Moon Halo
Perhaps you are someone who has noticed an ominous halo around a full moon on hazy nights of the year. Perhaps you wondered where it came from, that there must be some logical explaination. Or, perhaps, you thought it signaled the coming of the apocalypse. Well, the moon halo is in fact no such doomsday omen, but a perfectly explainable atmospheric phenomenon, and it doesn't just happen with the moon, but with the sun as well.
The moon halo, if you are lucky enough to see it, is a fantastical sight composed of a bright circle in the sky wrapped around the moon. When the conditions are just right, there may even be two halos. The cause of this halo is surprisingly simple. Sunlight, reflected off of the moons surface, is refraced by ice crystals in the atmosphere. On humid nights, when there's some moisture in the air, that moisture forms ice crystals at the higher altitudes where the temperature is cooler. This cooling with rising altitude is another atmostpheric phenomenon. When the sunlight reflected off of the moon travels though hexagonal ice crystals, the resulting rays emerge at 22 degrees from the plane which they entered in. The result is that light is focused at a regular distance all around the moon. A second halo may result from a further angle of refraction. The halo is most spectacular on nights when the moon is full.
Engineering a New Spinal Cord
Tissue engineering is a field at the forefront of modern science and medicine, and engineering a new spinal cord is just one goal its laborers are working towards. While she admits that regrowing a spinal cord is still a long way off, the young professor of Biomedical Engineering at Yale, Erin Lavik, sees her work as contributing to that eventual prospect. The main idea, says Dr. Lavik (http://www.yale.edu/opa/v32.n3/story1.html), is to provide a degradable scaffold for nerve cells to regrow missing parts of the nervous system. She is quick to point out that the age-old misconception about growing living nerve cells is completely fallacious. Not only can nerve cells be grown and survive, but nerve stem cells can form the axons and dendrites characteristic of those in a functioning nervous system.
Dr. Lavik entered her career in biomedical engineering from a career in materials science at MIT. She developed scaffolds of many different qualities, from faster degradation, to tube-like pores, to cubic pores, all from degradable polyesters, similar to those used for degradable sutures. Using scaffolds of many different types, cells can be grown in a given orientation. This is crucial to something like spinal cord repair, which demands that new cells grow and properly meet up with old cells.
The work Dr. Lavik's lab has done in this area is in rats. Rats with lesioned spinal cords, say a small section of spinal cord with one half of it's area excised, are ready subjects for implantation of tissue scaffolds. Adding nerve cells to these scaffolds results in new growth. Dr. Lavik's trials have yielded surprising results. Rats with scaffold implants where spinal cord tissue has been removed are able to regain a remarkable level of mobility in limbs below the area of damage. Rats without the scaffold drag their hind limbs behind them, as they have been immobilized. This is significant, but getting the nerve cells to actually become a new spinal cord is the hard part, and is still a long ways off. The scaffold prevents glial scarring, or accumulation of glial cells at the site of the damage, which might be the reason rats without the implanted scaffolds perform so poorly in physical tests.
Dr. Lavik has also been able to get some vascularization into the scaffold where the new nerve cells grow and this, she says, is crucial to further success because organs without blood cannot survive.
The long term effects of the scaffolds are also not known. In addition, nerve cells have not yet been connected at the ends of the scaffold, where the old and new tissue meet, and this too will be an important step in restoring spinal cord function. But the future looks bright for Dr. Lavik and her team, with much success and no end to further directions for their work. One interesting component of these tissue scaffolds is their ability to deliver drugs to the site of damage in a controlled way. Imagine, a spinal cord injury repaired with a polyester scaffold containing a drug therapy regimen and some nerve stem cells.
