Abstract
Commonly synthetic polyethylene glycol polyurethane (PEG–PU) hydrogels possess poor mechanical properties, such as robustness and toughness, which limits their load-bearing application. Hence, it remains a challenge to prepare PEG–PU hydrogels with excellent mechanical properties. Herein, a novel double-crosslinked (DC) PEG–PU hydrogel was fabricated by combining chemical with physical crosslinking, where trimethylolpropane (TMP) was used as the first chemical crosslinker and polyphenol compound tannic acid (TA) was introduced into the single crosslinked PU network by simple immersion process. The second physical crosslinking was formed by numerous hydrogen bonds between urethane groups of PU and phenol hydroxyl groups in TA, which can endow PEG–PU hydrogel with good mechanical properties, self-recovery and a self-healing capability. The research results indicated that as little as a 30 mg·mL−1 TA solution enhanced the tensile strength and fracture energy of PEG–PU hydrogel from 0.27 to 2.2 MPa, 2.0 to 9.6 KJ·m−2, respectively. Moreover, the DC PEG–PU hydrogel possessed good adhesiveness to diverse substrates because of TA abundant catechol groups. This work shows a simple and versatile method to prepare a multifunctional DC single network PEG–PU hydrogel with excellent mechanical properties, and is expected to facilitate developments in the biomedical field.
Highlights
Hydrogels can absorb a large amount of water molecules but not be dissolved in water, because they possess hydrophilic segments in their 3D crosslinked network [1,2]
polyethylene glycol polyurethane (PEG–PU) hydrogel with covalent crosslinking single network was synthesized by a simple pre-polymerization, in which TMP was used as the first crosslinker
The formation of porous structure arose because the frozen water molecules in PU hydrogel were removed by sublimating in vacuo, and the pores were left where ice crystals were first occupied
Summary
Hydrogels can absorb a large amount of water molecules but not be dissolved in water, because they possess hydrophilic segments in their 3D crosslinked network [1,2] On account of their admirable swelling property and eco-friendliness, hydrogels are applied in many fields such as medicine [3,4], agriculture [5,6] and cosmetics [7], etc. Divakaran et al prepared a DC PEG–PU hydrogel with the tensile strength of 0.7 MPa and the breaking elongation of 284% at equilibrium swelling state, in which 1,2,6-hexanetriol and curcumin were used as crosslinkers [34] These studies suggest that the DC PEG–PU hydrogels are able to be fabricated by using the polyhydroxy compound as the second crosslinking agent and the mechanical strength of obtained PEG–PU hydrogels is higher than the single crosslinked PEG–PU hydrogels, but their strength, stretchability and toughness need to be further improved
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