## 3 Results
### Images of Platelets and Granules by Traditional TEM  
Isolated resting platelets were round or ovoid biconvex discoid and had an average diameter of 2-3 um in the long axis. In a traditional EM, we could identify the mitochondria, vacuoles, and several membrane-bounded granules in the cytoplasm (Figure 2A). There were two major types of membrane-bounded granules. \(\alpha\)-Granules were abundant, homogeneous pale-staining, and about 200-300 nm in diameter. Dense granules were darkly stained and smaller than \(\alpha\)-granules. Since there were fewer dense granules, they were not as easily visible in sections. The platelet also contained round or elongated membrane-bounded vesicles or vacuoles that represented sections of the open canalicular system (OCS), the opening of which is located on the surface of the platelet (Figure 2A).  
Figure 1: Schematic diagram of the K-kit microchip. **(A)** The three-dimensional structure of the K-kit microchip, which is composed of silicon metal, appeared as an octagonal cuboid-like block (1.7 mm \(\times\) 1.4 mm \(\times\) 0.8 mm). There are two small sample chamber openings on the left and right ends of the long axis of the microchip. The liquid specimen can naturally enter the sample chamber by touching the specimen through the openings (as shown in the ovoid circle). The upper and lower sides of the microchip are depressed to form an observation window. Only the area of the observation window allows the electron beam of electron microscope to pass through the specimen to generate a high-resolution image of the specimen. **(B)** After the K-kit microchip is loaded with the liquid specimen, the two ends of the sample chamber are sealed, and the microchip is placed and fixed in the center of a copper grid (3 mm in diameter with a 1 mm diameter hole in the center). The grid combined with the microchip can be directly placed on the grid holder of a traditional electron microscope for ultrastructural examination.  
During the initial stage of activation, platelets showed pseudopodia formation and release of components from the granules (Figure 2B). Granules released their contents either directly onto the surface or into the OCS. We observed that granule contents were being released from the surface of activated platelets (asterisk in Figure 2B). In addition, a relatively central electron-dense core was usually separated from the membrane in \(\alpha\)-granules of activated platelets (arrowheads in Figure 2B). Dense granules were smaller than \(\alpha\)-granules, and had a high-density core surrounded by a stain-free rim (as shown in Figure 2B).  
Figure 2: Electron micrographs of resting and active human platelets. (**A**) A resting platelet is oval (with a long axis length of about 2 \(\upmu\)m), and filled with many membrane-bound granules. Most of these granules were \(\alpha\)-granules of about 200 nm in diameter that contained gray homogeneous substances. In addition, we could identify mitochondria and small vesicles in the cytoplasm. However, no dense granule was observed in this figure. The curved arrow indicates an opening of an open canalicular system (OCS) on the surface membrane of the resting platelet. (**B**) The active platelet showed the extended pseudopods. The \(\alpha\)-granules in the active platelets had a more-dense electron core (indicated by arrowheads) after activation. The curved arrow also indicates an opening of OCS on the surface membrane of the active platelet. In addition, we observed that granule substances were released from the membrane because the granule was in contact with the membrane and liquid substances were exuded (indicated by asterisk). A dense granule with a high-density core surrounded by a stain-free rim (indicated by arrow) can be seen in another platelet below the picture. \(\alpha\), \(\alpha\)-granule; D, dense granule; M, mitochondria; scale bar, 0.2 \(\upmu\)m.