RegeniTherix™: Optimised Wound Healing
Through Biomarker Detection in a Novel
Thermoreversible Hydrogel Dressing
Worsley GJ, Attree SL,
Knight AE & Horgan AM
Introduction
According to a recent Department of Health white paper (DH 2010a) the annual
budget for the National Health Service stands at over £102bn, and cost efficiency
savings are required. Studies indicate that an equivalent of 3% of this total
expenditure (roughly £3bn of the annual NHS budget) is required for the care
of chronic wounds (Posnett 2007). Unfortunately around 80% of the total cost of
chronic wound care is attributed to wound complications and delayed healing,
and a reduction in dressing cost would have a limited impact on the cost of care
(Drew 2007). Therefore the ability to rationally treat the underlying problems
The Smart Dressing Concept
One of our aims is to produce a system that will enable prompt medical
intervention through the early identification of the underlying causes of delayed
wound healing. This will improve patient quality of life and reduce the costs
associated with wound complications.
The Bioresorbable Scaffold
The smart dressing consists of three
components (see figure 1):-
A
1) A
bioresorbable scaffold to be
placed directly onto the wound.
2) A
thermoreversible hydrogel
which will be introduced following
application of the scaffold and
adsorb analytes via diffusion.
associated with poor or non-healing acute wounds and chronic wounds, that
are failing to advance to acute healing wounds, will allow improved clinical
management. We present here a wound care system developed as part of the
Technology Strategy Board RegeniTherix consortium.
B
The proprietary bioresorbable scaffold developed by our partners at Neotherix
has been rationally designed to meet several criteria. In particular the material
has been developed to support fibroblast migration and proliferation and to
act as a support for the thermoreversible hydrogel. The scanning electron
microscope image of the scaffold in Figure 2, gives an example of the
effect of fibre diameter on the pore size within the scaffold. These structural
characteristics along with the chemical composition of the scaffold were
evaluated to select for optimal performance.
A
3) A
rapid point-of-care device to
measure analyte entrapped in
the hydrogel.
B
C
Figure 2. The RegeniTherix concept.
A) The ‘Smart’ dressing consisting of a
bioresorbable scaffold and the thermally
reversible hydrogel. B) Point of care testing from
the hydrogel trapped analyte.
The Thermoreversible Hydrogel
The proprietary thermoreversible
hydrogel has been specifically
formulated so that its lower gelation
temperature is beneath skin
temperature but higher than normal
room temperatures. This will allow
the point-of-care practitioner to
manipulate the polymer as a liquid
solution; once applied directly to
the scaffold/wound surface it will
heat to above its lower gelation
point and form a gel. Gelation of
the triblock polymer solution is a
physical change brought about by
changes in the polymer solubility
as the temperature is changed.
At temperatures below the Lower
Consolute Solution Temperature
(LCST) of the poly(lactide-coglycolide) (PLGA) polymer blocks,
the triblock copolymer is soluble
in water.
Point-of-Care Analyser
As the temperature is increased
above the LCST, hydrogel bonding
between the PLGA blocks and water
is disrupted resulting in the polymer
becoming increasingly insoluble.
Between the PLGA blocks in the
triblock copolymer is a region that
remains water soluble across the
temperature range. The insoluble
PLGA blocks are able to form
microdomains and bridges between
the polymer chains resulting in gel
formation (see Figure 3). Because
this is a physical process and no
permanent chemical changes occur
it is fully reversible, and the gel is
able to cycle between its liquid and
gel state in response to changes in
temperature. This feature enables us
to release the trapped analyte from
the gel for analysis when we revert it
back into its solution form.
Figure 3. Representation
of a bridged micelle gel
network formed by a
PLG-PEO-PLGA triblock
copolymer above the
LCST of the PLGA block.
The PLGA block forms
insoluble microdomains
( ), surrounded and
interconnected by the
solvated PEO block ( ).
Conclusion
We are developing a smart
dressing system that is designed to
enable point-of-care practitioners
to improve wound management
and reduce the cost associated with
poor wound healing. This will be
Figure 2. Scanning Electron Micrographs of the bioresorbable scaffold demonstrating the tunable nature of
fibre diameter and pore size. A) Fibre mean diameter 1.7 μm. B) Fibre mean diameter 3.3 μm.
C) Fibre mean diameter 6.0 μm.
We have developed a quantitative
duplex assay for the detection of
wound markers Interleukin-6 and
Tumour Necrosis Factor alpha in
hydrogel-based samples. The assay
is an improvement upon a technique
that is becoming a more common
point-of-care assay: the Lateral
Flow Immunosensor (see Figure 4).
With the use of multiple, spectrally
discrete, fluorescent microspheres
it is possible to quantify the
concentration of two or more
analytes contained within the gel
in a single test. This is achieved
through coating multiple capture
antibodies within a test-line.
The signal from each type of
microsphere, which is proportional
to the wound marker concentration,
is read using a commercially
available fluorescence strip reader.
Our assays have been validated
using real human plasma and
hydrogel based samples (see
Figure 4 B). The system has a
detection limit of 48.5 pg/ml for
Interleukin 6 and 55.5 pg/ml for
Tumour Necrosis Factor alpha,
fulfilling the sensitivity requirement
for these wound biomarkers.
A
B
Figure 4. A) The Lateral Flow Immunoassay.
Sample placed upon the sample pad flows along
the strip via capillary action. As the sample moves
conjugate beads are resuspended from the
conjugate pad and flow along with the sample
down the strip. The solution passes the test-line
where an immunosandwich is formed if analyte is
present. The amount of analyte within the sample
is assessed through the intensity of conjugate
build up at the test line. Multiple conjugate species
if distinguishable can be present within an assay
for the detection of different multiple analytes.
B) Graphs A and B show dose response curves
for Interleukin 6 and TNF alpha using multiplex
reagents and hydrogel based samples.
References
achieved through the measurement
of wound markers at the bedside
and faster clinical intervention.
Department of Health (2010) Equity and Excellence. Liberating the NHS. ISBN 9780101788120
Drew P, Posnett J, Rusling L. The cost of wound care for a local population in England. Int J
Wound 2007; 4: 149-55.
Posnett J, Frank PJ. The costs of skin breakdown and ulceration in the UK. In: Pownall M, ed.
Skin Breakdown: The Silent Epidemic. Smith and Nephew Foundation, Hull; 2007: pp 6-12.
Acknowledgments
We would like to thank our project partners:Neotherix Ltd
SensaPharmc Ltd
Complement Genomics Ltd