Nothing Sticks to a new Bioinspired coating for medical devices
Putting things in the body can be tricky, I mean we need things from joint replacements to cardiac implants and dialysis machines, these medical devices are needed to enhance or save lives on a daily basis. However, any device implanted in the body or in contact with flowing blood faces two critical challenges that can threaten the life of the patient the device is meant to help: blood clotting and bacterial infection. Problems that sound easier to fix than they actually are.
Thankfully now a team and engineers may have a solution. They developed a new surface coating for medical devices using materials already approved by the Food and Drug Administration (FDA). The coating repelled blood from more than 20 medically relevant substrates the team tested – made of plastic to glass and metal – and also suppressed biofilm formation. But wait there’s more! (I’ve always wanted to be able to say that)
The team implanted medical-grade tubing and catheters coated with the material in large blood vessels in pigs, and it prevented blood from clotting for at least eight hours without the use of blood thinners such as heparin. Heparin is unfortunately notorious for causing potentially lethal side-effects like excessive bleeding, but is often a necessary evil in medical treatments where clotting is a risk.
“Devising a way to prevent blood clotting without using anticoagulants is one of the holy grails in medicine,” said Don Ingber, M.D., Ph.D. and senior author of the study.
The idea for the coating evolved from SLIPS, a pioneering surface technology developed by coauthor Joanna Aizenberg, Ph.D. and the Amy Smith Berylson Professor of Materials Science at Harvard SEAS. SLIPS stands for Slippery Liquid-Infused Porous Surfaces. Inspired by the slippery surface of the carnivorous pitcher plant, which enables the plant to capture insects, SLIPS repels nearly any material it contacts. The liquid layer on the surface provides a barrier to everything from ice to crude oil and blood.
“Traditional SLIPS uses porous, textured surface substrates to immobilize the liquid layer whereas medical surfaces are mostly flat and smooth – so we further adapted our approach by capitalizing on the natural roughness of chemically modified surfaces of medical devices,” said Aizenberg.
“This is yet another incarnation of the highly customizable SLIPS platform that can be designed to create slippery, non-adhesive surfaces on any material.”
The team developed a super-repellent coating that can be adhered to existing, approved medical devices. In a two-step surface-coating process, they chemically attached a monolayer of perfluorocarbon, which is similar to Teflon. Then they added a layer of liquid perfluorocarbon, which is widely used in medicine for applications such as liquid ventilation for infants with breathing challenges, blood substitution, eye surgery, and more. The team calls the tethered perfluorocarbon plus the liquid layer a Tethered-Liquid Perfluorocarbon surface, or TLP for short.
In addition to working seamlessly when coated on more than 20 different medical surfaces and lasting for more than eight hours to prevent clots in a pig under relatively high blood flow rates without the use of heparin, the TLP coating achieved the following results (presented in cool list form):
- TLP-treated medical tubing was stored for more than a year under normal temperature and humidity conditions and still prevented clot formation
- The TLP surface remained stable under the full range of clinically relevant physiological shear stresses, or rates of blood flow seen in catheters and central lines, all the way up to dialysis machines
- It repelled the components of blood that cause clotting (fibrin and platelets)
- When bacteria called Pseudomonas aeruginosa were grown in TLP-coated medical tubing for more than six weeks, less than one in a billion bacteria were able to adhere. Central lines coated with TLP significantly reduce sepsis from Central-Line Mediated Bloodstream Infections (CLABSI). (Sepsis is a life-threatening blood infection caused by bacteria, and a significant risk for patients with implanted medical devices.)
Out of sheer curiosity, the researchers even tested a TLP-coated surface with a gecko – the superstar of sticking whose footpads contain many thousands of hairlike structures with tremendous adhesive strength. The gecko was unable to hold on.
“We were wonderfully surprised by how well the TLP coating worked, particularly in vivo without heparin,” said one of the co-lead authors, Anna Waterhouse, Ph.D., who was easily impressed by the gecko trick. “Usually the blood will start to clot within an hour in the extracorporeal circuit, so our experiments really demonstrate the clinical relevance of this new coating.”
While most of the team’s demonstrations were performed on medical devices such as catheters and perfusion tubing using relatively simple setups, they say there is a lot more on the horizon.
“We feel this is just the beginning of how we might test this for use in the clinic,” said co-lead author Daniel Leslie, Ph.D.
Next the team hopes to test the coating on a number of other medical devices and see what sticks… yes that was a horrible pun and yes I will spare my readers of any more of them. Another interesting thing to mention is that this research was funded, in part, by DARPA one of my favorite defence contractors. An interesting if not useless little fact about the research.
Don Ingber et. al (2014). A bioinspired omniphobic surface coating on medical devices prevents thrombosis and biofouling Nature Biotechnology : 10.1038/nbt.3020