Quirks & Quarks·Analysis

Injectable gels could help repair heart tissue and spinal cord injuries

Bob McDonald’s blog: Advanced new bioengineered materials could be used to help difficult-to-repair tissues heal.

Bob McDonald’s blog: Synthetic materials can promote healing in challenging tissues

A section of a spinal cord treated with the scaffolding gel with protein signalling molecules. Regenerated neurons (red) regrew within the lesion. (Samuel I. Stupp Laboratory/Northwestern University)

A team of researchers at McGill University in Montreal and another at Northwestern University in Chicago have developed new techniques that use injections of gel-like materials to facilitate the repair of systems in the body that are difficult to treat.

When it comes to medicine, we often think of treatments to repair the body in the form of invasive surgery or drugs to promote healing. But these two new approaches involve simple injections of special gels that can be delivered directly to the site of injury and help with the repair process.

Tough and flexible enough for the heart

The first example involves a hydrogel that's tough and flexible enough to create a healing structural environment when injected into dynamic tissues like a beating heart or vocal cords. 

This illustration shows the use of injectable hydrogel as an implant to fill a wound and to restore the voice. (Sepideh Mohammadi)

The problem with tissues like heart muscle is that the heart never stops beating, so anything injected into them will have difficulty maintaining its structure without fracturing. That makes it difficult for cells and blood vessels to grow into the injured site. It's one of the reasons plastic bandages were designed to be flexible to stay in place even on a kid that never stops moving. 

Most hydrogels either aren't strong enough to withstand the motion of the heart or vocal cords, or not porous enough for cells to proliferate within them and allow gases or nutrients to pass through. 

VIDEO The vocal cord bioreactor simulates the biomechanics of vocal cords to test the hydrogels.

The new gel hits the sweet spot, so it can not only withstand and flex along with the extreme biomechanical motions of certain tissues, but also create a structure that promotes the growth of new cells and the transport of crucial gases and nutrients. 

To test the gel's durability, the scientists rigged up artificial vocal cords made of the gel material that vibrated 120 times per second for two hours a day, seven days a week — through 6 million cycles of openings and closings, without breaking. 

The researchers tested three different hydrogels using the vocal cord bioreactor. While the new hydrogel remained stable, the two standard hydrogels, which represent most existing injectable hydrogels, did not survive the test. (Sareh Taheri)

When they tested how well one of the main cell types in the vocal cords could grow within the gel, they found it provided a cell-friendly three dimensional growing environment. 

The scientists believe the gel could restore the voice of those suffering from laryngeal cancer or be used for heart muscle repair and drug delivery, all by simple injection.

Self-assembling healing scaffold

The second group developed materials that can self-assemble into nanofibres with biological signals that can trigger cells to repair and regenerate in damaged tissues, like with a spinal cord injury, which otherwise would not heal. 

Starting out as a liquid, the biologically active materials form nanofibres that turn into a gel, which mimics the environment of the spinal cord. By tweaking the structural part of the nanofibre-forming materials, the researchers got them to vibrate in just the right way to connect with nerve cells. 

Nanofibres containing molecules with two different bioactive signals (green and orange) more effectively engage cell receptors (yellow and blue) as a result of the molecules’ fast motion. (Mark Seniw)

The more dynamic the motion was or the more the molecules danced, the better the nerve cells were able to grow and reconnect. The treatment also encouraged the growth of myelin, a sheath that forms around the nerves to protect them from further injury, like the plastic coating around an electrical wire.

This therapy has the potential to change the lives of those with complete spinal injury where less than 3 per cent of people fully recover basic functions. While this treatment is only a lab experiment performed on mice at the moment, the researchers are looking for federal approval to move forward on clinical trials on humans.

VIDEO The results of the treatment where partially paralyzed mice regained the ability to move their lower limbs. 

The interesting aspect of these two injectable therapies is how they combine medicine with engineering and materials sciences. Engineers are always looking for materials that are strong yet flexible, whether they be large bendable carbon fibre wings on airliners, or in this case, strong flexible gels that can withstand the harsh environment within the body. 

It can also become a positive step away from more invasive techniques to repair difficult-to-treat tissues by using a simple needle in the right place instead that may, one day, allow for someone with a spinal cord injury to walk again.



Bob McDonald is the host of CBC Radio's award-winning weekly science program, Quirks & Quarks. He is also a science commentator for CBC News Network and CBC-TV's The National. He has received 12 honorary degrees and is an Officer of the Order of Canada.