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Reversible control of molecular self-assembly is omnipresent in adaptive biological systems, yet its realization in artificial systems remains a major challenge. Using scanning tunneling microscopy and density functional theory calculations, we show that a 2D supramolecular network formed by terthienobenzenetricarboxylic acid (TTBTA) can undergo a reversible structural transition between a porous and dense phase in response to different molecular signals (trimethyltripyrazolotriazine (TMTPT) and C 60 ). TMTPT molecules can induce a phase transition from the TTBTA honeycomb to the dense phase, whereas a reverse transition can be triggered by introducing C 60 molecules. This response stems from the selective association between signal molecules and TTBTA polymorphs. The successful realization of reversible molecular transformation represents important progress in controlling supramolecular surface nanostructures and could be potentially applicable in various areas of nanotechnology, including phase control, molecular sensing, and "smart" switchable surfaces.

We report the synthesis and properties of two π-functional heteroaromatic tetracarboxylic acids (isomeric tetrathienoanthracene derivatives 2-TTATA and 3-TTATA) and their self-assembly on highly oriented pyrolytic graphite. Using scanning tunneling microscopy at the liquid-solid interface we show how slight geometric differences between the two isomers (position of sulfur in the molecule) lead to dramatic changes in monolayer structure. While 3-TTATA self-assembles exclusively in a highly ordered porous network via dimeric R(2)(2)(8) hydrogen-bonding connection (synthon), 2-TTATA is polymorphic, forming a less ordered porous network via R(2)(2)(8) synthons as well as a close-packed network via rare tetrameric R(4)(4)(16) synthons. Density functional theory calculations show that the self-assembly direction is governed by the angle between the carboxylic groups and secondary interactions with sulfur atoms.

The human body is an intricate biochemical-mechanical system, with an exceedingly precise hierarchical organization in which all components work together in harmony across a wide range of dimensions. Many fundamental biological processes take place at surfaces and interfaces (e.g., cell-matrix interactions), and these occur on the nanoscale. For this reason, current health-related research is actively following a biomimetic approach in learning how to create new biocompatible materials with nanostructured features. The ultimate aim is to reproduce and enhance the natural nanoscale elements present in the human body and to thereby develop new materials with improved biological activities. Progress in this area requires a multidisciplinary effort at the interface of biology, physics, and chemistry. In this Review, the major techniques that have been adopted to yield novel nanostructured versions of familiar biomaterials, focusing particularly on metals, are presented and the way in which nanometric surface cues can beneficially guide biological processes, exerting influence on cellular behavior, is illustrated.

In the field of regenerative medicine, nanoscale physical cuing is clearly becoming a compelling determinant of cell behavior. Developing effective methods for making nanostructured surfaces with well-defined physicochemical properties is thus mandatory for the rational design of functional biomaterials. Here, we demonstrate the versatility of simple chemical oxidative patterning to create unique nanotopographical surfaces that influence the behavior of various cell types, modulate the expression of key determinants of cell activity, and offer the potential of harnessing the power of stem cells. These findings promise to lead to a new generation of improved metal implants with intelligent surfaces that can control biological response at the site of healing.

Surface modification of titanium and its alloys is of great importance for their practical application as biomedical implants. We have studied and compared assembly of dodecylphosphoric acid on commercial polished and on nanostructured titanium disks. The latter were produced by chemical etching that created nanoscale pits of typical size of about 20 nm. Enhanced hydrophobicity and high molecular density were obtained after functionalization of the nanotextured substrate. Aging tests showed a lifetime of the organic films of about one month in phosphate buffer. The samples were characterized by means of infrared spectroscopy, contact angle measurements, ellipsometry, and atomic force and scanning tunneling microscopies.