A process for preparing a modified heat-treated platelet pellet lysate, said process comprising the steps of: a) Providing a platelet pellet lysate, b) Heat-treating the platelet pellet lysate at a temperature of 55° C. to 65° C. during 20 to 40 minutes, c) Purifying the heat-treated platelet pellet lysate of step b) so as to obtain a modified heat treated platelet pellet lysate having a total protein content of less than 70% of the total protein content of the platelet pellet lysate of step a).