CELLS AND MEMBRANES - Nanoindentation with Biological Applications - page 320

1.2. Soft tissue membrane
Soft tissue normally provides connections and supports for structures
or organs in the body. For example, skin, blood vessel and cornea are
a few among many tissue membranes. In general, they are anisotropic
and inhomogeneous materials exercising mechanical non-linearity and
viscoelasticity. Most soft tissues resemble nonlinear stiff gels with
significant internal loss when subject to mechanical shear, but become
fluidic under compression. 5
1.3. Hydrogel membrane
A hydrogel is a polymeric chain network that is insoluble in an aqueous
environment, yet contains very high water content (up to 99%).
Resembling natural tissues with excellent biocompatibility and
processing amiability, these biomimetic gels are widely used in
biomedical applications such as prosthetic tissues and artificial skins for
wound healing. Among limited types of hydrogels successfully used in
tissue engineering or drug delivery, agarose and alginate are most
popular due to their excellent availability and biocompatibility. Agarose
is natural polymer derived from agar, while alginate is derived from
seaweed. However, hydrogel-based tissues in general possess poor
mechanical properties compared with their natural counterparts
(commonly 100 times lower). Various methods have been developed
to improve their mechanical properties, e.g ., UV cross-linking. 6 In order
to gauge and to validate their performance, there is an urgent need to
develop synergistic mechanical characterization techniques.
2. ExperimentalSetup
There are a few experimental techniques to characterize the mechanical
properties of biological cells and membranes. To align with the main
theme of this topic, only indentation-based methods and instruments are
discussed in this chapter.