Lasers lead way to new nerves

U of T researchers have seen the light‚ when it comes to tissue regeneration. Professor Molly Stoichet of the Institute for Biomaterials and Biomedical Engineering (IBBME) and her former Ph.D. student Ying Luo have found a way to get nerve cells to grow using laser beams. Their work appears in the prestigious journal Nature Materials.

Stoichet and Luo are working towards repairing severed nerves‚ both in the spinal cord and in the rest of the body. By getting two severed ends to grow and reconnect‚ nerves could once again flow with information‚ and somebody paralysed by a stabbing wound to the spine may not have to face a lifetime in a wheelchair.

Theirs is not the first method of regrowing damaged nervous tissue‚ but it is far more elegant than older methods. The “goldstandard” for dealing with an injury to the nervous system has always been an autograph—the removal of tissue from another‚ less crucial part of the body and placing it in the injured site‚ as is commonly done for burn victims with undamaged skin from‚ say‚ the buttocks. “This whole field of tissue engineering‚ or regenerative medicine‚ part of the excitement is‚ ‘well‚ what if you didn’t have to do that?’ because when you autograph you create a secondary injury‚ so the idea is to come up with a synthetic replacement‚” says Stoichet.

But not to create synthetic tissue that would remain in the body permanently‚ but to create a kind of temporary scaffolding for somebody’s own tissue to use to grow properly.

Several kinds of temporary synthetics are already available—dissolvable stitches have been used in dental surgery for several years now‚ and there are similar materials used to repair skin and cartilage. Stoichet herself has developed a synthetic scaffolding for bone tissue to grow in‚ Osteofoam‚ which dissolves after new bone has grown through the porous material. Although not on the market yet‚ there is good reason to believe that Osteofoam will find practical use in the very near future.

Tissue regeneration is a huge area of research‚ and a large number of scientists are now trying to come up with ways to repair severed spinal cords and peripheral nerves. But regrowing nervous tissue is considerably more difficult than growing other types of tissue. “The bar is much higher‚” says Stoichet. Nerve cells not only need to grow‚ they need to grow in precisely the right way in order for signals from the brain to reach their proper targets‚ and likewise for sensations from the body to reach the right part of the brain. The highways of the nervous system need to be connected in a particular pattern‚ otherwise a signal intended to move the foot might simply cause a twitch in the knee.

So how do you get a nerve cell to grow in the direction you want it to?

“The idea was‚ ‘let’s start with something nonadhesive‚ agarose [a gel–like substance]‚ and let’s try and create volumes that are adhesive‚’ so we would have adhesive molecules separated by nonadhesive molecules to guide the growth of the nerves.” Nerve cells would be attracted to the adhesive areas at the same time as repelled by the nonadhesive areas‚ and hopefully would grow in just the right direction.

So Stoichet and her former Ph.D. student Ying Luo used a modified agarose gel that‚ if light were shined on it‚ would change chemically.

When photons of light strike the agarose‚ some chemicals are released from the agarose molecules‚ creating new molecules that adhere to growing nerve cells. By striking the agarose gel with lasers they were then able to create channels in the gel—not true physical channels‚ just adhesive areas in the gel.

“So we’re not zapping holes‚” says Stoichet‚ “we’re just changing the chemistry between here and here‚” she says‚ pointing on at the origin and destination of the nerve cell on a diagram.

One further reason that Stoichet’s research is of particular interest is that it does not require the use of new cells. It is the body’s own severed nerves that could be reconnected. There is no need to use stem cells‚ bringing in all the controversy along with them. Stoichet’s method‚ although with no clear practical applications in the foreseeable future‚ could lead to a method of “guided regeneration‚” helping the body’s own nerve cells to reconnect.

“I think it’s really exciting research‚” she said.