Cells and Materials


Low-temperature isotropic pyrolytic carbon (LTIC) is the preferred material for mechanical heart valve prosthetics due to its durability and good thromboresistance, although thromboembolic complications remain a significant clinical problem. LTlC morphology has been previously studied using scanning (SEM) and transmission electron microscopy (TEM), and scanning tunneling microscopy (STM). However, these microscopies have limitations with imaging rough surfaces. In this study, LTIC valve leaflets from CarboMedics, Inc. and St. Jude Medical, Inc. were prepared and polished exactly as used in clinical prosthetics, and examined at magnifications up to macromolecular resolution using stereo-pair low-voltage SEM (LV -SEM). LV -SEM reveals that LTIC leaflets have a complex topography of 10 nm to 1 ~m features, with height differences of 100- 500 nm occurring over lateral distances of 10-50 nm. Compared to previous reports using conventional SEM and STM, LV -SEM shows a much rougher surface. In contrast to studies that have reported minimal platelet interaction with LTIC, very ex tensive adhesion and spreading were observed. That our observations are different from previous reports may be ex plained by the physics of SEM image formation at low and conventional (higher) accelerating voltages. Due to the low atomic density of LTIC and platelets, obscuration of small features due to specimen coatings, and since platelets closely follow LTIC's three-dimensional contours, the surface sensitivity of conventional SEM is unable to provide sufficient contrast to image either the material topography or thin adherent platelets. These results suggest that the ex tent of platelet interaction on L TIC vascular prosthetics may have been previously underestimated .