Surface coating may prevent blood clots in medical implants

Zwitterions — a common macromolecule found in human cells — are being used by researchers at The University of Sydney to create materials that could stop blood clots from forming in medical devices like heart valves and stents. Such devices play a crucial role in saving lives, yet proteins in blood can cling to the sides of the medical implants, building up over time and forming a blood clot; an occurrence that often requires invasive surgery to remove or replace the implant.

Zwitterions are a remarkable molecule because they are positive and negative at the same time, making them neutral — the word ‘Zwitter’ meaning ‘hybrid’ in German. These molecules are especially effective at forming bonds with water molecules and are already in our cells as part of the cell membrane. They create a thin layer of water and make sure blood and other proteins travel through the heart and other organs without sticking to other surfaces.

Now, inspired by the cell membrane, biomaterials engineer Dr Sina Naficy is leading a research team developing heart valves that are more resistant to blood clots — homing in on the zwitterion’s chemically neutral but water-loving ability.

“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,” Naficy said.

“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,” Naficy added. “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.”

A zwitterionic coating has been created by the team, and it has been found that on areas of the material ‘painted’ with the coating — only a few nanometres thick — it successfully created a layer and bubble of water, like a ‘watery armour’. On material without the coating, it repelled and spread water beyond the material’s boundaries.

A spiral painted in a zwitterionic coating is revealed after it is dipped in water with food dye. Image ©Ivy Shih/University of Sydney.

“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,” said another University of Sydney researcher, Dr Sepehr Talebian, who along with Naficy is a member of The University of Sydney Nano Institute. The team’s greatest challenge is to determine how many zwitterions are ‘just right’; something the university has described as “a biomedical goldilocks problem”.

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‘The interplay between grafting density and protein biofouling of polymer brushes: curious case of polyzwitterions’, a 2025 paper by the team on the potential of zwitterions in biomedicine — intended to provide an in-depth blueprint for the design of surface coating technologies — has been published open access in Cell Biomaterials and you can read it at doi.org/10.1016/j.celbio.2024.100005.

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Top image caption: A heart painted in a zwitterionic coating is revealed after it is submerged in water with food dye. Image ©Ivy Shih/University of Sydney.