If you’re unfortunate enough to have a serious laceration in an arm or leg, you know from movies and so forth — hopefully not from personal experience — that you can apply a tourniquet or direct pressure to control the bleeding. But a bleeding wound like that on the head, neck, torso, or internal tissues certainly can’t be treated with a tourniquet and may not respond to direct pressure, either. Then what?
Imagine being able to apply a paste to the wound, shine some light on it, and have the wound seal up and stop bleeding in less than a minute. A group of researchers from China and Canada have teamed up with a highly venomous pit viper, Bothrops atrox, to provide just this kind of solution. They reported it July 14 in Science Advances.
There are three parts to this:
1) We need a gel that sets quickly to seal up the wound, even if it’s bleeding profusely
2) We want the blood to clot up around the wound, and quickly
3) The whole thing’s got to be nontoxic and biocompatible, so there are no ill effects
To get a grip on Step 1, let’s talk about tires! You may know that a process called vulcanization toughens up rubber to make it roadworthy. It works because of crosslinking, where we get long, chainlike molecules to link together to form a sort of mesh. For rubber, we add sulfur and ovenlike heat (Δ), and we get this to happen:
Now, we can’t very well heat a wound up to 300°F, so we’re going to need a way to do this more easily in the field.
In 2017, a Harvard-MIT-Tufts group found a way to do this sort of thing using visible light. They modified gelatin, which is made up of protein chains, to have crosslinkable hooks on it. They called the product GelMA (methacrylated gelatin). Traditionally, you need to use UV light to get these chains to link together:
You don’t want to hit a wound with lots of ultraviolet light, though, and cause even more damage. But the Harvard-MIT-Tufts group got it to work using the visible light-absorbing molecule eosin Y as a catalyst. You can check out their paper for the mechanism, which is a little more detailed than I can do justice to here.
The gist, though, is this: When eosin Y absorbs blue or green light, it goes into an excited state that allows it to catalyze the formation of free radicals, which get transferred to the hooks, allowing them to link together. Eosin Y is red in color, but after it goes through this process, it turns yellow. That’s great, because it allows you to see when your setting process is done.
This picture sums it all up: (1) Put some red GelMA goop in a vial, (2) Shine blue or green light on it for a minute, (3) It sets!
Man, I wish I could get Jell-O to set that quickly. I have to wait at least two hours!
You can imagine how great this is for binding and sealing up wounds out in the field. No need for stitches or anything like that. It should also be very useful in surgeries.
The only problem with gel adhesives like this is that the setting process can get disrupted by severe bleeding. Wounds will eventually clot naturally, but if there’s a lot of bleeding, that won’t happen fast enough. Here’s where we get some help from the pit viper.
For blood to clot, red blood cells and platelets need to collect around the wound, and then they get wrapped up, as if within a net, by strands of a protein called fibrin. Fibrin comes from the snipping of a protein called fibrinogen, and the snipper is still another protein called thrombin:
The pit viper’s venom contains a protein called hemocoagulase. The catchier name for it is “reptilase”. It acts just like thrombin — that is, it snips fibrinogen to make fibrin — but unlike thrombin, it’s not regulated by anything in the human body. With no brakes, it just keeps rolling along until it gets trapped within a big blood clot.
Fortunately, in order to get reptilase, we don’t need to squeeze snake heads to collect venom anymore. With genetic engineering, now we can make lots of it in yeast.
Now let’s see how well reptilase can make blood clot up when it’s loaded into some GelMA. What we have here is quick-setting reptilase-flavored Jell-O. The authors call it HAD (hemostatic adhesive). These are pictures of whole blood that was in contact for 3 minutes with either plain GelMA or with GelMA plus reptilase (HAD):
After 3 minutes with HAD, you can see the blood is extremely clotted, the red blood cells wrapped in lots of fibrin. In fact, enough clotting occurs with HAD to stop a wound from bleeding within about 45 seconds.
With no treatment, blood around a wound (or out in the open) tends to clot within 5 to 6 minutes. We’ve all gotten moderate cuts, and that time sounds about right. And that’s exactly what was seen in this test. The current standard sealant that surgeons use is “fibrin glue” (fibrinogen and thrombin in a sealant goop), but fibrin glue took about 75 seconds to induce the same amount of clotting as HAD achieved in 45.
HAD goop is able to penetrate into the “nooks and crannies” of a wound, so once it sets, it’s hard to dislodge. Visible light from the blue-light pen can penetrate at least 2.5 mm into tissue, so you can get a pretty thick seal this way.
In a real rat model, a lacerated abdominal aorta was sealed quickly with HAD. If you were a rat surgeon, you might do this:
The stoppage of bleeding was maintained here even after twisting and bending. In fact, HAD showed almost ten times the shear strength and adhesive strength of fibrin glue. That means a patient treated in the field can withstand more movement, making things easier and less risky for the EMTs.
Now, one last thing we want to check is what happens to this goop once it sets. Is the body able to metabolize it away? Does it kill any cells?
You can see below that a blob of HAD gel implanted under the skin of a rat disappears fairly quickly. In 28 days, it only weighs about 18% of what it originally did.
This implanted blob caused only a minimal inflammatory response, much less than an actual wound would cause. When HAD gel was tested on cultured fibroblast cells, more than 98% of them survived over 5 days, and that was within the margin of error compared to untreated cells. In other words, this stuff is nontoxic.
Kibret Mequanint from the University of Western Ontario, who was involved in the project, said:
The next phase of study, which is underway, is to translate the tissue 'super glue' discovery to the clinic. We envision that [it] will be used in saving lives on the battlefield, or other accidental traumas like car crashes. The applicator easily fits in first aid kits too.
So, as is often the case, we must say thanks to nature and marvel at what evolution has wrought. We have got to preserve the wild, because it has so much more to teach us.
As the aptly named Seal (hee hee) says to sum up this situation, “Fast change is arriving. Slow change is moving out.”