Nanotechnology has received increased attention in the biological research field. The important examples are (1) the usage of nanoparticles in optical and magnetic resonance imaging; 1,2 (2) the demonstration of potential application of metal nanoshells and carbon nanotubes for the treatment of tumor and cancer cells; 3,4 and (3) the application of nanowire-based transistors to electrically detect specific biomolecules. 5,6 In all of these cases, the nanomaterials are functioning either inside the cells or at the vicinity of the surface of biomolecules. Direct interconnection of the cells to the external world by interfacing nanomaterials may afford great opportunities to probe and manipulate biological processes occurring inside the cells, across the membranes, and between neighboring cells. 7,8 A nanoscale material with high aspect ratio is a good candidate for this application. For instance, silicon nanowires (SiNWs, d ) 1-100 nm) are a few orders of magnitude smaller in diameter than mammalian cells (d cell ∼ on the order of 10 µm) yet comparable to the sizes of various intracellular biomolecules. The nanowires have high aspect ratio (<10 3 ) and yet are sufficiently rigid to be mechanically manipulated. The nanometer scale diameter and the high aspect ratio of SiNWs make them readily accessible to the interiors of living cells, which may facilitate the study of the complex regulatory and signaling patterns at the molecular level.In this Communication, we present the first demonstration of a direct interface of silicon nanowires with mammalian cells such as mouse embryonic stem (mES) cells and human embryonic kidney (HEK 293T) cells without any external force. The cells were cultured on a silicon (Si) substrate with a vertically aligned SiNW array on it. The penetration of the SiNW array into individual cells naturally occurred during the cell incubation. The cells survived up to several days on the nanowire substrates. The longevity of the cells was highly dependent on the diameter of SiNWs. Furthermore, successful maintenance of cardiac myocytes derived from mES cells on the wire array substrates was observed, and gene delivery using the SiNW array was demonstrated.SiNWs were synthesized vertically aligned with respect to Si-(111) substrates via chemical vapor deposition as described earlier. 9 The diameter of the nanowires was controlled by the size of gold nanoparticles that were used as catalytic seeds for the nanowire synthesis or by reducing the diameter of Si nanowires via oxidation and subsequent hydrofluoric (HF) acid etching step. 10 The SiNW substrates had a native oxide layer and were used without any surface modification unless otherwise specified. Before any exposure to living cells, the substrates were sterilized in a solvent of 70% ethanol and 30% sterile water.First, physical interaction between the nanowires and the cells was studied using confocal microscopy and scanning electron microscopy (SEM). Mouse embryonic stem cells stably expressing green fluorescent protein (GFP) were cultured o...

(SPB) or y.y.kim@leeds.ac.uk (YYK). 2Structural biominerals are inorganic/organic composites that exhibit remarkable mechanical properties. However, the structure-property relationships of even the simplest building unitmineral single crystals containing embedded macromolecules -remain poorly understood. Here, by means of a model biomineral made from calcite single crystals containing glycine (0-7 mol%) or aspartic acid (0-4 mol%), we elucidate the origin of the superior hardness of biogenic calcite.We analyzed lattice distortions in these model crystals by using x-ray diffraction and molecular dynamics simulations, and by means of solid-state nuclear magnetic resonance show that the amino acids are incorporated as individual molecules. We also demonstrate that nanoindentation hardness increased with amino acid content, reaching values equivalent to their biogenic counterparts. A dislocation pinning model reveals that the enhanced hardness is determined by the force required to cut covalent bonds in the molecules.3 Biominerals such as bones, teeth and seashells are characterized by properties optimized for their functions. Despite being formed from brittle minerals and flexible polymers, nature demonstrates that it is possible to generate materials with strengths and toughnesses appropriate for structural applications 1 . At one level, the mechanical properties of these hierarchically structured materials are modelled as classical composites consisting of a mineral phase embedded in an organic matrix 2 . However, the single crystal mineral building blocks of biominerals are also composites 3 , containing both aggregates of biomacromolecules as large as 20 nm 4,5 and inorganic impurities 6,7 . While it should be entirely possible to employ this simple biogenic strategy in materials synthesis 8,9 , the strengthening and toughening mechanisms that result from these inclusions are still poorly understood 10,11 . This work addresses this challenge by analyzing hardening mechanisms in a simple model biomineral system: calcite single crystals containing known amounts of amino acids. We report synthetic calcite crystals with hardnesses equivalent to those of their biogenic counterparts, and offer a detailed explanation for the observed hardening.Since plastic deformation in single crystals occurs by the motion of dislocations, hardness is enhanced by features that inhibit dislocation motion. The mechanisms by which guest species may harden ionic single crystals generally fall into two categories. Second phase particles directly block dislocation motion, requiring a dislocation to either cut through (shear) a particle or bypass it by a diffusive process to keep going 12 . Solutes (point defects) do not directly block dislocation motion, but the stress fields of the dislocations interact with those associated with misfitting solutes, retarding dislocation motion 12 . Biominerals, notably calcite, often deform plastically by twinning 11 , but since twins grow by motion of "twinning dislocations" 13 , these concep...

Biogenic single-crystal composites, such as sea urchin spines and calcitic prisms from mollusk shells, contain organic macromolecules inside of inorganic single-crystal matrices. The nanoscale internal structure of these materials, however, is poorly understood, especially how the biomacromolecules are distributed within the crystals without signifi cantly disrupting the crystalline lattice. Here, annular dark-fi eld scanning transmission electron microscopy and electron tomography reveal, in three dimensions, how biomacromolecules are distributed within the calcitic prisms from Atrina rigida shells. Disk-like nanopatches, whose scattering intensity is consistent with organic inclusions, are observed to be anisotropically arranged within a continuous, single-crystalline calcite matrix. These nanopatches are preferentially aligned with the (000 l ) planes of calcite. Along the crystallographic c-axis, there are alternating organic-rich and -poor regions on a length scale of tens of nanometers, while, in the ab plane, the distribution of nanopatches is more random and uniform. The structural features elucidated in this work have relevance to understanding the structure-property relationships and formation mechanisms of biominerals, as well as to the development of bioinspired strategies to extrinsically tune the properties of single-crystals.

No abstract

Abstract