Artificial Materials to Repair Damaged Nerves and Disappear

Plastic biomaterials would electrically stimulate nerves to grow faster

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This segment is part of the IEEE Spectrum series “The New Medicine

Susan Hassler: Burns, cuts, and surgeries can harm nerves, leaving people without muscle control. In severe injuries, nerves don’t regrow on their own. Scientists in Austin, Texas, are making artificial materials that will repair damaged nerves and disappear when their job’s done. Phil Ross has more.

[door click and slam; footsteps]

Craig Milroy: We’ve made films, and—sorry, these have been cut up a little bit for analysis, but—these are conductive, but they’re also elastic.

Phil Ross: In a large, brightly lit laboratory at the University of Texas in Austin, Craig Milroy holds up small pieces of a black, rubbery film.

Craig Milroy: And these—so, you can stretch them. And this…

[stretching sound]

Phil Ross: Milroy is a chemical engineering graduate student. He’s trying to blend flexible plastics with plastics that conduct electricity.

Craig Milroy: The materials don’t like to be together, okay? And so, part of the challenge is to get just chemically dissimilar stuff to blend together and to be happy together.

Phil Ross: Now he has to make them safe for use in people. He wants to create a material that would electrically stimulate nerves to grow faster. These engineers believe it’s a way to help heal injured nerves.

Christine Schmidt: We’re developing a number of different biomaterials that could be used to regenerate nerve tissue.

Phil Ross: Biomedical engineer Christine Schmidt is leading the nerve regeneration efforts. She wants to find a material that would provide all the right conditions for injured nerves to heal and grow and then vanish once the nerves are healed.

[voices in laboratory]

Phil Ross: When nerves are severed, nerve fibers, or axons, cannot grow across large gaps between the two ends. So surgeons have to transplant nerves from another part of the body. And for spinal cord injuries, there’s nothing they can do.

Christine Schmidt: So the materials that we’re working with would basically be implanted at those sites of injury so the axons have a substrate, a substance, along which to migrate and to regenerate.

Phil Ross: Normally, nerves grow by attaching to proteins and sugars in body tissue. Chemical and electrical signals guide this growth. Creating artificial materials that provide nerves with all those growing conditions is challenging, Schmidt says.

Christine Schmidt: What are the correct signals we need to put into these grafts? What size pathways do we need? What pathways are they going to want to follow? Those are all questions we’re trying to address right now.

Phil Ross: The researchers have learned a lot from cells studied in a glass dish. For instance, certain proteins trigger nerve growth. So the researchers implant their artificial materials with cells that secrete those proteins. One of the materials they’re working with is that stretchy plastic Milroy showed us. Another is a natural, Jello-like compound that’s used in arthritis injections. Graduate student Eric Spivey uses a laser beam to draw lines inside gobs of this gel.

Eric Spivey: We use pulse lasers to generate what’s called multiphoton excitation. All that means is it allows us to create a lot of energy at the focal point of the laser that we can use to do specific kinds of chemistry.

[ambient talk and humming]

Phil Ross: The gel is soaked with liquid protein that becomes hard when it’s heated, just like an egg. Looking through a microscope, Spivey moves the tiny red laser point around inside the gel. Soon he’s made an intricate pattern of proteins that look like spaghetti strands suspended inside the Jello.

Eric Spivey: And so, you can think about [it] like an Etch-a-Sketch, really. It’s pretty—pretty neat to see.

Phil Ross: The researchers have already found that nerve cells grow along those protein strands. And they’ve come up with some tricks to control the growth direction. With their lab setup, though, they can only make millimeters of the gel. They need to make centimeters’ worth for animal implants. The group is also working on a gel that could be injected into the spinal cord to repair nerves.

Sydney Geissler: So I can show you a gel I just made a few minutes ago.

Phil Ross: Graduate student Sydney Geissler is in charge of this work.

Sydney Geissler: And then this one has collagen. This one has collagen and laminin.

Phil Ross: How hard or squishy the different gels are affects the development of stem cells in the spinal cord—specifically, what type of nerve cell they become, or, as Geissler calls it, differentiate into. She has found that in a softer gel, stem cells tend to become neurons.

Sydney Geissler: What I hope is that these gels—I will implant them with undifferentiated cells, and then these gels would direct the differentiation while they're inside of the spinal cord.

Phil Ross: The work is at an early stage. The researchers still face plenty of engineering challenges and extensive testing, in animals and outside. After that, they’ll need FDA [Food and Drug Administration] approval. But the implications, especially for spinal cord injury, could be huge. This is Phil Ross.

Photo: The Schmidt Lab/The University of Texas at Austin

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