The cause of axial rotation of the scoliotic spine

To explain the cause of axial rotation in a scoliotic vertebral column, the influence of the gravitation force on a spine with a C-scoliosis has been investigated by means of a mechanical model. In this model the gravitation force takes hold of the three-dimensionally curved vertebral column eccentrically. From these reflections it appears that the axial rotation in the scoliotic spine can be explained by the moment distribution caused by this eccentrical gravitation force. The moment distribution, necessary for correction of the spine, is supposed to be opposite to the moments caused by the gravitation force. The moment distribution caused by the Harrington and the Luque spinal correction systems are compared to the calculated optimum correction moments. It appears that the moment distribution for the Harrington and Luque methods, necessary for the correction of the lateral deviation, are almost the same as the calculated correction moments. But the axial rotation appears to be increasing instead of decreasing in both correction systems

Physical gels based on charge-driven co-assembly

Gels are used in a variety of products ranging from personal care products and food products to explosives. An important area where aqueous physical gels are applied is the water-based coatings industry. Currently, classical associative thickeners are used to form transient networks based on hydrophobic interactions. Although this technology has greatly improved the properties of water-based coatings, there remain some problems related to the use of these classical associative thickeners. In this Thesis we investigate aqueous physical gels based on interconnected polyelectrolyte complex micelles, as a new two-component associative thickener. The physical gels are prepared from an ABA triblock copolymer, with charged A-blocks and a neutral hydrophilic B-block, mixed with either an oppositely charged homopolymer or nanoparticle. Electrostatic interaction is the driving force for association of the oppositely charged components, leading to transient networks of interconnected flowerlike micelles or particles, depending on the origin of the oppositely charged component. The fact that we deal with a two-component system, as well as a completely different driving force for association, could potentially solve some of the current problems related to the use of the classical associative thickeners. Throughout this Thesis we have tried to link the microstructure of the gels to the macroscopic properties. We do so by combining microscopic experimental techniques, such as (dynamic) light scattering, small-angle X-ray scattering and (cryo-) scanning electron microscopy with macroscopic experimental techniques such as rheometry. In chapter 2 we show that we successfully prepared an aqueous multi-responsive reversible gel based on the bridging of polyelectrolyte complex micelles. At low concentrations these two oppositely charged polymers co-assemble spontaneously to form flowerlike polyelectrolyte complex micelles. If two micelles come close enough to each other, the micelles can become connected to each other, because a triblock copolymer can stick both end-blocks in two different micellar cores. This bridging is reversible, meaning that the micelles are continuously connected and disconnected. At high concentrations enough micelles become interconnected to form a percolating path through the sample, hence the solution becomes a physical gel. Due to the electrostatic driving force for the co-assembly of micelles, these gels are truly multi-responsive. The influence of the charge ratio on the formation of polyelectrolyte complex micelles and their networks is studied in detail in chapter 3. Our measurements suggest an asymmetry, with respect to the charge stoichiometric point, in the shape and size of the co-assembled complexes. In chapter 4 we take a closer look at the network topology and how this is influenced by total polymer concentration and salt concentration. In chapter 5 we show that it is possible to use charged inorganic nanoparticles as nodes in a transient network bridged by triblock copolymers with charged end-blocks. Since gels of this kind have never been described before, we named this class of gels 'Complex Composite Gels'.</p

Relaxation dynamics at different time scales in electrostatic complexes: Time-salt superposition

In this Letter we show that in the rheology of electrostatically assembled soft materials, salt concentration plays a similar role as temperature for polymer melts, and as strain rate for soft solids. We rescale linear and nonlinear rheological data of a set of model electrostatic complexes at different salt concentrations to access a range of time scales that is otherwise inaccessible. This provides new insights into the relaxation mechanisms of electrostatic complexes, which we rationalize in terms of a microscopic mechanism underlying salt-enhanced activated processe

Stress, life history and dental development: a histological study of mandrills (Mandrillus sphinx)

Dental development is frequently used to reconstruct life history in primates for which little other information exists. In addition to the regular growth increments visible in histological tooth sections, accentuated lines are thought to form at the time of stressful events in the lives of individual animals. However, our understanding of when, how and why such accentuated lines form in relation to stressful events is limited. In this thesis, I tested the hypothesis that accentuated lines in the enamel and dentine are associated with stressful events in the lives of semi-free-ranging mandrills (Mandrillus sphinx, Cercopithecidae) from the Centre International de Recherches Médicales de Franceville, Gabon. I used dates of birth and death to calibrate dental histology to calendar time and individual age. I then reconstructed dental development sequences for individual mandrills, providing a detailed overview of mandrill dental development. I report sex-specific dental development chronologies, crown extension rates and stages of dental development, and compare these to mandrill life history. Based on this dental development data, I matched the observed accentuated lines in the mandrill teeth with the dates of events in the mandrills’ lives. My results suggest that accentuated lines can correspond to potentially stressful events, including resumption of reproductive cycling in the mother and menstrual cycles, and in some occasions with parturitions. My results show that male mandrills might form accentuated lines at the time of potentially stressful events too, but most potentially stressful life history events for males take place after dental development is complete. Furthermore, my findings suggest that the number of accentuated lines recorded in teeth varies between individuals in a population, reflecting differences that may influence reproductive success

Remotely acting SMCHD1 gene regulatory elements: in silico prediction and identification of potential regulatory variants in patients with FSHD

Background: Facioscapulohumeral dystrophy (FSHD) is commonly associated with contraction of the D4Z4 macro-satellite repeat on chromosome 4q35 (FSHD1) or mutations in the SMCHD1 gene (FSHD2). Recent studies have shown that the clinical manifestation of FSHD1 can be modified by mutations in the SMCHD1 gene within a given family. The absence of either D4Z4 contraction or SMCHD1 mutations in a small cohort of patients suggests that the disease could also be due to disruption of gene regulation. In this study, we postulated that mutations responsible for exerting a modifier effect on FSHD might reside within remotely acting regulatory elements that have the potential to interact at a distance with their cognate gene promoter via chromatin looping. To explore this postulate, genome-wide Hi-C data were used to identify genomic fragments displaying the strongest interaction with the SMCHD1 gene. These fragments were then narrowed down to shorter regions using ENCODE and FANTOM data on transcription factor binding sites and epigenetic marks characteristic of promoters, enhancers and silencers