Researchers at the University of Sydney are creating a surface coating that may prevent blood clotting in stents and catheters. The study was published in Cell Biomaterials.
A spiral painted in a Zwitterionic coating is revealed after it is dipped in water with food dye. Image Credit: University of Sydney
Zwitterions are a common macromolecule found in human cells. Researchers at the University of Sydney also use them to develop materials that may prevent blood clots from forming in implants and medical equipment.
Medical devices like heart valves and stents are essential in saving lives, as between 500,000 and 600,000 Australians were estimated to have heart valve disease in 2021. However, over time, blood proteins may adhere to the sides of the medical implants and form a blood clot. Invasive surgery is frequently needed to replace or remove the implant.
Medical implants are constantly under pressure to perform in the human body. A heart valve is constantly under high pressure to pump blood, opening and closing half a billion times over 10 years.
Dr. Sina Naficy, Study Lead, University of Sydney
The research team developed heart valves that are more resistant to blood clots.
The current average lifespan of existing heart valve implants is less than 10 years and there is always a risk of them degrading or complications occurring. By using Zwitterion coated materials, we aim to decrease the risk of blood clots and increase the lifespan of heart valves and other medical implants.
Dr. Naficy, Faculty of Engineering and Member, School of Chemical and Biomedical Engineering, The University of Sydney Nano Institute
There are both positively and negatively charged molecules everywhere. Their mutual interaction is what propels life's chemistry.
Zwitterions are unique molecules that simultaneously carry positive and negative charges, resulting in an overall neutral charge. The German word "Zwitter," which means "hybrid," reflects this behavior. They also do a great job of bonding with molecules of water.
Zwitterions are already present in human cells as a component of the cell membrane. As they pass through the heart and other organs, they form a thin layer of water and ensure that blood and other proteins do not adhere to other surfaces.
“One of the biggest obstacles scientists want to crack is just how many Zwitterions are ‘just right’ – a biomedical goldilocks problem,” said Dr. Naficy.
The “Goldilocks Problem:” Just How Much Zwitterions is “Just Right?”
Dr. Naficy and their group focused on the Zwitterion's affinity for water and its chemical neutrality.
Similar to earlier scientific breakthroughs that drew inspiration from nature, Dr. Naficy's team is currently attempting to replicate the cell membrane. The research aims to create materials that might increase the longevity of medical implants.
The team has developed a zwitterionic coating that effectively produces a layer and bubble of water, resembling watery armor, on portions of the material that have been "painted" with the coating, which is only a few nanometers thick. Water is repelled and dispersed beyond the boundaries of the material on which the coating was not applied.
We are currently exploring new formulations capable of being chemically attached to the surface of any type of implant (made from tissues, metals, or plastics/rubbers) with the aim of reducing their interactions with blood.
Dr. Sepehr Talebian, School of Chemical and Biomedical Engineering, University of Sydney
The number of Zwitterions that are "just right" is a biomedical goldilocks problem, and it is one of the main challenges that scientists are trying to solve.
Demonstration of Zwitterion Surface Coating
The team recently explored the potential of zwitterions in biomedicine, offering a detailed blueprint for designing surface coating technologies.
“There is great potential but what is the best way to use Zwitterions? What is the ideal thickness of the coating? What concentration should we use? We cannot just dip an artificial heart valve in the Zwitterionic substance without investigating the best conditions. Too much, and it could make the clotting worse, too little, and the risk of blood clots remains,” said Dr. Talebian.
“We also need to investigate the best way to ‘anchor’ Zwitterions to the surface of a material, and the best environment for Zwitterions. This includes finding the best concentration of ‘salt’ in a solution with the Zwitterions. Too much salt makes Zwitterionic brushes clump together. We want them to spread evenly across surfaces,” said Dr. Talebian.
“The curious case of Zwitterions means researchers like us are working hard to find the optimal conditions for this macromolecule to realize their full potential,” said Dr. Talebian.
Zwitterions Coated Material, Video 2
University of Sydney researchers have developed a zwitterionic coating which binds with water, creating a watery layer. This is demonstrated here where a heart drawn with the coating is revealed after it is submerged in colored food dye. Video Credit: University of Sydney.
Journal Reference:
Talebian, S., et al. (2025) The interplay between grafting density and protein biofouling of polymer brushes: Curious case of polyzwitterions. Cell Biomaterials. doi.org/10.1016/j.celbio.2024.100005