Scientists grow new spinal discs

27 November 2018

Interview with

Robert Mauck, University of Pennsylvania

About one person in five suffers with a bad back, and a common culprit is wear and tear to the intervertebral discs that sit between the vertebrae that make up the backbone. These discs act as fleshy shock absorbers; they have a soft, jelly-like interior and a tough, elastic outer surface. But, as we age, they stiffen, shrink and deform, and can press painfully on nearby nerves. Artificial plastic and metal replacement discs are available, but these can also wear out, so scientists at the University of Pennsylvania have been exploring how to grow new spinal discs, in a dish. Georgia Mills heard how from Rob Mauck.

Rob - So the central premise of this therapy compared to what's available now, is that this is a living implant. It's an implant that will be made of a patient’s own cells and because the cells are there the cells will be doing what cells in muscular skeletal tissues do and that is continuously making new material and repairing damage and so our hope is that unlike metal and plastic implants, this will be a sort of self-sustaining biologic implant, as durable as your original living intervertebral disc.

Georgia - Right, so these squishy bits between the bones of the spine. You wanted to sort of create them from scratch?

Rob - Precisely.

Georgia - How did you go about doing that?

Rob - Essentially what we do is combine various elements together to create what we call a composite disc structure. And the way that goes about is we produce bio materials that represent the different substructures of the normal intervertebral disc. These are materials that are based on hydrogels -  sort of water swollen, networks sort of like jello. And that makes up the inner part of the country like that we've created. And then an outer part which is sort of a tough almost rubber band like structure that surrounds the gelatinous interior portion. Both of these materials were seeded with cells we use mesenchymal stem cells which can be harvested from adults and we grow these in the laboratory for a period of time until they start to take on characteristics of the native tissue.

Georgia - How do you make sure it gets to be the right size and shape?

Rob - So we realized that this is a big challenge to create such a large structure. So we started small and we started actually making these on a scale of a rat disc, just a couple millimeters in height and maybe five millimeters in diameter.

So we optimized all of that in a size that was a suitable for a small animal the rat, and we spent some time then evaluating it once we implanted it into a rat. After that we thought this is promising. Let's see what we can do with bigger length scales that would be more clinically relevant.

We next went to the goat cervical spine so the neck of a goat essentially, and we started building constructs that were designed to function at that length scale. So we started building bigger and bigger discs and growing those in culture in the laboratory. We got to the point where we were pretty happy with what we could produce in the laboratory, and so what we've done recently is actually started testing those in a large animal model in this model.

Georgia - Right so you've actually been putting these discs in to a living goat?

Rob - That's right yes. For the last couple of years we've actually been evaluating how these lab grown living intervertebral discs function, when we put them into a goat cervical spine.

Georgia - Right. And then after the discs have been put in, how did you work out how effective they were?

Rob - The main goal and the main function of the disc is mechanical. The cervical spine supports your head as you turn your head to the left or the right and the first thing we did was after a period of time of implantation, we asked how mechanically robust these tissues? Are maturing further after we implant them? Do they have the appropriate mechanical properties? So we compared their mechanical properties to the mechanical properties of a normal native goat disc?

Georgia - Did you get a goat to do yoga then?

Rob - No but we actually do have little motion sensors that were attached to their horns so that we can see how many times they move their heads around them and things like that.

Georgia - Right so if you've got a stiff necked goat it would come up on the sensors that it's not doing as good. So how did it compare?

Rob - It actually compared quite favorably. So when we measured the properties of these goat discs and compared them to the implanted ones after a period of about two months they actually matched or exceeded the native tissue properties and so we were quite excited about that.

Georgia - Oh wow. Do you think this could move into humans, an animal that walks about on two legs instead of four?

Rob - No absolutely and in fact we chose the goat because  - if you ever seen a goat - they have a fairly upright posture and they're very inquisitive animals. They use their heads a lot. They obviously run into each other and butt heads but they have an upright posture. So they use their necks in a manner very similar to how humans use their cervical spines as well.

And in fact as we've been getting this data, Harvey Smith my clinician colleague and I and Sarah Gullbrand who is another participant in the study have been talking about well what really is the next step? For us the next step let's start talking to the FDA the Food Drug Administration here in the U.S. about what it will take to transition this into phase One clinical trials in humans.

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