The effect of two hydrophilic monomers on the water uptake of a heterocyclic methacrylate system

The room temperature polymerising system poly(ethyl methacrylate) (PEM)/tetrahydrofurfuryl methcrylate (THFM) has been modified by replacing some of the THFM by hydroxyethyl methacrylate (HEMA) and hydroxypropyl methacrylate (HPM), respectively. In both cases, the equilibrium uptake of the parent system is reduced substantially, in spite of the hydrophilic nature of these monomers. The effect is less with HPM. Corresponding to these decreases in uptake are substantial increases in the diffusion coefficients. This points to changes from a cluster-dominated process, to a more continuum-based process in the dual monomer systems. Addition of chicken serum albumin to these systems increases water uptake. At higher levels of HEMA addition, there is a substantial increase in polymerisation exotherm.     

The behavior of novel hydrophilic composite bone cements in simulated body fluids

Composite bone cements were formulated with bioactive glass (MgO--SiO(2)--3CaO. P(2)O(5)) as the filler and hydrophilic matrix. The matrix was composed of a starch/cellulose acetate blend (SCA) as the solid component and a mixture of methylmethacrylate/acrylic acid (MMA/AA) as the liquid component. The curing parameters, mechanical properties, and bioactive behavior of these composite cements were determined. The addition of up to 30 wt % of glass improved both compressive modulus and yield strength and kept the maximum curing temperature at the same value presented by a typical acrylic-based commercial formulation. The lack of a strongly bonded interface (because no coupling agent was used) had important effects on the swelling and mechanical properties of the novel bone cements. However, bone cements containing AA did not show a bioactive behavior, because of the deleterious effect of this monomer on the calcium phosphate precipitation on the polymeric surfaces. Formulations without AA were prepared with MMA or 2-hydroxyethyl methacrylate (HEMA) as the liquid component. Only these formulations could form an apatite-like layer on their surface. These systems, therefore, are very promising: They are bioactive, hydrophilic, partially degradable, and present interesting mechanical properties. This combination of properties could facilitate the release of bioactive agents from the cement, allow bone ingrowth in the cement, and induce a press-fitting effect, improving the interfaces with both the prosthesis and the bone.     

The in vitro bioactivity of two novel hydrophilic, partially degradable bone cements

Composite bone cements were prepared with bioactive glasses (MgO-SiO(2)-3CaO.P(2)O(5)) of different reactivities. The matrix of these so-called hydrophilic, partially degradable and bioactive cements was composed of a starch/cellulose acetate blend and poly(2-hydroxyethyl methacrylate). The addition of 30 wt.% of glasses to this system made them bioactive in acellular medium: a dense apatite layer formed on the surface after 7 days of immersion in simulated body fluid. This was demonstrated both by microscopic and infrared spectroscopic techniques. The composition of the glass and, consequently, its structure was found to have important effects on the rate of the apatite formation. The combination of reactivity obtained by one formulation with the hydrophilic and degradable character of these cements makes them a very promising alternative to conventional acrylic bone cements, by allowing a better stabilization of the implant and a stronger adhesion to the bone.     

Adhesion of carboxylate cements to hydroxyapatite: I. The effect of the structure of aliphatic carboxylates on their uptake by hydroxyapatite

An investigation was made into the effect of the structure and functionality of aliphatic carboxylates on their sorption onto hydroxyapatite with a view to ascertaining factors affecting the adhesion of polyacrylate cements to tooth materials. In general, the amount of carboxylate sorbed was found to increase with the number of groups contained in the molecule. Thus, polyacrylate was found to be much more strongly sorbed than low molecular weight species. Sorption of the low molecular weight species appeared to be related to stereochemical factors rather than to the stability constants of their calcium chelates.     

Probing cell migration in confined environments by plasma lithography

Cellular processes are regulated by various mechanical and physical factors in their local microenvironment such as geometric confinements, cell-substrate interactions, and cell-cell contact. Systematic elucidation of these regulatory mechanisms is crucial for fundamental understanding of cell biology and for rational design of biomedical devices and regenerative medicine. Here, we report a generally applicable plasma lithography technique, which performs selective surface functionalization on large substrate areas, for achieving long-term, stable confinements with length scales from 100 nm to 1 cm toward the investigation of cell-microenvironment interactions. In particular, we applied plasma lithography for cellular confinement of neuroblastomas, myoblasts, endothelial cells, and mammary gland epithelial cells, and examined the motion of mouse embryonic fibroblasts in directionality-confined environments for studying the effect of confinements on migratory behavior. In conjunction with live cell imaging, the distance traveled, velocity, and angular motion of individual cells and collective cell migration behaviors were measured in confined environments with dimensions comparable to a cell. A critical length scale that a cell could conceivably occupy and migrate to was also identified by investigating the behaviors of cells using confined environments with subcellular length scales.     

The effect of hydrophilic adhesive monomers on the stability of type I collagen

The adsorption effects of adhesive monomers on the structural stability of type I collagen were studied at an acid pH condition for two monomers: 2-hydroxyethyl methacrylate (HEMA), a neutral monomer and N-methacryloyl glycine (NMGly), an acidic monomer. Differential scanning calorimetry (DSC) measurements were done to assess the denaturation temperature (Td), which is a measure of the structural stability of the proteins, including the bovine tendon collagen (BTC). While HEMA lowered the Td of the BTC linearly with HEMA concentrations, NMGly exhibited a two-step decrease of the Td. The rate of decrease in the Td by the NMGly was by far greater than the rate of decrease with the HEMA. The first step had a larger slope than the second step in the Td vs. CNMGly plot. The degree of adsorption of these two monomers to the BTC was estimated from infrared absorption measurements on the monomer solutions of various concentrations, before and after the immersion of the BTC. Both the adsorption of HEMA to the BTC and the Td of the BTC were linearly dependent on HEMA concentrations. Conversely, NMGly was adsorbed to the BTC, again, in a two-step decrease similar to the Td vs. CNMGLy profile. An enhanced adsorption of NMGly, which might be attributed to a strong electrostatic interaction, was observed below 0.013 mol%. Circular dichroism measurements of the collagen of the same type as the BTC, in the absence and in the presence of the monomers, revealed that the native collagen helix structure was scarcely affected by the monomers. From these observations, it was concluded that (1) both of the monomers were adsorbed onto the BTC, which thus destabilized the triple helical collagen structure, and that (2) the effect was higher for NMGly in which the electrostatic attraction with the oppositely charged collagen might be effective at a pH of 3. If compared to HEMA, an acidic NMGly is a potential monomer that binds strongly to collagen and one that is hardly hydrolyzed.     

Calcium phosphate cements: effect of fluorides on the setting and hardening of beta-tricalcium phosphate-dicalcium phosphate-calcite cements

Increasing amounts of fluoride ions have been found to increase the setting and hardening rates of beta-tricalcium phosphate-dicalcium phosphate dihydrate-calcite cements. Thus, fluoride-containing cements reached a diametral strength of about 1.5 MPa after 15 d, but the fluoride-free reference sample reached only 0.45 MPa. The acceleration of setting and hardening is correlated to an increased rate of hydroxyapatite formation in the cement at the expense of dicalcium phosphate dihydrate and calcite. Adding monocalcium phosphate monohydrate and fluoride to the blends resulted in a marked decrease of their setting time from about 1 h down to 8 min, without greatly affecting their final strength.     

The effect of cross-linking agents on acrylic bone cements containing radiopacifiers.

Poly(methylmethacrylate) PMMA, based cements are the most widely used bone cements in joint replacement surgery. Although, there are some disadvantages in the use of these cements, the clinical success rate is fairly high. Intrinsic radiopacity is difficult to achieve in these cements due to the constituent elements of the PMMA polymer. As radiopacity is an essential requirement, PMMA bone cements have been rendered radiopaque by blending heavy metal ion salts, which tend to adversely affect the mechanical and biological properties of the bone cement. In this study, dimethacrylate cross-linking agents were added to the monomer phase in order to generate a cross-linked matrix, with barium sulphate as a radiopaque agent. The results suggest that the mechanical properties can be improved or retained with the addition of such cross-linking agents.     

The effect of temperature on viscoelastic properties of glass ionomer cements and compomers

The objective of this study was to determine the viscoelastic properties of different types of glass ionomer cements (GICs) and compomers under varying temperature conditions found in the mouth. The materials tested were a conventional GIC (Aqua Ionofil U), a resin modified GIC (Fuji II LC), a highly viscous GIC (Voco Ionofil Molar), and two polyacid modified composite resins/compomers (Glasiosite and Dyract Flow). Six groups of four specimens were prepared from each material. One group was stored dry for 24 h and was subsequently tested dry at 21 degrees C. Each of the remaining five groups was stored for 24 h in distilled water at the temperatures 21, 30.5, 37, 43.5, and 50 degrees C, respectively, and was subsequently tested at that temperature. Shear storage modulus and loss tangent were determined by conducting dynamic torsional loading. Static shear moduli were determined by applying a constant torque (below the proportional limit of the materials) for 10 s and recording the angular deformation of the specimens. Data were analyzed by ANOVA and Duncan's test (alpha= 0.05). It was found that the viscoelastic properties varied significantly (p < 0.05) across the different materials. The compomer Glasiosite, with the highest filler content, and the highly viscous GIC Voco Ionofil Molar exhibited the highest elastic moduli and lowest loss tangents. Viscoelastic properties varied also significantly (p < 0.05) with temperature levels, but changes in the tested region were not indicative of a glass transition. Dynamic shear storage moduli were highly correlated to the static ones. Storage in water lowered the values of elastic moduli.     

The relationship between water absorption characteristics and the mechanical strength of resin-modified glass-ionomer cements in long-term water storage.

The purpose of this study is to elucidate the water absorption characteristics of resin-modified glass-ionomer cements and to also investigate the relationship between the characteristics and mechanical strength after long-term water storage. The mechanism of water diffusion in these cements is also discussed. Water absorption was measured using a gravimetric analysis for 12 m, while the diffusion coefficient was calculated using Fick's law of diffusion. Water solubility was determined based on the weight of the residue in the immersed water. The compressive and diametral tensile strength were measured at 1, 2, 6, and 12 m. A correlation was observed between the diffusion coefficient and equilibrium water uptake, which thus suggests the water in the cements to diffuse through micro-voids in accordance with the 'Free volumetric theory'. A correlation was seen between the solubility and diffusion coefficient of the cements. The deterioration ratio, defined as the ratio of the strength at 12 m versus that at 1 m, was also calculated. Finally, a negative correlation was observed between the deterioration ratio of the compressive strength and the diffusion coefficients of the cements.     

Erosion process of calcium hydroxide cements in water.

Erosion process of calcium hydroxide cements was examined for 7 days by chemical analysis of eluates and observation of structural change of the eroded cements when the cements were immersed in water at 37 degrees C. The elution of salicylate from the set cements as well as that of Ca continued during the immersion time. In the early stage of the erosion, unreacted Ca(OH)2 was preferentially extracted from the cements in comparison with Ca-alkyl salicylate chelate of the cement matrix. The elution rate of N-ethyl o- and p-toluene sulphonamides, which were contained as plasticizer, was higher than those of Ca and salicylate. Insoluble inorganic filler remained at the surface of the cements after extraction of unreacted Ca(OH)2 and disintegration of the cement matrix. Types of salicylate ester seemed to affect the cement durability.     

The effect of feeding on defecation behaviour in pigs.

The effect of eating on defecation behaviour was investigated in four 20-30 kg pigs. Rectal distention stimulation was performed pre- and postprandially at 10 cm from the anus with a 5 cm latex balloon. Volume was increased in steps of 10 ml up to 200 ml of air or until balloon defecation. Dependent measures were volume, rectal pressure, determined with a solid state pressure transducer inside the balloon probe, rectal compliance, and an index of distention induced contractile activity. The volume and pressure required to elicit defecation was significantly lower after feeding (p less than 0.01). Distention induced contractile activity was significantly increased near defecation threshold, but pre- and postprandial conditions were not different. There was no difference in rectal compliance pre- and postprandially. These results suggest that eating lowers defecation threshold in terms of distention volume and rectal pressure, and that these changes are not dependent on altered rectal compliance or changes in distention induced motor activity.     

The effect of the Ebbinghaus illusion on grasping behaviour of children

Within the context of the Ebbinghaus illusion, adults regularly misjudge the physical size of a centre disc, yet scale their hand aperture according to its actual size. Separate visual pathways for perception and action are assumed to account for this finding. The dorsal visual stream is said to elaborate on egocentric (visuomotor), while the ventral stream is involved in allocentric transformations (object recognition). This study examines the ontogenetic development of this dissociation between perception and action in 35 children between the ages of 5 and 12 years. We report four major results. First, when children judged object size without grasping the disc, their judgements were deceived by the illusion to the same extent as adults. However, when asked to estimate size and then to grasp the disc, young children's (5-7 years) perceptual judgements became unreliable, while adults were still reliably deceived by the illusion in 80% of their trials. Second, the younger the children, the more their aperture was affected by the illusional surround. Discs of the same size were grasped with a smaller aperture when surrounded by a small annulus, although they were perceived as being larger. Third, young children used the largest safety margin during grasping. Fourth, the reliance on visual feedback decreased with increasing age, which was documented by shorter movement times and earlier maximum hand opening during grasping in the older children (feedforward control). Our results indicate that grasping behaviour in children is subject to an interaction between ventral and dorsal processes. Both pathways seem not to be functionally segregated in early and middle childhood. The data are inconclusive about whether young children predominantly use a specific visual stream for either a perceptual or motor task. However, our data demonstrate that children were relying on both visual processing streams during perceptual as well as visuomotor tasks. We found that children used egocentric cues to make perceptual judgements, while their grasping gestures were not exclusively shaped by viewer-centred but also by object-centred information.     

The physico-mechanical consequences of exposing glass ionomer cements to water during setting

The effect of exposing glass ionomer cement to water during the first 48 hours after mixing was studied. The strength of the set cement was only reduced if exposure to water occurred within the first hour after mixing. The gel matrix formed during the setting reaction was shown to be the source of fluoride ions released when glass ionomer cement is placed in water. The degree of hydration, rate of fluoride release, and degree of cross-linking of the gel matrix were all shown to be affected by the water ingress during the setting reaction. Finally the fluoride release from the cements was found to cease within six months of exposure to water indicating that only fluoride ions released into the gel matrix during the setting reaction are available to protect surrounding tooth structure.     

Combined effect of strontium and pyrophosphate on the properties of brushite cements

In this study we report the synthesis of strontium-containing brushite cement with good cohesion and a diametral tensile strength (DTS) of 5 MPa. The cement powder, composed of β-tricalcium phosphate (β-TCP) and monocalcium phosphate, was adjusted by different concentrations of strontium and pyrophosphate ions. The cement liquid phase was 2 M phosphoric acid solution. The cement cohesion and mechanical properties were measured after being aged in water for 24 h at 37 °C. It was found that at low concentration both strontium and pyrophosphate ions inhibit the cement setting reaction. However, the final setting time was significantly reduced when SrCl₂ increased from 5 to 10 wt.% at pyrophosphate concentrations equal to or higher than 2.16 wt.%. The incorporation of strontium ions did not increase the DTS of brushite cements significantly. In contrast, the addition of pyrophosphate ions did increase the DTS of brushite cements significantly. When both ions were added simultaneously, the brushite cement with a Sr²⁺ content of 5 wt.% had the highest DTS value. Nevertheless, the DTS values of Sr-containing cements were significantly reduced if the pyrophosphate concentration was higher than 2.16 wt.%. The Sr²⁺ ions had a negative effect on brushite cement cohesion, although the solid weight loss started to decrease at Sr²⁺ concentrations higher than 5 wt.%.     

Precursors of hydrophilic polymers, 3. The potentiometric behaviour of isotactic and atactic poly(2-dimethylaminoethyl methacrylate) in water/ethanol solutions

The dissociation constants of partially ionized isotactic and atactic poly(2-dimethylaminoethyl methacrylate) in water/ethanol solutions were measured. The strong dependence of the apparent dissociation constant on the degree of ionization of the macromolecule is discussed using viscometric data and compared with the properties of low-molecular-weight model compounds. The values of the internal dissociation constants at various ionic strength in various water/ethanol solutions were obtained by extrapolation of the apparent dissociation constants to zero ionization degree of the macromolecule. The conformational structures of macromolecules in solution are discussed.     

DMTA analysis for long-term mechanical behaviour prediction of PMMA-based bone cements

Poly(methyl methacrylate) (PMMA) is commonly used as acrylic bone cement to fix bone implants. In vivo degradation of bone cement may lead to a decrease in mechanical properties and result in aseptic loosening. Creeping can promote failure of the implant. This study used dynamic mechanical thermal analysis (DMTA) equipment, in the 0.01 to 50 Hz frequency range, to investigate the dynamic viscoelastic relaxation characteristics of CMW^?, PROFIT QUIRÚRGICO and PALACOS PMMA-based bone cements. Their initial moduli were measured as 2450, 1850 and 1710 MPa, respectively. Relaxation master curves displayed similar features. The DMTA temperature range was between 20 and 75°C. Predictions for long-term relaxation moduli were analyzed and compared against published experimental data. The comparison revealed that master curves obtain using the time-temperature-superposition principle (TTSP) present a much slower relaxation modulus compared to long-term experimental data above 1000 s. However, extrapolations based on a time-power law applied to isothermal experimental data allow better long-term predictions.     

The effect of ball milling grinding pathways on the bulk and reactivity properties of calcium phosphate cements

Calcium phosphate cements (CPCs) are significant alternatives to autologous bone grafting. CPCs can be composed of biphasic or multiphase calcium phosphate (CaP) compounds. A common way to process CPCs is by ball milling. Ball milling can be used for grinding or mechanosynthesis. The aim of this study was to determine the effect of well-defined ball milling grinding parameters, applied via different milling pathways, on the properties of CPCs. Starting CaP compounds used included α-tricalcium phosphate, dicalcium phosphate anhydrous and precipitated hydroxyapatite. Scanning electron microscopy showed changes in the powder morphology, which were related to the behavior of the starting CaP materials. Specific surface area (SSA) and particle size (PS) measurements exposed the effect of ball milling on the CaP compounds and CPC powders. X-ray diffraction revealed no effect of ball milling pathways or milling time on the composition of CPCs or the starting materials, but affected their crystallographic properties. No contamination of the milling media or transformation into an amorphous calcium phosphate compound was found. The milling pathways affected setting and cohesion. Fourier transform infrared spectroscopy (FTIR) revealed differences on the CPC v?-PO?3? bands according to the interaction, created between the CaP compounds by the milling pathways. FTIR confirmed that the milling pathways changed the crystallographic properties. This study demonstrates that the pathways used for milling grinding modify the PS, SSA, and crystallographic properties of the powders, without affecting their composition. These modifications affected the bulk and reactivity properties of the CPCs by creating different setting and cohesion behaviors.     

The effect of urine on the investigatory behaviour of male albino mice

The investigatory behaviour of male albino mice was studied in a test tank containing a sheet of unprinted newspaper as substrate. The first test category consisted of clean paper, whilst in all others one half of the paper was spotted with the following liquids respectively: (1) water, (2) normal male urine, (3) castrate male urine, (4) urine of testosterone-injected castrate males, and (5) urine of oil-injected castrate males. Preference for either half was measured by the accumulated time spent in each half and an approximate measure of activity was obtained by the number of entries into both halves. The results indicate the presence of a pheromonal factor in normal male urine which discourages prolonged investigation of an area marked with such urine. Castration eliminates the above effect, whereas treatment with testosterone propionate re-establishes it thus indicating that the urinary factor is androgen-dependent. The relevance of these results to the concepts of territoriality is discussed.