Nano-sized Micelles Used to Treat Spinal Cord Injury

Micelles are commonly used in biomedicine to deliver drugs to tissue

Spinal cord injuries can be the most devastating of any type of injury sustained in an accident. The injuries can leave the victim paralyzed and can lead to death. Research into the treatment of spinal cord injuries is well funded and being undertaken around the world.

A group of researchers at Purdue University have discovered a new way to repair damaged nerve fibers in spinal cord injuries. The researchers are using nano-spheres injected into the blood shortly after the accident to repair the nerve fibers. The nano-spheres are synthetic copolymer micelles.

These spheres are used for drug delivery and are about 60nm in size making them about 100 times smaller than the diameter of a red blood cell. The spheres are being studied as a method to deliver drugs to targeted cells in the body, like cancer cells. The Purdue researchers have demonstrated that the micelles themselves can repair damaged axons. Axons are nerve fibers in the body that transmit electrical impulses to the spinal cord.

"That was a very surprising discovery," said Ji-Xin Cheng, an professor in the Weldon School of Biomedical Engineering and Department of Chemistry. "Micelles have been used for 30 years as drug-delivery vehicles in research, but no one has ever used them directly as a medicine."

One of the features of these micelles is that they combine two types of polymers. One of the polymers is hydrophobic and the other is hydrophilic (water hating and water loving). The hydrophobic polymer can be loaded with drugs to treat disease.

In the Purdue research, the micelles are used instead of conventional membrane sealing agents. The outside of the micelles can be coated with poly ethylene glycol (PEG) and with the coating they are not quickly filtered by the kidney or captured by the liver. That gives the micelles enough time to reach the site of tissue and nerve damage inside the body. The researchers say that the micelles coated with PEG can be used in non-toxic concentrations.

"With the micelles, you need only about 1/100,000th the concentration of regular polyethylene glycol," Cheng said.

Researchers at Purdue have been using PEG to treat spinal cord injuries in animals and have shown that PEG targets damaged cells and seals the damaged area thereby reducing further damage. The PEG also helps to restore cell function.

During testing the researchers found that treatment with PEG without using micelles was able to restore about 18% of axons in a segment of damaged spinal cord. When treated with PEG infused micelles 60% of the axons in the damaged area recovered. Micelle treated animals recovered the coordinated use of all four limbs while those treated without micelles did not.

The experiment mimics what happens in a traumatic spinal cord injury and the findings have shown that the treatment with micelles could be used to repair damage caused to the spinal cord from compression injuries. The research is funded by a grant from Showalter Trust from Purdue and a grant from the Indiana Spinal Cord and Brain Injury Research Fund.