We have investigated the effect of changes in microstructure, surface energy, surface charge condition and electronic conduction on the interaction of human platelets with silicon modified hydrogenated amorphous carbon films (a-C:H:Si or Si-DLC). Results based on Raman spectroscopy, Scanning electron microscopy, X-ray photo-electronspectroscopy, surface energy measurements, electrical resistivity, contact potential difference, and thermal annealing indicates a correlation between some of the measured values and the interaction of the films with human blood platelets. Statistical analysis of platelet aggregation on the films using the Student's t-test indicated differences between platelet aggregation on the modified films compared to the as-deposited film at a p-value of