Poly(2-oxazolines) in biological and biomedical application contexts.

Polyoxazolines of various architectures and chemical functionalities can be prepared in a living and therefore controlled manner via cationic ring-opening polymerisation. They have found widespread applications, ranging from coatings to pigment dispersants. Furthermore, several polyoxazolines are water-soluble or amphiphilic and relatively non-toxic, which makes them interesting as biomaterials. This paper reviews the development of polyoxazoline-based polymers in biological and biomedical application contexts since the beginning of the millennium. This includes nanoscalar systems such as membranes and nanoparticles, drug and gene delivery applications, as well as stimuli-responsive systems

Effect of adhesion geometry and rigidity on cellular force distributions

The behaviour and fate of tissue cells is controlled by the rigidity and geometry of their adhesive environment, possibly through forces localized to sites of adhesion. We introduce a mechanical model that predicts cellular force distributions for cells adhering to adhesive patterns with different geometries and rigidities. For continuous adhesion along a closed contour, forces are predicted to be localized to the corners. For discrete sites of adhesion, the model predicts the forces to be mainly determined by the lateral pull of the cell contour. With increasing distance between two neighboring sites of adhesion, the adhesion force increases because cell shape results in steeper pulling directions. Softer substrates result in smaller forces. Our predictions agree well with experimental force patterns measured on pillar assays.Comment: 4 pages, Revtex with 4 figure

Unifying autocatalytic and zeroth order branching models for growing actin networks

The directed polymerization of actin networks is an essential element of many biological processes, including cell migration. Different theoretical models considering the interplay between the underlying processes of polymerization, capping and branching have resulted in conflicting predictions. One of the main reasons for this discrepancy is the assumption of a branching reaction that is either first order (autocatalytic) or zeroth order in the number of existing filaments. Here we introduce a unifying framework from which the two established scenarios emerge as limiting cases for low and high filament number. A smooth transition between the two cases is found at intermediate conditions. We also derive a threshold for the capping rate, above which autocatalytic growth is predicted at sufficiently low filament number. Below the threshold, zeroth order characteristics are predicted to dominate the dynamics of the network for all accessible filament numbers. Together, this allows cells to grow stable actin networks over a large range of different conditions.Comment: revtex, 5 pages, 4 figure

Stability of freely falling granular streams

A freely falling stream of weakly cohesive granular particles is modeled and analysed with help of event driven simulations and continuum hydrodynamics. The former show a breakup of the stream into droplets, whose size is measured as a function of cohesive energy. Extensional flow is an exact solution of the one-dimensional Navier-Stokes equation, corresponding to a strain rate, decaying like 1/t from its initial value, gammaDot0. Expanding around this basic state, we show that the flow is stable for short times (gammaDot0 * t << 1), whereas for long times (gammaDot0 * t >> 1) perturbations of all wavelength grow. The growthrate of a given wavelength depends on the instant of time when the fluctuation occurs, so that the observable patterns can vary considerably.Comment: 4 page, 5 figures. Submitted to PRL. Supplementary material: see http://wwwuser.gwdg.de/~sulrich/research/#Publication

Інтерактивний контроль при формоутворенні багатогабаритних деталей

Physical phenomenon of warping (springing) can be observed as a technological heritage after large-dimensional articles forming or curing and consequent cooling of composite articles. This phenomenon can be seen as gaps between ready article contour and forming jig contour. Deviation degree of ready article surface from theoretical contour and article dimensions has to be controlled during manufacturing. Application of auxiliary controlling jig leads to expenses and labor-manufacturability increasing. Possibility of application forming jig with inserted jet gages is considered for articles shape controlling. Such gages and realization of acoustic methods allow to control not only final article shape but also geometry on intermediate stages of manufacturing.Після формоутворення багатогабаритних листових деталей з листових механічних заготовок або полімеризації і охолодження деталей з композитних матеріалів проявляється технологічна спадковість у вигляді викривлення (пружнення). Це спостерігається у вигляді неприлягання готової деталі до формозадаючої поверхні технологічного оснащення. При контролі якості формозміни необхідно вимірювати ступінь порушення форми і розмірів. Застосування контрольної оснастки дорого і складно. Розглянуто можливість використання для контролю формозадаючої оснастки з встановленими в ній повітряними струминними датчиками. Такі датчики і застосування акустичних методів дозволяють контролювати не тільки кінцеву форму заготовки, а й форму заготовки на попередваріантних етапах формозміни