The silicon wafer hydrophobized with OTS was immersed into water to observe the surface in-situ by tapping-mode AFM. A large number of nano-size domain images were found on the surface. Their shapes were characterized by the height image procedure of AFM, and the differences of the properties compared to those of the bare surface were analyzed using the phase image procedure and the interaction force curves. All the results consistently implied that the domains represent the nanoscopic bubbles attached on the surface. This was confirmed by the fact that no domain was observed in the case of the surfaces hydrophobized in the AFM fluid cell without exposure to air. The apparent contact angle of the bubbles was much smaller than that expected macroscopically, which was postulated to be the reason bubbles were able to sit stably on the surface.

To clarify the origin of the long-range attraction between hydrophobic surfaces in water, the interaction between the surfaces silanated by the popular method (type I) and that between the surfaces silanated without exposing to air (type II) were examined using an atomic force microscope (AFM) and their characteristics were compared. The interaction between type I surfaces was long-ranged, and a discontinuous step appeared in the approaching and separating force curves, respectively, whereas the interaction between type II surfaces was short-ranged and no step was found. Once type II surfaces were exposed to air, however, the similar interaction to that for type I surfaces appeared. As for type I surfaces, the force curves depended on the local property of the surface, and the interaction in the first cycle of force measurements differed from those in the later cycles. These findings enabled us to estimate the following mechanism for the long-range attraction. When surfaces are hydrophobized, they are usually exposed to air during the hydrophobizing reaction or in the drying process. Then they are immersed in water to measure the interaction without removing microscopic bubbles on the surfaces completely. These bubbles coalesce before the surfaces contact and generate a strong long-range interaction. Hence, this interaction is not the genuine hydrophobic attraction.

The temperature-induced structural changes of a thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) layer grafted onto a silica substrate were investigated in aqueous solution using an atomic force microscope (AFM) and a quartz crystal microbalance with dissipation (QCM-D). A PNIPAM layer was grafted onto the silicon wafer surface by free radical polymerization of NIPAM to obtain a high molecular weight polymer layer with low-grafting density overall. By AFM imaging, the transition of the grafted PNIPAM chains from a brush-like to a mushroom-like state was clearly visualized: The surface images of the plate were featureless at temperatures below the LCST commensurate with a brush-like layer, whereas above the LCST, a large number of domain structures with a characteristic size of approximately 100 nm were seen on the surface. Both frequency and dissipation data obtained using QCM-D showed a significant change at the LCST. Analysis of these data confirmed that the observed PNIPAM structural transition was caused by a collapse of the brush-like structure as a result of dehydration of the polymer chains.

Periodontitis is a localized infectious disease caused by periodontopathic bacteria, such as Porphyromonas gingivalis. Recently, it has been suggested that bacterial infections may contribute to the onset and the progression of Alzheimer’s disease (AD). However, we do not have any evidence about a causative relationship between periodontitis and AD. In this study, we investigated by using a transgenic mouse model of AD whether periodontitis evoked by P. gingivalis modulates the pathological features of AD. Cognitive function was significantly impaired in periodontitis-induced APP-Tg mice, compared to that in control APP-Tg mice. Levels of Amiloid β (Aβ) deposition, Aβ40, and Aβ42 in both the hippocampus and cortex were higher in inoculated APP-Tg mice than in control APP-Tg mice. Furthermore, levels of IL-1β and TNF-α in the brain were higher in inoculated mice than in control mice. The levels of LPS were increased in the serum and brain of P. gingivalis-inoculated mice. P. gingivalis LPS-induced production of Aβ40 and Aβ42 in neural cell cultures and strongly enhanced TNF-α and IL-1β production in a culture of microglial cells primed with Aβ. Periodontitis evoked by P. gingivalis may exacerbate brain Aβ deposition, leading to enhanced cognitive impairments, by a mechanism that involves triggering brain inflammation.

The effect of grafting density on the phase transition behavior of poly(N-isopropylacrylamide) (PNIPAM) grafted onto a flat substrate was investigated using an atomic force microscope (AFM) and a quartz crystal microbalance (QCM-D). We prepared PNIPAM brush layers at three different grafting densities on silicon wafers using a “grafting from” atom transfer radical polymerization (ATRP) approach. AFM imaging in water at various temperatures showed that the transition behavior of the grafted PNIPAM chains from a brush-like to a mushroom-like morphology was dependent on the grafting density: the images change abruptly from essentially featureless to domain structures across the LCST for the low-density surface, whereas the change in the images becomes less abrupt with increasing polymer graft density. The QCM-D data also indicated a significant dependence of the layer properties on the grafting density, confirming the behavior differences suggested by the AFM images. In particular, the dissipation data strongly suggest that the magnitude of lateral aggregation for the PNIPAM chains depends on the grafting density. A similar effect of grafting density was also observed for the phase transition as a function of salt concentration in sodium sulfate solutions.

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