Water/solid interfaces play crucial roles in a wide range of physicochemical and technological processes. However, our microscopic understanding of the interfacial water under ambient temperature is relatively primitive. Herein, we report the direct experimental construction of two-dimensional (2D) ice-like water layer on hydrophilic surface at room temperature by using environment-controlled atomic force microscopy. In contrast to the prevailing view that nanoscale confinement is needed for the formation of 2D ice-like water, we find that 2D ice-like water can form on mica surface at temperatures above the freezing point without confinement. The 2D ice-like water layer shows epitaxial relation with the underlying mica lattice and good thermostability. In addition, the growth of ice-like water layer can be well controlled by the mechanical force from the scanning tip. Furthermore, the friction properties of 2D ice-like water layer are also probed by friction force microscopy. It is found that the ice-like water layer can dramatically reduce the friction. These results provide deep understanding of 2D ice-like water formation on solid surfaces without nanoscale confinement and suggest means of growing 2D ices on surfaces at room temperature.

Hydration lubrication has long been invoked to account for the ultralow sliding friction between charged surfaces in aqueous environments, but still not well understood at molecular-level. Herein, we explored the lubrication effect of hydrated halogen anions on positively charged surface at the atomic scale by using three-dimensional atomic force microscopy and friction force microscopy. Atomically resolved three-dimensional imaging revealed that the anion layer was topped by a few hydration layers. The mechanical properties of the hydration layers were found mainly dependent on the concentration of electrolyte solutions and independent of the species of hydrated anions. Atomic-scale friction experiments showed that the hydration friction coefficient and friction dissipation at low concentrations were orders of magnitude lower than that at high concentrations and in pure water. Superlubricity can be achieved in low concentration electrolyte solution. These results indicated that the changes of electrolyte solution concentrations led to different adsorption state of anions on the positively charged surface which gave rise to the difference of the friction behaviors. The findings in this study reveal the role of hydrated anions in hydration lubrication and provide deep insights into the origins of hydration lubrication.

Load-dependent friction hysteresis is an intriguing phenomenon that occurs in many materials, where the friction measured during unloading is larger than that measured during loading for a given normal load. However, the mechanism underlying this behavior is still not well understood. In this work, temperature- controlled friction force microscopy was utilized to explore the origin of friction hysteresis on exfoliated monolayer graphene. The experimental observations show that environmental adsorbates from ambient air play an important role in the load dependence of friction. Specifically, the existence of environmental adsorbates between the tip and graphene surface gives rise to an enhanced tip-graphene adhesion force, which leads to a positive friction hysteresis where the friction force is larger during unloading than during loading. In contrast to positive friction hysteresis, a negative friction hysteresis where the friction force is smaller during unloading than during loading is observed through the removal of the environmental adsorbates upon in situ annealing. It is proposed that the measured friction hysteresis originates from the hysteresis in the contact area caused by environmental adsorbates between the tip and graphene. These findings provide a revised understanding of the friction hysteresis in monolayer graphene in terms of environmental adsorbates.

Cellular differentiation can be affected by the extracellular environment, particularly extracellular substrates. The nanotopography of the substrate may be involved in the mechanisms of cellular differentiation in vivo. Organelles are major players in various cellular functions; however, the influence of nanotopography on organelles has not yet been elucidated. In the present study, a micropit-nanotube topography (MNT) was fabricated on the titanium surface, and organelle-specific fluorescent probes were used to detect the intracellular organelle organization of MG63 cells. Communication between organelles, identified by organelle-specific GTPase expression, was evaluated by quantitative polymerase chain reaction and western blotting. Transmission electron microscopy was performed to evaluate the organelle structure. There were no significant differences in organelle distribution or number between the MNT and flat surface. However, organelle-specific GTPases on the MNT were dramatically downregulated. In addition, obvious endoplasmic reticulum lumen dilation was observed on the MNT surface, and the unfolded protein response (UPR) was also initiated. Regarding the relationships among organelle trafficking, UPR, and osteogenic differentiation, our findings may provide important insights into the signal transduction induced by nanotopography.

The molecular-level identification of a chiral recognition process of phthalocyanine (Pc) was studied on a Cu(100) surface by scanning tunneling microscopy (STM). STM revealed that a chiral Pc molecule forms a series of metastable dimer configurations with other Pc molecules. Eventually, the Pc molecule recognizes another Pc molecule with the same chirality to form a stable dimer configuration. Homochiral dimers were found on the Cu surface, demonstrating the chiral specificity of Pc dimerization. The mechanism for this chiral recognition process is identified, disclosing the critical role of the particular adsorption geometry of the chiral dimers on the Cu surface.

Osteocytes are the main bone cells embedded in the bone matrix where they form a large surface-area network called the lacunar-canalicular network (LCN), interconnecting their resident spaces with the lacunae by the canaliculi. Increasing evidence points toward osteocytes playing a pivotal role in maintaining bone quality. On the one hand, osteocytes transmit mechanical strain and microenvironmental signals through the LCN to regulate the activity of osteoblasts and osteoclasts; on the other hand, osteocytes are suggested to be able to remodel the LCN-associated bone matrix. However, due to the challenges involved in the assessment and characterization of the LCN-associated bone matrix, little is known about its structure and the corresponding mechanical properties. In this work, we used quantitative nanomechanical mapping, backscattered electron imaging, and nanoindentation to characterize the LCN-associated bone matrix. The results show that the techniques can be used to probe the LCN-associated bone matrix. Nanoindentation and quantitative mechanical mapping reveal spatially inhomogeneous mechanical properties of the bone matrix associated with the osteocyte lacunae and canaliculi. The obtained nano-topography and corresponding nano-mechanical maps reveal altered mechanical properties in the immediate vicinity of the osteocyte lacunae and canaliculi, which cannot be explained solely by the topographic change.

3D DNA origami holds tremendous potential for the encapsulation and selective release of therapeutic drugs. Observations of the real-time performance of these structures in physiological environments will contribute to the development of future applications. We investigated the degradation kinetics of 3D DNA box origami in serum by using high-speed atomic force microscope optimized for imaging 3D DNA origami in real time. The time resolution allowed to characterize the stages of serum effects on individual 3D DNA boxes origami with nanometer resolution. Our results indicate that the digestion process is a combination of rapid collapse and slow degradation phases. Damage to box origami occurs mainly in the collapse phase. Thus, the structural stability of 3D DNA box origami should be improved, especially in the collapse phase, before these structures are used in clinical applications.