Wolfgang Pfeiler

Alterations of biochemical and two-dimensional biomechanical properties of human skin in diabetes mellitus as compared to effects of in vitro non-enzymatic glycation.

OBJECTIVE The aim of this study was to evaluate whether multiaxial analysis of diabetes-specific biomechanical changes generated in vitro by non-enzymatic glycation of human skin samples from healthy subjects reflect the changes seen in skin from subjects with diabetes mellitus. DESIGN Descriptive study. BACKGROUND Non-enzymatic glycation of skin in vitro causes an increased stiffness comparable to in vivo changes seen in diabetic patients. These changes are probably due to increased cross-linking of collagen molecules. METHODS Skin specimens from 7 subjects with diabetes mellitus and 7 controls (age range: 74-90) were analyzed for biomechanical changes using a multiaxial tensile testing device. Control skins from healthy individuals in the age range of 50-65 yr were artificially glycated. One part of these samples was coincubated with the glycation inhibitor aminoguanidine. Glycation of tissues was determined by measuring fluorescence of solubilized samples. Multiaxial biomechanical analysis allows the determination of maximum (a(I)) and minimum elastic modulus (a(II)). These parameters describe the amplitude of the elastic stress response, which is exponentially related to strain. RESULTS Principal stresses, both maximum and minimum, were increased in skins from diabetic subjects as compared to controls. The increases of the principal stresses were comparable to those obtained by in vitro glycation of normal skins. CONCLUSION These results, which can be detected unequivocally with the multiaxial test mode, show that our in vitro model closely reflects changes in skin samples from individuals with diabetes mellitus. Aminoguanidine partially inhibited these as well as biochemical changes. RELEVANCE Multiaxial testing of in vitro glycated skin samples can be used as a model for in vivo changes caused by diabetes mellitus. In addition, therapeutical effects of aminoguanidine, an inhibitor of non-enzymatic glycation, can be monitored in this model.

Kinetics of defect recovery and long-range ordering in Ni3Al + B—II. Atomic jump processes studied by “order-order” relaxation experiments

Fine isothermal relaxations of the degree of long-range order (LRO) in the homogeneous intermetallic compound Ni{sub 76}Al{sub 24} + 0.19 at.% B (400 wt. ppm) were examined by means of residual resistometry. It was found that two parallel relaxation processes are involved in the phenomenon. The processes dramatically differed in the relaxation rates, but showed close activation energies exceeding 4 eV. A model explaining the occurrence of two parallel relaxation processes and based on the vacancy thermodynamics in L1{sub 2} superstructure is proposed. The evaluated high activation energy for LRO kinetics is attributed to specific modes of vacancy diffusion involving jumps between different sublattices. It is compared with the activation energies of diffusion in Ni{sub 3}Al exhibited by several ternary elements occupying the sublattice of Al. In these terms, the inadequacy of relating Ni diffusion data to the parameters of LRO kinetics in Ni{sub 3}Al is indicated.

Atomic ordering in alloys: stable states and kinetics

Abstract Ordering in alloys is a topic of growing technological and scientific interest within the field of materials science. This is because the advantageous high temperature and corrosion properties of intermetallic compounds are linked to the effect of long-range ordering. Ordering effects as observed by electrical resistometry are discussed in this paper with respect to stable states of order (thermal equilibrium) and the ordering relaxation kinetics leading from one stable state to another. Examples are given on CuPt (L1 1 ), CuAu (L1 0 ), Cu 3 Au (L1 2 ), Ni 3 Al (L1 2 ) and FeAl (B2).

L12-long-range order in Cu3Au: kinetics and equilibrium as studied by residual resistivity

Abstract The evolution of L12-long-range order in Cu3Au was studied as a function of temperature by means of residual resistivity measurement. Kinetics as well as temperature dependence of equilibrium values of the LRO-parameter were studied during isothermal annealing and the LRO-equilibrium values obtained were compared with model calculations and X-ray diffraction measurements. Comparing the analyses of order-order relaxations with those of disorder–order relaxations, information is gained on the growth kinetics of ordered antiphase domains.

Long-range ordering in B2 FeAl: a resistometric study

Abstract Changes in the degree of order have been studied by residual electrical resistivity measurement (REST) in B2 long-range ordered Fe–44.8 at.% Al during isochronal and isothermal step-annealing temperature treatment. Restricted atomic mobility starts already below about 500 K. Assuming the vacancy concentration to remain constant over an extended temperature range, as known from the literature, the complicated variations of resistivity with temperature can be explained by two regimes of ordering: a fast local ordering due to the restricted motion of the vacancies at low temperatures and a very slow global adjustment of long-range order (LRO) within the total sample volume. Kinetic parameters are determined from the detailed process analysis of the ordering kinetics during isothermal small-step annealing. Using these parameters, the results of isochronal annealing treatment can be calculated with a very good correspondence to experiment.

Differential scanning calorimetry, biochemical, and biomechanical analysis of human skin from individuals with diabetes mellitus

The aim of this work was to compare biochemical, two‐dimensional biomechanical and calorimetric parameters of diabetic skin vs. control skin. Skin specimens taken from the palms and backs of the hands of aged persons with non‐insulin‐dependent diabetes mellitus (NIDDM) and of controls (CO) were compared (age range 68–85 years). Only skin specimens from individuals with diabetes mellitus (DM) showed an increased fluorescence specific for the formation of advanced glycation end‐products (AGEs) and the presence of tissue AGEs, such as Ne‐(Carboxymethyl)lysine (CML). Differential scanning calorimetry (DSC) revealed an elevation of the heat flow per unit mass during collagen denaturation in diabetic skin samples. However, the temperatures of the heat flow maximum and the onset of the phase transformation were not uniformly altered. Young′s moduli were found to be increased in diabetic skin and correlated with AGE‐fluorescence and tissue AGEs. The ratio between the Youngs moduli, which defines a measure for the degree of anisotropy, was higher for dorsal skins from hands. In dorsal skin specimens from diabetic subjects the degree of anisotropy was more pronounced than in healthy controls. In general, neither of the measured parameters showed any correlation with age. However, E1 moduli were clearly associated with the duration of diabetes. Anat Rec 259:327–333, 2000.

Energetics of point defect formation in Ni3Al

Abstract Vacancy and anti-site defect formation energies in L1 2 -ordered Ni 3 Al are calculated by ab initio approaches. Based on a statistical-thermodynamic model the thermodynamic activities of both components are derived as a function of temperature and composition. Comparison with measured activities demonstrates the high reliability of the ab initio approach to defect formation.

Atomic short-range order in CuMn alloys

Abstract The establishment of atomic short-range order (SRO) has been investigated in CuMn alloys (5, 8,13,16,20 at. % Mn) by measurement of the electrical resistivity during isochronal and isothermal annealing. An increasing degree of SRO is accompanied by a reduction of resistivity; this effect increases with Mn concentration. For 8,13 and 16 at. % Mn SRO kinetics turn out to deviate significantly from single exponential behavior with a maximum at 13 at. % Mn, whereas at 5 and 20 at. % Mn SRO is adjusted in a single exponential process. For data analysis three methods are used: a sum of two and three exponentials as well as a log-normal spectrum of relaxation times. The strong interaction between second-nearest-neighbor atoms in CuMn seems to be essential for SRO kinetics but of minor importance for the value of SRO-induced resistivity change.

L11 Long-range order in CuPt: A comparison between X-ray and residual resistivity measurements

Abstract The evolution of L11 long-range order (LRO) in Cu–50 at%Pt was studied as a function of temperature in parallel by means of X-ray diffraction and measurements of residual resistivity. An excellent agreement between both experimental methods results, using the well-known Rossiter formalism for evaluation of LRO-parameter from resistivity measurement. Results of X-ray diffraction were used to study the changes of the lattice parameter and the lattice distortion by the rhombohedral superstructure as a function of the degree of LRO.

Ordering kinetics in Ni3Al by molecular dynamics

We present molecular dynamics simulations of ordering kinetics in the Ni3Al alloy performed within the embedded atom method (EAM) as a scheme for interatomic potentials. The simulation cell containing 1372 atoms was initially perfectly L12-long-range ordered. After having artificially created one vacancy by removing at random one Ni-atom, the dynamics of the system was simulated at constant temperature and pressure. Atoms are found to migrate predominantly via jumps to nearest-neighbour (nn) vacancies. The number of antisites is low in comparison to the total number of atomic jumps. Therefore most of the jumps are ineffective for ordering kinetics causing only temporary change of the chemical order. Accordingly, the jumps creating antisites are most often followed by reverse jumps. Antisite defects are created as nn antisite pairs. This result is in agreement with predictions based on a model originally formulated within Monte Carlo simulations. 2002 Published by Elsevier Science B.V.