Effect of Intramonolayer Hydrogen Bonding of Carboxyl Groups in Self-assembled Monolayers on a Single Force with Phenylurea on an AFM Probe Tip

Insights into spheroids formation in cellulose nanofibrils and Matrigel hydrogels using AFM-based techniques

The recent FDA decision to eliminate animal testing requirements emphasises the role of cell models, such as spheroids, as regulatory test alternatives for investigations of cellular behaviour, drug responses, and disease modelling. The influence of environment on spheroid formation are incompletely understood, leading to uncertainty in matrix selection for scaffold-based 3D culture. This study uses atomic force microscopy-based techniques to quantify cell adhesion to Matrigel and cellulose nanofibrils (CNF), and cell-cell adhesion forces, and their role in spheroid formation of hepatocellular carcinoma (HepG2) and induced pluripotent stem cells (iPS(IMR90)-4). Results showed different cell behaviour in CNF and Matrigel cultures. Both cell lines formed compact spheroids in CNF but loose cell aggregates in Matrigel. Interestingly, the type of cell adhesion protein, and not the bond strength, appeared to be a key factor in the formation of compact spheroids. The gene expression of E- and N-cadherins, proteins on cell membrane responsible for cell-cell interactions, was increased in CNF culture, leading to formation of compact spheroids while Matrigel culture induced integrin-laminin binding and downregulated E-cadherin expression, resulting in looser cell aggregates. These findings enhance our understanding of cell-biomaterial interactions in 3D cultures and offer insights for improved 3D cell models, culture biomaterials, and applications in drug research.

In situ scrutinize the adsorption of sulfamethoxazole in water using AFM force spectroscopy: Molecular adhesion force determination and fractionation

The interaction force of a typical antibiotic molecule during adsorption has never been experimentally determined and fractionated, which hindered the evolution of removal strategies. In this study, sulfamethoxazole (SMX) as a typical antibiotic was stably immobilized onto an atomic force microscopy (AFM) tip without affecting original properties. The SMX modified AFM tip visualized the potential adsorption sites on a graphene oxide (GO) nanosheet for the first time by mapping the SMX adhesion force distribution. Moreover, the interaction force of a single SMX molecule to GO was determined at 38.6 pN which was subsequently fractionated into the hydrophobic (17.9 pN) and π-π (160.0 pN) attractions as well as the electrostatic repulsion (- 139.3 pN) at pH: 5.7. As compared with highly-ordered pyrolytic graphite (HOPG), the introduced oxygen containing groups on GO not only reduced the hydrophobic interaction but also generated an opposite electrostatic repulsion force to SMX. This study experimentally and theoretically revealed the adhesion mechanisms of SMX and potentially other sulfonamide antibiotics in molecular level, which may contribute to the study of antibiotic environmental transportation and the development of next-generation antibiotic remediation protocols.

Characterization of bromide ions in charge-stacked zwitterionic micellar systems

A novel zwitterionic surfactant, N-dodecyl-N,N,N',N'-tetra-methyl-ethylene-di-ammonio-propane-sulfonate bromide (DEPB), has been synthesized, and Br(-) involved in the micellar system has been characterized by potentiometry, NMR, and X-ray absorption fine structure (XAFS). Although the dissociation degree of Br(-) from the micelle evaluated by potentiometry almost agrees with that determined by NMR, the former is significantly smaller than the latter over the entire range of concentrations of DEPB. This is explained by assuming that the bromide ions in the micellar system have several different peripheral structures. XAFS has given significant insight into the hydration structures of Br(-) involved in the system. Some of the bromide ions partitioned into the micelle are dehydrated and are directly bound by the ammonium groups in the DEP molecules. However, some of the bromide ions are still completely hydrated even when they are partitioned into the micelles. The average hydration number of the bromide ions directly bound by the ammonium groups was determined to be approximately 3.3. The partial dehydration of Br(-) is possibly facilitated by the characteristic hydration circumstances provided by the charge-stacked structure of the surfactant and by the resulting thick palisade layer of the DEP micelle.