Comparison of mechanical properties of orthodontic nickel-titanium wires]

Two packages each, containing 10 wires per package, of different batches of 25 different types of orthodontic archwires made of super-elastic nickel-titanium alloys measuring 0.41 x 0.56 mm2, were investigated. The wires were characterized by obtaining the following measurements at an ambient temperature of 37 degrees: a three-point bending test with the supporting points spaced 10 mm apart, and determination of the torque/bending angle curves using a pure bending test. The force/deflection curves provided the parameters characterizing the super-elastic unloading plateau: average force, slope and endpoint. From the torque/bending angle curves, the parameters average torque, plateau endpoint and the elasticity parameters were determined. Average force (0.8-4.5 N), endpoint (0.2-0.9 mm) and the slope of the unloading plateau (0.2-2.1 N/mm) of the three-point bending test clearly differed for individual wires. Significant differences were also seen for average torque (1.5-11.5 Nmm), unloading plateau endpoint (2.7-20.0 degrees) and elasticity parameters epsilon 4, E4, E5 and E6 in the pure bending test. Individual batches showed only minor differences. The results permit the conclusion to be drawn that super-elasticity is applicable to only a small portion of the wires examined. Although other wires showed super-elastic behaviour, the unloading plateaus has a force level of up to 6 N, and cannot be recommended for orthodontic application. The super-elastic plateau is often of use only for deflections greater than 1.5 mm. The use of super-elastic archwires made of nickel-titanium alloys makes sense only when the elastic properties of the respective wires are known. This makes the provision by the manufacturer of relevant data on the elastic properties of wires a necessity.     

Itô versus Stratonovich calculus in random population growth

The context is the general stochastic differential equation (SDE) model dN/dt=N(g(N)+sigmaepsilon(t)) for population growth in a randomly fluctuating environment. Here, N=N(t) is the population size at time t, g(N) is the 'average' per capita growth rate (we work with a general almost arbitrary function g), and sigmaepsilon(t) is the effect of environmental fluctuations (sigma>0, epsilon(t) standard white noise). There are two main stochastic calculus used to interpret the SDE, It? calculus and Stratonovich calculus. They yield different solutions and even qualitatively different predictions (on extinction, for example). So, there is a controversy on which calculus one should use. We will resolve the controversy and show that the real issue is merely semantic. It is due to the informal interpretation of g(x) as being an (unspecified) 'average' per capita growth rate (when population size is x). The implicit assumption usually made in the literature is that the 'average' growth rate is the same for both calculi, when indeed this rate should be defined in terms of the observed process. We prove that, when using It? calculus, g(N) is indeed the arithmetic average growth rate R(a)(x) and, when using Stratonovich calculus, g(N) is indeed the geometric average growth rate R(g)(x). Writing the solutions of the SDE in terms of a well-defined average, R(a)(x) or R(g)(x), instead of an undefined 'average' g(x), we prove that the two calculi yield exactly the same solution. The apparent difference was due to the semantic confusion of taking the informal term 'average growth rate' as meaning the same average.     

Linking stem cell function and growth pattern of intestinal organoids

Intestinal stem cells (ISCs) require well-defined signals from their environment in order to carry out their specific functions. Most of these signals are provided by neighboring cells that form a stem cell niche, whose shape and cellular composition self-organize. Major features of this self-organization can be studied in ISC-derived organoid culture. In this system, manipulation of essential pathways of stem cell maintenance and differentiation results in well-described growth phenotypes.We here provide an individual cell-based model of intestinal organoids that enables a mechanistic explanation of the observed growth phenotypes. In simulation studies of the 3D structure of expanding organoids, we investigate interdependences between Wnt- and Notch-signaling which control the shape of the stem cell niche and, thus, the growth pattern of the organoids. Similar to in vitro experiments, changes of pathway activities alter the cellular composition of the organoids and, thereby, affect their shape. Exogenous Wnt enforces transitions from branched into a cyst-like growth pattern; known to occur spontaneously during long term organoid expansion. Based on our simulation results, we predict that the cyst-like pattern is associated with biomechanical changes of the cells which assign them a growth advantage. The results suggest ongoing stem cell adaptation to in vitro conditions during long term expansion by stabilizing Wnt-activity.Our study exemplifies the potential of individual cell-based modeling in unraveling links between molecular stem cell regulation and 3D growth of tissues. This kind of modeling combines experimental results in the fields of stem cell biology and cell biomechanics constituting a prerequisite for a better understanding of tissue regeneration as well as developmental processes.     

3-D model analysis of the maxilla of infants with lip-jaw-palate clefts]

For the investigation of three-dimensional morphological changes in the maxilla of children with cleft lip and palate, the use of two-dimensional test analysis is inadequate. Since no standardised three-dimensional method has so far been available, a three-dimensional digital, computer-aided procedure was developed to visualize and metrically analyse the growth of the edentulous maxilla of infants with cleft lip and palate. Chronologically consecutive casts of the maxillas (obtained at the ages of one week, and three, six and twelve months) of five children with complete unilateral CLP were measured optically with the instrument Micromeasure 70. Following digitation, the casts were reconstructed in the computer, aligned and superimposed using the Orthosurf program. The distances between the surfaces were then measured; in addition, the surfaces were segmented perpendicular to the alveolar crest at reference points C1, C1', C2, C2' and I. The volumes of the resulting segments were determined and compare with one another. Specially designed software automated the following steps: 1. identification of reference points; 2. alignment of the cloud of points in a system of coordinates, and 3. identification of the alveolar crest. Our initial results show that (1) the new method enables visualization of the extent and direction of morphological changes of the mucosal surface, and (2) reproducible quantification of these changes via the determination of changes in the volume of defined alveolar segments. The three-dimensional analysis presented here permits a comprehensive three-dimensional measurement of the models of the edentulous maxilla of infants with cleft lip and palate.     

Suitability of Vader for transposon-mediated mutagenesis in Aspergillus niger

The filamentous fungus Aspergillus niger is widely used in biotechnological applications. Strain CBS513.88 is known to harbor 21 copies of the nonautonomous transposon Vader. Upon selection of chlorate-resistant A. niger colonies, one Vader copy was found integrated in the nirA gene. This copy was used for vector construction and development of a transposon-tagging method. Vader showed an excision frequency of about 1 in 2.2 × 10(5) conidiospores. A total of 95 of 97 colonies analyzed exhibited an excision event at the DNA level, and Vader footprints were found. By employing thermal asymmetric interlaced (TAIL)-PCR, the reintegration sites of 21 independent excision events were determined. All reintegration events occurred within or very close to genes. Therefore, this method can be used for transposon mutagenesis in A. niger.     

Effects of taurolidine and octreotide on tumor growth and lipid peroxidation after staging-laparoscopy in ductal pancreatic cancer

Irrigation with taurolidine after laparoscopy decreases tumor growth in colon carcinoma. In pancreatic cancer subcutaneous therapy with octreotide decreases oxidative stress and carcinogenesis as well. However, it is still unclear, whether irrigation with taurolidine or octreotide after laparoscopic pancreatic biopsy reduces tumor growth in pancreatic cancer as well. In 60 Syrian hamsters ductal pancreatic adenocarcinoma was induced by weekly injection of 10mg/kg body weight N-nitrosobis-2-oxopropylamine s.c. for 10 weeks. In week 16 laparoscopic pancreatic biopsy by use of carbon dioxide was performed (gr. 1, n = 20) with subsequent laparoscopic irrigation with taurolidine (gr. 2, n = 20) or octreotide (gr. 3, n = 20). In week 25 hamsters were sacrificed. Our results show that macroscopic visible primary tumors were found in only one animal of the taurolidine group (5.9%), compared to 42.1% in the saline and 62.5% in the octreotide group (P<0.05). Carcinomas were smaller after saline (6+/-23 mm(2)) than after octreotide irrigation (70+/-120 mm(2), P<0.05). In conclusion this study showed that laparoscopic irrigation with taurolidine after pancreatic biopsy inhibited tumor growth in ductal pancreatic adenocarcinoma.     

Modelling animal growth in random environments: An application using nonparametric estimation

We study a stochastic differential equation growth model to describe individual growth in random environments. In particular, in this paper, we discuss the estimation of the drift and the diffusion coefficients using nonparametric methods for the case of nonequidistant data for several trajectories. We illustrate the methodology by using bovine growth data. Our goal is to assess: (i) if the parametric models (with specific functional forms for the drift and the diffusion coefficients) previously used by us to describe the evolution of bovine weight were adequate choices; (ii) whether some alternative specific parameterized functional forms of these coefficients might be suggested for further parametric analysis of this data.