Thus, an accurate measurement of stiffness and growth is fundamental to understanding cellular proliferation in cancer. Capturing these biophysical properties of cancer cells over the duration of their growth cycle through MEMS devices can help provide a better insight into the mechanics of the metastasis of cancer cells. Meanwhile, many MEMS sensing devices still require further development and characterization to reliably investigate long-term cell behaviors. This dissertation focuses on characterization of our MEMS resonant sensors to address current challenges in the measurement of long-term biophysical behaviors of cells across its cell cycle. The amplitude and frequency of MEMS resonant pedestal sensors were used in conjunction with a vibration induced and optically-sensed phase shift of target light incident on an adhering sample to extract the loss tangent - a measure of the relative viscoelasticity of soft materials. This observed phase shift, combined with a representative two-degree-of-freedom Kelvin-Voigt model, is used to simultaneously obtain the elasticity (stiffness), viscosity and mass associated with individual adherent cancer cells. The research is unique as it decouples the heterogeneity of individual cells in our population and further refines our viscoelastic solution space. This novel development enables long-term simultaneous measurement of changes in stiffness and mass of normal and cancerous cells over time. This is the first investigation of the time-varying simultaneous measurement of viscoelasticity and mass for individual adherent cells using our MEMS resonant sensors