Zwitterions sound likes a distant cousin of Twitter (X), but in fact they are a common macromolecule found in human cells. Scientists at the University of Sydney are also now using Zwitterions to create materials that could stop blood clots from forming in medical devices and implants.
With 500,000–600,000 Australians living with heart valve disease ( in 2021 ),medical devices like heart valves and stents play a crucial role in saving lives. But proteins in blood can cling to the sides of the medical implants, building up over time and forming a blood clot. Often this requires invasive surgery to remove or replace 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," says Dr Sina Naficy , who leads a research team developing 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," says Dr Naficy, from the University's School of Chemical and Biomedical Engineering , Faculty of Engineering.
The world is full of positively and negatively charged molecules. Their interaction with one another drives the chemistry of life.
Zwitterions are a remarkable molecule because they are positive and negative at the same time, making them neutral. The word 'Zwitter' reflects this behaviour – it means 'hybrid' in German. They are also very effective at forming bonds with water molecules.
Zwitterions 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.
THE GOLDILOCKS PROBLEM: JUST HOW MUCH ZWITTERIONS IS 'JUST RIGHT'?
Dr Naficy and his team homed in on the Zwitterion's chemically neutral but water loving ability.
Like previous scientific discoveries inspired by nature, Dr Naficy's team was inspired by the cell membrane and is currently working to mimic this. The researchers' aim is to design materials that could extend the lifespan of medical implants.
Currently the team has created a zwitterionic coating where, 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.
"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 Dr Sepehr Talebian from the School of Chemical and Biomedical Engineering.
One of the biggest obstacles scientists want to crack is just how many Zwitterions are 'just right' – a biomedical goldilocks problem.
The team recently published a review in Cell Biomaterials on the potential of Zwitterions in the biomedicine, providing an in-depth blueprint for the design of 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.
"The curious case of Zwitterions means researchers like us are working hard to find the optimal conditions for this macromolecule to realise their full potential."
