Degree Of Interdigitation Research Articles

Complex Phase Transitions of Fully Rigid Sphere-Rod Amphiphiles Induced by Solvent Polarity in Dilute Solutions.

We report complex macrophase and microphase transitions of rigid amphiphiles with spherical Keggin molecular clusters as the solvophilic block and rod-like rigid oligofluorene (OF) as the solvophobic block in mixed solvents of water and polar organic solvent. By properly adjusting the solvent polarity, the amphiphiles are found to respond accordingly by self-assembling into multilayered incomplete onion-like structures (10-25 vol % THF), single-layered vesicular structures (60 vol % THF), and an unexpected macrophase separation in the middle (40-50 vol % THF), which is due to the anomalous trends in Keggin solubility as a result of the nature of TBA+ counterions. The rigidity of the OF block prevents the amphiphile from assembling by following the rule of packing parameters; instead, interdigitation among different rods leads to the formation of the solvophobic domain to achieve self-assembly. The incomplete onion structures are controlled by the interdigitation of rigid rods for the number of layers and the electrostatic interaction among Keggin head groups for the interlayer distance. When the degree of interdigitation becomes lower, the self-assembly process shows a trend that can be explained by the traditional rule of packing parameter. This study demonstrates the formation of different self-assembled structures by rigid amphiphiles and their transitions induced by solvent composition. The self-assembly (microphase separation) of rigid amphiphiles in a dilute solution could indeed represent a broad area containing complicated, uncharted rules.

The Common Retention Practices Among Orthodontists from Different Countries.

To investigate the most common retention practices, factors influencing the retention protocol, and the differences among orthodontists regarding retention practices. An online validated questionnaire was anonymously sent to 3,000 orthodontic residents and clinicians. The survey consisted of 19 questions regarding the participants' demographics, prescribed retention appliances, factors affecting retention appliance choices, and adjunctive retention procedures. Descriptive statistics, Chi2 and Kendall's Tau-b tests were applied. Five hundred fifty-five orthodontic residents and clinicians, 53.3% males and 46.7% females, completed the survey, indicating a response rate of 18.5%. Although participants' demographics, type of treatment and pre-treatment malocclusion influence the choice of retention protocols, thermoplastic retainers (TR) were the most popular retention regime for the maxillary arch for both adults (47.4%) and adolescents (42.3%). Bonded retainers (BR) were the favored option for the mandibular arch (44.9% of adults and 40.7% of adolescents). The degree of arch expansion (64.1%) and the degree of interdigitation (50.1%) after treatment were the most influential factors for the choice of the preferred type of retainers by the respondents. 68.6% of the participants thought professional retention guidelines would be useful. Thermoplastic retainers were the most common retention appliances for adults and adolescents in the maxilla. At the same time, BR was the most favored retainer in the mandibular arch, with clinical experience, practice setting, and malocclusion- and treatment-related factors influencing the type of the chosen appliance. The demographic differences and the uneven participation in the survey need to be considered while interpreting the findings of this study.

Structural Phenomena in a Vesicle Membrane Obtained through an Evolution Experiment: A Study Based on MD Simulations.

The chemical evolution of biomolecules was clearly affected by the overall extreme environmental conditions found on Early Earth. Periodic temperature changes inside the Earth's crust may have played a role in the emergence and survival of functional peptides embedded in vesicular compartments. In this study, all-atom molecular dynamic (MD) simulations were used to elucidate the effect of temperature on the properties of functionalized vesicle membranes. A plausible prebiotic system was selected, constituted by a model membrane bilayer from an equimolar mixture of long-chain fatty acids and fatty amines, and an octapeptide, KSPFPFAA, previously identified as an optimized functional peptide in an evolution experiment. This peptide tends to form the largest spontaneous aggregates at higher temperatures, thereby enhancing the pore-formation process and the eventual transfer of essential molecules in a prebiotic scenario. The analyses also suggest that peptide-amphiphile interactions affect the structural properties of the membrane, with a significant increase in the degree of interdigitation at the lowest temperatures under study.

The Surface and Hydration Properties of Lipid Droplets

Lipid droplets (LDs) are energy storage organelles composed of neutral lipids, such as triacylglycerol (TG) and sterol esters, surrounded by a phospholipid (PL) monolayer. Their central role in metabolism, complex life cycle, and unique lipid monolayer surface have garnered great attention over the last decade. In this article, results from the largest and longest all-atom simulations to date suggest that 5–8% of the LD surface is occupied by TG molecules, a number that exceeds the maximal solubility reported for TGs in PL bilayers (2.8%). Two distinct classes of TG molecules that interact with the LD monolayer are found. Those at the monolayer surface (SURF-TG) are ordered like PLs with the glycerol moiety exposed to water, creating a significant amount of chemically unique packing defects, and the acyl chains extended toward the LD center. In contrast, the TGs that intercalate just into the PL tail region (CORE-TG) are disordered and increase the amount of PL packing defects and the PL tail order. The degree of interdigitation caused by CORE-TG is stable and determines the width of the TG-PL overlap, whereas that caused by SURF-TG fluctuates and is highly correlated with the area per PL or the expansion of the monolayer. Thus, when the supply of PLs is limited, SURF-TG may reduce surface tension by behaving as a secondary membrane component. The hydration properties of the simulated LD systems demonstrate ∼10 times more water in the LD core than previously reported. Collectively, the reported surface and hydration properties are expected to play a direct role in the mechanisms by which proteins target and interact with LDs.

A Complex Interrelationship between Temperature-Dependent Polyquaterthiophene (PQT) Structural and Electrical Properties

The influence of annealing temperature on the structural and electrical properties of conjugated poly(dodecyl-quaterthiophene) (PQT-12) polymer films is exploited. The temperature induced changes of structural parameters are monitored by in situ grazing incident X-ray diffraction (GIXD) and the conductivity. They are complemented by studies of the dielectric properties using variable angle spectroscopic ellipsometry (VASE). An increase of the scattered intensity, the size of the crystalline domains, and the current response is observed for a first thermal cycle with stepwise heating up to 90 °C, which revealed two polymorphs with different degrees of interdigitation in PQT-12. Irreversible changes are observed for the second cycle with a higher thermal budget up to 140 °C and are connected with a transition from the highly ordered to powder-like disordered phase for the main PQT-12 form whereas the second polymorph with stronger interdigitation completely vanished. In agreement with these observations hig...

Morphology and Electronic Properties of N,N′-Ditridecylperylene-3,4,9,10-tetracarboxylic Diimide Layered Aggregates: From Structural Predictions to Charge Transport

The morphology of layered aggregates of N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C13), a prototypical n-type semiconductor for organic electronic devices, was investigated by molecular dynamics and corroborated by metadynamics simulations. Calculations were targeted to ordered 3D aggregates, differing in the relative orientation of the perylene π-cores and on the degree of interdigitation among contiguous planar layers. Our simulations indicated the noninterdigitated cofacial structure as the thermodynamically most stable form of ordered PTCDI-C13 aggregates, in both bulk crystals and bilayers. Other structures, however, may occur in the growth of PTCDI-C13 under kinetic conditions. Density functional theory calculations were also performed to evaluate the relative total electronic energy of 3D crystals of PTCDI-C13 and related transfer integrals, correlating structure with potential charge-transport properties in devices. The most stable ordered aggregated form of PTCDI-C13 exhibits significant transfer integrals for electrons and accounts for the remarkable n-type charge-transport properties observed in thin films grown under thermodynamic conditions. The effect of structural disorder on charge-transport properties was also assessed by computing transfer integrals in PTCDI-C13 layers at the interface with a model surface. Targeting a strategic material for organic electronics, this work also highlights an integrated computational approach to simulate the structure and energetics of competing 3D morphologies in thin films and to shed light on the details of ordered structures that are responsible for the charge transport in small-molecule organic semiconductors.

Commissioning and quality assurance for VMAT delivery systems: An efficient time-resolved system using real-time EPID imaging.

An ideal commissioning and quality assurance (QA) program for Volumetric Modulated Arc Therapy (VMAT) delivery systems should assess the performance of each individual dynamic component as a function of gantry angle. Procedures within such a program should also be time-efficient, independent of the delivery system and be sensitive to all types of errors. The purpose of this work is to develop a system for automated time-resolved commissioning and QA of VMAT control systems which meets these criteria. The procedures developed within this work rely solely on images obtained, using an electronic portal imaging device (EPID) without the presence of a phantom. During the delivery of specially designed VMAT test plans, EPID frames were acquired at 9.5Hz, using a frame grabber. The set of test plans was developed to individually assess the performance of the dose delivery and multileaf collimator (MLC) control systems under varying levels of delivery complexities. An in-house software tool was developed to automatically extract features from the EPID images and evaluate the following characteristics as a function of gantry angle: dose delivery accuracy, dose rate constancy, beam profile constancy, gantry speed constancy, dynamic MLC positioning accuracy, MLC speed and acceleration constancy, and synchronization between gantry angle, MLC positioning and dose rate. Machine log files were also acquired during each delivery and subsequently compared to information extracted from EPID image frames. The largest difference between measured and planned dose at any gantry angle was 0.8% which correlated with rapid changes in dose rate and gantry speed. For all other test plans, the dose delivered was within 0.25% of the planned dose for all gantry angles. Profile constancy was not found to vary with gantry angle for tests where gantry speed and dose rate were constant, however, for tests with varying dose rate and gantry speed, segments with lower dose rate and higher gantry speed exhibited less profile stability. MLC positional accuracy was not observed to be dependent on the degree of interdigitation. MLC speed was measured for each individual leaf and slower leaf speeds were shown to be compensated for by lower dose rates. The test procedures were found to be sensitive to 1mm systematic MLC errors, 1mm random MLC errors, 0.4mm MLC gap errors and synchronization errors between the MLC, dose rate and gantry angle controls systems of 1°. In general, parameters measured by both EPID and log files agreed with the plan, however, a greater average departure from the plan was evidenced by the EPID measurements. QA test plans and analysis methods have been developed to assess the performance of each dynamic component of VMAT deliveries individually and as a function of gantry angle. This methodology relies solely on time-resolved EPID imaging without the presence of a phantom and has been shown to be sensitive to a range of delivery errors. The procedures developed in this work are both comprehensive and time-efficient and can be used for streamlined commissioning and QA of VMAT delivery systems.

Cranial suture complexity in caviomorph rodents (Rodentia; Ctenohystrica).

Due to their flexibility, sutures are regions that experience greater strains than the surrounding rigid cranial bones. Cranial sutures differ in their degree of interdigitation or complexity. There is evidence indicating that a more convoluted suture better enables the absorption of high stresses coming from dynamic masticatory forces, and other functions. The Order Rodentia is an interesting clade to study this because of its taxa with diverse chewing modes. Due to repeated loading resulting from gnawing and grinding, energy absorption by the sutures might be a crucial factor in these mammals. Species within the infraorder Caviomorpha were chosen as a case study because of their ecomorphological and dietary diversity. This study compared five sutures from the rostrum and cranial vault across seven caviomorph families, and assessed their complexity by means of the relative length and fractal dimension. Across these rodents, cranial sutures are morphologically quite diverse. We found that the sutures connecting the rostrum with the vault were relatively more interdigitated than those in the cranial vault itself, especially premaxillofrontal sutures. Suture interdigitation was higher in species that display chisel-tooth digging and burrowing behaviors, especially in the families Ctenomyidae and Octodontidae, than those in families Dasyproctidae and Cuniculidae, which have more gracile masticatory systems. The reconstruction of the ancestral character state, on family and species phylogeny, points toward low suture interdigitation (i.e., low length ratio) as a likely ancestral state for interfrontal, premaxillofrontal and maxillofrontal sutures. Interspecific differences in suture morphology shown here might represent adaptations to different mechanical demands (i.e., soft vs. tough foods) or behaviors (e.g., chisel-tooth digging), which evolved in close association with the diverse environments occupied by caviomorph rodents.

A new mathematical model for pattern formation by cranial sutures

Cranial sutures are narrow mesenchymal tissues that connect skull bones to each other. Given that they serve as growth centers in the skull, these undifferentiated tissues play crucial roles in skull development. Cranial sutures are also of clinical importance, because the premature fusion of skull bones results in a pathological condition called craniosynostosis. In newborns, skull sutures are wide and straight; during adolescence, they become thinner and start winding to form an interdigitating pattern. From a functional aspect, as the degree of interdigitation becomes larger, the strength of the connection between bones increases. However, the mechanisms underlying the maintenance of mesenchymal narrow bands or formation of interdigitation remain poorly understood. In the present study, we presented a new mathematical model that can reproduce the suture width maintenance and interdigitation formation. We can predict the width of the mesenchyme bands and wavelengths of suture interdigitations from the model.

Atomistic simulations of pH-dependent self-assembly of micelle and bilayer from fatty acids

Detailed knowledge of the self-assembly and phase behavior of pH-sensitive surfactants has implications in areas such as targeted drug delivery. Here we present a study of the formation of micelle and bilayer from lauric acids using a state-of-the-art simulation technique, continuous constant pH molecular dynamics (CpHMD) with conformational sampling in explicit solvent and the pH-based replica-exchange protocol. We find that at high pH conditions a spherical micelle is formed, while at low pH conditions a bilayer is formed with a considerable degree of interdigitation. The mid-point of the phase transition is in good agreement with experiment. Preliminary investigation also reveals that the effect of counterions and salt screening shifts the transition mid-point and does not change the structure of the surfactant assembly. Based on these data we suggest that CpHMD simulations may be applied to computational design of surfactant-based nano devices in the future.

A Clinical Comparative Study on Low Versus Medium Viscosity PolyMethylMetAcrylate Bone Cement in Percutaneous Vertebroplasty

Comparative, prospective follow-up study. Comparison of outcome between patients treated with Percutaneous VertebroPlasty (PVP) using low and medium viscosity PolyMethylMetAcrylate (PMMA) bone cement. Viscosity is the characterizing parameter of PMMA bone cement, currently the standard augmentation material in PVP, and influences interdigitation, cement distribution inside the vertebral body, injected volume and extravasation, thereby affecting the clinical outcome of PVP. Currently, low, medium, and high viscosity PMMA bone cements are used interchangeably. However, effect of viscosity on clinical outcome in patients with Osteoporotic Vertebral Compression Fractures (OVCFs) has not yet been explicit subject of investigation. Follow-up was conducted using a 0 to 10 Pain Intensity Numerical Rating Scale (PI-NRS) and the Short Form 36 (SF-36) Quality of Life questionnaire before PVP and at 7 days (PI-NRS only), 1, 3, and 12 months after PVP. Injected cement volume, degree of interdigitation, and cement leakage were analyzed on direct postoperative computed tomography scanning. At 6 and 52 weeks and at suspicion, patients were analyzed for new fractures. A total of 30 consecutive patients received PVP using low viscosity PMMA bone cement (OsteoPal-V) for 62 OVCFs, followed by 34 patients who received PVP using medium viscosity PMMA bone cement (Disc-O-Tech) for 67 OVCFs. Results regarding PI-NRS and SF-36 were comparable between both groups. Postoperative comparison of injected cement volume, degree of interdigitation, proportion of bipedicular procedures, incidence of new vertebral fractures and complications revealed no differences between both groups. Viscosity was identified as a risk factor for the occurrence of cement leakage (yes/no, OR: 2.925, 95% confidence interval: [1.072-7.984], P = 0.036). No major differences in clinical outcome after PVP in OVCFs using low and medium viscosity PMMA bone cement were found. Viscosity of PMMA bone cement was identified as an independent predictor of cement leakage.

Liquid crystalline side chain methacrylic azo containing polymers

This paper describes the synthesis and characterisation of methacrylic liquid crystalline side chain polymer containing azo group, with (PM6OAn) and without (PM6An) hydroxyl group. The characterisation was done by using a polarised light microscope (PLM), differential thermal analysis (DTA), and X-ray diffractometry. All compounds developed bilayer smectic phase, with a certain degree of interdigitation between the layers. Poly[{3-hydroxy-4-[(E)-(4-octyloxyphenyl)diazenyl]phenoxy}hexyl]-2-methyl-prop-2-enoate (PM6OA8) exhibits a smectic A phase, whereas the other polymers show a SmC phase. Pyroelectric investigations show only an antiferroelectric behaviour for poly [{3-hydroxy-4-[(E)-(4-dodecyloxyphenyl)diazenyl]phenoxy}hexyl]-2-methylprop-2-enoate (PM6OA12) and a paraelectric behaviour for PM6OA8, poly[{4-[(E)-(4-dodecyloxyphenyl)diazenyl]phenoxy}hexyl]-2-methylprop-2-enoate (PM6A12) and poly [{4-[(E)-(4-octyloxyphenyl) diazenyl] phenoxy} hexyl]-2-methylprop-2-enoate (PM6A8). Finally, the E-Z photoisomerisation of the chromophores in solution was probed to exist in PM6A12 and PM6A8.

Self-Organization in Semifluorinated Polymers

Alkyl-perfluoroalkyl compounds are known to form a microphase-separated structure due to the thermodynamic immiscibility between the fluorinated and the protonated segments [1,2]. Many similarities between bulk and surface structures of such polymers were found in the past [2,3,4] which can be explained by both microphase separation in the bulk as well as surface segregation of the fluorinated parts. Basing on this concept, polymers with chemically different main chains were attached with alkylperfluoroalkyl side chains (particularly, oxydecylperfluorodecyl chains, -O-(CH2) 10-(CF 2) 9-CF 3). Combined investigations by means of temperature-dependent X-ray scattering, molecular modeling and DSC measurements were performed to characterize the bulk structure in dependence on the flexibility of the main chain as well as the density of side chains. The polymers under investigation show one or more phase transitions in the temperature range from room temperature to 300 °C which can be assigned as transitions between different smectic structures. These phases are characterized to have positive as well as negative expansion coefficients, respectively, indicating changes of the tilt angle of the side chains and/or the degree of interdigitation. The polymer melts feature a high memory behavior evidenced by reversed imaging of the scattering patterns in the heating and cooling runs.

Comparative analysis of cranial suture complexity in the genus Caiman (Crocodylia, Alligatoridae).

The variation in degrees of interdigitation (complexity) in cranial sutures among species of Caiman in different skull regions was studied by fractal analysis. Our findings show that there is a small species effect in the fractal dimension of cranial sutures, but most variation is accounted for by regional differentiation within the skull. There is also a significant interaction between species and cranial regions. The braincase sutures show higher fractal dimension than the facial skull sutures for all three species. The fractal dimension of nasal-maxilla suture is larger in Caiman latirostris than in the other species. The braincase sutures show higher fractal dimensions in C. sclerops than in the other species. The results suggest that different regions of the skull in caimans are under differential functional stress and the braincase sutures must counteract stronger disarticulation forces than the facial sutures. The larger fractal dimension shown by C. latirostris in facial sutures has probably a functional basis also. Caiman latirostris is known to have preferences for harder food items than the other species.

Simulation Studies of Ultrathin Films of Linear and Branched Alkanes on a Metal Substrate

Ultrathin liquid films of three hexadecane isomers and of squalane physisorbed on a flat metal (Au(111)) surface have been studied by Monte Carlo and molecular dynamics simulations. Density oscillations arising from the layering of methyl and methylene groups on the surface are observed in all films. Branched molecules exhibit a decreased tendency to layer and an enhancement in the degree of interdigitation. Comparisons are made with recent surface force experiments and other simulation studies.

Is the complexity of the human sagittal suture related to the size of the temporal muscle?

We have tested the hypothesis that temporal muscle size determines the degree of interdigitation of the human sagittal suture by comparing male and female skulls of Europeans and Australian aborigines. Temporal muscle length, area of the temporal aperture and estimated muscle volume were greater in males than in females of each racial group. Sexual dimorphism of the complexity of the sagittal suture was not confirmed in either race. However, the suture was less complex in aborigines than Europeans despite the volume of the temporal muscle being larger in the former group. We conclude, therefore, that although the morphology of the sagittal suture is an epigenetic character, it is not mechanically influenced by muscle size. A simple quantitation of suture form may however be useful in assigning unknown skulls to a particular race.

Molecular dynamics and X-ray scattering simulations of cyclic siloxane-based liquid crystal mesogens

Abstract Molecular dynamics simulations of cyclic siloxane-based liquid crystals offer new insights into the conformational flexibility of these materials. Interdigitation between the cholesteryl-4′-allyloxybenzoate and biphenyl-4′-allyloxybenzoate mesogens pendant on the cyclic siloxane ring is observed in the simulated structures. All molecular models considered viz. disc, cone, and cylinder, display a large conformational flexibility, which is important regarding the liquid crystalline phase behavior. The disc molecular model exhibits the largest flexibility as indicated by mean dihedral angles and their range for certain principal torsions, evaluated from the molecular dynamics simulations. Results from the dynamics simulations of cylinder molecular pairs indicate a significant amount of conformational flexibility in the siloxane rings. The degree of interdigitation between mesogens is dependent on the flexibility of the siloxane rings, as shown by calculations for a fixed ring system resulting in les...

An ultrastructural study comparing new gingival tissue attachment on chemically exposed fibrils and retained periodontal ligament.

Successful periodontal healing has been demonstrated in animals following application of citric acid to exposed root surface. However, we have been unable to achieve comparable results on clinical patients. Accordingly, the present study, using monkeys, was designed to re-evaluate the degree of interdigitation of newly-formed gingival fibrils with ones exposed to citric acid compared to normal attachment tissues of the retained periodontal ligament. We found that superficial collagen fibrils in both cases suffer degradation following normal inflammation and healing secondary to flap surgery. On retained periodontal ligament tissues, this change was limited to superficial levels and newly-formed collagen fibrils were linked immediately with old ones. In contrast, when exposed collagen fibrils were conditioned by exposure to citric acid, the degradative change occurred more deeply, and healing was delayed. Thus, the citric acid may not be the best choice of root treatments in terms of promoting better gingival tissue attachment. Furthermore, the results indicated that fibrils preserved on the root should not be curetted as possible during flap surgery as they offer an improved chance for optimal reattachment.

Mechanical properties of cranial sutures

Many bones in mammalian skulls are linked together by cranial sutures, connective tissue joints that are morphologically variable and show different levels of interdigitation among and within species. The goal of this investigation was to determine whether sections of skull with cranial sutures have different mechanical properties than adjacent sections without sutures, and if these properties are enhanced with increased interdigitation. To test these hypotheses, bending strength and impact energy absorption were measured for samples of goat ( Capra hircus) cranial bone without sutures and with sutures of different degrees of interdigitation. Bending strength was measured under both dynamic (9.7 mm displacement s −1) and relatively static (0.8 mm s −1) conditions, and at either speed, increased sutural interdigitation provided increased strength during three-point bending. However, except for very highly interdigitated sutures loaded slowly, sutures were not as strong in bending as bone. In contrast, sutures absorbed from 16% to 100% more energy per unit volume during impact loading than did bone. This five-fold increase in energy absorption by the sutures was significantly correlated with increased sutural interdigitation.

Elaborations of the basal surface of the cells of the Malpighian tubules of an insect

Electrical measurements of membrane potential and resistance using intracellular microelectrodes showed that the fluid-secreting parts of the Malpighian tubules of Rhodnius have superficial regions different in electrical properties from the main body of the cell. The membrane potential in these superficial regions was smaller by 30–40 mV, but showed a standard depolarization on changing the potassium concentration of the bathing medium. The response to changes in the external chloride concentration also differed in the two regions, a finding that was reinforced by different responses to the drug, furosemide. Electron microscopy of the basal regions of the cells revealed many long cellular projections that run parallel to the cell surface and interdigitate with similar projections from neighbouring cells. The degree of interdigitation was examined by marking individual cells with alcian blue or by horseradish peroxidase injection. A survey of the published micrographs of insect Malpighian tubules shows that most have similar projections on their basal surfaces and not the simple basal infoldings previously supposed.