Figure 3: Whole-blood incubation with thrombin-responsive and non-responsive gels.

Gels with low, medium and high degrees of CL (storage moduli of 3, 8 and 16 kPa respectively, see Supplementary Fig. S1) on glass supports were incubated with freshly drawn human whole blood at a ratio of 2 ml blood per 6.3 cm² gel surface area for 3 h. (a) Heparin release during the incubation. The heparin release from the gels with thrombin-cleavable sequence correlated strongly with the degree of CL. These released heparin concentrations reach pharmacologically relevant levels. All heparin release was through enzymatic degradation of the peptide crosslinker, as no heparin was released from the gels without that linker. (b) F1+2 peptide and (c) platelet factor 4 release were determined in plasma by ELISA and reflect plasmatic coagulation activation and platelet activation, respectively. The elevated plasmatic heparin concentrations produced by the cleavable gels enhanced their thromboresistant properties, seen as decreased thrombin formation (F1+2 peptide) and platelet response. (mean±s.d., n=6 in all panels; asterisks indicate P<0.05 in analysis of variance (ANOVA) with Student–Newman–Keuls post-hoc analysis).