Roll-to-Roll, Shrink-Induced Superhydrophobic Surfaces for Antibacterial Applications, Enhanced Point-of-Care Detection, and Blood Anticoagulation

Superhydrophobic (SH) surfaces are desirable because of their unique anti-wetting behavior. Fluid prefers to bead up (contact angle >150˚) and roll off (contact angle hysteresis <10˚) a SH surface because micro- and nanostructure features trap air pockets. Fluid only adheres to the peaks of the structures, causing minimal adhesion to the surface. Here, shrink-induced SH plastics are fabricated for a plethora of applications, including antibacterial applications, enhanced point-of-care (POC) detection, and reduced blood coagulation. Additionally, these purely structural SH surfaces are achieved in a roll-to-roll (R2R) platform for scalable manufacturing.Because their self-cleaning and water resistant properties, structurally modified SH surfaces prohibit bacterial growth and obviate bacterial chemical resistance. Antibacterial properties are demonstrated in a variety of SH plastics by preventing gram-negative Escherichia coli (E. coli) bacterial growth >150x compared to flat when fluid is rinsed and >20x without rinsing. Therefore, a robust and stable means to prevent bacteria growth is possible. Next, protein in urine is detected using a simple colorimetric output by evaporating droplets on a SH surface. Contrary to evaporation on a flat surface, evaporation on a SH surface allows fluid to dramatically concentrate because the weak adhesion constantly decreases the footprint area. On a SH surface, molecules in solution are confined to a footprint area 8.5x smaller than the original. By concentrating molecules, greater than 160x improvements in detection sensitivity are achieved compared to controls. Utility is demonstrated by detecting protein in urine in the pre-eclampsia range (150-300µgmL-1) for pregnant women.Further, SH surfaces repel bodily fluids including blood, urine, and saliva. Importantly, the surfaces minimize blood adhesion, leading to reduced blood coagulation without the need for anticoagulants. SH surfaces have >4200x and >28x reduction of blood residue area and volume compared to the non-structured controls of the same material. In addition, blood clotting area is reduced >5x using whole blood directly from the patient. In this study, biocompatible SH surfaces are achieved using commodity shrink-wrap film and are scaled up for R2R manufacturing. The purely structural modification negates complex and expensive post processing, and SH features are achieved in commercially-available and FDA-approved plastics

Shrink-Induced Superhydrophobic and Antibacterial Surfaces in Consumer Plastics

<div><p>Structurally modified superhydrophobic surfaces have become particularly desirable as stable antibacterial surfaces. Because their self-cleaning and water resistant properties prohibit bacteria growth, structurally modified superhydrophobic surfaces obviate bacterial resistance common with chemical agents, and therefore a robust and stable means to prevent bacteria growth is possible. In this study, we present a rapid fabrication method for creating such superhydrophobic surfaces in consumer hard plastic materials with resulting antibacterial effects. To replace complex fabrication materials and techniques, the initial mold is made with commodity shrink-wrap film and is compatible with large plastic roll-to-roll manufacturing and scale-up techniques. This method involves a purely structural modification free of chemical additives leading to its inherent consistency over time and successive recasting from the same molds. Finally, antibacterial properties are demonstrated in polystyrene (PS), polycarbonate (PC), and polyethylene (PE) by demonstrating the prevention of gram-negative <i>Escherichia coli</i> (<i>E. coli</i>) bacteria growth on our structured plastic surfaces.</p></div

Top down SEM images and AFM of the structurally modified surfaces' multiscale structures were taken.

<p>Features are shown in (<b>A</b>) shrunk, bimetallic PO, (<b>B</b>) transferred in PDMS, and (<b>C</b>) imprinted in PS from PDMS. Scale bar is 10 µm for the large SEM images and 2 µm for the insets. (<b>D</b>) AFM 3D image of the morphology and height profile.</p

Calculated values of the solid fraction (Φ) were found using the average flat CA (<i>θ_Y</i>) and the average structurally modified CA (<i>θ_C</i>).

<p>Calculated values of the solid fraction (Φ) were found using the average flat CA (<i>θ_Y</i>) and the average structurally modified CA (<i>θ_C</i>).</p

Graphs depicting CA and SA for the structurally modified surfaces compared to flat.

<p>(<b>A</b>) Contact angle measurements of structurally modified and flat PDMS, PS, PC, and PE. (<b>B</b>) Sliding angle measurements of structurally modified and flat PDMS, PS, PC, and PE. <b>+</b>represents measurements >90°.</p