After viewing so much great works here I am thinking of posting this but it’s my first (completed) work with this GREAT program so let it be then. As title says…
Hey, nice start!
My only real crit is the roundness of your blood-cells. You should try to flatten them to have a more blood-cell-ish look. Also, you seem to have some artifacts on the wall surfaces in the back.
I like it though.
i like the style! some depth of field blur would soften the background some and make the nanobots really pop out. this could make a neat animation.
Neat 
I like it.
You know, this is a periodic favorite among posters. I think there was a tutorial on SSS or something a while back that dealt with blood cells. I can’t find it off the top of my mouse cursor, but it might be a fun look-see anyway.
For a real crit, you might want to add some more blood cells both fore and aft then do as treatkor recommends and add some motion blur. This would both break the frame and, like he said, cause those bots to really pop!
As it is, all the cells and bots are centered far inside the edges of the image…
Hope this helps.
nice render, it seems as though it could use a volumetric effect though. mist would work, or maybe a red spot halo.
Tnx for comments surely I’m gona do the things you all recommended. This is indeed the greatest community I participate. And I think that is most powerfull weapon of blender.
Tnx again, see ya quickly.
PS
Is there any way I could save Z depth as image, to use it later in postwork?
Yup, there totally is. It’s a node thing, but it isn’t that hard. Just open up the scene node editor and connect the z output of the scene node to a map value node, then to a colour ramp node, I believe. You’ll need to monkey around with the map value node, but you should eventually get an image you can hook up to a ‘file output’ node.
Great work. The only recommendation I would have is for the blood cell and vein wall texture. You might want to check out thistopic, as they post some fantastic settings there.