Investigation On Mechanical Properties Of Eggshell Membranes Based On Nanoindentation

The eggshell membrane(ESM) is a natural biopolymer material, which owns uniquely porous network structure and consists of the inner and outer membranes. Currently, the eggshell membrane has been applied in such fields, medicine, electrochemistry, biometrics, etc. Because ESM is regarded as a kind of soft matter or viscoelastic solid, it is extraordinarily significant to reveal the relationship between its structure and performance. The paper, based on nanoindentation technique, mainly explores the mechanical properties of raw ESM and includes the following three aspects:(1) The modulus and hardness of ESM was investigated with quasi-static measurement. This aspect studies the variation of elastic modulus and hardness of ESM with penetration depth through continuous stiffness measurement. When ESM is penetrated into some depth, the stress-strain curves of ESM are measured and the effect of strain rate on stress is discussed. The deformation mechanism for the membrane-substrate system of inner and outer membrane is analyzed by observing the scanning morphology of residual indentation. The correctness of modulus and hardness in comparison with the results of literature and experiment is carried out.(2) The test of creep and relaxation properties of ESM is carried out with quasi-static approach. The creep and relaxation properties of ESM are tested via adopting the pattern of load and displacement control. The impact of the loading and displacement levels, loading rates, holding time on the viscoelastic performance is primarily analyzed. The creep stress exponent, creep compliance, relaxation modulus and average pore size of ESM are obtained by fitting the experimental results. The distinction of viscoelasitc properties and structure between inner and outer layers is explained on the basis of poroelastic theory.(3) The viscoelastic properites of ESM are obtained with dynamic measurement. This aspect of test is mainly concerned by measuring the storage modulus, loss modulus, loss factor of ESM as a function of force frequency with the method of sinusoidal loading. The reason which leads to the difference of viscous dampening property between inner and outer membrane are illustrated. The influence of penetration depth and loading rate on the dynamic experiment is discussed in detail. The maximum depth and minimum loading rate which make the mechanical behavior of ESM keep in linear viscoelasticity range are determined. The storage modulus is gained by dynamic and quasi-static measurement, respectively.In conclusion, it is found that the outer membrane has the higher stiffness and hardness than the inner one in dried state. The outer ESM shows more apparent relaxation properties and stronger capacity to resist creep deformation. Compared with the outer membrane, the inner one has the larger viscous dampening. Both inner and outer membranes reveal more prominent elasticity behavior than viscosity behavior. The work of this paper will provide references for the bionic application of the eggshell membrane.