1. Department of Biomedical Engineering; University of Groningen and; University Medical Center Groningen; Antonius Deusinglaan 1 9713 AV Groningen The Netherlands
2. DSM Research; P. O. Box 18 6160 MD Geleen The Netherlands
3. Department of Polymer Chemistry; University of Groningen; Nijenborgh 4 9747 AG Groningen The Netherlands
4. Trobas gelatine BV; Steenstraat 9 5107 NE Dongen The Netherlands