In this video as part of The Motley Fool's "Ask a Fool" series, Fool health-care analyst David Williamson takes a question from a Fool reader, who writes, "What's your Foolish opinion on Organovo (NASDAQ:ONVO)? Buy, sell, or hold?"

David introduces investors to the company, which is working to develop the ability to use 3-D printing technology to create human livers, which would facilitate medical testing for liver toxicity without having to test on actual humans. David also warns that even though this is a potentially disruptive force, it's still so early in the development of its product that there's still a lot of risk for investors here, and he advises keeping this as no more than a tiny percentage of any investment portfolio.