Biomedical subjects

H Amenitsch

Publications and source records attributed to H Amenitsch.

21 records · Page 2Linked to original sources

PubMed1998

Fibrillar structure and mechanical properties of collagen.

Collagen type I is among the most important stress-carrying protein structures in mammals. Despite their importance for the outstanding mechanical properties of this tissue, there is still a lack of understanding of the processes that lead to the specific shape of the stress-strain curve of collagen. Recent in situ synchrotron X-ray scattering experiments suggest that several different processes could dominate depending on the amount of strain. While at small strains there is a straightening of kinks in the collagen structure, first at the fibrillar then at the molecular level, higher strains lead to molecular gliding within the fibrils and ultimately to a disruption of the fibril structure. Moreover, it was observed that the strain within collagen fibrils is always considerably smaller than in the whole tendon. This phenomenon is still very poorly understood but points toward the existence of additional gliding processes occurring at the interfibrillar level.

Animals↗

PubMed1998

Studies on the 14.5 nm meridional X-ray diffraction reflection during length changes of intact frog muscle fibres.

The intensity of the 14.5 nm meridional reflection (M3) from activated skeletal muscle fibres was studied in both single fibres and fibre bundles during the imposition of length changes. During shortening at small load, the intensity of the reflection decreased within 2 ms to less than 20% of isometric intensity, then recovered partially during the remainder of the shortening. When shortening was terminated, recovery of intensity was delayed. Small shortening steps (0.5% fibre length) produced a fall in M3 intensity (IM3) delayed by ca. 250 microseconds compared to the fall in tension. For larger step releases (1% fibre length), the fall in IM3 was not delayed. The fall in IM3 could be almost completely reversed by a subsequent restretch applied within 1.5 ms. Beyond 10 ms after the initial release, the restretch caused a further fall in intensity. A rapid step stretch (0.5% fibre length) also caused a fall in IM3 without delay, which was partially reversed by a release applied within 10 ms. A second small release applied 3 ms (or less) after the first caused a second fall in M3 intensity, but without delay and with faster time course. Small amplitude sinusoidal length oscillations (0.15-0.2% sarcomere; 1 kHz) caused a sinusoidal change in M3 intensity, which was 180 degrees out of phase with the force oscillations, and lacked distortion during its release phase.

Animals↗

PubMed1998

Trapping of short-lived intermediates in phospholipid phase transitions: the L* alpha phase.

Time-resolved small-angle X-ray diffraction of liquid-crystalline phospholipid-water systems under temperature or pressure jump conditions has demonstrated the existence of an ordered, intermediate L alpha phase, with a sub-second lifetime, designated as the L* alpha-phase. The lamellar repeat spacing is, universally, 0.3 nm smaller than that of the parent phase, irrespective of the lipid composition and of the jump conditions, provided that the jump leads to a net volume expansion of the phase. The presence of salts, most notably LiCl, leads to a prolongation of the lifetime. The results suggest a non-monotonic potential function for the interbilayer water thickness.

Membranes, Artificial↗