Nanoindentation of histological specimens: Mapping the elastic properties of soft tissues

Abstract

Although alterations in the gross mechanical properties of dynamic and compliant tissues have a major impact on human health and morbidity, there are no well-established techniques to characterize the micromechanical properties of tissues such as blood vessels and lungs. We have used nanoindentation to spatially map the micromechanical properties of 5-mum-thick sections of ferret aorta and vena cava and to relate these mechanical properties to the histological distribution of fluorescent elastic fibers. To decouple the effect of the glass substrate on our analysis of the nanoindentation data, we have used the extended Oliver and Pharr method. The elastic modulus of the aorta decreased progressively from 35 MPa in the adventitial (outermost) layer to 8 MPa at the intimal (innermost) layer. In contrast, the vena cava was relatively stiff, with an elastic modulus >30 MPa in both the extracellular matrix-rich adventitial and intimal regions of the vessel. The central, highly cellularized, medial layer of the vena cava, however, had an invariant elastic modulus of ~20 MPa. In extracellular matrix-rich regions of the tissue, the elastic modulus, as determined by nanoindentation, was inversely correlated with elastic fiber density. Thus, we show it is possible to distinguish and spatially resolve differences in the micromechanical properties of large arteries and veins, which are related to the tissue microstructure.

Acquisition of Structure-guiding and Structure-forming Properties during Maturation from the Pro-silicatein to the Silicatein Form

“…For the nanoindentation experiments the TriboScope nanoindenter (Hysitron, Minneapolis, MN) mounted on an atomic force microscope (AFM) (Veeco, Santa Barbara, CA) was used following the procedure described by Li et al (26) and Akhtar et al (27). A spherical diamond tip of 1 m radius was used.…”

“…Indent locations were selected manually with each indent situated at least 3 m apart. The characteristics for the properties of the glass substrate (Young's modulus, E ϭ 70 GPa and Poisson's ratio, ϭ 0.23) were adopted from Akhtar et al (27). Prior to each nanoindentation test, the thermal drift was recorded and implemented in the assessment of the hardness and elastic modulus analyses.…”

Tissue elasticity and the ageing elastic fibre

“…5a-c Measuring biomechanical properties at increasing length scales. a In general, the elastic moduli of the constituent ECM molecules are higher than elastic moduli of the connective tissues themselves (Akhtar et al 2009). In order, therefore, to understand the mechanical role played by age-related changes in molecular abundance, distribution and structure it is necessary to characterise the mechanical properties of tissues at the nano-scopic, micro-scopic and macro-scopic lengths scales.…”

Quantifying Micro-mechanical Properties of Soft Biological Tissues with Scanning Acoustic Microscopy

“…The use of higher frequency excitation provides higher spatial resolution but reduces signal level dramatically due to attenuation. When operated at 1GHz, the spatial resolution of the SAM is about 1 μm, which is considerably better than what is currently achievable through nanoindentation [2] and makes SAM potentially a high spatial resolution tool for the study of the micromechanical properties of biological tissue. Furthermore, SAM imaging is both non-destructive and occurs in a hydrated environment, thereby facilitating the imaging of native tissue structures.…”