Paper
Journal of Materials Chemistry B
domains (Fig. 4(A)).24b,26 It was interesting to note that, all
hydrogels exhibited a negative thermo-responsive swelling
behavior. Exposure of the hydrogels to a higher temperature
(37 1C) led to shrinking in volume. For gel 1-3 and gel 4, they
contracted more at 37 1C than at 20 1C. Comparing HEAA
containing copolymer with PEGMEA containing copolymer, we
can see incorporation of more PEG reduced de-swelling and
shrinkage of the gel confirming other work indicating that
increasing PEG content decreased the thermo-responsiveness
and slows the phase transition of such copolymers.27 When the
hydrogels were exposed to 20 1C again, they recovered their
initial swelling ratio. Swelling of the hydrogels was reversibly
changed between the two temperatures. The interesting swelling
properties of the copolymers show they may find some potential
applications in drug delivery as the decrease in the volume of the
gel will result in release of entrapped drug.
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Conclusions
In conclusion, we describe the design and synthesis of hydrogel
adhesives, which combine a mussel inspired adhesion compo-
nent DOPA, with a biocompatible PEG segment in a highly
branched structure. The resulting polymer forms gels in a short
time after UV curing, and these gels possess strong cohesive
strength. The lap-shear strength of the adhesives could be
increased by substituting HEAA for PEGMEA (i.e. reducing the
PEG content) and it was found that those containing the cross-
linking segment PEGDMA were stronger than those with PEGDA.
The tissue adhesive potential was demonstrated through lap-shear
adhesion measurements on both borosilicate glass and porcine
skin, and also through tensile test measurements on a bovine
heart tissue wound model, producing bond strengths greater
than PEG-based adhesives. This novel class of thermo-sensitive
copolymers with low cytotoxicity represents a facile and versatile
synthetic route to strong mussel-inspired polymer hydrogels with
an accurately controlled swelling to fit in different clinical applica-
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Acknowledgements
Health Research Board (HRB) of Ireland and Science Foundation
Ireland (SFI), SFI Principal Investigator programme, DEBRA
Ireland, University College Dublin, Strategic and Major Initiative
2014 are gratefully acknowledged for funding.
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