It
is desired to create skin strain sensors composed of multifunctional
conductive hydrogels with excellent toughness and adhesion properties
to sustain cyclic loadings during use and facilitate the electrical
signal transmission. Herein, we prepared transparent, compliant, and
adhesive zwitterionic nanocomposite hydrogels with excellent mechanical
properties. The incorporated zwitterionic polymers can form interchain
dipole–dipole associations to offer additional physical cross-linking
of the network. The hydrogels show a high fracture elongation up to
2000%, a fracture strength up to 0.27 MPa, and a fracture toughness
up to 2.45 MJ/m3. Moreover, the reversible physical interaction
imparts the hydrogels with rapid self-healing ability without any
stimuli. The hydrogels are adhesive to many surfaces including polyelectrolyte
hydrogels, skin, glasses, silicone rubbers, and nitrile rubbers. The
presence of abundant zwitterionic groups facilitates ionic conductivity
in the hydrogels. The combination of these properties enables the
hydrogels to act as strain sensors with high sensitivity (gauge factor
= 1.8). The strategy to design the tough, adhesive, self-healable,
and conductive hydrogels as skin strain sensors by the zwitterionic
nanocomposite hydrogels is promising for practical applications.
Four 3-D coordination polymers of lanthanide with a tetra(amino acid) ligand, 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetrapropionic acid (H4L, 1), were synthesized. The structure of the Gd(III) complex was characterized. The fluorescence of the Eu(III) complex can be modulated by Ag+.
Tough and self-adhesive zwitterionic hydrogels with ionic conductivity have been prepared, showing high and linear strain sensitivity for detecting human motions.
Biotissue adhesives and antibacterial materials have great potential applications in wound dressing, implantable devices, and bioelectronics. In this study, stretchable tissue adhesive hydrogels with intrinsic antibacterial properties have been demonstrated by copolymerizing zwitterionic monomers with ionic monomers. The hydrogels are stretchable to about 900% strain and show a modulus of 4−9 kPa. The zwitterionic moieties provide strong dipole−dipole interaction, electrostatic interaction, and hydrogen bonding with the skin surface, and thus show adhesion strength values of 1−4 kPa to skin. Meanwhile, the copolymerized cationic or anionic monomers break the intrinsic electrostatic stoichiometry of the zwitterionic units and thus mediate the electrostatic interactions and the adhesion strength with the surface. The stretchable hydrogels form a robust and compliant (due to low modulus and stretchability) adhesive to skin, rubber, glass, and plastics, and could be repeatedly peeled-off and readhered to the skin. Moreover, the abundant quaternary ammonium (QA) groups in the zwitterionic moieties and the added QA groups endow it outstanding antibacterial properties (>99%). These stretchable tissue adhesive antibacterial hydrogels are promising for wound dressings and implantable devices.
Responsive
hydrogel actuators have promising applications in diverse
fields. Most hydrogel actuators are limited by slow actuation or shape
transformations. This work reports on snap-buckling motivated jumping
of thermoresponsive hydrogel bilayers. The bilayers are composed of
poly(NIPAM-co-DMAPMA)/clay hydrogel with different
lower critical solution temperatures in each layer, and thus undergo
slow reversible curling/uncurling at temperature changes. The gels
are adhesive to numerous materials including aluminum. The adhesion
between the gels and an aluminum ratchet is utilized to constrain
the thermoresponsive deformation of the bilayers to store elastic
energy. When the accumulated elastic energy overwhelms the gel–aluminum
adhesion, snap-buckling takes place to abruptly release the accumulated
energy, which motivates the bilayer to jump. The jumping direction,
start time, height, and distance are controlled by the geometry of
the bilayers or the ratchet. This work paves a novel way for the rapid
actuation of responsive hydrogels in a controlled manner and may stimulate
the development of novel hydrogel devices.
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