Boston Scientific ($BSX) has signed an agreement to buy Sadra Medical, a development-stage company in Los Gatos, California, for up to $450 million. The agreement calls for an upfront payment of $225 million plus additional potential payments of up to $225 million upon achievement of specified regulatory and revenue-based milestones through 2016. The company has been a strategic investor in Sadra since 2006. According to a Boston Sci release, Sadra is developing the first fully repositionable device for percutaneous aortic valve replacement to treat patients with severe aortic stenosis. Boston Scientific release