Fracture mechanics of the cell wall of Chara corallina

Previous mechanical studies using algae have concentrated on cell extension and growth using creep-type experiments, but there appears to be no publis hed study of their failure properties. The mechanical strength of single la rge internode cell walls (up to 2 mm diameter and 100 mm in length) of the charophyte (giant alga) Chara corallina was determined by dissecting cells to give sheets of cell wall, which were then notched and fractured under te nsion. Tensile tests, using a range of notch sizes, were conducted on cell walls of varying age and maturity to establish their notch sensitivity and to investigate the propagation of cracks in plant cell walls. The thickness and stiffness of the walls increased with age whereas their strength was l ittle affected. The strength of unnotched walls was estimated as 47 +/- 13 MPa, comparable to that of some grasses but an order of magnitude higher th an that published for model bacterial cellulose composite walls. The streng th was notch-sensitive and the critical stress intensity factor K-1c was es timated to be 0.63 +/- 0.19 MNm(-3/2), comparable to published values for g rasses.