Scientists say they have made a breakthrough on developing a contraceptive pill that only needs to be taken once a month. The pill, which so far has only been tested in pigs, uses a new star-shaped drug delivery system that stays in the digestive tract for days or weeks after being swallowed, researchers from Harvard’s Brigham and Women’s Hospital and the Massachusetts Institute of Technology reported in the journal Science Translational Medicine. The gelatine capsule, which has so far only been tested on pigs, dissolves in the stomach to release a six-armed star-shaped polymer structure that sits in the stomach for at least three weeks and releases synthetic hormones to prevent pregnancy. The experimental capsule is still years away from drugstores, but researchers reported Wednesday that it worked as designed in a key test in animals. The Bill and Melinda Gates Foundation is investing $13 million for further development of the once-a-month pill, in hopes of eventually improving family planning options in developing countries. The research was mostly funded by the Bill and Melinda Gates Foundation, which urged the team to develop new long-lasting contraceptive drugs to reduce the risk of unintended pregnancies. To make it work, researchers looked for materials that could survive a highly acidic fluid, and discovered that two types of polyurethane could work well for the arms and the central core of the star-shaped capsule. Once the capsule reaches the stomach, it expands and becomes lodged in place. The contraceptive drug, which is loaded in the pill, is then released at a controlled rate over time. The capsule is designed to break down after three or four weeks, and will exit the body through the digestive tract. Langer said further research is being conducted to develop the pill for human tests, which he hoped would be possible within three to five years.