WASHINGTON, June 25 (Xinhua) -- U.S. scientists have developed an oral delivery method that may allow diabetics to keep their blood sugar levels in check by swallowing a pill rather than injecting themselves with a needle once or twice daily.

The potential delivery method, described in a study published on Monday in the Proceedings of the National Academy of Sciences, promised to improve the quality of life for up to 40 million people with type 1 diabetes worldwide.

Insulin therapy, by injection just under the skin or delivered by an insulin pump, generally keeps the glucose levels of most diabetics in check.

"But many people fail to adhere to that regimen due to pain, phobia of needles, and the interference with normal activities," said the paper's senior author Samir Mitragotri, Hiller Professor of Bioengineering at Harvard University.

Finding a way to deliver insulin orally has been elusive because the protein does not fare well when it encounters the stomach's acidic environment and it is poorly absorbed out of the intestine.

The key to the new approach is to carry insulin in an ionic liquid comprised of choline and geranic acid that is then put inside a capsule with an acid-resistant enteric coating, according to the study.

The formulation is biocompatible, easy to manufacture, and can be stored for up to two months at room temperature without degrading, which is longer than some injectable insulin products currently on the market, according to the study.

The researchers encapsulated the insulin-ionic liquid formulation in an enteric coating, which can resist breakdown by gastric acids in the gut.

The polymer coating dissolves when it reaches a more alkaline environment in the small intestine, where the ionic liquid carrying insulin is released.

When a protein molecule such as insulin enters the intestine, there are many enzymes whose function is to degrade the proteins into smaller amino acids, according to the paper's first author Amrita Banerjee, who conducted the research while working as a postdoctoral fellow in Mitragotri's lab.

The choline-geranic acid formulation was shown to be adept at penetrating two final barriers: the layer of mucus lining the intestine and the tight cell junctions of the intestine wall, through which large-molecule drugs such as insulin cannot easily pass.

Banerjee said that ionic liquid-borne insulin could be prepared in a one-step process so that it could be readily scaled up for inexpensive industrial production.

Mitragotri planned to conduct more animal tests of the formulation as well as long-term toxicological and bioavailability studies.

The United States Food and Drug Administration has established a daily recommended dose of choline, a vitamin-like essential nutrient. Geranic acid, a chemical that naturally occurs in cardamom and lemongrass, is widely used as a food additive.