Most viruses and bioparticles endocytosed by cells have characteristic sizes in the range of tens to hundreds of nanometers. The process of viruses entering and leaving animal cells is mediated by the binding interaction between ligand molecules on the viral capid and their receptor molecules on the cell membrane. How does the size of a bioparticle affect receptor-mediated endocytosis? Here, we study how a cell membrane containing diffusive mobile receptors wraps around a ligand-coated cylindrical or spherical particle. It is shown that particles in the size range of tens to hundreds of nanometers can enter or exit cells via wrapping even in the absence of clathrin or caveolin coats, and an optimal particles size exists for the smallest wrapping time. This model can also be extended to include the effect of clathrin coat. The results seem to show broad agreement with experimental observations. cell adhesion ͉ vesicle budding ͉ virus ͉ biomembrane ͉ receptor-ligand binding R eceptor-mediated endocytosis is one of the most important processes with which viruses and bioparticles can enter or leave an animal cell. Viruses have thousands of different shapes and sizes. Most viruses show a characteristic size in the range of tens to hundreds of nanometers (1, 2). Equipped with a limited amount of nucleic acid, viruses propagate by parasitizing host cells and multiplying their viral nucleic acid and protein capsid via the biochemical machinery of the host. The life cycle of a virus follows a sequential route through various compartments of the host as illustrated in Fig. 1 (3). It takes only 20-40 min for many bacterial phages to finish one life cycle from infection to lysis. For most animal viruses, entering and leaving a host cell are mediated by specific binding of outer coat proteins (such as hemagglutinin in the case of influenza viruses) to specific mobile receptors on the host cell surface.It has been generally assumed that the endocytosis of viruses is associated with the formation of a clathrin coat at the inner membrane leaflet (4). Typically, clathrin coats can generate a membrane radius of curvature as small as Ϸ50 nm. The formation of such small buds has been explained in terms of the bending elasticity concept by considering topological defects of the clathrin network (5). More recently, however, it has been shown that influenza viruses can enter cells even if the formation of clathrin coats are inhibited (6, 7). Here, we develop a model to explain the mechanism of clathrin-free entry of viruses into cells. This model can easily be extended to account for the effect of a clathrin coat.The endocytic pathway is also of interest for understanding possible mechanisms by which nanomaterials might enter into human or animal cells, a significant issue for the development of gene and drug delivery tools (8, 9), as well as for assessing the potential hazard of nanotechnology on ecology and human health (10)(11)(12)(13)(14).Experimental studies on targeted drug delivery into cells have identified particle size as an...

This volume emphasizes fundamental concepts, both on the development of mathematical models of fracture phenomena and on the analysis of these models. Cases involving stress waves impinging on cracks, tractions suddenly applied to the faces of cracks, and rapid crack growth and arrest are considered in detail. Most of the work is concerned with the behavior of nominally elastic materials, but available results on elastic-plastic and elastic-viscoplastic materials are included. Connections to experimental results and to applications in structural mechanics, seismology, and materials science are noted whenever possible.

Thin film mechanical behavior and stress presents a technological challenge for materials scientists, physicists and engineers. This book provides a comprehensive coverage of the major issues and topics dealing with stress, defect formation, surface evolution and allied effects in thin film materials. Physical phenomena are examined from the continuum down to the sub-microscopic length scales, with the connections between the structure of the material and its behavior described. Theoretical concepts are underpinned by discussions on experimental methodology and observations. Fundamental scientific concepts are embedded through sample calculations, a broad range of case studies with practical applications, thorough referencing, and end of chapter problems. With solutions to problems available on-line, this book will be essential for graduate courses on thin films and the classic reference for researchers in the field.

We present a model for compressive stress generation during thin film growth in which the driving force is an increase in the surface chemical potential caused by the deposition of atoms from the vapor. The increase in surface chemical potential induces atoms to flow into the grain boundary, creating a compressive stress in the film. We develop kinetic equations to describe the stress evolution and dependence on growth parameters. The model is used to explain measurements of relaxation when growth is terminated and the dependence of the steady-state stress on growth rate.

Theory of Viscoelasticity, By Ii. :\1. ('hrislell'PII, ""adellli" Press, 1",'., ,Jalluary, 1\)71. REVIEWED BY, L. B, FREUND'I~ view of t.he srnnll n\lmher of available boob which prescnt. a thol'Ough de~eripl.ion of thc behnviol' of vis"onlast.i('. mal crinls, t.his book, wrilten by all :H'tive ('onl.riIHlt.or 10 t.lw field, sholild bc welcomed by t.llOs" enginccrs and resparchcrs intel'(~sted in L1w ~uhj"d. Tlw hook pres,~nls a develoPJllcnt. of t.he phenomenological t hcory of viH'o

A recent trend in seismology has been to model the earthquake source as a dynamically extending shear crack, and several basic concepts which seem to be important in this modeling process are examined. First, the universal spatial dependence of the plane elastodynamic stress and velocity fields near a sharp propagating crack tip is demonstrated for both subsonic and transsonic crack speeds, and the corresponding energy release rates are considered. Next, a class of steady state shear crack propagation problems is analyzed, based on both a direct stress analysis approach and an energy integral approach which obviates the need for a complete stress analysis in some cases. Several distinct stress differences which correspond to some of the common definitions of stress drop are involved in the analysis of these simple problems. Finally, some analytical considerations are presented which are relevant to rupture velocity determination for transient shear crack growth according to various fracture criteria, such as the critical stress intensity factor criterion, the critical energy release rate criterion, and the critical stress level criterion. Possible effects of spatially nonuniform stress drop and frictional resistance on rupture propagation are also discussed.

Two main assumptions which underlie the Stoney formula relating substrate curvature to mismatch strain in a bonded thin film are that the film is very thin compared to the substrate, and the deformations are infinitesimally small. Expressions for the curvature-strain relationship are derived for cases in which these assumptions are relaxed, thereby providing a basis for interpretation of experimental observations for a broader class of film-substrate configurations.

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