Unexpected hydrophobicity on self-assembled monolayers terminated with two hydrophilic hydroxyl groups

Unexpectedly resisting protein adsorption on self-assembled monolayers terminated with two hydrophilic hydroxyl groups

OH-terminated self-assembled monolayers, as protein-resistant surfaces, have significant potential in biocompatible implant devices, which can avoid or reduce adverse reactions caused by protein adhesion to biomaterial surfaces, such as thrombosis, immune response and inflammation. Here, molecular dynamics simulations were performed to evaluate the degree of protein adsorption on the self-assembled monolayer terminated with two hydrophilic OH groups ((OH)2-SAM) at packing densities (Σ) of 4.5 nm-2 and 6.5 nm-2, respectively. The results show that the structure of the (OH)2-SAM itself, i.e., a nearly perfect hexagonal-ice-like hydrogen bond structure in the OH matrix of the (OH)2-SAM at Σ = 4.5 nm-2 sharply reduces the number of hydrogen bonds (i.e., 0.7 ± 0.27) formed between the hydrophobic (OH)2-SAM surface and protein. While for Σ = 6.5 nm-2, the hydrophilic (OH)2-SAM surface can provide more hydrogen bonding sites to form hydrogen bonds (i.e., 6.2 ± 1.07) with protein. The number of hydrogen bonds formed between the (OH)2-SAM and protein at Σ = 6.5 nm-2 is ∼8 times higher than that at Σ = 4.5 nm-2, reflecting the excellent resistance to protein adsorption exhibited by the structure of the (OH)2-SAM itself at Σ = 4.5 nm-2. Compared with a traditional physical barrier effect formed by a large number of hydrogen bonds between the (OH)2-SAM and water at Σ = 6.5 nm-2, the structure of the (OH)2-SAM itself at Σ = 4.5 nm-2 proposed in this study significantly improves the performance of the (OH)2-SAM resistance to protein adsorption, which provides new insights into the mechanism of resistance to protein adsorption on the (OH)2-SAM.

Fiber-based photothermal, UV-resistant, and self-cleaning coatings fabricated by silicon grafted copolymers of chitosan derivatives and gallic acid

Superhydrophobic and hydrophobic properties are generally created by adopting low surface free energy materials. Therefore, most studies have focused on creating surface hydrophobicity by using hydrophobic or fluorinated materials. However, few studies are reported on realizing surface hydrophobicity by directly introducing hydrophilic molecules, which is also a challenge. Herein, with platinum nanozyme as the catalyst, the novel hydrophobic coatings have been rapidly gained via anchoring the polymer of hydrophilic gallic acid and chitosan or chitosan quaternary ammonium salt onto cotton fabric surface. Notably, the novel hydrophobic coatings exhibit significant advances compared with conventional hydrophobic ones created by utilizing fluorinated or hydrophobic materials, which breaks the limitation of employing low surface energy materials for gaining surface hydrophobicity. Subsequently, the sodium methyl silicate was grafted on the polymer's coatings to strengthen surface hydrophobicity and the abrasion resistance of hydrophobicity. Interestingly, the heating could induce the hydrophilicity of cotton fabric to recover to hydrophobicity. Moreover, the hydrophobic coatings also possess good photothermal conversion, UV resistance, and anti-oxidation activity for self-cleaning application and oil water separation. Briefly, the present work may open a new direction for preparing novel hydrophobic coatings by combining gallic acid and chitosan-based macromolecular carbohydrates.