Which kinds of innovations make for incremental enhancements in the hands of large companies and which are meaningful enough to sustain a venture-backed start-up company? In a mature market for coronary stents dominated by large companies, start-ups developing new stents need to find the answers. Areas of innovation fall into four basic categories: improving stent safety and biocompatibility, avoiding the need for dual antiplatelet therapy, enhancing deliverability, and introducing specialty stents for complex vessels. Three companies profiled here have a plan for taking sufficient market share, reducing risk, and rewarding investors.

Most medical device start-ups seeking to tap into the enormous drug-eluting stent market have focused on novel stent or stent platform design, on the theory that drug efficacy is a given. But X-Cell Medical is betting that they've come up with a better drug. And they're making their case by stressing the importance of safety.

A preview of the emerging health care companies profiled in the current issue of Start-Up. This month's profile group, Convergence: What's Next at the Nexus?, features profiles of Direct-Haler, EndoBionics, Polymerix and X-Cell Medical. Plus these Start-Ups across Health Care: Discovery Genomics, FoldRx and Neuronetics.

Renowned cardiologist Martin Leon, MD, found himself growing frustrated with the tendency of start-ups to bring physicians into the develeopment program too late, when major but critical changes would be impractical if not outright impossible. So Leon and partner Yuval Binur, of Medica Venture Partners, set out to define a new model for device start-up creation, Accelerated Technologies Inc. The company has launched five new cardiovascular device companies and is about to launch a sixth.