W. Richard Bowen and Nidal Hilal 4

276 10. FuTuRE PRosPECTs
most AFM studies have so far been carried out under ambient conditions,
whereas many industrial processes operate at reduced or elevated temperatures
and pressures. The more recent development of hot–cold stages
has made possible the application of AFM for both imaging and quantification
of forces of interactions in the temperature range between �90°C
and 250°C. Future development of pressure cells to enable the operation
at both vacuum and pressures higher than atmospheric will further widen
the range of process-relevant environments for further studies.
The application of process engineering knowledge to biotechnology
and medicine is showing huge potential. The integration of cutting-edge
techniques to develop tailored cellular micro-environments as model
systems has proven essential for the systematic investigation of a number
of physiological processes in cell biology. From these studies, it has
become apparent that restoring native functionalities using smart extracellular
matrix (ECM), or tissue, depends on adequate consideration of
interconnected processes that are regulated by biochemical, physical and
mechanical factors in the ECM.
AFM, with its proven capability for nanoscale measurements of biomolecular
interactions, and physical and mechanical properties of materials,
is expected to continue to make invaluable contributions to cell biology
and biotechnology fields. However, new developments are desirable
to improve measurement reliability and to understand the factors that
determine measurement reproducibility. In the same way as closed-loop
scanners have greatly enhanced the metrological capabilities of AFM and
hence the precision in measurement of large biological samples (such as
living cells), there is still much scope for improvements associated with
force measurements. This may be in the area of probe fabrication, providing
cheap sources of cantilevers with high-tolerance spring constants or more
likely in reliable, accurate, non-destructive and (hopefully) simple protocols
for the calibration of existing probe types. Such improvements may
in turn provide an impetus for the development and widespread use of
mathematical modelling (such as the use of finite element techniques) to
interpret force curves in the context of heterogeneous cellular structures –
modern computing now makes such data fitting a tractable problem. Such
approaches require close collaboration between biologists, engineers and
physical scientists.
The integration of AFM and optical techniques for simultaneous interrogation
of biochemical functionalities with physical/mechanical properties
of a cell offers huge benefits and is likely to attract increasing research
efforts. High-speed optical imaging offers the possibility of monitoring
processes that are currently too fast for AFM to interrogate. The present
developments of high-speed AFM imaging are certainly encouraging.
However, progress is required to minimise the tip-surface interactions
that, at these speeds, greatly perturb the surface being imaged.