When Loren Peterson moved ZyStor Therapeutics from St. Louis, Mo., to Milwaukee in the early 2000s, he had trouble finding other health care and biotechnology startups to keep him company. “It was pretty much a desert,” recalled Peterson, who sold ZyStor and its line of enzyme replacement therapies to BioMarin Pharmaceutical Inc. in 2010. Today, Milwaukee’s once-arid life sciences landscape is sprouting more ideas and emerging companies. It’s a trend that was on display Thursday at Milwaukee’s University Club during a pitch event that featured five promising health-tech ideas as well as two innovations in advanced materials.