Potentialities of ultrasounds for the nondestructive evaluation of cell adhesion

The aim of this paper is to present the potentialities of ultrasounds to investigate the mechanical properties of a cell/substrate interface. The adhesion process plays a major role in the development of osteoblastic cells on various substrates used in orthopedic applications such as metals, bioceramics, etc. Particularly, cell adherence appears to be a critical factor in the colonization process. High-frequency and low-power ultrasounds seem to be an appropriate tool for a nondestructive evaluation of interface properties. First, we present the results obtained with bulk longitudinal and shear waves under an arbitrary incidence over an aluminum-adhesive interface. This study was performed for an industrial application of bonding. The results clearly show the sensitivity of shear waves for the evaluation of the adhesion quality owing to the shear solicitations at the interface they induce. A model of ultrasound interactions with a boundary subject to varying degrees of adhesion has been developed and compared to the experiments. Second, we investigated osteoblastic cell cultures with a high-frequency acoustic microscope working at 50 MHz. The images obtained in the shear mode reveal a better contrast than those obtained in the longitudinal mode. For the time being, these results are qualitative, and theoretical models have to be developed according to the point of view of biologists.