The Research On Preparation And Properties Of AuNPs-PNIPAm/PAAm Hydrogel Actuator Based On Photothermal Conversion Mechanism

Hydrogel is a kind of cross-linked hydrophilic polymer network.It can retain a lot of water and maintain its own three-dimensional structure from dissolved.Hydrogels have drawn numerous attention since the application of hydrogels in the biomedical field in the early 1950 s by Vigelitt and his colleagues.In the past decades,people have designed and synthesized a large number of different kinds of hydrogels,which have a wide range of applications in medicine and drug testing.Traditional hydrogel has the function of carrying and transporting,and can release the substance uniformly and continuously.Different from traditional hydrogels whose property does not change obviously,smart hydrogels can make a specific response to changes in the external environment,when external physical or chemical conditions change such as p H,temperature,solvent,pressure,ionic strength,light,and concentration of specific biomolecules,they can dramatically change their volume,degrade,or develop sol-gel phase change.Environmental triggers can be utilized to achieve specific functions such as drug release,protein isolation and muscle activity.In recent years,hydrogel actuator,as new type device,receives extensive attention due to distinct advantages: mimic human functionality,adaption in aqueous environments,simple designs,and potential applications in various fields,including biology,medicine,microfluidics,and robotics.Among the stimuli-responsive actuators,light-driven actuators are particularly attractive devices.Light enables the rapid on–off switching and higher spatial and temporal resolution than other stimuli.Furthermore,light as a stimulus enables facile operation with removing complex step of installing wire.Here,photothermal hydrogel actuators are designed and fabricated to accomplish a precise hand-like manipulation of encapsulating and finger-like one-by-one bending by light.A thermo-responsive poly(N-isopropylacrylamide)(PNIPAm)active layer and a non-thermo-responsive poly(acrylamide)passive layer are combined to generate a thermal-expansion coefficient mismatch among the interface and this energy eventually transforms into a bending motion.PNIPAm hydrogels undergo a reversible and significant volume reduction above the lower critical solution temperature(LCST)of about 32 ℃.However,acrylamide,which has the similar chemical structure,does not have this unique heat shrinking property.When the outside temperature changes,volume does not change.As an energy transformation agent,the gold nanoparticles doped in the PNIPAm hydrogel absorb the light energy and transform it into thermal energy effectively.Au NPs exhibit surface plasmon resonance(SPR)light absorption because 6s electrons in the conduction band for Au NPs correlated with the electromagnetic field of the incoming light cause collective oscillations of the electron gas.Besides their plasmon resonances,these plasmonic noble metal nanoparticles also have strong absorption on the high-energy due to intrinsic interband transitions.When the two are coupled,sample illumination through exposure to light at wavelengths that coincide with the NPs absorption maxima allows for photothermal heat generation.The resulting nanocomposite actuators exhibit flexible,reversible motions and local hand-like finger flexion driven by either flood illumination or local irradiation.The developed programmable actuators are expected to be an attractive candidate for the next generation of “smart” soft robots.