Coatings & surface treatment
much harder to uniformly coat a braided catheter shaft, a laser-cut stent, or a multilumen catheter in high-volume manufacturing while maintaining batch-to-batch consistency. That is why process development and coating validation often become just as important as coating chemistry itself.”
Emerging coating approaches Where zwitterionic coatings use hydrophilicity to resist fouling, superhydrophobic surfaces take a different approach and draw inspiration from the lotus leaf. They combine low surface energy with micro- or nanoscale surface roughness to create very high water contact angles. Under suitable conditions, this reduces the contact area between a liquid and the underlying material, making proteins, cells and other contaminants less likely to adhere to and accumulate on the surface. Superhydrophobic chemistry includes many approaches, but many incorporate micro- or nanostructures into the implant surface. Combining low surface energy with surface roughness can trap a layer of air between the material and the surrounding liquid, further reducing direct contact. Maintaining this trapped-air layer during prolonged exposure to complex physiological fluids remains an important challenge for long-term implant applications. Silver and silver-containing materials have recognised antimicrobial properties and have been used for many years in wound dressings, catheters and some medical device coatings. Surmodics is developing an antibacterial coating platform that integrates EVQ- 218, EVOQ’s spherical silver metamaterial, into its hydrophilic coating systems. EVQ-218 is produced using a patented high-energy laser-ablation process. The approach is intended to add antimicrobial activity while preserving properties such as lubricity, durability and particulate performance. Laboratory testing of EVQ-218 has demonstrated broad-spectrum antimicrobial activity across more than 64 bacterial, fungal and mycobacterial isolates. Separate serial-passage studies across all six ESKAPE pathogens found no measurable increase in antimicrobial resistance after 30 passages under the conditions tested.
Surmodics’ established hydrophilic coating systems are already deployed across thousands of commercial medical devices. The combined Surmodics and EVQ- 218 antimicrobial coating system, however, remains in development and has not been reviewed or cleared by the US Food and Drug Administration. Regulatory clearance would be required before commercial use as a medical device.
“One technology I’m particularly excited about is surface-immobilised antimicrobial peptides (AMPs),” states Teh. “These peptides are part of our innate immune system and can disrupt bacterial cell membranes within minutes.” AMPs provide localised contact-killing activity without releasing significant amounts of active agent into the surrounding tissue.
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“Because the mechanism is based on physical disruption of bacterial membranes rather than targeting specific metabolic pathways, it is also considered less susceptible to the development of bacterial resistance,” says Teh. A key challenge for this coating technology is maintaining peptide stability and activity over prolonged implantation, particularly in the presence of serum proteins and proteolytic enzymes. “Another very promising approach is nitric oxide-generating or nitric oxide-releasing coatings, particularly for blood-contacting implants,” says Teh. Nitric oxide is naturally produced by healthy vascular endothelial cells and serves multiple biological functions: it inhibits platelet activation, reduces inflammation, promotes wound healing and possesses broad-spectrum antimicrobial activity. “Modern catalytic coatings can continuously generate low levels of nitric oxide from endogenous blood components, allowing them to mimic the function of a healthy endothelium without requiring an external drug reservoir,” explains Teh. Controlling the amount and duration of nitric oxide generation over prolonged use remains an active area of development. “Perhaps the most fascinating technology from a materials science perspective is nano-topographical antibacterial surfaces,” states Teh. “These surfaces are inspired by nature – particularly the wings of cicadas and dragonflies – which possess nano-scale pillar structures capable of physically stretching and rupturing bacterial cell membranes upon contact.” The antibacterial effect arises from the surface architecture rather than from a released chemical. Research supports mechanical deformation and rupture as key mechanisms, although effectiveness depends on factors such as surface geometry and bacterial species. Advances in nanoimprinting and precision surface fabrication techniques are making these surfaces increasingly practical to manufacture. One direction for medical device protection and infection prevention is multifunctional surface engineering. “An implant may use a zwitterionic layer to minimise protein fouling, together with a non- leaching antimicrobial surface to suppress bacterial colonisation, while also incorporating lubricious or haemocompatible properties depending on the clinical application,” explains Teh. Such approaches could reduce reliance on a single bacteria-inhibiting mechanism while combining anti-fouling, antimicrobial and device-performance properties. The search for PFAS-free alternatives is also accelerating, although fluoropolymers remain important in many medical devices where their combination of properties is difficult to replace. “Medical manufacturers are actively seeking alternatives to fluorinated materials while maintaining high lubricity and durability,” says Teh. “By combining PFAS-free materials with zwitterionic surface chemistry, the industry is charting a very attractive pathway for next-generation implantable devices.” ●
www.medicaldevice-developments.com
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