Rapid Transitions of Thermo-Responsive Polymer Networks
Responsive polymers have many key uses including drug delivery, switchable biocompatible coatings, and advanced biointerfaces in bioanalytical devices. Thermo-responsive polymers, where changing the temperature stimulates changes in the polymer properties, are the most common in biomedical applications.
All thermo-responsive polymers have a lower critical solution temperature (LCST). Above or below this temperature determines the state of the polymer. Lowering the temperature of the polymer to below the LCST causes the polymer to exhibit a hydrophilic state in which the structure expands or swells and contains high amounts of water molecules. Increasing the temperature to above the LCST causes the polymer to exhibit a hydrophobic state in which the structure collapses and expels water molecules from its proximity.
Thermo-responsive polymer networks have many different external parameters that affect the response speeds of the collapsing and swelling states. With ambient temperature control and a plasmonic heating technique that optically excites localized surface plasmon (LSP) modes on the surface of Au nanoparticles, the temperature of the polymer hydrogel layer can be precisely manipulated.
By testing different bulk temperatures, longer heating beam pulses, and a variety of temperature change increases, researchers realized response times as low as 1.5 ms for the collapsing state and single digit milliseconds for the swelling state of the polymer hydrogel. With the investigated complex and different response times of thermo-responsive polymer networks, advances can be made in biomedical and miniature actuator applications.
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