The mechanical properties of epithelial cells are modulated by structural changes in keratin intermediate filament networks. To investigate the relationship between network architecture and viscoelasticity, we assembled keratin filaments from recombinant keratin proteins 8 (K8) and 18 (K18) in the presence of divalent ions (Mg(2+)). We probed the viscoelastic modulus of the network by tracking the movement of microspheres embedded in the network during assembly, and studied the network architecture using scanning electron microscopy. Addition of Mg(2+) at physiological concentrations (<1 mM) resulted in networks whose structure was similar to that of keratin networks in epithelial cells. Moreover, the elastic moduli of networks assembled in vitro were found to be within the same magnitude as those measured in keratin networks of detergent-extracted epithelial cells. These findings suggest that Mg(2+)-induced filament cross-linking represents a valid model for studying the cytoskeletal mechanics of keratin networks.

The International Classification of Functioning, Disability and Health (ICF) consists of more than 1 400 items. Due to its size and complexity, using the ICF is hardly feasible in practice. Moreover, the severity of problems is given only on a five-point scale (qualifiers), which seems too insensitive for measurement of changes. Thus, in cooperation with four rehabilitation hospitals, Jacobi, Urban & Kaluscha have identified 148 relevant items for musculoskeletal diseases. For easier usage we assigned mnemonic three letter codes to these items, e. g. WAL for the item "Walking" (ICF d450). Then the physician assigns those few items which he and/or the patient consider most important. The severity of the problem is judged on a scale from 0 (no restriction) to 100 (maximum restriction) for each item. By drawing a bar on the scale the physician gives an interval instead of just a single point (fuzzy judgement). The centre of the interval represents the severity of the problem and the width represents the uncertainty of judgement, e. g. when there is no gold standard for measurement or when the problem varies with time. As both the assignment of descriptors from an item pool and the fuzzy judgements are a new approach to medical documentation, we carried out this pilot study to examine acceptance and feasibility of the approach. In the pilot study, 264 in-patients in four rehabilitation clinics have been included. 138 (94%) of the 148 descriptors in the item pool have been used. Altogether there were 1,764 single judgements. On average six descriptors per patient have been assigned, giving an efficient and precise individual documentation. This is an advantage of the documentation principle called combination of terms compared to the principle of classification. In contrast to the ICF core sets patients may get individual sets of descriptors as appropriate. On discharge, the judgements were about 25 points better compared to admission. During treatment the fluctuations of disorders decreased and the certainty of the judgements increased, resulting in reduction of interval width of 2.8 points. The feedback of the rehabilitation clinics involved showed good acceptance and feasibility. Our data can easily be mapped into the ICF. In addition to ICF core sets, our approach could facilitate the use of the ICF in practical settings.

The cytoskeleton of epithelial cells consists of three types of filament systems: microtubules, actin filaments and intermediate filaments (IFs). Here, we took a closer look at type I and type II IF proteins, i.e. keratins. They are hallmark constituents of epithelial cells and are responsible for the generation of stiffness, the cellular response to mechanical stimuli and the integrity of entire cell layers. Thereby, keratin networks constitute an important instrument for cells to adapt to their environment. In particular, we applied models to characterize the assembly of keratin K8 and K18 into elongated filaments as a means for network formation. For this purpose, we measured the length of in vitro assembled keratin K8/K18 filaments by transmission electron microscopy at different time points. We evaluated the experimental data of the longitudinal annealing reaction using two models from polymer chemistry: the Schulz–Zimm model and the condensation polymerization model. In both scenarios one has to make assumptions about the reaction process. We compare how well the models fit the measured data and thus determine which assumptions fit best. Based on mathematical modelling of experimental filament assembly data we define basic mechanistic properties of the elongation reaction process.

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