Electrostatic stretching of hyaluronic acid molecule and cutting with AFM probe

Precipitation direction of dispersed hyaluronic acid (HA) molecules during electrostatic stretching was studied by using AFM imaging. Several microlitters of 1 g/L HA solution was dropped on a thermally oxidized Si substrate and dried at room temperature, applying square voltage of 20 V-pp with frequency of 1 or 30 MHz. Under these conditions, the HA molecules were stretched and dispersed on the substrate surface after the droplet was dried. The HA molecules stretched to the direction perpendicular to the outline edge of the shrinking HA solution, independent of the direction of electric field, applied voltage and its frequency. Based on these results, precipitation and stretching mechanism of the molecule from the HA solution was discussed briefly. Moreover, we demonstrated possibility of molecular surgery by indicating that the stretched HA molecules could be cut with an AFM probe.