▎ 摘　　要

NOVELTY - Composite hydrogel (208) comprises graphene oxide flakes distributed in and covalently bonded to a thermo-responsive hydrogel polymer, where the swelling ratio for the composite hydrogel is at least 50% greater than the swelling ratio for the thermo-responsive hydrogel polymer in the absence of the graphene oxide flakes at a temperature below the lowest critical solution temperature of the composite hydrogel. USE - The composite hydrogel is useful in a microfluidic device, lens structure (all claimed), micromechanical systems, microelectromechanical systems and lab-on-a-chip devices. ADVANTAGE - The composite hydrogel: has a swelling ratio of at least 50%, preferably at least 100% greater than the swelling ratio of the thermo-responsive hydrogel polymer in the absence of graphene oxide flakes at 10 degrees C (claimed); utilizes the graphene oxide flakes, which exhibits good thermal conductivity and high photothermal conversion capabilities for infrared radiation, and reduces the volume of material needed to provide an operable actuator; is photopatternable; and provides the microlenses with fast response characteristics. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for: (1) a microfluidic device comprising: a flow channel (202) having an internal surface (204) that defines an internal diameter (206) of the flow channel; and a valve comprising the composite hydrogel affixed to the internal surface of the flow channel, where in a swollen state, the composite hydrogel has a volume sufficient to block fluid flow through the flow channel; (2) a method (M1) for using the microfluidic device, comprising heating the composite hydrogel in the swollen state to a temperature sufficient to shrink the volume of the swollen composite hydrogel and permit fluid flow though the flow channel; (3) a lens structure comprising: a fluid cavity; a fluid housed within the fluid cavity, where the fluid forms a meniscus configured to act as a lens; and a ring actuator comprising the composite hydrogel disposed around the fluid, where, when the composite hydrogel is in a swollen state the lens has a first focal length, and when the composite hydrogel is in an un-swollen state the lens has a second focal length that differs from the first focal length; and (4) a method (M2) for using the lens structure, comprising heating the composite hydrogel in the swollen state to a temperature sufficient to shrink the volume of the swollen composite hydrogel, thus changing the focal length of the lens. DESCRIPTION OF DRAWING(S) - The figure shows a cross-sectional view of a microfluidic channel having a micro valve fabricated from the composite hydrogel in a closed position. Flow channel (202) Internal surface (204) Internal diameter (206) Composite hydrogel (208)