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Zwitterions 鈥� a common macromolecule found in human cells 鈥� are being used by researchers at 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 鈥� the word 鈥榋witter鈥� meaning 鈥榟ybrid鈥� 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 鈥� homing in on the zwitterion鈥檚 chemically neutral but water-loving ability.

鈥淢edical 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,鈥� Naficy said.

鈥淭he 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,鈥� Naficy added. 鈥淏y using Zwitterion-coated materials, we aim to decrease the risk of blood clots and increase the lifespan of heart valves and other medical implants.鈥�

A zwitterionic coating has been created by the team, and it has been found that on areas of the material 鈥榩ainted鈥� with the coating 鈥� only a few nanometres thick 鈥� it successfully created a layer and bubble of water, like a 鈥榳atery armour鈥�. On material without the coating, it repelled and spread water beyond the material鈥檚 boundaries.

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

鈥淲e 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,鈥� said another University of Sydney researcher, Dr Sepehr Talebian, who along with Naficy is a member of聽. The team鈥檚 greatest challenge is to determine how many zwitterions are 鈥榡ust right鈥�; something the university has described as 鈥渁 biomedical goldilocks problem鈥�.

鈥楾he interplay between grafting density and protein biofouling of polymer brushes: curious case of polyzwitterions鈥�, a 2025 paper by the team on the potential of zwitterions in biomedicine 鈥� intended to provide an in-depth blueprint for the design of surface coating technologies 鈥� has been published open access in Cell Biomaterials and you can read it at .

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