Molecular engineering of cellular environments: cell adhesion to nano-digital surfaces.

Engineering of the cellular microenvironment has become a valuable means to guide cellular activities such as spreading, motility, differentiation, proliferation, or apoptosis. This chapter summarizes recent approaches to surface patterning such as topography and chemical patterning from the micrometer to the nanometer scale, and illustrates their application to cellular studies. Particular attention is devoted to nanolithography with self-assembled diblock copolymer micelles that are biofunctionalized with peptide ligands-a method that offers unsurpassed spatial resolution for the positioning of signaling molecules over extended surface areas.

Mimicking cellular environments by nanostructured soft interfaces.

We present herein an innovative technique for decorating soft polymer surfaces with metallic nanostructures fabricated by diblock copolymer micelle nanolithography. Thus far, such nanolithography has been limited to plasma-resistant inorganic substrates such as glass. Our new development is based on the transfer of nanopatterns from glass to soft substrates.

Influence of surface roughness on gecko adhesion.

In this study we show the influence of surface roughness on gecko adhesion on both the nano- and macroscales. We present experimental data for the force necessary to pull off single spatulae from hard rough substrates and also detail observations on living geckos clinging to various surfaces. Both experiments consistently show that the effective adhesion shows a minimum for a root mean square roughness ranging from 100 to 300nm.

Site-specific presentation of single recombinant proteins in defined nanoarrays.

The authors describe the deposition of single biomolecules on substrates at defined spacing by pure self-assembly. The substrate is equipped with an array of 8 nm large gold particles which form the template for biomolecule binding. The authors verified the successful binding of single biomolecules via specific antibody labeling and imaging by fluorescence microscopy.

Shearing of fibrillar adhesive microstructure: friction and shear-related changes in pull-off force.

To characterize the effect of shearing on function of fibrillar adhesive microstructure, friction and shear-related changes in pull-off force of a biomimetic polyvinylsiloxane mushroom-shaped fibrillar adhesive microstructure were studied. In contrast to a control flat surface, which exhibited pronounced stick-slip motion accompanied with high friction, the fibrillar microstructure demonstrated a stable and smooth sliding with a friction coefficient approximately four times lower. The structured contact also manifested zero pull-off force in a sheared state, while the flat surface exhibited highly scattered and unreliable pull-off force when affected by contact shearing.

Adhesion of bioinspired micropatterned surfaces: effects of pillar radius, aspect ratio, and preload.

Inspired by biological attachment systems, micropatterned elastomeric surfaces with pillars of different heights (between 2.5 and 80 microm) and radii (between 2.5 and 25 microm) were fabricated.

Cell-assisted assembly of colloidal crystallites.

Many cells ingest foreign particles through a process known as phagocytosis. It now turns out that some cell types organize phagocytosed microparticles into crystalline arrays. Much like the classic crystallization of colloidal particles in a thermal bath, crystallization within the cell is driven by the spatial confinement of mutually repelling particles, in this case by the cell membrane.

Cellular chemomechanics at interfaces: sensing, integration and response.

Living cells are complex entities whose remarkable, emergent capacity to sense, integrate, and respond to environmental cues relies on an intricate series of interactions among the cell's macromolecular components. Defects in mechanosensing, transduction,or responses underlie many diseases such as cancers, immune disorders, cardiac hypertrophy, genetic malformations, and neuropathies. Here, we highlight micro- and nanotechnology-based tools that have been used to study how chemical and mechanical cues modulate the responses of single cells in contact with the extracellular environment.

Cell spreading and focal adhesion dynamics are regulated by spacing of integrin ligands.

Integrin-mediated adhesion is regulated by multiple features of the adhesive surface, including its chemical composition, topography, and physical properties. In this study we investigated integrin lateral clustering, as a mechanism to control integrin functions, by characterizing the effect of nanoscale variations in the spacing between adhesive RGD ligands on cell spreading, migration, and focal adhesion dynamics. For this purpose, we used nanopatterned surfaces, containing RGD-biofunctionalized gold dots, surrounded by passivated gaps.

Biomimetic mushroom-shaped fibrillar adhesive microstructure.

To improve the adhesive properties of artificial fibrillar contact structures, the attachment systems of beetles from the family Chrysomelidae were chosen to serve as a model. Biomimetic mushroom-shaped fibrillar adhesive microstructure inspired by these systems was characterized using a variety of measurement techniques and compared with a control flat surface made of the same material. Results revealed that pull-off force and peel strength of the structured specimens are more than twice those of the flat specimens.

Physicochemical properties of functional surfaces in pitchers of the carnivorous plant Nepenthes alata Blanco (Nepenthaceae).

Pitchers of the carnivorous plant Nepenthes alata are highly specialized organs adapted to attract, capture, and digest animals, mostly insects. They consist of several well distinguishable zones, differing in macro-morphology, surface microstructure, and functions. Since physicochemical properties of these surfaces may influence insect adhesion, we measured contact angles of non-polar (diiodomethane) and polar liquids (water and ethylene glycol) and estimated the free surface energy of 1) the lid, 2) the peristome, 3) the waxy surface of the slippery zone, and 4) the glandular surface of the digestive zone in N.

Biomaterials: silk-like secretion from tarantula feet.

An unsuspected attachment mechanism may help these huge spiders to avoid catastrophic falls. Spiders spin silk from specialized structures known as abdominal spinnerets--a defining feature of the creatures--and this is deployed to capture prey, protect themselves, reproduce and disperse. Here we show that zebra tarantulas (Aphonopelma seemanni) from Costa Rica also secrete silk from their feet to provide adhesion during locomotion, enabling these spiders to cling to smooth vertical surfaces.

Surface molecular view of colloidal gelation.

We investigate the phase behavior of surface-functionalized silica colloids at both the molecular and macroscopic levels. This investigation allows us to relate collective properties such as aggregation, gelation, and aging directly to molecular interfacial behavior. By using surface-specific vibrational spectroscopy, we reveal dramatic changes in the conformation of alkyl chains terminating submicrometer silica particles.

Material structure, stiffness, and adhesion: why attachment pads of the grasshopper (Tettigonia viridissima) adhere more strongly than those of the locust (Locusta migratoria) (Insecta: Orthoptera).

The morphology, ultrastructure, effective elastic modulus, and adhesive properties of two different smooth-type attachment pads were studied in two orthopteran species. Tettigonia viridissima (Ensifera) and Locusta migratoria (Caelifera) have a similar structural organization of their attachment pads. They both possess a flexible exocuticle, where the cuticular fibrils are fused into relatively large rods oriented at an angle to the surface.

Friction and adhesion in the tarsal and metatarsal scopulae of spiders.

Friction and adhesion forces of the ventral surface of tarsi and metatarsi were measured in the bird spider Aphonopelma seemanni (Theraphosidae) and the hunting spider Cupiennius salei (Ctenidae). Adhesion measurements revealed no detectable attractive forces when the ventral surfaces of the leg segments were loaded and unloaded against the flat smooth glass surface. Strong friction anisotropy was observed: friction was considerably higher during sliding in the distal direction.

Flaw tolerant bulk and surface nanostructures of biological systems.

Bone-like biological materials have achieved superior mechanical properties through hierarchical composite structures of mineral and protein. Gecko and many insects have evolved hierarchical surface structures to achieve extraordinary adhesion capabilities. We show that the nanometer scale plays a key role in allowing these biological systems to achieve their superior properties.

Encapsulation of pt-labelled DNA molecules inside carbon nanotubes.

Experiments on encapsulating Pt-labelled DNA molecules inside multiwalled carbon nanotubes (MWCNT) were performed under temperature and pressure conditions of 400K and 3 Bar. The DNA-CNT hybrids were purified via agarose gel electrophoresis and analyzed via high resolution transmission electron microscopy (HR-TEM) and energy dispersive X-ray spectroscopy (EDX). The results showed that the Pt-labelled DNA molecules attached to the outside walls of CNTs could be removed by electrophoresis.

Stretching short DNAs in electrolytes.

This paper is aimed at a combined theoretical and numerical study of the force-extension relation of a short DNA molecule stretched in an electrolyte. A theoretical formula based on a recent discrete wormlike chain (WLC) model of Kierfeld et al. (Eur Phys.

Scaling effects of wet adhesion in biological attachment systems.

Insects have evolved fibrillar attachment devices based on wet adhesion to attach themselves to a variety of surfaces. This paper investigates the scaling effects of wet adhesion mediated by a liquid bridge between a fiber and a solid surface. The influences of liquid volume and contact angles are discussed via a scaling law indicating that the adhesive strength can be enhanced by contact size reduction.

Adhesion design maps for bio-inspired attachment systems.

Fibrous surface structures can improve the adhesion of objects to other surfaces. Animals, such as flies and geckos, take advantage of this principle by developing "hairy" contact structures which ensure controlled and repeatable adhesion and detachment. Mathematical models for fiber adhesion predict pronounced dependencies of contact performance on the geometry and the elastic properties of the fibers.

Cytotoxicity of single-wall carbon nanotubes on human fibroblasts.

We present a toxicological assessment of five carbon nanomaterials on human fibroblast cells in vitro. We correlate the physico-chemical characteristics of these nanomaterials to their toxic effect per se, i.e.

Lateral spacing of integrin ligands influences cell spreading and focal adhesion assembly.

Cell-extracellular matrix (cell-ECM) interactions mediated by integrin receptors are essential for providing positional and environmental information necessary for many cell functions, such as proliferation, differentiation and survival. In vitro studies on cell adhesion to randomly adsorbed molecules on substrates have been limited to sub-micrometer patches, thus preventing the detailed study of structural arrangement of integrins and their ligands. In this article, we illustrate the role of the distance between integrin ligands, namely the RGD (arginine-glycine-aspartate) sequence present in ECM proteins, in the control of cell adhesion.

Cellular unbinding forces of initial adhesion processes on nanopatterned surfaces probed with magnetic tweezers.

To study the dependence of unbinding forces on the distance of molecularly defined and integrin specific c(-RGDfK-) ligand patches in initial cellular adhesion processes, we developed a magnetic tweezers setup for applying vertical forces of up to 200 pN to rat embryonic fibroblasts. The ligand patch distance is controlled with a hexagonally close packed pattern of biofunctionalized gold nanoparticles prepared by block-copolymer micelle nanolithography. Each gold nanoparticle potentially activates up to one alpha(v)beta(3)-integrin.

Force-induced adsorption and anisotropic growth of focal adhesions.

Focal adhesions are micrometer-sized protein aggregates that connect actin stress fibers to the extracellular matrix, a network of macromolecules surrounding tissue cells. The actin fibers are under tension due to actin-myosin contractility. Recent measurements have shown that as the actin force is increased, these adhesions grow in size and in the direction of the force.