I need to draw a schematic model for the interaction between tumor cells and their microenvironment. Can anyone please recommended software that you use to draw such biological or cellular models? Many thanks.
It somewhat depends at what resolution you want to work at. Have you looked at http://www.celldesigner.org already (free/open source)? In the commercial domain, I can recommend Pathway Studio by Elsevier (just google it; URL seems to change periodically).
One trick in PowerPoint is to setup the page /slide to a poster or A2. Larger the page size, better the print quality. Make use of free-hand drawings, color gradient etc,. Group them and save as a tiff or other formats. It's more convenient with a Macbook trackpad than a windows one. Other free alternative applications are Blender, sketchbook express, Inkscape.