This paper attempts an assessment of the current understanding of the phenomenon of "serrated plastic flow", which manifests itself as serrations, load drops, jerkiness or other discontinuities in the stress-strain curves obtained in constant extension rate tensile tests, and as sudden bursts of strain in constant loading rate tests and in constant load (stress) creep tests (the so called staircase creep). Though one can identify at least seven physical processes that can cause serrations, the discussion here is restricted mainly to serrated yielding in tension tests originating from dynamic strain ageing (DS^). The characteristics of the five types of serrations that have been identified so far and the experimental conditions under which they occur are discussed. The various models of serrated flow that have been put forward are reviewed critically. Some recent results on 316 stainless steel are presented to illustrate the effects of grain size, temperature and strain rate on serrated flow. Manifestations of DS^ other than serrations such as a negative strain rate sensitivity, positive temperature dependence for flow stress and work hardening, and the ductility minimum are also discussed. Finally the various issues to be resolved are enumerated.

To cite this article: Yuana Y, Oosterkamp TH, Bahatyrova S, Ashcroft B, Garcia Rodriguez P, Bertina RM, Osanto S. Atomic force microscopy: a novel approach to the detection of nanosized blood microparticles. J Thromb Haemost 2010; 8: 315À23.See also Freyssinet J-M, Toti F. Membrane microparticle determination: at least seeing whatÕs being sized! This issue, pp 311À4.Summary. Background: Microparticles (MPs) are small vesicles released from cells of different origin, bearing surface antigens from parental cells. Elevated numbers of blood MPs have been reported in (cardio)vascular disorders and cancer. Most of these MPs are derived from platelets. Objectives: To investigate whether atomic force microscopy (AFM) can be used to detect platelet-derived MPs and to define their size distribution. Methods: Blood MPs isolated from seven blood donors and three cancer patients were immobilized on a modified mica surface coated with an antibody against CD41 prior to AFM imaging. AFM was performed in liquid-tapping mode to detect CD41-positive MPs. In parallel, numbers of CD41-positive MPs were measured using flow cytometry. Mouse IgG 1 isotype control was used as a negative control. Results: AFM topography measurements of the number of CD41-positive MPs were reproducible (coefficient of variation = 16%). Assuming a spherical shape of unbound MPs, the calculated diameter of CD41-positive MPs (d sph ) ranged from 10 to 475 nm (mean: 67.5 ± 26.5 nm) and from 5 to 204 nm (mean: 51.4 ± 14.9 nm) in blood donors and cancer patients, respectively. Numbers of CD41-positive MPs were 1000-fold higher than those measured by flow cytometry (3À702 · 10 9 L )1 plasma vs.11À626 · 10 6 L )1 plasma). After filtration of isolated MPs through a 0.22-lm filter, CD41-positive MPs were still detectable in the filtrate by AFM (mean d sph : 37.2 ± 11.6 nm), but not by flow cytometry. Conclusions: AFM provides a novel method for the sensitive detection of defined subsets of MPs in the nanosize range, far below the lower limit of what can be measured by conventional flow cytometry.

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