The role of the membrane in the hen's egg as a model for increasing the toughness of engineered brittle materials

Eggshell and the attached membrane are the focus of many fields of research, but their mechanical properties as a biomineralised composite are seldom explored. This investigation aimed to asses the influence of the membrane on energy dissipation during macroscopic structure failure, and if this effect could be reproduced with artificial membranes for later use in biomimetic materials. Compression tests followed by fracture pattern analysis were conducted for five types of manipulated egg halves: samples with and without the natural membrane, and three samples where the membrane was replaced with artificial membranes made from epoxy resin, polyurethane resin, or wood glue. To preserve the shell's shape, the natural membrane was removed with NaClO. Significant differences regarding the fracture forces between samples with the natural membrane and no membrane (20 % decrease of average), and the natural and artificial membranes (30 % increase of average) were measured. Fracture pattern analysis and investigation of the total work performed during compression testing revealed the highest improvements in toughness for the artificial polyurethane-resin membrane. Without any membrane, very small amounts of work were required to completely shatter the egg, and no fragment cohesion was observed. The presence of the membrane significantly enhanced the effective toughness of the eggshell, and the biomimetic abstraction of this concept is considered feasible for further investigation involving engineered brittle materials.