Influence of carboxyl group density on neuron cell attachment and differentiation behavior: gradient-guided neurite outgrowth.

A UV pre-irradiation step followed by a UV grafting step was used to graft poly(acrylic acid) (PAA) on polymeric substrates. These substrates were then used to investigate the influence of carboxyl groups (-COOH) on cell behavior. Both the attachment and differentiation behaviors of C17.2 cells showed a -COOH group density-dependent response. In order to achieve an even distribution of cells on a -COOH gradient surface for neuron differentiation studies, an Ar plasma post-treatment was applied to the PAA-grafted surfaces. It greatly improved the cell adhesion properties with little damage to -COOH groups. This allows uniform distributions of seeded cells even on substrates with -COOH gradients. A linear or stepped -COOH gradient was found to be capable of serving as a repelling cue to guide the outgrowth of neurites from C17.2 cells. Up to 3.7 times more cells developed neurites growing down the -COOH gradient than growing up it.