In 1991 he spun out the company Thromb-X nv from the KU Leuven in Belgium. The primary focus of Thromb-X was in the cardiovascular space with an initial effort to develop staphylokinase as a more affordable thrombolytic medicine compared to t-PA ("poor man's t-PA"). With the constitution of ThromboGenics Ltd in Ireland in 1998, the company expanded its R&D scope to include cardiovascular, oncology and ophthalmology programs. ThromboGenics developed ocriplasmin, a truncated form of plasmin, for the treatment of vitreomacular traction in the eye. Disappointed by the, in his opinion inadequate strategic and commercial governance of the company, Collen left ThromboGenics as Chairman and board member in December 2013.