Finally I finished the mechanical part using a solid base of polyacetal polymer and a drawer slider. The base was modeled using a router and is very robust. I ´ll post the measurements for the base later. The arduino code needs a little bit of work but I plan to finish it this comming week
https://github.com/naroom/OpenSyringePump/blob/master/openSyringePump/openSyringePump.pde