Organic & Non Organic Shell Hardness Using Nanoindentation

There have been many studies on egg shell hardness in food science research, but it is now the primary makeup of egg shells, calcium carbonate, that is of interest in the development of biomaterials. Synthetic biomaterials have emerged for bone regeneration, among many other uses, providing improved biocompatibility, biodegradability and mechanical properties. Calcium carbonate has been widely studied as a composite in the life sciences, materials science and nanotechnology. Given the wide range of applications needing improved functional and structural properties, it is critical that mechanical properties are known and controlled during formulation of the composite.

Beyond the many traditional mechanical tests (hardness, adhesion, compression, puncture, yield strength, etc.), today’s quality control of advanced, sensitive materials, from gels to brittle materials, requires greater precision and reliability. Traditional mechanical instrumentation, designed for bulk materials, fails to provide the sensitive load control and resolution required. As the size of the material tested became of greater interest, nanoindentation provided a reliable method to obtain essential mechanical information on smaller surfaces, as in biomaterials research. The challenges of biomaterials have required mechanical testing capable of accurate load control on extremely soft to brittle materials, and tests that once needed multiple instruments can now be performed on a single system.

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In conclusion, we have shown how the NANOVEA Mechanical Tester, in nanoindentation mode, provides precise measurement of the mechanical properties of egg shells. Eggs from organically fed chickens were shown to be harder than those from non-organically fed chickens, demonstrating how the composition of biomaterials can affect their behavior for various applications.

Other tests possible with the same system include fracture toughness, fatigue testing and many others; a puncture test with a specific tip geometry could test the resistance of a full egg, and multiple-cycle loading can test fatigue and yield strength. For soft applications such as gels, DMA (dynamic mechanical analysis) measures viscoelastic properties including loss and storage moduli. The NANOVEA nano module suits this testing because its feedback response precisely controls the applied load: the contact point on soft materials is determined by direct load measurement, and its 50 mm movement range accommodates biomaterials such as brain samples. With the controlled XY stage, the same instrument can also measure scratch and marring properties, the coefficient of friction and multi-pass wear.