Preparation and High-temperature Anti-adhesion Behavior of a Slippery Surface on Stainless Steel

The overall goal of this experiment is to describe how to fabricate slippery surfaces with high-temperature resistance and to investigate the anti-adhesion effect of the as-prepared surfaces at high temperatures. This method can help answer key questions in the biomedicine field. Such as, soft tissue adhesion problem on the electrosurgical instruments.

The main advantage of this technique is that the prepared slip surfaces can achieve excellent adhesion at high temperatures. Demonstrating the procedure will be Liu Guang, a graduate student from my laboratory. To begin this procedure, design and fabricate the photomask as outlined in the text protocol.

Next, wash the stainless steel plate in alkaline solutions at room temperature for 15 minutes. Using an ultrasonic cleaning machine, thoroughly clean the plate at working frequency of 40 kilohertz in an ultrasonic power of 500 watts. Then rinse it sequentially with deionized water and hexane, acetone, and ethanol for 10 minutes each.

Place the washed plate on a hotplate set to 150 degrees Celsius. Cover the stainless steel with a sheet of aluminum foil and leave it on the hotplate for 30 minutes to dry. After this, transfer the steel to a spin cutter placing it in the center.

Using a dropper, deposit about 1 milliliter of positive photoresist on the plate starting from the center and moving toward the edge until the entire plate is covered. Next start the spin cutter spinning at 700 rpm for six seconds and then increase to 1500 rpm for 15 seconds to evenly spread the photoresist. Then release the vacuum valve.

Using a pair of tweezers, remove the coated steel from the spin cutter. Keep the steel on a hotplate at 120 degrees Celsius for two minutes to bake the photoresist. Next transfer the stainless steel to the vacuum valve of the photomatography machine.

Set the exposure time to 25 seconds and turn the photomatography machine on. After this remove the steel. Submerge it in developer solution for one minute to remove the photoresist without exposing it to UV light.

Then remove the plate from the developer solution and wash it with deionized water. Dry the washed plate under nitrogen gas. Next place the dried steel on a hotplate.

Bake it at 120 degrees Celsius for two minutes. Using an upright microscope with a magnification of 100 times, inspect the obtained photoresist texture on the stainless steel. To begin, prepare 200 milliliters of chemical etching solution in a 500 milliliter beaker.

Then add the stainless steel. Leave the plate in the solution for 10 minutes. Using tweezers, remove the chemically etched steel.

Wash with deionized water for one minute. Dry using nitrogen gas. Use an ultrasonic cleaning machine to clean the steel in acetone for five minutes to remove the photoresist texture.

Next dry the etched plate with the nitrogen gas. Use a steady stream of deionized water to clean the chemically etched stainless steel. Dry with nitrogen gas.

Using a hotplate, heat the steel to 100 degrees Celsius for 30 minutes to completely dry the surface. Next transfer the steel to an RF plasma machine. Use an RF power of 100 watts, a system pressure of 100 millibar, and flow rate of 20 SSCM to hydroxylate the steel with an O2 plasma treatment for 10 minutes.

After this prepare one milliliter OTS solution in anhydrous toluene. Transfer the etched steel in the OTS solution. Seal the beaker and let it rest for four hours at room temperature.

Then remove the steel from the solution and clean it with anhydrous toluene. Using an ultrasonic cleaning machine, clean the plate for 10 minutes. Dry it with nitrogen gas.

To begin use a dropper to deposit approximately 10 milliliters of silicone oil onto the OTS coated chemically etched stainless steel. Next use an optical stereomicroscope to observe the wetting process of the silicone on the steel surface. Place the steel plate in a vertical position for one hour to remove any excess oil.

Then deposit a four microliter droplet of water on the slippery silicon surface. Load the steel into an optical microscope and tilt it to about two degrees. At a low magnification, observe the water droplet to confirm that it can easily move on the slippery surface.

Using tweezers, transfer the steel onto a hotplate. Set the temperature to analyze the anti-wetting behaviors at different high temperatures as outlined in the text protocol. Fix a high-speed camera to a tripod and direct it toward the steel.

After adjusting the focus, use a microsyringe to deposit 10 microliters of water on the slippery surface and record the movement of the water droplet at a frame rate of 500 hertz. Stop recording when the droplet slides off the steel slippery surface. Then analyze the slippery surface's anti-adhesion effects on soft tissue as outlined in the test protocol.

In this study, a slippery surface is prepared by adding silicone oil to OTS coated chemically etched stainless steel. After the wetting processing is complete, a visible oil layer can be distinguished from the dry surface. The slippery property is then investigated depositing a droplet of water on the prepared surface when it is oriented at an angle of two degrees.

The yellow dotted line marks the point of contact and the water droplet is seen to float and slide along the surface. Next the anti-wetting behaviors are investigated at various high temperatures. At 200 degrees Celsius, the water droplet is initially seen to firmly contact the surface but that contact decreases over time.

At 6200 milliseconds, the droplet begins to slide off the surface. At 250 degrees Celsius, the initial contact area of the droplet is seen to be significantly smaller. At this temperature, the droplet begins sliding off the surface after only 800 milliseconds.

However, at 300 degrees Celsius the droplet is immediately unstable on contact and slides off the surface rapidly after only 250 milliseconds. Then the anti-adhesion effect of the slippery surface on soft tissue is evaluated my measuring the adhesion force. The adhesion force is seen to be 0.80 plus or minus 0.18 newtons on the smooth stainless steel and 0.04 plus or minus 0.02 newtons on the slippery surface.

Thus, there was an order of magnitude difference in the adhesion force between the slippery surface and the smooth stainless steel surface. Once mastered, this technique can be done in 12 hours if it is performed properly. This method can provide insight into designing and fabricating electrosurgical instruments with slippery surfaces for effective adhesion effect.

It can also be applied to other systems such as lubrication of controls and adhesion of agents. While attempting this procedure, it's important to remember to avoid touching the hotplate when it is at high temperatures. After its development, this technique paved the way for researchers in the field of biomedical engineering to solve soft tissue adhesion problems in electrosurgical instruments.

After watching this video, you should have a good understanding of how to fabricate a slippery surface with high temperature resistance.