Control of Intermolecular Interactions toward the Production of Free-Standing Interfacial Polydopamine Films

Abstract

Aggregation of the polydopamine (PDA) molecular building blocks at the air/water interface leads to obtaining large surface nanometric-thin films. This mechanism follows two possible pathways, namely, covalent or non-covalent self-assembly, which result in a different degree of structure order and, consequently, different structural properties. Control of this mechanism could be vital for applications that require true self-support PDA free-standing films, for example, electrochemical sensing or membrane technology. Here, we are considering the impact of boric acid (BA) and Cu2+ ions on the mentioned mechanism exclusively for the free-standing films from the air/water interface. We have employed and refined our own spectroscopic reflectometry method to achieve an exceptionally high real-time control over the thickness growth. It turned out that BA and Cu2+ ions significantly impact the film growth process. Reduction of the nanoparticles size and their number was examined via UV–vis spectroscopy and transmission electron microscopy, showing a colossal reduction in the mean diameter of nanoparticles in the case of BA and a moderate reduction in the case of Cu2+. This modification is leading to significant enhancement of the process efficiency through moderation of the topological properties of the films, as revealed by atomic force microscopy. Next, applying infrared, Raman, and X-ray photoelectron spectroscopy, we presented small amounts of metal (B or Cu) in the final structure of PDA and simultaneously their vital role in the oxidation mechanism and cross-linking through covalent or non-covalent bonds. Therefore, we revealed the possibility of synthesizing films via the expected self-assembly mechanism which has hitherto been out of control. Moreover, modification of mechanical properties toward exceptionally elastic films through the BA-assisted synthesis pathway was shown by achieving Young’s modulus value up to 24.1 ± 5.6 and 18.3 ± 6.4 GPa, using nanoindentation and Brillouin light scattering, respectively.

Co-immobilization of Ciprofloxacin and Chlorhexidine as a Broad-Spectrum Antimicrobial Dual-Drug Coating for Poly(vinyl chloride) (PVC)-Based Endotracheal Tubes

“…In turn, the CHX immobilization on the pDA film caused a modest increment of surface roughness, as illustrated in Figure A. It has been recently reported that the mechanical properties of pDA films can be coordinated by the addition of new molecules . Previous findings demonstrated the higher surface roughness on CHX coatings due to the occurrence of CHX aggregates and several protrusions on the grafted pDA layer .…”

“…The lack of an unambiguous pDA structure and clear mechanistic studies driving its formation make the understanding of its interaction with other molecules very complex and speculative. Due to the very nature of the functionalization process, involving the immersion of samples in antimicrobial solutions for long periods (∼18 h), it is mostly expected that favorable physical (noncovalent) adsorption/interaction occurs either by interference in the network of hydrogen (H) bonding between chains or involving π–π stacking, van der Waals forces, and hydrophobic interactions. , Therefore, this approach will lead to the development of a release system.…”

“…Due to the very nature of the functionalization process, involving the immersion of samples in antimicrobial solutions for long periods (∼18 h), it is mostly expected that favorable physical (noncovalent) adsorption/ interaction occurs either by interference in the network of hydrogen (H) bonding between chains or involving π−π stacking, van der Waals forces, and hydrophobic interactions. 29,30 Therefore, this approach will lead to the development of a release system. A quick qualitative inspection of the contact antimicrobial and release abilities of CIP and CHX on the modified PVC surfaces at 24 h upon immobilization (Table S1) demonstrated that CHX and CIP could retain dose-dependent antimicrobial/ release activities against major VAP-related species, providing evidence of the successfulness of the employed one-step pDAassisted immobilization approach.…”

TiO2/PDA Multilayer Nanocomposites with Exceptionally Sharp Large-Scale Interfaces and Nitrogen Doping Gradient

“…It most likely indicates the coordination of nitrogen to titanium atoms on the TiO 2 surface. , This is particularly reasonable because PDA adheres to surfaces via catechol and amino groups containing nitrogen. The peaks N2 and N3 cannot be assigned with certainty because they overlap with peaks typical for PDA (primary and secondary amine groups), which are also visible for shorter etching times (Figures S1 and S2). However, it is visible that the intensity of N1 increases with an increasing etching time.…”

“…We have previously shown that PDA free-standing films produced at the air/water interface (a/w-PDA) are characterized by a 2D-like laminar structure, 14 which can be obtained on a large scale (up to several cm) while maintaining homogeneity and continuity, 15 and are easily transferable to any desired substrate due to their extraordinary mechanical properties. 16 Ex situ transferred PDA is a thin layer of PDA that is free-standing on the water surface and can be transferred to another desired surface. Such nanometrically thin a/w-PDA films transferred ex situ to the surfaces of semiconductors (ZnO and TiO 2 ) can create efficient and stable heterojunctions useful in photocatalytic reactions.…”