This review gives a brief overview of microvalves, and focuses on the actuation mechanisms and their applications. One of the stumbling blocks for successful miniaturization and commercialization of fully integrated microfluidic systems was the development of reliable microvalves. Applications of the microvalves include flow regulation, on/off switching and sealing of liquids, gases or vacuums. Microvalves have been developed in the form of active or passive microvalves employing mechanical, non-mechanical and external systems. Even though great progress has been made during the last 20 years, there is plenty of room for further improving the performance of existing microvalves.

http://iopscience.iop.org/article/10.1088/0960-1317/16/5/R01/pdf

A review of microvalves

Stimuli-responsive hydrogels are materials with great potential for development of active functionalities in fluidics and micro-fluidics. Based on the current state of research on pH sensors, hydrogel sensors are described qualitatively and quantitatively for the first time. The review introduces the physical background of the special properties of stimuli-responsive hydrogels. Following, transducers are described which are able to convert the non-electrical changes of the physical properties of stimuli-responsive hydrogels into an electrical signal. Finally, the specific sensor properties, design rules and general conditions for sensor applications are discussed.

/pdf/review-on-hydrogel-based-ph-sensors-and-microsensors-2qfhirc0w6.pdf

Review on Hydrogel-based pH Sensors and Microsensors.

Smart polymers: Physical forms and bioengineering applications

A surgical device comprising a container and a tether used for delivering a sterile appliance into a body cavity during endoscopic procedures. Once positioned in the body cavity, a force is applied to the container through the tether. The force opens the container and releases the sterile appliance into the body cavity. In various embodiments, gas or liquid may be used to open the container.

Sterile appliance delivery device for endoscopic procedures

Surgical instruments and methods for closing a gastrotomy. In various embodiments, the surgical instrument may comprise an overtube that supports a clip magazine therein that houses a plurality of tissue apposition clips in an orientation wherein the upper and lower clip arms thereof are releasably supported in an open orientation. Various embodiments are configured to operably accommodate one or more tissue grasping members for grasping the tissue. Other embodiments comprise clip dispensing adapters that may be affixed to the distal end of an endoscope. The various adapters are configured to support a tissue apposition clip such that the upper and lower clip arms thereof are initially supported in an open orientation relative to each other to enable grasped tissue to be drawn therein. Various tissue apposition clips are disclosed which may be used in connection with conventional tissue anchors and/or sutures.

Tissue apposition clip application devices and methods

This paper reports on the fabrication and test of a hydrogel-actuated microvalve that responds to changes in the concentration of specific chemical species in an external liquid environment. The microvalve consists of a thin hydrogel, sandwiched between a stiff porous membrane and a flexible silicone rubber diaphragm. Swelling and deswelling of the hydrogel, which results from the diffusion of chemical species through the porous membrane is accompanied by the deflection of the diaphragm and hence closure and opening of the valve intake orifice. A phenylboronic-acid-based hydrogel was used to construct a smart microvalve that responds to the changes in the glucose and pH concentrations. The fastest response time (for a pH concentration cycle) achieved was 7 min using a 30-/spl mu/m-thick hydrogel and a 60-/spl mu/m-thick porous membrane with 0.1 /spl mu/m pore size and 40% porosity.

/pdf/a-hydrogel-actuated-environmentally-sensitive-microvalve-for-49h6m3so1m.pdf

A hydrogel-actuated environmentally sensitive microvalve for active flow control

The invention provides hydrogel compositions, components, and hydrogel-actuated or mediated devices, and methods for the incorporation of hydrogel microscale components in microscale devices and systems. The methods and devices result in active microvalves that are useful in microfluidic applications, including analyte sensing, in process chemical and fermentation stream monitoring, and drug delivery. In particular, the devices are useful for controlled drug delivery either in response to a pre-determined stimulus or for pulsatile delivery.

Hydrogel compositions, devices, and microscale components

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A hydrogel-actuated environmentally sensitive microvalve for active flow control

Hydrogel compositions, devices, and microscale components