Design and fabrication of aspiration microfluidic channel for oocyte characterization

The development potential for oocytes can be predicted by their mechanical properties. One important parameter that is measured to calculate oocyte hardness is Cortical Tension (CT). In this work, for the first time, we present the design, simulation, and fabrication of a new aspiration microfluidic chip to measure the CT of oocytes and then predict their maturation capability in the Germinal Vesicle (GV) stage. This high-performance technique facilitates oocyte characterization and is a promising alternative to traditional methods such as MicroPipette Aspiration (MPA). The proposed technique involves considerably simpler operation, less specialized equipment, and less technical skill than MPA. The proposed microfluidic channel also promises faster measurements. It is shown that in order to completely continue the growth process of oocytes in GV stage, the CT should be in a certain range: very low or very high CTs lead to unsuccessful growth. The obtained results show that 79% of oocytes with the CT between 1.5 and 3 nN/μm reach the Metaphase II (MII) stage, whereas the growth for 78% of oocytes with the CT less than 1.5 nN/μm or higher than 3 nN/μm stops at the GV or Germinal Vesicle Break Down (GVBD) stages. Another property, k_vis, that points to the viscous behavior of oocytes is also measured. It is seen that 80% of GV oocytes with the k_vis values between 15 and 30 k Pa s/m reach the MII stage.

A microfluidic platform for trapping, releasing and super-resolution imaging of single cells

A multi-layer device, combining hydrodynamic trapping with microfluidic valving techniques, has been developed for on-chip manipulation and imaging of single cells and particles. Such a device contains a flow layer with trapping channels to capture single particles or cells and a control layer with valve channels to selectively control the trap and release processes. Particles and cells have been successfully trapped and released using the proposed device. The device enables the trapping of single particles with a trapping efficiency of greater than 95%, and allows for single particles and cells to be trapped, released and manipulated by simply controlling corresponding valves. Moreover, the trap and release processes are found to be compatible with biological samples like cells. Our device allows stable immobilisation of large numbers of single cells in a few minutes, significantly easing the experiment setup for single-cell characterisation and offering a stable platform for both single-molecule and super-resolution imaging. Proof-of-concept super- resolution imaging experiments with mouse embryonic stem cells (mESCs) have been conducted by exploiting super-resolution photoactivated localisation microscopy (PALM). Cells and nuclei were stably trapped and imaged. Centromeres of ∼200 nm size could be identified with a localisation precision of <15 nm.

A microfluidic device for the hydrodynamic immobilisation of living fission yeast cells for super-resolution imaging

We describe a microfluidic device designed specifically for the reversible immobilisation of Schizosaccharomyces pombe (Fission Yeast) cells to facilitate live cell super-resolution microscopy. Photo-Activation Localisation Microscopy (PALM) is used to create detailed super-resolution images within living cells with a modal accuracy of >25 nm in the lateral dimensions. The novel flow design captures and holds cells in a well-defined array with minimal effect on the normal growth kinetics. Cells are held over several hours and can continue to grow and divide within the device during fluorescence imaging.