Bacteria may allow recreation of bones

After biting into a piece of Nata de Coco, a high fiber, zero fat Filipino dessert, it is hard to imagine that bacteria, not humans, synthesize the bulk of this sweet treat.

You can thank Gluconacetobacter, a non-pathogenic, cellulose-producing bacterium, for the popular Filipino dessert. And if dessert is not enough to bolster the little creature’s resume, add to it the fact that the bacterium’s by-product has the potential to save our bones and our body.

“The cellulose is edible, it is totally safe. The bacteria that we culture are used as a food source,” said Stacy Hutchens, a University of Tennessee graduate student. “The bacteria are grown in coconut milk in the Filipino dessert Nata de Coco. That really interested me since I am of Filipino descent.”

The FDA recently approved the request by Xylos Corporation, based in Langhorne, Pa., to use bacterial cellulose for skin grafting and regeneration. Hutchens’ goal is to expand the biomedical use of the bacterial product by modifying the material so that it can replace human bone.

“Because the cellulose is already recognized by the FDA, it will make it a lot easier to go forward and get an approval for (the bone grafting) application,” Hutchens said.

The bacteria secrete a polysaccharide layer, called a pellicle, as their cloak of protection against ultraviolet radiation and drying.

“These bacteria are like spiders that swim around and weave this pure cellulose into a mesh,” she said. Requiring oxygen for survival, these aerobic bacteria primarily live at the surface of their liquid home, which consists of yeast, glucose, protein and water.”

Braiding and overlapping the ribbons, the bacteria then twist the cellulose into crystal lattice layers that lie on top of each other, giving depth to the cellulose layer.

“We just lift off that layer, clean it, and then we are ready to use it. It is similar to tissue,” Hutchens said, which is perfect for her experiment to infuse a bone-replicating material inside the polysaccharide fibers.

Hydrogen bonds hold together the web of nanofibrils that the bacteria weave, which makes the cellulose layer coalesce into a gel. Because it holds water, the structure is highly permeable, which Hutchens uses to her advantage when trying to mimic bone structures.

Hutchens’s idea for using bacterial cellulose to replicate bone began four years ago when she went to Oak Ridge National Laboratory as summer student. She heard of an initial experiment showing that Nata de Coco cellulose cubes soaked in calcium and phosphate solutions formed a white mineral; Hutchens was then eager to start a research project where she would synthesize a bone replacement material using a similar method. Citing National Laboratory chemical scientist Barbara Evans’ work as a starting point, Hutchens ran with the idea of infusing the mineral found in bone into bacterial cellulose for her master’s and now doctoral work.

She first learned to how to culture Gluconacetobacter and its cellulose byproduct. Then the biomedical engineering student had to figure how to produce a bone-like structure from the bacteria’s gel. She became especially interested in bone replacement after a family member required the use of bone grafts to reinforce the bone in their jaw prior to dental implantation surgery.

Submerging the cellulose in calcium and then phosphate solutions, Hutchens was able to form calcium-deficient hydroxyapatite, which is the main mineral component for bone and stimulates bone growth and regeneration when implanted, she said. But with limited access to the analysis equipment she needed, it was difficult for Hutchens advance her project beyond an idea.

In the last two years she has been able to analyze the material properties of her bone gel with Dr. Roberto Benson in the Materials Science and Engineering Department at UTK, which she said has really kick-started her research. Comparing her synthetic calcium-phosphate material to actual bone, Hutchens found that the nanostructure was very similar.

“It really reminded me of bone itself,” she said.

Whether this bioengineered bone will grow in the body is unknown, but that is the UTK student’s next research step. Hutchens is preparing the paperwork required to conduct a biological study where she will implant her bone-like gel into an animal model. That test will determine whether the bone gel can attract developing bone cells, or osteoblasts, to an injured area and elicit bone regeneration.

Since bone is the second most implanted tissue next to blood, Hutchens’s bone gel might be the answer for the short supply of cadaver tissue that surgeons use when humans severely damage bone tissue or need reconstructive surgery. Hugh O’Neill, one of Hutchens’ mentors at Oak Ridge National Laboratory, said that the bone gel is ideal because it is clean and it is not immunogenic.

“There are a lot of safety issues with cadaver bone,” said Barbara Evans, Hutchens’s second advisor who works with O’Neill at National Laboratory. “There might be some disease or problem that the family was not aware of and that can be really dangerous for transplants.”

She cited a case where Biomedical Tissue Services, a New Jersey company, was accused of harvesting cadaver tissue without notifying the deceased families. Because the company did not follow FDA guidelines or contact the family for permission to use the tissue, its actions increased the risk for doctors to use diseased tissue, raising the probability for infection in the tissue recipient. Even tissue from reputable companies could pose a threat due to difficulties in screening donors.

Hutchens’ bone gel would solve the sanitary issues that complicate tissue transplants because cellulose is a pure hypoallergenic material. The gel that encases Hutchens’ bone-mimicking formula remains clean throughout the bone-mineral development procedure, and she keeps the material sterile through autoclaving. Since the demand for human bone tissue is hard to supply, Hutchens’ synthetic material would ease surgeons’ needs to find bone donors and subject patients to multiple operations.

There is still a lot to learn, Hutchens said. Time and testing will decide if the Gluconacetobacter cellulose will have the major affects on the biomedical engineering field it has had on the sweets industry.