McMaster researchers develop “smart surface” that repels and accepts specific substances

All photos by Kevin Patrick Robbins, McMaster University.

A team of researchers at McMaster University have devised a “smart surface” that not only repels bacteria, viruses, and living cells but can also be modified to accept specific substances as well, proving useful in medical applications.

Utilizing nanotechnology referred to as surfaces, mixed self-assembled monolayers (SAM) one theoretical possibility would be the ability for replacement heart valves or vascular grafts to bond to the body without risk of infection, blood clotting or rejection. Additionally, the repellent coating has the potential to separate blood and urine from non-targeted elements, reducing the percentage of false positives/negatives in medical testing.  

“The challenge with biomedical applications is that you want bacteria or things in the blood that could cause clotting, to be repelled from the surface,” says Tohid Didar of McMaster’s Department of Mechanical Engineering and School of Biomedical Engineering and the senior author of a recent paper published on the research. “But if you’re putting an implant into someone you also want the tissue around it to attach and integrate with the implant.”

A comparison of how blood droplets behave on a control surface at left and the repellent surface at right.

Dr. Didar and the team at McMaster have added a tiny layer of SAM onto a surface of an implant and then added an FDA approved liquid lubricant that’s compatible with the SAM layer. He equates the SAM layer and the added lubricant to the Teflon layer found on cookware and the oil that is added to a pan to help with the cooking process.

In making the technology “smarter” the research team has identified target markers – specific molecules they are looking for that would match that of the surface layer.  Those molecules basically build themselves into lubricant layer that’s applied to the device, creating a level of cohesion needed to work. The team published their research in a paper titled Lubricant-Infused Surfaces with Built-In Functional Biomolecules Exhibit Simultaneous Repellency and Tunable Cell Adhesion.

“The challenge for us was to make the technology a little bit smarter so that not only would it repels everything, but it promotes adhesion of certain targets on the surface. That’s what this new paper is about,” Didar says.

While this type of technology has been around since as early as 2011—with a research team at Harvard doing the initial research—limitations held it back from medical applications. According to Dr. Didar, the limitations were caused by the coatings natural reaction to repel everything, and only recently has research begun into modifying those reactions. Instead, the technology has worked well from a consumer perspective – windshield wipers, waterproofing phones and repelling bacteria from food-preparation areas. 

The original idea for these repellent surfaces comes from the Nepenthes pitcher plant, which has a super slippery surface that repels everything but that bugs that fall into its trap.

According to McMaster PhD student in Biomedical Engineering and co-author of the study Sara Imani, the repellent coating and a synthetic heart valve could eliminate the need for medicines such as warfarin, which is used to prevent blood clots.

Here, Didar holds a section of catheter that has been coated with the new surface.

“Nobody has tested these on people or even on animals for an extended period of time. We’ve done these tests on implants for up to five or six days,” says Didar. “We’re working with cardiovascular surgeons and they think that if you can prevent clogging and rejection for a couple of days, then the tissue can integrate so the cells could completely cover the surface. You might not even need to add lubricant down the road.”

For now, Didar believes that these few days are the critical test as to whether or not the body will accept or reject the implant. If rejection hasn’t occurred after six days, “things are looking good for the SAM coating.”

Outside the body, selectively designed repellent surfaces could make the aforementioned diagnostic tests much more accurate by allowing only the particular target of a test—a virus, bacterium or cancer cell, for example—to stick to the biosensor that is looking for it, a critical advantage given the challenges of testing in complex fluids such as blood and urine.

The researchers, who collaborated with Jeffrey Weitz of the Thrombosis & Atherosclerosis Research Institute at Hamilton Health Sciences to understand the challenges related to making successful implants, are now working on the next stages of research to get their work into clinical use. The next phase would be animal and human trials, and Didar and the team are also looking for industry-specific companies to partner with them on the project.

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