Stuff the Sausage Casings in Favor of Better Biomaterials
What do kidney dialysis and processed meat have in common? The answer: sausage casings!
Back in the ‘30s, the Dutch doctor Willem Kolff was trying to build an artificial kidney and was desperately seeking a substance to use for tubing. It needed to be able to hold blood but porous enough so that waste products such as urea would diffuse right through it.
Artificial sausage casings made of chemically modified cellulose fit the bill. (Kolff’s colleagues thought he was rather eccentric, but he ended up inventing the dialysis machine.)
Kolff is just one of many medical inventors who’ve waxed creative over the years. They’ve used mattress stuffing and industrial lubricants in breast implants, textiles such as Dacron and velour to make artery grafts and materials found in ladies’ girdles for parts of artificial hearts. “Without people doing these things, we never would have seen the enormous progress we’ve seen,” says Robert Langer, professor of chemical and biomedical engineering at the Massachusetts Institute of Technology.
But there can also be drawbacks to getting medical inspiration from one’s breakfast hot links or lingerie. Those materials weren’t designed with the medical purpose in mind and thus can be less than perfect for the job.
Dialysis tubing, for instance, can cause blood clots to form. Dacron grafts can only get so narrow before (again) clotting becomes a problem.
Thus it may make sense to design biomaterials from scratch, Langer says, so you can brainstorm precisely the properties you want.
Langer’s been doing that ever since he was a hospital chemical engineer in the ‘70s and observing how medical materials were derived. “I just thought, gee, we could do better,” he says.
Suppose, for example, you want some kind of fancy biomaterial that’ll allow you to deliver a medicine slowly, over a period of time. Langer designed just such a substance from scratch using the following reasoning:
* You want to embed the medicine in a substance that disintegrates slowly from the outside, releasing the drug as it does so.
* The substance should be nontoxic (of course) and “hydrophobic,” or water-hating, so the drug inside is protected from release all at once.
* It should be held together by chemical bonds that can be slowly chipped away. It’s better to use bonds degraded by water rather than by one of our body’s enzymes, because amounts of enzymes can vary a lot between people, whereas we’re all chock-full of water.
* Different drugs need to be released at different rates, a goal that is niftily achieved by mixing two different substances together with different ratios.
The substance that Langer came up with after a lot of cooking in the chem lab is being used to slowly deliver chemotherapy to people with a certain kind of brain cancer. Other futuristic substances and methods are in the works in Langer’s lair--such as smart medical chips that could be embedded under the skin to deliver different drugs when needed. (A diabetic, for instance, could get a squirt of insulin every time the chip sensed that sugar levels were getting too high.)
And the lab has come up with a “Star Trek"-like method for getting drugs into people and samples of blood chemicals out of them without piercing the skin. (Could jabbing people with needles one day seem medieval?) You apply a surge of ultrasound, which alters the skin’s structure and makes it porous for a second. Drugs go in, sugar and cholesterol samples come out. (Normally, only small chemicals such as nicotine can get across the skin barrier.) The method, in clinical trials right now, is harmless, Langer says. “And it doesn’t hurt--I’ve had it done to myself.”
“Smart sutures” are also in Langer’s cookbook. Anyone with a kid will have seen those squooshy blobs shaped like hands that stick on walls and that can be manhandled yet miraculously regain their shape.
Langer and co-workers have developed biomedical materials that “remember” their shape as well--and, oh, how handy they could be. Imagine threading a thing that looks like a piece of string through a narrow incision in a body. Once inside, ta da! Warmed by body heat, the string alters its form--not into a hand (though that would be feasible, to say nothing of startling) but into a knot that deftly ties itself.
Langer and colleagues have made such biodegradable sutures and used them to tie up wounds in a rat. But why stop with a knot? “You could make it from whatever shape you want--maybe a string that turns into a stent to keep blood vessels open, like one of those Chinese finger puzzles,” Langer says. “You can put all kinds of small things through tiny incisions and they can convert to whatever shape you want. It’ll change the way we do medicine.”
If you have an idea for a Booster Shots topic, write or e-mail Rosie Mestel at the Los Angeles Times, 202 W. 1st. St., Los Angeles, CA 90012, firstname.lastname@example.org.