Frozen extracellular matrix preserves its thrombogenicity after thawing, while Matrigel induces a poor platelet response.

Two putative substitutes for fresh endothelial cell (EC) extracellular matrix (ECM), frozen ECM and Matrigel, were studied using a parallel-plate perfusion system and platelet deposition was evaluated morphometrically. Coverslips covered with ECM were stored frozen at-30 C for 0 (fresh ECM), 1, 2, 3 or 4 weeks. The ability of frozen ECM to support platelet adhesion after freezing was analyzed under three experimental approaches, perfusing blood: (i) at different shear rates; (ii) on a highly reactive ECM obtained from stimulated EC; and (iii) on ECM incubated with a monoclonal antibody against laminin (LM). Matrigel, alone or mixed with different fractions of wet cryoprecipitate, was layered on coverslips as a thin uniform coat, and perfused, as was done with the frozen ECM. Platelet deposition onto fresh ECM was 21.3 1.5%, 25.5 2.1% and 30.8 2.4% (at shear rates of 300, 800 and 1300/s, respectively) and 40.0 3.8% in PMA stimulated ECM perfused at 800/s. Values obtained on frozen ECM did not vary from those obtained using fresh ECM. Results from perfusion studies using ECM preincubated with an anti-laminin antibody and observations from immunofluorescence studies indicated that the presence and distribution of the adhesive proteins in frozen ECM were similar to those observed on fresh ECM. Platelet deposition on Matrigel was practically absent. Addition of a 20% cryoprecipitate fraction partially restored its thrombogenicity. Our results indicate that when ECM is kept frozen for up to 4 weeks, it behaves as fresh ECM in perfusion studies. On the contrary, Matrigel is not a suitable substrate to support platelet attachment under flow conditions.