An important unsolved problem in bioengineering is learning to control polymer-cell interactions. Achieving this control can allow engineering of artificial tissues as an alternative to organ transplantation, the development of materials for targeted drug delivery, and surfaces that detect diseased cells or even biological warfare agents. We describe the development of “combinatorial biosurface chip” (CBC) technology for high-throughput assays of the effects of polymer surface energy and chemistry on cell function. It was shown recently that thickness has a strong effect on the surface energy of poly(3-octylthiophene-2,5-diyl) (P3OT), a semiconductor in its undoped state. With this in mind, the overall objective of this research is to develop thickness gradient libraries (120 – 200 nm) of semi-conductive P3OT for regulating proliferation in osteoblasts (bone-forming cells). We demonstrate that P3OT thickness has an effect on MC3T3-E1 cell proliferation as higher proliferation is observed between 120 - 130 nm for cells cultured for a period of one day. Also, surface chemistry has an effect on proliferation as the proliferation ratio is significantly higher on P3OT after one day compared to the control tissue culture polystyrene dishes.