The end of blood clots?

Materials World magazine
1 Mar 2017

Nanotube-covered titanium could be used in blood-repellent medical implants. Ellis Davies reports.

Stents, catheters and other medical implants put the patient at risk of blood clotting or infection, leading to further health issues and surgery. In the pursuit of a solution, Dr Arun Kota and Dr Ketul Popat of Colorado State University, USA, have brought together materials science and biomedicine to grow superhemophobic titanium, a material that repels blood, with the potential to be used in clot-resistant surgical implants. 

Blood clots can occur after titanium is implanted because of the continuous contact it has with blood. Over a short time scale this does not cause a problem, but over a prolonged period of time, ranging from a few months to a year, blood begins to clot around the implant. Once the clotting begins, more blood clots on top of it, and a secondary surgery is needed despite the patient taking medications to slow the process. ‘The holy grail of the medical device industry is a way to solve this problem,’ said Kota. 

‘I come from a materials background, more specifically surfaces and copings, whereas Ketul has a biomedical background, being an expert in hemocompatabilty,’ Kota told Materials World. The pair realised the potential for combining their expertise, and began to grow superhemophobic surfaces at Kota’s lab, which specialises in omniphobic and hydrophobic surfaces. These surfaces allow for only around 1% of the liquid to touch the surface of the implant. This is an alternative approach to the usual methods of pursuing hemocompatabilty, which often centre on the use of philic materials, meaning that they have an affinity to blood. 

The surfaces work in a similar fashion to a lotus leaf, which is also able to repel liquid. Instead of making full contact with the surface, the liquid meets a layer of trapped air between itself and the solid, reducing the amount of contact. The less contact made, the smaller the chance of blood clotting. 

Kota and Popat took pieces of titanium and grew nanotubes on them using an anodisation method, which gave the material a textured surface. ‘Superomniphobics are made by combining texture with low-surface-energy fluorination chemistry. We added the chemistry through a process called silanisation [covering the surface with organofunctional alkoxysilane molecules] and by combining these we were able to create a surface that is extremely repellent, so that a liquid drop will bounce, bead up and roll off,’ Kota explained. Professor Sarah Cartmell of the University of Manchester, UK, told Materials World about a possible challenge the study may face going forward. 'In my experience, a film of nanotubes can be a little bit flaky. So, it's important to increase the stability of the surface – you wouldn't want to have a fantastic surface that might flake off,' she said.

The researchers tested a variety of different textures and titanium surfaces to compare the platelet adhesion and activation. They discovered that using fluorinated nanotubes produced the best results. ‘The first steps in clotting are the blood platelets adhering to the surface and activating. Once this happens they form networks and can clot all over the surface,’ said Kota. The surfaces were then compared to non-textured titanium, which showed that the superhemophobic surfaces had a significantly lower adhesion and activation rate, less than 10% that of the standard titanium. 

While the tests were carried out in a static condition, using blood droplets that sat still on the surfaces, the team will need to conduct tests in which the blood is flowing past the surface to simulate vascular application. 'This is an exciting piece of work that has a lot of potential,' said Cartmell, commenting that the possible challenges of cost, manufacturing and stability could all be addressed. The next step would be to test the implant in an animal model before going for FDA approval. Kota said that, ‘There is quite some ways to go, probably at least four-to-five years,’ before a commercial implant could be made from the repellent titanium.