The color and starkness of this photograph works well in the overall theme. I believe that the composition could create some more impact in the long run by creating some diagonal flow in the image with the placement of the needles. The parallels are more static and diagonals creating triangles within the image would create some added dynamics in the composition. Just some food for thought :)
6 - Good. Good colors. Criticism; 'if only' the end of the needle were sharper for more 'effect', make this better in my opinion. Perhaps a little more space at the top too or a variation in composition, not sure. White at the fore left is too blown out and detracts slightly, but fairly minor.
Very nice, the drop on the end is a great addition! The only suggestion I have is the background, the white blends in too much with the top of the syringes. Nice composition.