Biomedical subjects

F E Filisko

Publications and source records attributed to F E Filisko.

11 recordsLinked to original sources

PubMed2005

Compression of dispersions to high stress under electric fields: effects of concentration and dispersing oil.

Dispersions of various concentrations (15-35%) were prepared in silicone oils of vastly different viscosities (40, 1000, 10,000, and 30,000 mPa s) and compressed to high values of stress while under an electric field of 2 kV/mm. A purpose of this study was to observe the effect of compression and E field simultaneously on these dispersions and assess predictions of most common and relevant theories. As shown, static stresses of over 1000 kPa could readily be obtained although the data presented here were held below 300 kPa to protect the load cell and equipment. The results are compared to and discussed in terms of a power law fit for stress vs gap since most theories predict such a dependence. The PL exponents fall around 3 ranges: (-2), (-3), and much less than (-3). The PL coefficients however reflect in systematic way the viscosities of the dispersing oils. The compressive stress vs strain behavior is studied with regard to particle concentration and dispersing oil viscosity.

Journal Article↗

PubMed2001

The effects of moisture on the dielectric relaxation of urethane dimethacrylate polymer and composites.

Dielectric characterization evaluated the influence of sorbed moisture on urethane dimethacrylate (UDMA) polymer matrix and unsilanated and silanated zirconia-silica (ZS)-filled UDMA composites. The moisture content (MC) of samples tested ranged from 0 to 7.32% with maximum values for UDMA, silanated and unsilanated ZS-filled UDMA were 3.72, 6.0 and 7.32%, respectively. Dielectric spectra were measured from 0.053 to 100 kHz and from -180 to 180;C. Small MC stiffened the polymers, which was shown by a shift of beta-peaks to higher temperatures, a decrease in the half width of bands and an increase in the change of activation energies. Higher MC resulted in water plasticizing the polymer by shifting the beta-peaks to lower temperatures. Maximum water sorption restricted the motion of the polymer chains and the b-peaks shifted to higher temperatures. Further, increasing MC shifted the a-relaxation to lower temperatures in both UDMA and composites. However, in composites with unsilanated ZS, a new relaxation occurred at high temperatures and low frequencies which was attributed to Maxwell-Wagner-Sillars (MWS) polarization. Thus, in UDMA, water occurs as fragments that form non-freezing clusters. However, in unsilanated ZS-UDMA composites, bulk water can exist at the polymer-filler interface and form disordered structures of ice at low temperatures which can evaporate at high temperatures. Silanated ZS-UDMA composites function similarly to UDMA at low MC but are more plasticized at high temperatures.

Absorption↗

PubMed2000

The effects of different additives on the dielectric relaxation and the dynamic mechanical properties of urethane dimethacrylate.

The polymer-filler interaction of a dental composite was examined by dielectric measurements to determine how a non-compatible inorganic phase modifies the molecular behaviour of the polymer chains and how modification of this phase by silanation can affect these molecular behaviours. Urethane dimethacrylate (UDMA) monomer and zirconia-silica (ZS) powder were used as organic and inorganic phases, respectively. 3-Acryloxypropyltrimethoxysilane (MAPM) and 4-aminobutyltriethoxysilane (ABTE) were used as silanating coupling agents. The components of the composite were mixed in different ratios after treating the filler with from 0 to 30 times the minimum uniform coverage with the silane, then the composite was made into thin films. The dielectric spectra of five replicas for each filler-monomer ratio were measured, and three replicas were measured for each silane and for each amount of silane used to treat the filler. Increasing the filler concentration in the composites decreased the intensity of Tan(delta)epsilon for the alpha- and beta-relaxations, where the beta-relaxations also became broader and the alpha-relaxations were totally obstructed. The alpha-relaxations were shifted to higher temperatures, while the beta-relaxations were shifted to lower temperatures. Filler treatment with small amounts of MAPM shifted the alpha-relaxations to higher temperatures; they were shifted back to lower temperatures when the filler was treated with large amounts of silane. Filler treatment with large amounts of ABTE (30-fold) caused an extra peak to emerge in the high-temperature region. It can be concluded that increasing filler concentration restricts the mobility of the main chains and decreases the thickness of the surface layer, while allowing more movement of the local chains. Filler treatment with MAPM was shown to be a compatible coupling agent with the ZS and the UDMA systems. Such compatibility was observed through the effectiveness of the chemical linkage of the silane to the filler and the polymer without forming a separate inter-phase. Filler treatment with ABTE was shown to be an incompatible coupling agent for the ZS-filled UDMA system. The incompatibility was observed by the occurrence of a new peak that characterizes an inter-phase.

Acrylates↗

PubMed1998

Effects of curing time and filler concentration on curing and postcuring of urethane dimethacrylate composites: a microcalorimetric study.

The isothermal enthalpy changes with time of a dental composite were examined by microcalorimetry to isolate the effects of different filler concentrations and curing times on chemical aging of these composites. Urethane dimethacrylate (UDMA) monomer, zirconia-silica (ZS) powder, and 3-methacryloxypropyltrimethoxysilane (MAPM) were used as organic and inorganic matrices, and a coupling agent, respectively. The composite was mixed in different ratios and cured by visible light. The enthalpy changes with time for 0, 15, 45, 75% ZS-filled UDMA and 75% MAPM-silanated ZS-filled UDMA cured for 13, 30, 90, 150, and 300 s were measured at 37.0 degrees, 57.0 degrees, and 65.5 degrees C until equilibrium. Increased curing time and filler concentration caused the excess enthalpy changes (dH) and their rate of change (dH/dt) to increase with annealing time and apparent equilibrium was reached faster. In addition, dH showed nonlinear dependence with the increase in filler concentration by showing a maxima for samples containing 25 wt% filler. Further, filler silanation caused dH/dt to increase and required shorter times to reach apparent equilibrium. dH also reached a minimum when samples contained silanated filler, compared to composites containing unsilanated filler. It was concluded that the shorter curing time caused the occurrence of spontaneous densification, which facilitated continual resin curing; and longer curing time caused higher crosslinking of the organic phase. Moderate concentration of inorganic phase restricts the molecular motion of the surface layer of polymer onto filler particles, and the polymer is regarded as highly crosslinked, while a higher filler concentration forms aggregates that are covered by the polymer which causes a decrease in the molecular packing of the resin, and is reflected as low enthalpy values. Finally, silanation of the filler showed a highly endothermic reaction that is probably due to breaking and forming of bonds at the interface between the organic and the inorganic phases in the composites.

Calorimetry↗

PubMed1996

Preparation and characterization of high-surface-area polymer substrates for microcalorimetry.

The preparation and characterization of high-surface-area polymeric substrates suitable for the microcalorimetry of protein adsorption are described. High-surface-area polystyrene, poly(styrene-co-butyl methacrylate) and poly(styrene-co-allyl alcohol) were prepared by adsorbing polymer from solution onto fumed silica. Verification of adsorption of polystyrene by silica was determined by noting peak shifts of the surface silanol group in the infrared. The amount of polymer adsorbed was determined from adsorption isotherms. The minimum thickness of polystyrene required to mask silicon oxide properties was found to be that thickness at which contact angles became constant, about 35 A. Polymer densities were measured. Water contact angles on each polymer surface indicate that poly(styrene-co-allyl alcohol) has the surface most wettable by water. Polymer-water interfacial energies were estimated from pendant drop results and a harmonic mean equation along with contact angles. Two methods were used to estimate the polar and dispersion components of the three polymers. Both methods predicted polystyrene to have the highest interfacial energy against water, and one method predicted poly(styrene-co-allyl alcohol) to have the lowest. A Wilhelmy plate study verified the change in interfacial properties as a function of contact time with water. A study of the heats of adsorption of lysozyme by each substrate using a modified Tien-Calvet microcalorimeter demonstrated the suitability of the substrates for microcalorimetry.

Adsorption↗

PubMed1991

Cytotoxicity of a BIS-GMA dental composite before and after leaching in organic solvents.

Cell culture techniques were used to determine the source of cytotoxic agents in a commercial BIS-GMA composite. The material was polymerized according to the manufacturer's directions and leachable components were removed by room temperature extraction in ethanol, chloroform, or toluene. The leachable components in the extracts were identified using infrared spectrographic analysis. Thin layer chromatographic analysis was used to determine the number of constituents. These constituents were separated by gas chromatography and then identified by mass spectrographic analysis. Succinic dehydrogenase activity and radioactive labeling with tritiated leucine were used to evaluate cell metabolism and protein synthesis, respectively. The infrared analysis of the extracts showed that the primary component was unreacted BIS-GMA. Trace amounts of 2-hydroxy-4-methoxy-benzophenone, a light stabilizer, as well as a phenyl ester of benzoic acid which was probably degraded from BIS-GMA, were detected by the mass spectrographic method. The removal of leachable components caused a 90% decrease in toxicity compared to the nonextracted BIS-GMA samples. The extracted BIS-GMA samples showed no cellular response compared to the Teflon negative control.

Animals↗

PubMed1986

Character of adsorbed bovine serum albumin from adsorption enthalpies.

Heats of adsorption of BSA onto polystyrene and polycarbonate were determined microcalorimetrically. The polymers were coated onto 50 nm alumina particles which were immersed in buffer for the measurements. Experimental variations to isolate the various component reactions of the integral heats included adsorption of native and denatured BSA from solution, adsorption onto substrates precoated with BSA, varying the thicknesses of adsorbed BSA by varying concentrations of the adsorbing solutions, and determining the denaturation energy by solution of the solid native and denatured BSA into a denaturing solvent.

Adsorption↗

PubMed1982

Polyphosphazenes: effect of molecular motions on thrombogenesis.

The effect and interrelationship between primary (segmental backbone) and secondary (side chain) molecular motions on thrombogenesis, independent of morphological order/disorder, crystallinity, and/or associated water is elucidated using an amorphous hydrophobic polymer of poly-[(trifluoroethoxy) (fluoroalkoxy)phosphazene] PNF. The results indicate that thrombogenesis for an amorphous hydrophobic polymer is sensitive and dependent on the degrees and types of primary and secondary molecular motions at the polymer interface.

Animals↗

PubMed1980

Tear energy of elastomers for maxillofacial applications.

The energy necessary to generate a unit area of torn surfaces was measured for six elastomers with low moduli of elasticity. Four polyurethane materials and two commercial maxillofacial materials were included. The latter had tear energy values between 0.63 and 6.56 erg/cm2, while the polyurethanes ranged from 8.49 to 50.0 erg/cm2. Three of the materials demonstrated non-Hookian behaviour during testing, violating an assumption of the tear energy analysis. A method of compensating for this discrepancy is described.

Chemical Phenomena↗

PubMed1978

Polyurethane elastomers as maxillofacial prosthetic materials.

A series of polyurethane elastomers based on an aliphatic diisocyanate and a polyether macroglycol was polymerized with various cross-link densities and OH/NCO ratios. Stoichiometries yielding between 8,600 and 12,900 gm/mole/crosslink and an OH/NCO ratio of 1.1 resulted in polymers with the low modulus, yet high strength and elongation necessary for maxillofacial applications.

Butylene Glycols↗

PubMed1978

Ultrastructural deformation of collagen.

Ultrastructure deformation studies of reconstituted and native rat tail tendon collagen revealed that deformation occurs primarily in the non-staining and presumably non-polar proline rich regions for all ages examined. At low deformation (tension and compression) the deformation occurs somewhat more between the a2 and b1 and b2 and c2 bands than within the rest of the d period. At moderate elongations (greater than 40%), the deformation becomes localized between the c2 and d bands, with subfibrils on the order of 3-15 nm being drawn across the openings between the c2 and d bands. At high elongations (100% or greater) d period splitting occur on a regular basis between the c2 and d bands, along with a retraction of the 64 nm repeat period into 60 nm segments. It is in this deformation region that the effects of molecular slip and the apparent association of the acid mucopolysaccharides can be noted. These results suggest that crosslinking, if increasing as a function of age, does not affect the deformation characteristics of the individual fibrils and that changes with age in mechanical properties should be sought in changes in the fibril size and their interaction with the surrounding matrix.

Aging↗