Uniaxial compression measurement device for investigation of the mechanical stability of biofilms

The mechanical stability of biofilms is important for biotechnology, as slo ughing of the biomass due to mechanical failure of the biofilm matrix can l ead to severe interferences with biofilm processes. In cases of biofouling, biofilms have to be removed, in which case their mechanical stability must be overcome. The apparent modulus of elasticity and the yield strength as obtained from uniaxial compression experiments can be taken as parameters i ndicative for the mechanical stability of a biofilm. A film rheometer is pr esented which allows for the determination of these quantities, using mode! biofilms of Pseudomonas aeruginosa grown on membrane filters. The compress ive stress-strain behaviour up to the point of failure is recorded at a com pression speed of 1 mum s(-1). In accordance with the stress-strain curve, the investigated biofilm can be described as viscoelastic material, which d emonstrates plastic flow properties. The extracellular polymeric substances (EPS), which keep biofilms together, form a temporary network of fluctuati ng junction points. Above the yield point, the gel structure fails and the system behaves as a highly viscous fluid. The apparent modulus of elasticit y and the yield point are considered to be useful parameters for characteri zing the mechanical properties of biofilms. (C) 2001 Elsevier Science B.V. All rights reserved.