A quasistatic nanoindentation technique, enhanced by scanning probe microscopy, was used to measure cuticle stiffness of live Drosophila melanogaster during its larval, pupal, and early adult development in vivo. Stiffness was defined as the reduced elastic modulus (E(r)), which is a material property related to the elastic modulus. E(r) was measured at the local contact while indenting the live sample at a constant loading rate using a spherical tip. E(r) was derived from the resultant force-displacement curves. Insect cuticle exhibits viscoelastic behavior. Constant loading rate quasistatic measurements were used so that the effects of viscosity and contact force adhesion introduced systematic measurement effects. E(r) values were as follows: larvae, mean (SE), 0.39 (0.01) MPa; the puparium without evidence of adult structures 15.43 (1.78) MPa; and the adult, measured in the puparium at the completion of metamorphosis, 4.37 (0.31) MPa. Thus, as expected, the puparium and adult cuticle were very much stiffer than larval cuticle. Results also indicated stiffness variation that related to developmental events. This study has shown that this quasistatic nanoindentation-scanning probe microscopy approach is a suitable method for analyzing live biological samples.

Ultrasonically induced nanoscale fatigue and friction reduction phenomena are researched for nanometer order thick protective overcoats. The newly developed method described here is a synergy of the nanometer scale quantitative nanoindentation/scratch technique and ultrasonic excitation. A standing ultrasonic wave is generated at the sample holder during the quasi-static nanoindentation/scratch test at an excitation frequency of several hundreds of kilohertz. Due to the fact that high strain rates are being generated at the surface of the sample, nanofatigue phenomenon followed by delamination and overcoat chipping can be observed. Statistical investigation of fatigue inducing parameters, such as critical quasistatic load and amplitude of oscillations, leads to a means of comparative sample characterization.

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