Photo Credit: Courtesy of 3DStockPhoto ( image)
You cannot hope to print 0.5mm columns with a 0.4mm print head successfully using an FDM printer. Basically, you are asking the printer to lay down tiny blobs of filament, one of top of another. You have two options:
Use a finer nozzle (e.g. 0.1mm). However, such nozzles are reported as being very difficult to use.
Switch to a different printing technology (e.g. SLA). Resin and powder-based printers have much finer resolutions, and will have no difficulty printing the model that you describe.