Biomedical Engineering Reference
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later in Fig. 10-5 ). One remarkable and unique feature is the simultaneity
of surface scanning and indentation of biomembranes. In the present
context, the instrument is also capable of the now-celebrated “Relative
Microelastic Mapping” 10 , i.e. to resolve the local mechanical compliance
and material properties of a single biological cell. AFM-based indentation
recently becomes an attractive method to investigate cellular nano-
biomechanics. Properties such as elastic modulus of cell membranes, 11
turgor pressure, and surface properties of a single bacterium 12 can be
quantified to a certain accuracy surpassing many conventional methods.
Force
Cantilever beam
(with a spring
constant)
α
Indentation
depth
Elastic
biomembranes
Figure 10-2. Schematic of an AFM applied for nanoindentation test.
2.3. Nanoindentation
Micro- and nano-indentation have been widely used to characterize a
wide range of hard materials such as ceramics, metals and hard
biomaterials ( e.g. natural and prosthetic bones, hydroxyapatite). External
load is applied to the sample surface via the hard indenters of steel,
diamond or silicon nitride in the shapes of sphere, Vickers (square based
pyramid), Knoop (rectangular based pyramid) and Berkovich (triangular
based pyramid), leaving a permanent dent. Hardness of the sample is
defined to be the ratio of applied load to the indenter-sample contact area
 
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