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PubMed1989

A hypothetical explanation for the aging of skin. Chronologic alteration of the three-dimensional arrangement of collagen and elastic fibers in connective tissue.

To provide a morphologic basis for a better understanding of the "aging" of human skin, the authors studied the three-dimensional arrangement and chronological alterations of the fibrous components of the connective tissue using rats aged 2 weeks to 24 months with a new technique for scanning electron microscopy. These studies showed that with postnatal growth there was a dynamic rearrangement of the collagen and elastic fibers: an ordered arrangement of mature collagen bundles was attained by producing a distortion of the elastic fiber meshwork of relatively straight fibers. During adulthood, there was a subsequent tortuosity of the distorted elastic fibers coupled with an incomplete rebuilding of the elastic fiber network, laid down in a form to interlock with the collagen bundles. These changes provide a model for explaining manifestations of aged skin, such as laxity, sagging, and wrinkling. The tortuously fixed elastic fibers imply that they have been stretched and have lost their original elasticity and ability to restitute short and straight. Interlocking of both collagen and elastic fibers should disturb the two independent fibrous systems, as would normally be the case, and thus decrease tissue compliance.

Aging↗
PubMed1988

Electron microscopic observations on the formation of elastic fibres in cultures of aortic medial cells and adventitial cells.

The formation of elastic fibres was observed in the cultured cells derived from the tunica media and the tunica adventitia of mouse aorta. Bundles of myofilaments with dense bodies were abundantly observed in the cytoplasm of the cultured medial cells, and numerous bundles of microfibrillar components were present in the intercellular spaces. Fine granules of approximately 50 nm in diameter were observed in the bundles of microfibrillar components. It was supposed that these fine granules of elastin fused with each other and formed elastic aggregates and then formed large elastic clumps. Numerous bundles of microfibrillar components were also present in the intercellular spaces of the cultured adventitial cells. Elastic aggregates were scarcely observed in the bundles of microfibrillar components. However, large elastic clumps as observed in the medial cell culture could not be found in the adventitial cell culture. It is suggested that the formation of large elastic clumps might be related to the sheet structures or lamellae of elastic fibres in the tunica media.

Animals↗
PubMed1996

Matrix proteins with high affinity for calcium ions are associated with mineralization within the elastic fibers of pseudoxanthoma elasticum dermis.

Ultrathin sections from the dermis of five normal subjects and from 10 patients suffering from pseudoxanthoma elasticum (PXE) were analyzed by immunoelectron microscopy with the aim of identifying and localizing proteins associated with the mineral precipitates within the altered elastic fibers. Serial sections were processed by indirect immunogold cytochemistry using primary antibodies against human fibronectin, vitronectin, bone sialoprotein, alkaline phosphatase, osteonectin, and osteopontin. In the latter two cases, antibodies against synthetic peptides were also used. The results indicate that normal elastic fibers contained osteopontin, and that this protein was associated with the apparently normal elastin as well as with the needle-shaped mineral precipitates in the elastic fibers of patients. On the contrary, significant amounts of vitronectin, alkaline phosphatase and, less, of bone sialoprotein were associated with the polymorphous mineral precipitates inside the elastic fibers. Large amounts of osteonectin and fibronectin, together with vitronectin, were localized on the microfilament aggregates, which were often associated with altered elastic fibers in PXE dermis and were never visualized in the dermis of control subjects. The results seem to indicate once more that PXE is a complex disorder of the fibroblast synthetic control. Elastic fiber mineralization might be considered a secondary event, which could depend on the abnormal synthesis and accumulation within the elastic fibers of proteins that are normally involved in mineralization processes.

Adolescent↗
PubMed1996

Distribution of elastic system fibres in human fetal liver.

Elastic system fibres are extracellular matrix components found in different organs for which they provide elasticity and some mechanical resistance. Oxytalan, elaunin and elastic fibres, which possess graduated amounts of elastin, are the 3 forms of elastic system fibres that are identifiable by their tinctorial and ultrastructural features. The distribution of these fibres in adult human liver is well-established but little, if anything, is known about them in fetal liver. The distribution of elastic system fibres was therefore investigated in human fetal liver, and the process of elastogenesis characterised. Specimens of liver from 24 human fetuses ranging in age from 13 to 38 wk postfertilisation were studied. The results are presented in relation to gestational age and the size of the portal tracts. Portal tracts exhibited a network of oxytalan fibres at 13 wk; elaunin fibres appeared later after 20 wk postfertilisation. Elastogenesis occurred more rapidly in venous than in arterial walls, and in veins it was more evident in the adventitia. A microfibrillar network of oxytalan fibres was observed around biliary ducts from the outset of their development. Elastogenesis follows the sequence oxytalan, elaunin and elastic fibres, but the elastogenetic process only completes its maturation in arterial walls, thus leading to the internal elastic lamina.

Bile Ducts↗
PubMed1977

Force-extension characteristics of orthodontic elastics.

The force-extension characteristics for a wide range of elastics were determined. It was found that (1) selection of elastics were determined. It was found that (1) selection of elastics based on 3 x lumen size will probably result in more force being generated than was previously reported, (2) there is very little difference seen in force-extension characteristics when the two manufacturers' elastics are compared, and (3) for experimental purposes, elastic testing can be done in the dry state for force-extension characteristic studies. This investigation has shown that stretching an orthodontic elastic to twice its original lumen diameter produces a force which better represents the manufacturer's expected value. Keeping these principles in mind, a more effective tooth-moving force can be realized, enabling the clinician to properly select orthodontic elastics for intra- and intermaxillary biomechanical procedures.

Orthodontic Appliances↗
PubMed1992

In vitro high resolution intravascular imaging in muscular and elastic arteries.

High resolution (125-microns lateral, 55-microns axial) images of 16 muscular (femoral) and 15 elastic (common carotid) human arteries were made in vitro with use of a prototype 45-MHz intravascular imaging system. Four distinct regions of scattering, excluding plaque, were identified in the ultrasound images corresponding histologically to the adventitia, media, thickened intima and elastic laminae, both internal and external. Arterial samples imaged under pressure and in a collapsed state underwent dimensional changes but exhibited similar levels of backscatter amplitude. All the elastic arteries displayed a prominent echogenic media, whereas all the muscular arteries displayed an echolucent media. Scattering from the internal elastic lamina in muscular arteries provided an excellent landmark for defining the location and extent of intimal thickening or plaque. In elastic arteries the internal elastic lamina could not be distinguished from the echogenic media; consequently, the boundary between the media and intimal layer was indistinct. Differences in the relative concentration and organization of collagen and elastin were found to provide a consistent explanation for the differences in scattering that were observed between individual layers within an artery as well as between muscular and elastic arteries.

Arteriosclerosis↗
PubMed2003

Interaction of elastic bodies via surface forces. 2. Exponential decay.

Our goal is to study theoretically the effect of deformation on the exponentially decaying interaction of two elastic solids separated by a thin liquid film. The deformed shape of the surfaces and the contribution of the elasticity to the total force, i.e., an additional term present between elastic bodies, are calculated from continuum elastic theory via a new asymptotic technique. Both the deformation and the contribution of the elasticity to the force are found to be significant on the length scale over which the surface force acts. The surface deformation is exponentially decaying with a decay length equal to that of the original surface interaction. It is especially important for large and/or rapidly changing force. The contribution of the elasticity is also exponentially decaying, but with half the decay length. Its strength depends on the elastic constants and size of the solids and on the magnitude and gradient of the original surface force. Depending on how the separation is detected, it can appear either as an attractive or as a repulsive contribution to the force. Our results open the possibility of recalculating the measured force to the interaction free energy.

Journal Article↗
PubMed2005

An elastic-plastic hybrid adhesion model for contacting rough surfaces in the presence of molecularly thin lubricant.

The study of adhesion has received considerable attention in recent years, partly due to advances in the design and fabrication of micro/nano devices. Many adhesion investigations are centered on single-spherical-contact models, which include the classic Johnson-Kendall-Roberts (JKR), improved Derjaguin-Muller-Toporov (IDMT), and Maugis-Dugdale (MD) models. Based on the IDMT single-asperity model, adhesive rough surface contact models have also been developed, which are valid for elastic and elastic-plastic contact conditions. A limitation of the IDMT-based models is that they are only valid for application cases with low adhesion parameter values. In this research, a contacting rough surface adhesion model was developed by combining an extended Maugis-Dugdale (EMD) model (which is only valid for elastic contacts) with an IDMT-based elastic-plastic adhesion model. The proposed model, termed the elastic-plastic hybrid adhesion model, is valid for the entire adhesion parameter range and also for elastic-plastic contacts. The proposed model gives results similar to the EMD rough surface model when the contact is primarily elastic. Moreover, the proposed model was compared to an IDMT-based model (ISBL model) and both gave similar results for contacts with low adhesion parameter values. With high adhesion parameter values, the ISBL model fails, whereas the proposed model correctly predicts higher adhesion. Last, based on the stiffness of the external force, the instability for adhesive rough surfaces in contact was also discussed, and it was postulated that a high peak value of the external force stiffness directly relates to the unstable contact process.

Journal Article↗
PubMed1999

Interactions of elastic and rigid vesicles with human skin in vitro: electron microscopy and two-photon excitation microscopy.

Interactions between vesicle formulations and human skin were studied, in vitro, in relation to their composition and elasticity. The skin ultrastructure was investigated using transmission electron microscopy (TEM), freeze-fracture electron microscopy (FFEM) and two-photon fluorescence microscopy (TPE). The main difference between the vesicle formulations was their elasticity. Elastic vesicle formulations contained bilayer forming surfactants/lipids and single-chain surfactant octaoxyethylenelaurate-ester (PEG-8-L), whereas rigid vesicles contained bilayer surfactants in combination with cholesterol. TEM results showed three types of interactions after non-occlusive application of elastic PEG-8-L containing vesicle formulations on human skin: (1) the presence of spherical lipid structures containing or surrounded by electron dense spots; (2) oligolamellar vesicles were observed between the corneocytes in the upper part of the stratum corneum; and (3) large areas containing lipids, surfactants and electron dense spots were observed deeper down into the stratum corneum. Furthermore, after treatment with vesicles containing PEG-8-L and a saturated C12-chain surfactant, small stacks of bilayers were found in intercellular spaces of the stratum corneum. Rigid vesicles affected only the most apical corneocytes to some extent. FFEM observations supported the TEM findings. Major morphological changes in the intercellular lipid bilayer structure were only observed after treatment with PEG-8-L containing elastic vesicles. TPE showed a distinct difference in penetration pathways after non-occlusive application of elastic or rigid vesicles. After treatment with elastic vesicles, thread-like channels were formed within the entire stratum corneum and the polygonal cell shape of corneocytes could not be distinguished. Fluorescent label incorporated in rigid vesicles was confined to the intercellular spaces of the upper 2-5 micrometer of the stratum corneum and the cell contours could still be distinguished.

Freeze Fracturing↗
PubMedDate not supplied

The effect of intraarticular anesthesia and elastic bandage on elbow proprioception.

Twenty uninjured male volunteers were studied to characterize normal elbow proprioception and to investigate the effect of applying an elastic bandage to the extremity and injection of an intraarticular anesthetic. A modified Biodex dynamometer was used to study position sense and detection of motion. In part 1 of the study position sense was tested by flexing the elbow to a predetermined angle, returning to the starting position, and then asking the subject to identify that angle. In part 2 detection of motion was tested by asking the subject to disengage the apparatus by pressing a stop button when movement was detected. The testing conditions in part 1 and part 2 were repeated after the elbow was wrapped with an elastic bandage and again after an intraarticular injection of 3 cc 1% lidocaine with the bandage removed. Ten additional subjects underwent testing of both elbows to examine the effect of arm dominance. Mean position sense was within 3.3 degrees+/-1.3 degrees of the actual angle in trials without an elastic bandage or an anesthetic. A significant improvement in position sense was observed (2.2 degrees+/-1.2 degrees) after an elastic bandage was applied (P < .004). No significant difference was seen in position sense after lidocaine was injected. The mean threshold for detection of motion in trials without an elastic bandage or an anesthetic was 4.21 degrees+/-1.56 degrees. No significant differences were seen in detection of motion observed with the elastic bandage or intraarticular anesthetic. No significant differences were seen between dominant and nondominant extremities for both position sense and detection of motion. The application of an elastic bandage improved position sense, suggesting that tactile cues from cutaneous or other extraarticular receptors may play a role in elbow proprioception. Intraarticular anesthesia, however, had little effect, suggesting that intracapsular receptors play a lesser role in elbow proprioception. The determination of proprioceptive qualities for the normal elbow can aid in the understanding of elbow function and provide a basis for defining its role in elbow dysfunction.

Adult↗
PubMed2004

Extremes of some foam properties and elasticity of thin foam films near the critical micelle concentration.

The elasticity of open and closed thin foam films is analyzed. The elasticity modulus of a closed film is shown to be additive with respect to contributions from Gibbs elasticity and disjoining pressure. A detailed expression for the film elasticity modulus explains the pronounced maxima of foaminess and foam stability near the critical micelle concentration observed earlier in many experiments. A theory of transversal elasticity of thin foam films is formulated under conditions excluding the action of Gibbs elasticity. Near the critical micelle concentration, the theory predicts maxima of the transversal elasticity modulus and of the films thickness as functions of concentration at a given disjoining pressure. The prediction has been verified experimentally by measuring the film thickness in equilibrium foam as a function of height.

Journal Article↗
PubMed1999

Determinations of PCB within a project to develop cleanup methods for PCB-containing elastic sealant used in outdoor joints between concrete blocks in buildings.

Determinations of PCB were carried out as part of a project aimed at developing cleanup methods for PCB-containing elastic sealant used in outdoor joints between concrete blocks. The goals of the project were to develop methods, which minimise the spread of PCB to the outdoor environment and to indoor air, and which keep the PCB levels as low as reasonably possible in the workplace environment whilst removing the elastic sealant. The following PCB determinations were carried out: (1) concentration in the elastic sealant; (2) concentration in the concrete close to the sealant; (3) concentration in soil; (4) concentration in the indoor air; and (5) concentration in the air in the workplace environment. The cleanup process consisted of a number of different steps: (1) cutting the elastic sealant with an oscillating knife; (2) grinding the concrete with a mechanical machine; (3) sawing the concrete with a mechanical saw and (4) cutting the concrete with a mechanical chisel. In all these different steps a high capacity vacuum cleaner connected to the machines was used. The elastic sealant contained 4.7 to 8.1% total PCB of a technical product with a composition most similar to Clophene A40. The concrete close to the sealant (first 2 mm) contained 0.12 and 1.7% total PCB at two different places. The pattern of the PCB in the concrete resembled that of the sealant. PCB concentrations in the soil from the ground close to the building were 0.1 and 0.3 ppm at two different places before the remedial action. The source of the PCB in the soil is most likely the sealant as the PCB pattern is similar for the two materials. The PCB levels in the workplace air at the beginning of the project, when the techniques were not fully developed, were generally above the occupational exposure limit of 10 micrograms m-3 (up to 120 micrograms m-3). Later when the techniques were optimised to better take care of dust and gases produced during the cutting and grinding etc., the levels were below or close to 10 micrograms m-3. The pattern of the PCB in the workplace air was different from that of the sealant and contained higher levels of lighter components. The PCB concentrations in the indoor air were measured before and during the remedial process. The levels were around 600 ng m-3 and there was no significant increase during the removal of the sealant. The PCB level after the remedial action will be measured later. The pattern of the PCB in the indoor air was different from that of the sealant as well as from that of the workplace air. Higher levels of the lighter PCB were present indoors compared to the composition in both workplace air and in sealant. Extracts of PCB were analysed by GC-MS with a SIM method (selected ion monitoring). Standard procedures were used for extraction of solid materials. For the air samples an OVS tube was used with XAD-2 as adsorbent. The filter and adsorbent were extracted with toluene. This work shows that it is important to perform remedial action of PCB-containing elastic sealant as: (1) there is a spread of PCB to the indoor air giving high enough concentrations to make this the main PCB load on humans living in the apartments studied in this project; (2) large amounts are spread to the soil from these sealants; and (3) many of the PCB-containing elastic sealants used need to be changed from a functional perspective.

Air Pollution, Indoor↗
PubMed2003

The many growth rates and elasticities of populations in random environments.

Despite considerable interest in the dynamics of populations subject to temporally varying environments, alternate population growth rates and their sensitivities remain incompletely understood. For a Markovian environment, we compare and contrast the meanings of the stochastic growth rate (lambdaS), the growth rate of average population (lambdaM), the growth rate for average transition rates (lambdaA), and the growth rate of an aggregate represented by a megamatrix (shown here to equal lambdaM). We distinguish these growth rates by the averages that define them. We illustrate our results using data on an understory shrub in a hurricane-disturbed landscape, employing a range of hurricane frequencies. We demonstrate important differences among growth rates: lambdaS lambdaM. We show that stochastic elasticity, ESij, and megamatrix elasticity, EMij, describe a complex perturbation of both means and variances of rates by the same proportion. Megamatrix elasticities respond slightly and stochastic elasticities respond strongly to changing the frequency of disturbance in the habitat (in our example, the frequency of hurricanes). The elasticity EAij of lambdaA does not predict changes in the other elasticities. Because ES, although commonly utilized, is difficult to interpret, we introduce elasticities with a more direct interpretation: ESmu for perturbations of means and ESsigma for variances. We argue that a fundamental tool for studying selection pressures in varying environments is the response of growth rate to vital rates in all habitat states.

Ardisia↗
PubMed1992

Effect of the vertical force component of Class II elastics on the anterior intrusive force of maxillary archwire.

Class II elastics are usually employed in the treatment of excessive overbite and overjet with the Begg technique. The effect of Class II elastics on bite opening and the extent of such an effect is uncertain. This article, based on measurements of 30 cases, illustrates that the effect of the vertical component of force from Class II elastics in reducing the intrusive force generated by the anchor bands in the upper archwire is less than previously believed. The position of the circles in the archwire for intermaxillary elastics has the greatest influence on the anterior intrusive force of the upper archwire. The direction of the Class II elastics and the length of the dental arch (a negative correlation) came second, while the force actually exerted by the elastics had the smallest influence. It is, therefore, suggested that the position of the intermaxillary elastic circles should be located according to the differing clinical objectives.

Dental Stress Analysis↗
PubMed2003

Photo-elastic stress analysis of initial alignment archwires.

Photo-elastic models replicating a lower arch with a moderate degree of lower incisor crowding and a palatally displaced maxillary canine were used to evaluate the stresses transmitted to the roots of the teeth by initial alignment archwires. Six initial alignment archwires were compared, two multi-strand stainless steel wires, two non-super-elastic (stabilized martensitic form) nickel titanium wires, and two stress-induced super-elastic (austenitic active) nickel titanium wires. Three specimens of each archwire type were tested. Analysis of the photo-elastic fringe patterns, in the medium supporting the teeth, revealed that the non-super-elastic nickel titanium archwires produced the highest shear stresses (P = 0.001). However, the shear stresses generated by the super-elastic alignment archwires and the multi-strand stainless steel archwires were very similar (P = 1.00). These results show that even in situations where large deflections of initial alignment archwires are required, super-elastic archwires do not appear to have any marked advantage over multi-strand stainless steel alignment archwires in terms of the stresses transferred to the roots of the teeth.

Analysis of Variance↗
PubMed2004

Granular packings: nonlinear elasticity, sound propagation, and collective relaxation dynamics.

Experiments on isotropic compression of a granular assembly of spheres show that the shear and bulk moduli vary with the confining pressure faster than the 1/3 power law predicted by Hertz-Mindlin effective medium theories of contact elasticity. Moreover, the ratio between the moduli is found to be larger than the prediction of the elastic theory by a constant value. The understanding of these discrepancies has been a long-standing question in the field of granular matter. Here we perform a test of the applicability of elasticity theory to granular materials. We perform sound propagation experiments, numerical simulations, and theoretical studies to understand the elastic response of a deforming granular assembly of soft spheres under isotropic loading. Our results for the behavior of the elastic moduli of the system agree very well with experiments. We show that the elasticity partially describes the experimental and numerical results for a system under compressional loads. However, it drastically fails for systems under shear perturbations, particularly for packings without tangential forces and friction. Our work indicates that a correct treatment should include not only the purely elastic response but also collective relaxation mechanisms related to structural disorder and nonaffine motion of grains.

Journal Article↗
PubMed1997

Pressure differences of elastic compression stockings at the ankle region.

BACKGROUND: Elastic compression stockings are widely used medical devices for the prevention of edema and treatment of venous diseases. Many beneficial effects have been described in the past. The exact amount of pressure underneath elastic compression stockings at different areas of the leg remains controversial. OBJECTIVE: To examine the pressure at the skin underneath class II elastic compression stockings at different places around the ankle at the B level. METHODS: Patients with known venous insufficiency and regularly using class II elastic therapeutic compression stockings (25-35 mm Hg) for venous diseases were included. All subjects were wearing completely new stockings at the time of the study. Measurements were performed with an electropneumatic interface pressure measuring device (Oxford Pressure Monitor MK II) with inflatable small sensoring cells. Six sensors were placed around the smallest circumference at the ankle (B-area). The highest and lowest recordings as well as the means were evaluated. RESULTS: The mean pressure of class II elastic stockings measured around the ankle was 24.7 mm Hg (SD, 8.4). The lowest pressures were found at the medial site (18.3 mm Hg; 74% of the mean), and the highest at the pretibial zone (33.9 mm Hg, 137%). CONCLUSIONS: The pressure exerted by pressure class II elastic compression stockings a the medial site just above the ankle (B area) is too low to have influence and improve the venous insufficiency. For phlebology this is the target area. It might be a reason for the high recurrence rate of venous ulcers even if patients wear stockings. Also, the mean pressure of class II stockings was found to be below the normal levels of its pressure class (25-35 mm Hg according to the European CEN classification). The results advocate the use of pressure class III elastic compression stocking more often and the use of pelottes or foam pads.

Ankle↗
PubMed2000

MR-Intracranial pressure (ICP): a method to measure intracranial elastance and pressure noninvasively by means of MR imaging: baboon and human study.

PURPOSE: To develop a noninvasive method for intracranial elastance and intracranial pressure (ICP) measurement. MATERIALS AND METHODS: Intracranial volume and pressure changes were calculated from magnetic resonance (MR) imaging measurements of cerebrospinal fluid (CSF) and blood flow. The volume change was calculated from the net transcranial CSF and blood volumetric flow rates. The change in pressure was derived from the change in the CSF pressure gradient calculated from CSF velocity. An elastance index was derived from the ratio of pressure to volume change. The reproducibility of the elastance index measurement was established from four to five measurements in five healthy volunteers. The elastance index was measured and compared with invasive ICP measurements in five patients with an intraventricular catheter at MR imaging. False-positive and false-negative rates were established by using 25 measurements in eight healthy volunteers and six in four patients with chronically elevated ICP. RESULTS: The mean of the fractional SD of the elastance index in humans was 19.6%. The elastance index in the five patients with intraventricular catheters correlated well with the invasively measured ICP (R:(2) = 0.965; P: <.005). MR imaging-derived ICPs in the eight healthy volunteers were 4.2-12.4 mm Hg, all within normal range. Measurements in three of the four patients with chronically elevated ICP were 20.5-34.0 mm Hg, substantially higher than the normal limit. CONCLUSION: MR imaging-derived elastance index correlates with ICP over a wide range of ICP values. The sensitivity of the technique allows differentiation between normal and elevated ICP.

Adult↗