Liquid seal for compact micropiston actuation at the capillary tip

Abstract

Actuators at the tip of a submillimetric catheter could facilitate in vivo interventional procedures at cellular scales by enabling tissue biopsy and manipulation or supporting active micro-optics. However, the dominance of frictional forces at this scale makes classical mechanism problematic. Here, we report the design of a microscale piston, with a maximum dimension of 150 μm, fabricated with two-photon lithography onto the tip of 140-μm-diameter capillaries. An oil drop method is used to create a seal between the piston and the cylinder that prevents any leakage below 185-mbar pressure difference while providing lubricated friction between moving parts. This piston generates forces that increase linearly with pressure up to 130 μN without breaking the liquid seal. The practical value of the design is demonstrated with its integration with a microgripper that can grasp, move, and release 50-μm microspheres. Such a mechanism opens the way to micrometer-size catheter actuation.

Microfluidics at Fiber Tip for Nanoliter Delivery and Sampling

“…The syringe advanced the liquid front just to the front of the capillary opening. The syringe advanced the liquid front so the capillary filled with liquid. As the 2PP passive valve was not hydrophobic (contact angle around 65° [ 14 ] ) it remained wet from previous droplets and the liquid overfilled the tube. The syringe retracted the liquid front. As the capillary was hydrophobic the liquid was removed more quickly than in the containing tube until being stopped by the 2PP passive valve.…”

“…2) The syringe advanced the liquid front so the capillary filled with liquid. As the 2PP passive valve was not hydrophobic (contact angle around 65° [ 14] ) it remained wet from previous droplets and the liquid overfilled the tube.…”

“…Direct printing at the fiber tip has been achieved for microlens arrays, [ 10 ] structured Surface enhanced Raman scattering (SERs) arrays [ 11 ] and optical waveguides, [ 12 ] force sensors, [ 13 ] or pneumatic actuators as in our previous work. [ 14 ] In this work, we chose to assemble the structure after printing to simplify the fabrication process while providing a more robust fixation resilient to shock and vibration. Such a fabrication process has been demonstrated for optical resonator [ 15 ] at the tip of optical fiber.…”

3D‐Printed Microinjection Needle Arrays via a Hybrid DLP‐Direct Laser Writing Strategy

“…DLP 3D printing is a vat photopolymerization approach in which a DLP projector is used to UV-crosslink a liquid-phase photocurable material in designated locations in a layer-by-layer manner to ultimately produce 3D objects composed of cured photomaterial. [62] Here, we leveraged DLP 3D printing to fabricate batches of arrayed capillaries in a single print run to overcome several drawbacks of recent esDLW approaches for printing 3D micro/nanostructured objects onto mesoscale fluidic components, such as micropiston-based microgrippers [63] and liquid biopsy systems [64] onto fluidic capillaries. First, the geometric control afforded by DLP 3D printing allows for each capillary to be designed with a variable OD to match the dimensions of the capillary base to those of the desired injector system.…”

A comparative review of artificial muscles for microsystem applications

“…Piezoelectric 127 and magnetic 170 actuators can be manipulated with high precision and high speed. Pneumatic artificial muscles have excellent force and locomotion outputs and have be used in microsurgery 171 . However, the response time is relatively long, and the precaution of gas leakage should be considered in some microsurgeries.…”