Biosensing Detection - Bioinspired Approaches for Human-Centric Technologies - page 99

Fig. 3.8 PDMS soft probe for stereocilia mechanical properties investigation: (a) finite element
method based simulation showing the ring deformation by force application on the probe tip; the
table shows the probe stiffness value in dependence to ring width. (b) A bird's eye picture of the
whole probe: from left to right , attaching pad, mechanical dumping ring, the V-shaped tip .(c)
Example of soft probe approaching the whole bundle of a bullfrog stereocilium

is based on circular mechanical elements (external radius is between 90 and
120 m) able to bear high deformations (Fig. 3.8a ). Tuning the geometrical

dimensions of this soft ring element (table in Fig. 3.8 ) allows obtaining soft probes
whose stiffness values match with the stereocilia bundle stiffness (Fig. 3.8b ). The
V-shaped tip, appropriately functionalized to be adherent to the hair bundle, pushes
the stereocilium as a whole (Fig. 3.8c ).
The probes have been successfully tested on Bullfrog hair cells in ex vivo
experiments. The PDMS soft probes can be designed with compliance matching
that of the cells to be studied, so that they can be used both to deliver stimuli and to
measure forces produced by a wide variety of cells moving back to the rest position.
These probes permit the identification of changes in hair cell stiffness and even
small oscillations with almost no perturbations, to better understand the mechanism
of adaptation and amplification of signal transduction in hair cells. The investiga-
tion of natural mechanoreceptor hair cell adaptation and amplification properties
opens new opportunities to understand illness related to ear-impaired people,
allowing the design for more efficient and miniaturized prostheses (Qualtieri
et al. 2010 ).

μ