Tuning cell adhesion on gradient poly(2-hydroxyethyl methacrylate)-grafted surfaces

A simple yet versatile method was developed to prepare a low-density polymerization initiator gradient, which was combined with surface-initiated atom transfer radical polymerization (ATRP) to produce a well-defined poly(2-hydroxyethyl methacrylate) (HEMA) gradient substrate. A smooth variation in film thickness was measured across the gradient, ranging from 20 A to over 80 A, but we observed a nonmonotonic variation in water contact angle. Fits of X-ray reflectivity profiles suggested that at the low graft density end, the polymer chain structure was in a "mushroom" regime, while the polymer chains at high graft density were in a "brush" regime. It was found that the "mushroom" region of the gradient could be made adhesive to cells by adsorbing adhesion proteins, and cell adhesion could be tuned by controlling the density of the polymer grafts. Fibroblasts were seeded on gradients precoated with fibronectin to test cellular responses to this novel substrate, but it was found that cell adhesion did not follow the expected trend; instead, saturated cell adhesion and spreading was found at the low grafting density region.     

A new concept in friction testing

Methods of measuring friction are reviewed and their shortcomings discussed. The advantages of using the wide range of test speeds, environmental conditions and recording facilities available on a tensile test machine are indicated and a new apparatus designed to fit a tensile tester is described. The design concepts are outlined in some detail and the factors limiting stick-slip motion are indicated. The apparatus can be used either for studies of materials or as an aid to product selection. Test results on a polyurethane rubber, covering a range of velocities and temperatures, illustrate the former, and tests on windscreen wiper blades under both wet and dry conditions illustrate the latter. Although primarily designed for testing the friction of polymers the apparatus is of universal application and can be used for measuring, against a chosen substrate, the coefficients of friction of metals, fabrics, paper, glass, leather, or any other material capable of being mounted in a vertical plane. It is not suitable for particulate matter such as sand, but could be used, for example, for studying the effect of floor finishes on a range of flooring materials.     

Nondestructive spatial heterodyne imaging of cold atoms

We demonstrate a new method for nondestructive imaging of laser-cooled atoms. This spatial heterodyne technique forms a phase image by interfering a strong reference laser beam with a weak probe beam that passes through the cold atom cloud. The figure of merit equals or exceeds that of phase-contrast imaging, and the technique can be used over a wider range of spatial scales. We show images of a dark-spot magneto-optic trap taken with imaging fluences as low as 61 pJ/cm(2) at a detuning of 11? , resulting in 0.0004 photons scattered per atom.     

Groups with Polycyclic Non-Normal Subgroups

The structure of groups in which many subgroups have a certain property X has been investigated for several choices of the property X. Groups whose non-normal subgroups satisfy certain finite rank conditions are studied in this article. In particular, a classification of groups in which every subgroup is either normal or polycyclic is given.(Dedicated to Mario Curzio on the occasion of his 70th birthday)1991 Mathematics Subject Classification: 20F16