Team:University College London/Module 2/Characterisation

Description | Design | Construction | Characterisation | Shear Device | Modelling | Results | Conclusions

Characterisation

The characterisation of curli expression will be done via a Congo Red agar assay. Congo Red is a diazo dye that causes cells expressing curlis to be stained red. Hence, Congo Red agar provides a convenient assay to determine if the expression of curlis has been successful.

Besides the expression of curlis, we also want to ascertain the shear resistance of the biofilm formed by the curliated cells. As such, we will also be analysing this by determining the critical shear forces involved in the attachment and detachment of cells from plastic surfaces. We will be doing this with a device modelled on the concept of a LH Fowler Cell Adhesion Measurement Module, which creates a variable shear gradient across the surface of the biofilm, thereby allowing us to ascertain the critical shear stresses at which our cells adhere and detach from the plastic surfaces.

The following equation allows us to determine the degree of shear stress our cells are exposed to in our experimental shear device:

τ_r = Shear stress at radius r [N.m^-2]

τ_c = Shear stress at critical radius [N.m^-2]

μ = Viscosity of fluid [N.s.m^-2]

N = Rotational speed of the shear device [s^-1]

r = Distance from the centre of the disc [m]

x = Distance between the top and bottom disc [m]

Hence by determining the critical shear radius at which cells begin to detach, we can determine the critical shear stress.