A study funded by DARPA (Defense Advanced Research Projects Agency), into limb regeneration for humans at the University of Tulane, led by Mimi Sammacro, was published. It showed that when high amounts of oxygen are applied to the severed bone, some regeneration of the bone is stimulated. This research holds promise for soldiers, injured victims and diabetics.
The results of this research were revealed in 2012 and are part of a much larger on-going project by the Department of Defence into limb regeneration and regenerative medicine.
This was first kick-started back in 2008 when DARPA funded an unprecedented $300 million with the controversy in the media of planning to regrow lost limbs for injured soldiers. Establishing what is called, Armed Forces Institute of Regenerative Medicine. Positively abbreviated AFIRM.
Mimi Sammacro, who led the study, says that 1 out of every 200 Americans has lost a limb. These kinds of injuries are expected to double in the next 40 years unless new advances in medical science are made. She explains that this is of particular concern, as amputation injuries have increased a lot caused by combat casualties and the rise in diabetics.
Salamanders and Humans
The salamander is the only vertebrate capable of regrowing its lost limbs. The same laboratory, but led by other researchers, has also been focusing on the salamander’s regenerative abilities in great detail.
While the salamander is able to regenerate entire limbs, humans like most mammals can only regenerate the fingertip.
Sammarco’s research, however, has been focused on the mouse model.
If the very end of the fingertip to around the nail bed is lost, it will grow back, certainly in very young children. Adults may not be able to do so, but there are new technologies now available as I wrote about at length in this article using the extracellular matrix, extracted from pig’s bladder.
If further of the finger is lost beyond the nail bed then regeneration cannot occur and the reasons for this were observed in 2013 in this study that I reviewed here.
Oxygenation Of The Wound
The Tulane lab has been studying which genes are turned on, along with the proteins and cellular activities, that get change at the injured site.
Sammacro figured that genes don’t just initiate regeneration on their own, there is a signaling process that is instructing them to do so. She thought what would happen if oxygen is playing a part? As oxygen is the primary signal that turns on various genes.
So the team exposed a thin layer of bone, taken from the amputation site, to high levels of oxygen, using a special incubator.
They discovered that exposing the regenerating bone to 20% oxygen, it will respond well but only at a certain time. Meaning that if you try this process too early like right after the amputation injury then it will not be effective.
The earth’s atmosphere is made up of 20% oxygen, however, that is higher than the level in the body which is said to be around 6%. In some areas of injury, the oxygen level may go down to only 1% because the blood vessels that would normally deliver oxygen to tissues, will retract after an injury.
The drop in oxygen levels is something of a mystery for those in the wound healing areas. Researchers are trying to figure out how to reinvigorate vasculature and how to oxygenate the wound site.
Sammacro argues that there is no hard and fast rule of when to flood the injured site with oxygen or when to drop the oxygen levels to encourage vasculature. She feels its all about timing and of course there is a sequence of growing things back. So perhaps oxygen can be the trigger that needs to be applied at a certain time.
In summary to this research, the scientists point out that even just partial regeneration of a limb, even just an inch, would make all the difference from walking or being confined to a wheelchair. Or from not able to pick up everyday items to be able to hold a cup of coffee in the morning.
With the extra length in stump length that would allow the patient to be able to do the things they did before, after their rehabilitation, like skiing for example. However, keeping in mind the long term goal of complete limb regeneration.
Further research can be found here of the influence on bone regeneration using oxygen techniques.