Direct additive manufacturing of hydrophobic microstructures using soft polymer

Soft polymers are essential for medical applications where biomimicking of soft biological structures is needed. The performance of these soft polymers can be boosted by incorporating hydrophobic re-entrant structures using 3D printing. However, the direct additive manufacturing via Digital Light Processing (DLP) of such structures using commercially available biocompatible soft polymers without photoabsorbers has not yet been explored. In this study, hydrophobic surfaces with re-entrant structures in the form of walls were 3D printed in a bottom-up DLP printer using a commercially available biocompatible polymer with shore hardness A90. These structures were printed in vertical orientation with respect to the building plate. Due to the adhesion of each printed layer to the vat membrane, bent structures were observed on the sides of the sample which allowed the partial intrusion of the water below the overhang. Even with this, the structures were able to prevent the full wetting of water into the structure. Anisotropic wetting was observed with water static contact angles reaching in the range of 144-149° and 112-115° for a 10 μL droplet as examined on different sides.