CONCLUSIONS AND OUTLOOK - Nanoindentation with Biological Applications - page 346

The development of a compliant material-optimized nanoindentation
system should driven by instrument manufacturers. For this to happen,
companies must be convinced of the economic need for such a
system; the thin films and microelectronic devices industries motivated
development of today's nanoindenters. Currently there are a number of
commercial nanoindentation systems on the market, and thus a number
of different manufacturers. Novel developments in the past decade or
more have included coupled instrumented indentation and AFM devices
and indenters that function inside the chamber of an electron microscope.
The developments continue to be driven towards advanced applications
for elastic-plastic materials, and not yet for biological systems.
It is hoped that this collection of chapters has demonstrated the
research potential for nanoindentation of biological materials, while
alluding to other related applications in biomedicine that would
justify the infrastructure and development costs of optimized system
development. The instrumentation requirements for an optimized
instrument were discussed in Chapter 3 of this volume, with particular
emphasis on load and displacement resolution and range, and the critical
need for environmental control. Data analysis techniques for materials
with responses more complex than elastic-plastic were summarized in
Chapters 4 and 5. Given the large body of literature that has supported
the widespread adoption of commercial indenters for elastic-plastic
materials, a similar research effort will be required in support of new
approaches to instrumentation and data analysis, to add to the relatively
small body of current literature reviewed in this volume. It is worth
noting at this point that the mechanical properties of biological materials
are more complicated than the simple linearly viscoelastic or poroelastic
approaches considered to date. Ongoing research into indentation of
materials exhibiting responses that are nonlinear viscoelastic, hyperelastic,
multiphasic and exhibiting advanced poroelastic behavior is still needed.
In conjunction with the development of hardware and software
optimized to handle soft, compliant and time-dependent materials, there
are additional considerations related to standards for the calibration of
indenter tips and validation of system performance. Material standards
development clearly presents a different need than instrumentation or