Biomedical subjects

Wolfgang Roth

Publications and source records attributed to Wolfgang Roth.

5 recordsLinked to original sources

PubMed2006

Long-term mechanical loading of chondrocyte-chitosan biocomposites in vitro enhanced their proteoglycan and collagen content.

One major problem in cartilage tissue engineering is the insufficient biochemical composition of the generated biocomposites. The aim of this study was to improve the collagen and proteoglycan deposition in tissue engineering constructs by application of long-term mechanical loading in culture. Chondrocyte-seeded chitosan biocomposites revealed a homogenous cell distribution, high viability (>95%) and maintenance of a rounded cell shape typical for chondrocytes over 3 weeks of load-free culture. Cyclic compression of chitosan biocomposites (0.1 Hz, amplitude 5-15%, 45 min on and 315 min off) was applied after two different preculture times (3, 21 days) for 3 weeks. At day 42 this resulted in enhanced mRNA levels for aggrecan and a significantly higher specific proteoglycan (5-fold, p<0.0002) and collagen type II (2-fold, p<0.02) deposition compared to unloaded controls. In sum, the chitosan scaffold was highly attractive for cartilage tissue engineering approaches and mechanical loading allowed to further improve the biochemical composition of these biocomposites.

Animals↗

PubMed2005

Competition between van der Waals and hydrogen bonding interactions: structure of the trans-1-naphthol/N(2) cluster.

The excitation energy in the multiphoton ionization spectrum of the trans-1-naphthol/N(2) cluster shows only a small red shift with respect to isolated naphthol, indicating a van der Waals pi-bound structure rather than a hydrogen-bonded one. To confirm this interpretation, high-level electronic structure calculations were performed for several pi- and hydrogen-bonded isomers of this cluster. The calculations were carried out at the second order Møller-Plesset (MP2) level of perturbation theory with the family of correlation consistent basis sets up to quintuple-zeta quality including corrections for the basis set superposition error and extrapolation to the MP2 complete basis set (CBS) limit. We report the optimal geometries, vibrational frequencies, and binding energies (D(e)), also corrected for harmonic zero-point energies (D(0)), for three energetically low-lying isomers. In all calculations the lowest energy structure was found to be an isomer with the N(2) molecule bound to the pi-system of the naphthol ring carrying the OH group. In the CBS limit its dissociation energy was computed to be D(0) = 2.67 kcal/mol (934 cm(-1)) as compared to D(0) = 1.28 kcal/mol (448 cm(-1)) for the H-bound structure. The electronic structure calculations therefore confirm the assignment of the experimental electronic spectrum corresponding to a van der Waals pi-bound structure. The energetic stabilization of the pi-bound isomer with respect to the hydrogen-bonded one is rather unexpected when compared with previous findings in related systems, in particular phenol/N(2).

Computer Simulation↗

PubMed2004

A cryo-jaw designed for in vitro tensile testing of the healing Achilles tendons in rats.

We present a simple but very secure non-compressive clamping device for in vitro tensile testing of the Achilles tendon in rats. Biomechanical studies were performed on 178 native and injured specimens without any registration of slippage out of the clamp. The average tensile strength of the native rat Achilles tendon was determined to be 48 N (+/-11 N) and its displacement to failure averaged 0.8 mm (+/-0.2 mm). The mean values for tensile strength within the injured tendons increased with time and were above the native tendon values from week 2 and later. Correspondingly, the displacement to failure decreased with time.

Achilles Tendon↗

PubMed2003

Rapid regulation of collagen but not metalloproteinase 1, 3, 13, 14 and tissue inhibitor of metalloproteinase 1, 2, 3 expression in response to mechanical loading of cartilage explants in vitro.

This study analyzes the molecular response of articular chondrocytes to short-term mechanical loading with a special focus on gene expression of molecules relevant for matrix turnover. Porcine cartilage explants were exposed to static and dynamic unconfined compression and viability of chondrocytes was assessed to define physiologic loading conditions. Cell death in the superficial layer correlated with mechanical loading and occurred at peak stresses >or=6 MPa and a cartilage compression above 45%. Chondrocytes in native cartilage matrix responded to dynamic loading by rapid and highly specific suppression of collagen expression. mRNA levels dropped 11-fold (collagen 2; 6 MPa, P=0.009) or 14-fold (collagen 1; 3 and 6 MPa, P=0.009) while levels of aggrecan, tenascin-c, matrix metalloproteinases (MMP1, 3, 13, 14), and their inhibitors (TIMP1-3) did not change significantly. Thus, dynamic mechanical loading rapidly shifted the balance between collagen and aggrecan/tenascin/MMP/TIMP expression. A better knowledge of the chondrocyte response to mechanical stress may improve our understanding of mechanically induced osteoarthrits.

Aggrecans↗

PubMed2003

Excited state dynamics and rapid internal conversion in a stable dipole molecule.

The excited singlet state of an azomethine ylide or 'stable dipole' exhibits an ultrafast radiationless relaxation after femtosecond laser excitation. These transients are observed before the excited state decays in an almost activationless manner, the barrier is 440 cm-1, to the ground state with a 1.5 ps lifetime. Cooling of the hot ground state is also apparent in the transient absorption data and in methanol decays with a 5.7 ps lifetime. The viscosity dependence of the fluorescence yield and lifetime in different solvents is small and far less pronounced than in triphenylmethane dyes. Surprisingly, the excited state decay is not due to twisting about the C-N bond of the ylide but it is caused by buckling of one of the rings as the nitrogen atom changes character from sp2 to sp3 hybridisation.

Journal Article↗