Potassium ion can critically effect the interaction between collagen microfibrils and mica leading to different ordered structures that vary dramatically with changing ion concentration. AFM images of the structures formed at different. ion concentrations appear to be intermediate stages in the progression from disordered to ordered film. At 200 mM potassium ion concentration, a nanometer-thick array of aligned and bundled microfibrils covering large areas can be created easily and reproducibly on mica.