Materials
Using zwitterionic polymers enhances the performance and biocompatibility of in- body medical devices, reducing fouling and improving longevity.
rate of stent coatings, and prevent the corrosion of stent alloys compared to other materials. Meanwhile, their haemocompatibility has helped in the development of better artificial vascular grafts that are not affected when they contact with blood – other coatings, such as oligo(ethylene glycol) (OEG), have allowed blood to coagulate, leading to thrombosis. Plus, the surface properties of zwitterionic polymers have also helped to prevent the adsorption of non-specific proteins in artificial heart valves. This is helpful for extracorporeal membrane oxygenation (ECMO) devices, too – these are respiratory support systems that pump blood through an artificial lung and back into the patient’s bloodstream. So, they’re constantly in contact with blood. “Zwitterionic polymer coatings resist the protein adsorption and platelet adhesion from human plasma, without the coating having an effect on the permeation of oxygen in the gas filtration membrane,” says Zhang. Another system in contact with blood is dialysis machines. Here, zwitterionic polymers have shown an ability to decrease cell adhesion and reduce protein adsorption, which leads to improved protection against toxins. They could also increase utilisation of VADs, which Zhang notes are often not an option due to their low haemocompatibility.
Other implantable medical devices could benefit from zwitterionic polymers, too – such as neuroprosthetics. “The low fouling, anti- [foreign body reaction] properties allow zwitterionic polymers to be used in implantable neuroprosthetics, to improve their performance and reduce inflammation to the brain once implanted,” says Zhang.
Implantable biosensors, such as glucose sensors, could also benefit. “For biosensing and detection, preventing non-specific protein adsorption increases the signal-to-noise ratio and improves the sensitivity of different biosensors,” Zhang explains. Another application for zwitterionic polymers is improving the performance and biocompatibility of
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different drug delivery vessels. Zwitterionic polymers can improve anti-cancer drug delivery because their anti-fouling and pH response properties enable the vessels to stay in the body longer, which in turn allows them to target the tumour properly while inhibiting its growth. Zwitterionic polymers also enhance cancer diagnosis processes by improving different medical imaging approaches – such as CT scans, MRI, and optical imaging. The zwitterionic coating prevents protein absorption on the contrast agents used in tumour imaging, which enables the agents to last longer in the body. This makes them easier to image. Then there’s ionic skins, which provide non-invasive health monitoring and diagnosis: zwitterionic polymers can be combined with hydrogen bonding networks to create stretchy, flexible materials that function as a wearable ‘skin’. Here, the strong hydration properties of the polymer surface can be used to form ion migration channels using an applied electric field. When this field is applied, cations and anion-resistant ions can be separated easily within the channel, ensuring the skin has a high ionic conductivity, and therefore, a higher sensitivity when monitoring. Finally, among other things, “zwitterionic polymers are being used to improve contact lenses, to mitigate their surface contamination and as a lubricating surface in artificial joints,” says Zhang. Their superhydrophilicity and anti-fouling properties prevent bacterial contamination and inflammatory reactions during use, making the lenses last longer.
More polymers on the market While there are many different types of zwitterionic polymers, they’re increasingly being used to improve the capabilities and longevity of various medical devices.
But when talking about disrupting the status quo – in this case, using PEG – we also have to talk about the commercial and clinical potential of new materials. Indeed, the only disadvantage of zwitterionic polymers that Zhang could think of is the cost and difficulties in processing them. Zwitterionic polymers are good coating materials, he says, but available coating technologies “may not always be [sophisticated] enough to ensure that the final coating performs to its potential”.
Some devices with zwitterionic polymers have already made it to market, yet others are still a work in progress, Zhang adds. “Most of those [on the market] use PMPC polymer, as PMPC was commercialised two decades ago. Other types of zwitterionic polymers are relatively new, and I believe they will be successfully commercialised soon.” With the advantages of these materials gaining steam, it probably won’t be long before we see more of them in real-world settings. ●
Medical Device Developments /
www.medicaldevice-developments.com
John-Fs-Pic/
Shutterstock.com
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