Coatings & surface treatment
in roughly 10–20% of cases, varying by study. Urinary catheters are a major source of healthcare-associated infections, accounting for most catheter-associated urinary tract infections (CAUTIs). Severe cases can lead to bloodstream infection, with mortality reported up to 10% in vulnerable patients.
Hydrophilic coatings provide some protection against this problem, in the sense that they are inherently anti-fouling. Because they are so slippery, it is hard for bacteria to adhere to the medical device surface. For instance, zwitterionic coatings – a type that has been drawing a lot of attention lately – work by pairing positively and negatively charged ions within the same molecule. This attracts water molecules, creating a watery barrier that bacteria struggle to colonise.
Other types of coating feature antimicrobial agents, such as antimicrobial peptides or silver nanoparticles, embedded within a polymer matrix. These work by damaging the outer membranes of any bacteria they encounter, leading to the destruction of the pathogen. Meanwhile, the research community is turning its focus to advanced coatings that bring together several different types of protection. A coating might repel bacteria, kill them and disrupt biofilm formation, either sequentially or simultaneously.
“Overall, the field of hydrophilic coatings is evolving from purely passive anti-fouling towards smart, stimuli-responsive active defence,” explains Hongyu Zhang, an associate professor in the Department of Mechanical Engineering at Tsinghua University, Beijing. “Current efforts focus on developing coating systems with improved biocompatibility and more robust anti-fouling efficacy across diverse physiological environments.”
He adds that some coatings now integrate therapeutic functions. For instance, drug-eluting hydrophilic coatings can be applied to coronary stents, delivering drugs in a time-controlled manner to prevent post-surgical complications. “These advances are expected to broaden the clinical applicability of hydrophilic coatings for infection-prone implanted medical devices,” says Zhang. Last year, Zhang’s team announced the development of a new hydrophilic lubricating coating for ureteral stents in ‘A Hydrophilic Lubricating Coating with Dual Functions of Antibacterial Adhesion and Urease- Responsive Bactericidal Activity for Urinary Tract Implantable Devices’. Ureteral stents (an implanted urinary device) are prone to bacterial colonisation: as many as 60–80% form a biofilm, with around 5% of patients developing a urinary tract infection as a result. Patients with diabetes mellitus or renal failure are at particular risk of serious consequences.
Put into practice
In common with other medical devices, ureteral stents can benefit from several types of hydrophilic coating. Some coatings use a passive, anti-fouling approach, applying zwitterionic polymers or other hydrophilic substances to form a robust layer of hydration. The idea is to prevent bacteria from sticking to the surface and forming biofilms. Others feature drug-eluting coatings. They gradually release antibiotics, antimicrobial peptides, or silver nanoparticles, with a view to killing any bacteria they contact. While both strategies have their benefits, Zhang maintains that each has its drawbacks too. “Drug- eluting systems often suffer from initial burst release,
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