To rule out the confounding effects of surface chemistry on the observed cell adhesion, we quantified adsorption of collagen on the implant surfaces indirectly by an immunologic approach: The devices, fixed in standard culture dishes, as explained earlier, were incubated with a solution containing 1 mg/mL type I collagen from rat tail (PAN Biotech GmbH, Aidenbach, Germany) on a rocking platform at room temperature overnight. After repeated rinsing with PBS+0.1% Tween (PBST), the devices were incubated with 1:2000 polyclonal antibody against type I rat collagen (mouse-anti-rat COL1A, sc-59772; Santa Cruz Biotechnology, Heidelberg, Germany) for 2 hours at room temperature. Excess antibody was washed off with PBST and FITC-labeled secondary antibody (goat-anti-mouse; Meridian Life Science Inc., Saco, ME) coupled to protein-G beads (Dynabeads; Invitrogen Dynal, Oslo, Norway) were added at a concentration of 2 × 106 beads per culture dish. After 1 hour of incubation at room temperature, unbound beads were rinsed off by repeated washing with PBST. The number of beads bound to collagen adsorbed to the implant surface was assessed with the same CLSM set-up described earlier. Because of the small size of the beads (2.8 ± 0.2 μm), a higher magnification was used than that used for the cell counts. Thus, we determined the average number of beads per 375 μm × 375 μm of surface area.