If you were to print with a viscous paste, which solution would you go for and why?
I have seen many extrusion mechanisms and tried to collect the different solutions in groups such as:
• plunger/syringe based;
• auger extruder based;
• moineau pump based;
• peristaltic pump based;
• gerotor pump based;
• baric.
Thank you @Nick_Kloski2 . I already had it checked, though I’m not sure whether it is air pressure (like in the Frostruder MK2 at http://www.thingiverse.com/thing:1143) or a motorised plunger that Hyrel3D uses (sort of like this ToolHead from @Imagine_3D_Printer at http://theimaginemachine.com/en/store/product/10-toolhead-ii).
In fact, I am quite interested in what @Norbert_Rovira suggests: not as precise as other solutions out there, but looks extremely light and small on the extrusion head. Could you please provide some specifications? I’m sorry, but even though I can understand some, I never really learned Spanish.
Thought you might be interested in this new Additive Manufacturing technique called Suspended Depositions by @Brian_Harms (http://nstrmnt.com/#/suspended-depositions/).
For what I see on the web page it looks like a direct stepper-driven peristaltic pump controls how the resin is distributed.
Was just suggesting a guy I know who works with his own designs of peristaltic pump:
@Luis_Rodriguez_Alcal
You can check some of his work in his blog: http://lyulyulyulyu.tumblr.com/
By the way, my blog is in Spanish and English, but I do not play with food for now 
I think each has its own pros and cons, so far i have just been playing with peristaltic extruders, my opinion is that really depends on the accuracy you want to reach and the viscosity of the material and how special it is (corrosive, safety issues, …). Also the amount of time you have to make it work…
And my bet is that Hyrel3d is motorized…but who knows ehhehe
Indeed. In fact, as I said, I am interested in your solution cause it is extremely light on the extrusion head - on a more solid, final system that would give some allowance for a higher printing speed. But I also reckon that filling the whole catheter before pumping the paste from the reservoir to the nozzle/needle produces some considerable amount of waste and - I am just thinking aloud - reduce the accuracy on more viscous liquids?
Tricky topic.
So, @Luis_Rodriguez_Alcal , what is in your experience the more accurate extrusion technique?
For what i know (limited), my opinion is that any linear flow pump properly set up is the best for accuracy, for example commercially you can get micro litters flows range, peristaltic is easy and clean BUT not lineal. In my case i overcome no-lineality issue with a long tube that works as a reservoir that “eats” pulsation, and after lots of retraction depending on the fluid’s viscosity.