tokens: ail & amp ; % 20used % 20as % 20nonhormonal % 20contraceptive & amp ; % 2Frna i % 2Dused % 2Das % 2Dnonhormonal % 2Dcontraceptive % 2F2007 % 2D10 % 2D23 -RSB- A group of researchers at Brigham and Women 's Hospital in Boston are focused on developing a new , nonhormonal contraceptive that uses RNAi technology to silence the ZP3 gene , which is required to fertilize an egg during ovulation .