Science & technology
Painting with platelets
How to hide surgical implants from the immune system
Platelets play an essential role in healing.
These curious beasts, are cell fragments rather than complete cells -- though they are still surrounded by cell membranes.
Their main job, in collaboration with a protein called fibrin, is to stem the flow of blood from wounds by causing clots.
They also encourage the regeneration of damaged tissue.
This sort of activity at wound sites might normally draw the attention of the immune system, but that does not happen because platelets carry special proteins in their membranes which render them invisible to immune surveillance.
Now, Wang Yunbing at Sichuan University in China writes in Matter that he has developed a way to apply these membranes to medical equipment of the sort destined for installation inside the human body.
That may stop the immune system attacking such grafts as foreign objects.
The idea of coating equipment with platelet membranes has been around for a while.
Since the relevant proteins were characterised 20 years ago, they have been used on numerous occasions to disguise nanoparticles employed for drug delivery.
That involves manipulating the surface electric charges of the nanoparticles to make them sufficiently and uniformly negative in a way which encourages the membrane to fuse with them.
For such small objects, this is reasonably simple.
But not for large ones.
Manipulating charge uniformly across a wide area is tricky, and no one has yet done it well enough to achieve successful fusion.
Dr Wang therefore wondered if it might be possible to entice membranes to fuse to a large surface by manipulating that surface in other ways.
Besides being attracted to negative charges, platelet membranes also spread easily and defect-free over “superhydrophilic” (exceptionally water-loving) surfaces.
With this in mind, he tested a superhydrophilic material based on a substance called polydopamine, which he knew from previous work binds to a range of materials including plastics, metals and ceramics.
So he gathered a team of colleagues together to fuse it to a metal stent.