research activities in 2007 - CSEM

Smart Wound Dressing with Integrated Biosensors
S. Pasche, R. Ischer, S. Angeloni, M. Liley, J. Luprano, G. Voirin
Specific biosensors are being developed for the in situ monitoring of wound healing, focusing on pH measurements and on the detection of
infection markers. Ambulatory, real-time monitoring will be made possible by integration of these sensors in wound dressings.
Online health monitoring often requires hospitalization, which
can become an expensive and inconvenient choice for the
patient. In this perspective, wearable sensors that allow in situ
biosensing without hospital surveillance constitute a very
promising technology. The European project BIOTEX (“biosensing
textile for health management”) [1] aims to integrate
sensors in textiles for medical applications. The CSEM goal is
to develop immunosensors for a continuous control of the
wound healing process, which are based on pH changes, as
well as on the concentration of an inflammatory protein, the
C-reactive protein (CRP).
Sensing principles include the use of responsive hydrogels
that swell in response to changes in the environment
(Figure 1a), and the use of functional surfaces that specifically
recognize the target protein (Figure 1b). Swelling of
pH-responsive hydrogels is a consequence of charging of the
polymer chains that form the hydrogel. Functional surfaces
rely on a dextran polymer layer (OptoDex ® ), which prevents
non-specific adsorption from the biological medium and at the
same time acts as covalent glue for immobilization of the
receptor molecules.
Figure 1: Sensing principle for (a) a responsive hydrogel, and (b) a
protein-selective surface
Detection is based on an optical signal, using the evanescent
field of light propagating along a waveguide, to probe
refractive index changes. Both hydrogel swelling and
biomolecule adsorption induce changes in the refractive index
above the surface, which affect the propagation of the
waveguide mode. An optical sensing system consisting of a
white light source (LED) and a detection spectrometer, which
can be easily integrated into a wound dressing patch, has
been designed (Figure 2).
Figure 2: Optical detection scheme, comprising illumination with
white light, light propagation along the waveguide, and wavelength
detection with a spectrometer.
This system allows in situ optical detection of volume changes
of a hydrogel layer deposited on a waveguide substrate, with
sensitivity better than 10 -4 refractive index units,
corresponding to polymer swelling on the order of 1% and to
an adsorbed mass of ~100 pg/mm 2 .
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Reversible optical monitoring of hydrogel swelling with
response to pH was demonstrated using a pH-responsive
hydrogel (Figure 3a). The range of pH sensitivity can be tuned
by changing the hydrogel chemistry. Monitoring of the
concentration of CRP was performed using a specific surface
chemistry with CRP receptors immobilized on dextran-coated
waveguide chips (Figure 3b).
a)
b)
Figure 3: In situ optical monitoring of (a) pH, using a pH-responsive
hydrogel, and (b) changes in the concentration of CRP in serum,
using a functional surface with immobilized CRP receptors.
In situ measurements are possible after integration of the
biosensor into a wearable sensing patch (< 0.2 cm 2 ) that is
connected via optical fibers to the detection system and power
supply (Figure 4).
Figure 4: Sensing patch design to be later integrated in the wound
dressing
The sensing patch will later be integrated into wound
dressings or bandages, which will provide online information
on the state of the wound healing process. This novel
technology will be particularly valuable in applications such as
the ambulatory supervision of skin grafts and ulcer treatments.
This work is partly funded by the European Commission,
FP6-IST-NMP-2-016789 and FP6-IST-026987. CSEM thanks
them for their support.
[1] www.biotex.eu.com