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PubMed1989

Dynamic mechanical thermal analysis of dental polymers. III. Heterocyclic methacrylates.

Four heterocyclic methacrylates were investigated with respect to their loss tangent and activation energy using a dynamic mechanical thermal analyser over a limited frequency range of 0.033 to 90 Hz. The linear regression lines obtained showed an Arrhenius-type relationship between transition temperature and frequency. Their low activation energies in comparison to poly(methyl methacrylate) and bis-phenol A based methacrylates was thought to be a direct consequence of their low molecular weights.

Acrylates↗
PubMed1990

Thermal analysis of bacteria by differential scanning calorimetry: relationship of protein denaturation in situ to maximum growth temperature.

Differential scanning calorimetry (DSC) was used to analyze thermal transitions in two strains of the thermophile Bacillus stearothermophilus (ATCC 12016 and WAT), the mesophile Bacillus megaterium and the psychrotroph Bacillus psychrophilus. The observed transitions, representing lipid melting and DNA and protein unfolding, are compared to the maximum growth temperature (Tmax) in each species as a means of identifying critical, thermolabile targets responsible for heat-induced inhibition of growth. A low temperature, lipid transition was detected in B. stearothermophilus and B. megaterium which varied slightly with Tmax but whose high temperature end is always 22-33 degrees C below Tmax. The transition temperature (Tm) of the main melting of DNA varies from 88 to 92 degrees C, 23-32 degrees C above Tmax. The main part of the profile representing irreversible transitions is resolvable into at least three distinct peaks and is identified primarily with protein denaturation. The onset temperature for denaturation (Tl), i.e., minimum temperature of detectable denaturation, is somewhat dependent on growth temperature (Tg). Tmax for B. stearothermophilus ATCC and WAT is 69 and 56 degrees C, respectively. For cells grown between 4 and 20 degrees C below Tmax, Tl is 2-4 degrees C lower than Tmax, demonstrating that some denaturation can be tolerated before complete inhibition of growth and suggesting that inhibition of growth is due to the denaturation of a critical protein with a Tm a few degrees above Tl or to the accumulation of denatured protein to a critical level. A similar pattern holds for B. megaterium and B. psychrophilus, except that Tmax is 48 and 32.5 degrees C (Tl = 45-46 degrees C and 30 degrees C), respectively. Thus, there is an excellent correlation between the onset of protein denaturation and maximum growth temperature for these three species of the same genus. This study also demonstrates the applicability of DSC for resolving transitions in intact cells on the basis of thermostability of cellular constituents and for obtaining an overall view of macromolecular stability.

Bacillus↗
PubMed1988

Thermal analysis of CHL V79 cells using differential scanning calorimetry: implications for hyperthermic cell killing and the heat shock response.

Differential scanning calorimetry (DSC) was used to assay thermal transitions that might be responsible for cell death and other responses to hyperthermia or heat shock, such as induction of heat shock proteins (HSP), in whole Chinese hamster lung V79 cells. Seven distinct peaks, six of which are irreversible, with transition temperatures from 49.5 degrees C to 98.9 degrees C are detectable. These primarily represent protein denaturation with minor contributions from DNA and RNA melting. The onset temperature of denaturation, 38.7 degrees C, is shifted to higher temperatures by prior heat shock at 43 degrees and 45 degrees C, indicative of irreversible denaturation occurring at these temperatures. Thus, using DSC it is possible to demonstrate significant denaturation in a mammalian cell line at temperatures and times of exposure sufficient to induce hyperthermic damage and HSP synthesis. A model was developed based on the assumption that the rate limiting step of hyperthermic cell killing is the denaturation of a critical target. A transition temperature of 46.3 degrees C is predicted for the critical target in V79 cells. No distinct transition is detectable by DSC at this temperature, implying that the critical target comprises a small fraction of total denaturable material. The short chain alcohols methanol, ethanol, isopropanol, and t-butanol are known hyperthermic sensitizers and ethanol is an inducer of HSP synthesis. These compounds non-specifically lower the denaturation temperature of cellular protein. Glycerol, a hyperthermic protector, non-specifically raises the denaturation temperature for proteins denaturing below 60 degrees C. Thus, there is a correlation between the effect of these compounds on protein denaturation in vivo and their effect on cellular sensitivity to hyperthermia.

Alcohols↗
PubMed2004

Thermal analysis of bone cement polymerisation at the cement-bone interface.

The two major problems that have been reported with the use of polymethylmethacrylate (PMMA) cement are thermal necrosis of surrounding bone due to the high heat generation during polymerisation and chemical necrosis due to unreacted monomer release. Computer models have been used to study the temperature and monomer distribution after cementation. In most of these models, however, polymerisation is modelled as temperature independent and cancellous bone is modelled as a continuum. Such models thus cannot account for the expected important role of the trabecular bone micro-structure. The aim of this study is to investigate the distribution of temperature and monomer leftover at the cancellous bone-cement interface during polymerisation for a realistic trabecular bone-cement micro-structure and realistic temperature-dependent polymerisation kinetics behaviour. A 3-D computer model of a piece of bovine cancellous bone that underwent pressurization with bone-cement was generated using a micro-computed tomography scanner. This geometry was used as the basis for a finite element model and a temperature-dependent problem for bone cement polymerisation kinetics was solved to simulate the bone cement polymerisation process in the vicinity of the interface. The transient temperature field throughout the interface was calculated, along with the polymerisation fraction distribution in the cement domain. The calculations revealed that the tips of the bone trabeculae that are embedded in the cement attain temperatures much higher than the average temperature of the bone volume. A small fraction of the bone (10%) is exposed to temperatures exceeding 70 degrees C, but the exposure time to these high temperatures is limited to 50s. In the region near the bone, the cement polymerisation fraction (about 84%) is less than that in the centre (where it is reaching values of over 96%). An important finding of this study thus is the fact that the bone tissue that is subjected to the highest temperatures is also subjected to high leftover monomer concentration. Furthermore the maximum bone temperature is reached relatively early, when monomer content in the neighbouring cement is still quite high.

Animals↗
PubMed1999

Thermal analysis characterization of aortic tissues for cardiac valve bioprostheses.

Two multistep extractions were achieved on porcine aortic tissues to obtain acellular matrices used for cardiac bioprostheses. The evaluation of structural modifications and the possible damage of extracellular matrix fibrous proteins were investigated by means of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Protein-water interactions and degradation temperatures were determined by TGA. DSC was used to characterize protein thermal transitions (glass transition and denaturation), which provided information on the dynamic structure of the aortic tissue components. Sodium dodecyl sulfate (SDS) extraction had a destructuring effect, while Triton and cholate treatments did not affect the structural integrity of either elastin and collagen. A DSC comparison showed that SDS destabilizes the collagen triple helical domain and swells the elastin network.

Absorption↗
PubMed1983

A simulation model for transient thermal analysis of restored teeth.

A theoretical model was developed to analyze the influence of various cement bases on temperature distribution and heat flow in restored teeth. A physical model of a molar was developed to simulate different thermal processes by simple parameter variation. The time-dependent temperature field was calculated using the finite element method (FEM). The values for material properties and thermal load were chosen from the dental literature. The results are in good agreement with clinical experimental research as published by Trowbridge et al. It is concluded that the model is a valid tool for further research with regard to the influence of restorative materials and cavity design on the thermal behavior of restored teeth.

Dental Cavity Lining↗
PubMed1995

Thermal analysis of the tertiary butyl alcohol-water system and its implications on freeze-drying.

Utilizing differential scanning calorimetry (DSC) for tertiary butyl alcohol (TBA) solutions a phase diagram was constructed for the TBA-water system. By utilizing thermal treatment during the DSC measurements the metastable states were eliminated. The phase diagram fit that for a congruently melting compound in which compound formation occurred with a maximum at 70% TBA representing pure TBA hydrate. Two eutectics occurred at 20% (Eutectic A) and 90% (Eutectic B). A freeze-drying microscope revealed that TBA altered the crystal habit of ice. A concentration of 3% TBA was required before large needle-shaped ice crystals became evident. The addition of 10% TBA to the system resulted in even finer needle-shaped ice crystals. At the eutectic compositions (20% and 90% TBA), the frozen eutectic mixture could not be resolved with the microscope because eutectic crystals are very small. The 70% TBA solution, which corresponds to the melting of pure TBA hydrate, formed very large hydrate crystals. The rate of sublimation of the TBA and water molecules was found to be concentration dependent. At concentrations below 20% TBA (water rich portion of the phase diagram) water molecules sublimed faster while at concentrations above 20% TBA (TBA rich portion of the phase diagram) TBA molecules sublimed faster. At the eutectic A composition, both TBA and water molecules sublimed at the same rate. This may be because all of the TBA molecules are strongly associated with each other in the form of a clathrate hydrate.

Butanols↗
PubMed2002

Charring characteristics of atmospheric organic particulate matter in thermal analysis.

The charring of organic materials during carbon analysis bythermal methods makes it difficult to differentiate elemental carbon (EC) from organic carbon (OC). Failure to correct for charring results in the overestimation of EC and the underestimation of OC. The charring characteristics andthermal behaviors of aerosol OC are studied by subjecting hexane and water extracts of ambient aerosols to various analysis conditions. The complete evolution of water-soluble organic carbon (WSOC) aerosol materials is found to require a temperature as high as 850 degrees C and the presence of oxygen. EC would be oxidized under these thermal conditions as well. As a result, thermal methods relying only on temperature for the differentiation of EC and OC would give unreliable OC and EC concentrations. Our investigation also reveals that WSOC accounts for a large fraction (13-66%) of charring, while hexane extractable organic compounds produce little charring. The extent of charring from WSOC, defined as the ratio between pyrolytically generated EC to the total WSOC, is found to increase with the WSOC loading in each analysis when the loadings are below a certain value. This ratio remains constant when the loadings are above this value. This may account for the high variability in the extent of charring among aerosol samples from different locations as well as among samples from a single location collected at different times. Charring is reduced if the residence time at each temperature step in a helium atmosphere is sufficiently long to allow for maximum C evolution at each step. Charring is also influenced by the presence of inorganic constituents such as ammonium bisulfate. For the few tested organic materials, it is observed that ammonium bisulfate enhances the charring of starch and cellulose but reduces the charring of levoglucosan.

Aerosols↗
PubMed2004

Thermal analysis of the human intervertebral disc.

Intervertebral disc (IVD) degeneration is one of the most common musculuskeletal disorders affecting western society. Degeneration alters the morphology and the mechanical properties of the discs. According to previous reports, DSC proved to be a suitable method for the demonstration of thermal consequences of local as well as global conformational changes in the structure of the human intervertebral discs. In the present study, a wide spectrum of degenerated IVD was examined by DSC. The results suggest that definitive differences exist between the stages of disc degeneration in calorimetric measures.

Adolescent↗
PubMed2006

Intra-luminal thermometry: is tissue type assignment a necessity for thermal analysis?

INTRODUCTION: Tissue type assignment, i.e. differentiation tumour from normal tissue, is a normal procedure for interstitial thermometry. In our department, thermometry in patients with a tumour in the lower pelvis is usually restricted to the intra-luminal tracks. It is unknown whether discrimination between normal and tumour tissue is relevant for deep regional hyperthermia thermal dosimetry using only intra-luminal tumour contact and tumour adjacent thermometry. This study has analysed the acquired temperature data in order to answer this question. PATIENTS AND METHODS: Seventy-five patients with locally advanced cervical carcinoma were selected randomly. Patients were treated with a two or three modality combination, i.e. radiotherapy +hyperthermia or radiotherapy + hyperthermia + chemotherapy from October 1997 to September 2003. The first 100 hyperthermia treatments fulfilling the only selection criterion: no displacement of the thermometry catheter along the insertion length during the treatment, were included in the study, resulting in 43 patients with one-to-five treatments/patient (median 2). Using RHyThM (Rotterdam Hyperthermia Thermal Modulator), for each single treatment tissue type, was defined on the basis of information given by a CT scan in radiotherapy position. A step change in the slope of the profile of the first temperature map was identified to verify the insertion length of the catheter. RESULTS: The average T50 (median temperature) in bladder tumour indicative, vagina tumour contact and rectum tumour indicative was 40.9 +/- 0.9 degrees C, 39.7 +/- 0.9 degrees C and 40.6 +/- 0.8 degrees C, respectively. The average normal tissue T50 in bladder, vagina and rectum was 40.8 +/- 0.9 degrees C, 40.1 +/- 0.9 degrees C and 40.7 +/- 0.8 degrees C, respectively. The differences between bladder tumour indicative T50 and bladder normal tissue T50 and also between vagina tumour contact T50 and vagina normal tissue T50 were significant ( p = 0.0001). No statistical difference was found between rectum tumour indicative t50 and rectum normal tissue T50. CONCLUSION: At present the cause of the temperature difference is not known. However, as the difference between tumour (indicative/contact) and normal tissue is very small and considering also the inaccuracy in the tissue type assignment it can be stated that this study does not provide sufficient evidence to conclude that the statistical difference has clinical relevance. Therefore, it was concluded that at this time there is no need to differentiate between normal and tumour tissue in intra-luminal thermometry.

Antineoplastic Agents↗
PubMed2000

Thermal analysis of the plasma membrane Ca2+-ATPase.

The plasma membrane Ca2+-ATPase is a well known enzyme in eucaryotes able to extrude calcium to the extracellular space in order to restore intracellular calcium to very low levels. This ATPase needs plasma membrane lipids such as acidic phospholipids in order to maintain its activity. In this study, we investigated the role that calcium and cholesterol play on the thermal stability of the Ca2+-ATPase isolated from cardiac sarcolemma and erythrocyte membranes. Calcium showed a stabilizing and protective effect when the enzyme was exposed to high temperatures. This stabilizing effect showed by calcium was potentiated in the presence of cholesterol. These protection effects were reflected on several thermodynamic parameters such as T50, deltaHvh and apparent deltaG, indicating that calcium might induce a conformational change stabilized in the presence of cholesterol that confers enzyme thermostability. The effect shown by cholesterol on deltaHvh and apparent deltaH++ open the possibility that this lipid decreases cooperativity during the induced transition. Despite that a binding site for cholesterol has not been identified in the plasma membrane Ca2+-ATPase, our results supports the proposal that this lipid interacts with the enzyme in a direct fashion.

Animals↗
PubMed2007

Fabrication and thermal analysis of submicron silver tubes prepared from electrospun fiber templates.

Submicron silver tubes have been synthesized by a polymer-based template approach. Two different approaches to metallization, electroless deposition and exchange plating, were evaluated within the template approach. Silver films with average thickness approximately 50-100 nm were deposited on polycarbonate fibers approximately 400 nm in diameter by each technique, resulting in tubes with a diameter between 450 and 500 nm after thermal degradation of core fibers. These nanomaterials were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and scanning thermal microscopy. The thermal conductivity of the silver submicron tubes was found to differ depending on the method of preparation, with tubes from electroless plating possessing relative thermal conductivity values that were 1 order of magnitude higher than that from exchange plating, 3000 W/m x K and 660 W/m x K, respectively. Interestingly, these results indicate that silver submicron tubes possess higher thermal conductivity than the bulk metal. This observation is discussed in the context of the continuous conduction path of the tubes and their high surface area-to-volume ratio.

Journal Article↗
PubMed2003

Water status and thermal analysis of alginate beads used in cryopreservation of plant germplasm.

Encapsulation and dehydration techniques using alginate beads are used increasingly for the pre-treatment of various plant materials for cryopreservation to improve survival post-cryogenic storage. This study reports the effects of the water content of beads (formed with 3% (w/v) alginic acid in liquid S-RIB), polymerisation time (in 100 mM calcium chloride solution), osmotic dehydration (in 0.75 M sucrose solution), and evaporative air desiccation on the thermal properties of alginate beads used in cryopreservation protocols. Experimental beads were assayed using a differential scanning calorimeter (DSC) with a cooling programme to -150 degrees C, followed by re-warming. Resultant thermograms were evaluated with particular reference to the onset temperature and enthalpy of the melt endotherm from which the quantities of frozen and unfrozen water were calculated. Treatments were applied sequentially to samples of beads and their thermal features evaluated at each stage of the protocol. Using 'standard' beads (40-55 mg fresh weight), formed using plastic disposable pipettes, the degree of polymerisation (>10 min) proportionally reduced their dry weight and increased their water content. Thermal characteristics of the beads were unaffected by polymerisation times >10 min, but the maximum level (23%) of unfrozen (osmotically inactive) water was achieved after 15 min polymerisation. Osmotic dehydration using 0.75 M sucrose significantly lowered bead water content and mean dry weight approximately doubled with 20-24 h immersion time. Bead desiccation in still air reduced their water content by 83% of fresh weight, whilst dry weight remained constant. After 8 h desiccation in air between 27 and 37% of the water in the bead was osmotically inactive (unfrozen) in DSC scans. Desiccation >18 h reduced this fraction to zero. The melt onset temperature and the enthalpy of melting were directly related to bead water content. The unfrozen water fraction increased substantially with reduced water content of the beads (from 23 to 37% of total water content), concomitant with a reduction in the ratio of unfrozen to frozen water from 1:3 to 1:2. For successful vitrification and the production of a glass that did not destabilise on rewarming, a bead water content of ca. 26% of fresh weight (0.4 g waterg(-1) dry weight) was required, much of which was osmotically inactive water. These data are discussed in relation to optimal pre-treatments for alginate bead encapsulation techniques used in the cryopreservation of a range of plant germplasm. It is proposed that increased standardisation of alginate beads, in terms of volume, fresh weight, and water content, is required to reduce the variability in physical and thermal features, which in turn will improve survival of plant samples post-cryopreservation.

Alginates↗
PubMed1989

A model for optical and thermal analysis of laser balloon angioplasty.

Laser balloon angioplasty is modeled using an infinitely long cylinder possessing axisymmetry. The balloon surface is assumed to be uniformly irradiated by diffuse light at 1060 nm delivered from within the inner balloon core. The diffusion approximation to the radiative transport equation is solved for a single layer of homogeneous medium enclosing the transparent fluid-filled balloon. The computed light fluence rate (W.cm-2) just beneath the tissue surface is 4.7 times the primary irradiance, owing to scattering and secondary irradiance from the "integrating cylinder" effect of backscattered light into the inner core. The transient temperature response of the heated tissue is then calculated using an implicit finite difference solution of the heat conduction equation for concentric layers of varying thermal properties. Finally, the extent of damage is analyzed using the Arrhenius rate process model. Changes in optical and thermal properties with temperature and thermal phase transitions have been omitted in all our analyses. Irradiances which decrease with time can produce a "temperature plateau" for a longer time period than a constant irradiance of equal total energy output. This may be clinically important. Flexible boundary conditions at the balloon interface permit simulation of a "hot contact surface," such as a black balloon absorbing all incident laser power. In this situation, the computed surface damage is consistently higher than that obtained by LBA of equivalent energy output.

Angioplasty, Balloon↗
PubMed2007

Physicochemical characterization of deflazacort: thermal analysis, crystallographic and spectroscopic study.

The solid state properties of deflazacort (1-(1beta,16alpha)-21-(acetyloxy)-11-hydroxy-2'-methyl-5'H-pregna-1,4-dieno[17,16-d]oxazole-3,20-dione, 1) were investigated using differential scanning calorimetry (DSC), thermogravimetry (TG), single-crystal X-ray diffraction, solid and liquid nuclear magnetic resonance spectroscopy ((13)C NMR), Fourier transform infrared and Raman spectroscopy (FTIR and FT Raman). From the trends observed in the crystal structure and spectral data some conclusions can be made about hydrogen bonding, molecular conformation and crystal packing. Compound 1 crystallizes in an orthorhombic cell, space group P2(1)2(1)2(1) and the following lattice parameters: a=11.2300(5), b=12.8161(8), c=16.171(1)A, V: 2327.4(2)A(3), D(c): 1.260g/cm(3), R1=0.0479, wR2=0.1012. The crystal structure is stabilized by intra and intermolecular interactions, which provides for a very closely packed form. The NMR data indicated that 1 shows a similar conformation in solid and liquid state; while, thermal data revealed that 1 follows a monophasic pattern with a DSC melting peak at 258.4 degrees C (DeltaH 99.7Jg(-1), n=3), indicating that 1 is thermally stable as solid; but, as liquid is unstable to undergo a thermal decomposition reaction. The reactivity of 1 toward light and moisture was examined via DSC and TLC. The data indicated that 1 do not interact with water to give hydrated forms or decomposition products; however, light degrades 1.

Binding Sites↗
PubMed1999

Physical characterization of the stratum corneum of an in vitro human skin equivalent produced by tissue engineering and its comparison with normal human skin by ATR-FTIR spectroscopy and thermal analysis (DSC).

An in vitro human skin equivalent may be obtained by culturing human keratinocytes on a collagen gel containing fibroblasts. The anchored skin equivalent cultured at the air-liquid interface closely resembles human skin and is acceptable for in vitro percutaneous absorption. However, it is still more permeable than human skin. Since intercellular lipids have been recognized to play an important role in skin permeability, infrared spectroscopy and differential scanning calorimetry were performed on the stratum corneum of bovine or human skin equivalents grown at different days of air-liquid culture. The symmetric and asymmetric CH(2) stretching vibrations suggested that for all days observed, the intercellular lipids were less organized than those in human skin, irrespective of whether bovine or human collagen was used. Different culture conditions were also tested and the medium without serum and no epidermal growth factor at the air-liquid culture showed results significantly more comparable to human skin. Actually, the thermal behavior of in vitro stratum corneum showed transitions at lower temperatures than human skin. The transition around 80 degrees C, in the form of a lipid-protein complex, was absent. These results showed that the structural arrangement of intercellular lipids and their thermodynamic properties hold a crucial role in the barrier function of the stratum corneum.

Animals↗
PubMed2003

Thermal analysis of trace levels of polymorphic impurity in salmeterol xinafoate samples.

PURPOSE: To quantify trace levels of polymorphic impurity in two salmeterol xinafoate (SX) Form I samples: granular SX (GSX) produced by fast-cooling crystallization and micronized SX (MSX) prepared from GSX by micronization. METHODS: SX-I and SX-II produced by solution enhanced dispersion by supercritical fluids (SEDS) were the reference polymorphs (100% pure) used for quantitative comparison. The percentage of polymorphic conversion, alpha, of each Form I sample to Form II was measured by differential scanning calorimetry (DSC) as a function of time (i.e., at different scanning speeds). The data were analyzed by the Avrami-Erofe'ev (AE) equation using an iterative fitting computer program. SX-I samples containing 1.24, 4.41, and 13.47% (w/w) of SX-II as physical mixtures were subjected to similar analysis and data treatment. A mathematical relationship based on an instantaneous nucleation model was derived to relate the AE rate constants, k, of pure SX-I and physical mixtures to weight percentage of SX-II. This relationship was then used to calculate the percentage polymorphic impurity of GSX and MSX from their k values. For relative comparison of the Form-II nuclei present, the k values of SX-I, GSX, and MSX were used to calculate their differences in free energy of nucleation. RESULTS: The AE equation affords good (r2 approximately equal to 0.81) to excellent (r2 approximately equal to 0.99) fits of data for the samples. The levels of polymorphic impurity in GSX and MSX are 0.16 and 0.62% (w/w), respectively. Based on the free energy differences of nucleation between the reference SX-I material and the other samples, the number (and size) of the Form II nuclei present in the samples rank in the order: MSX > GSX > SX-I. CONCLUSIONS: DSC is a useful tool for assessing the polymorphic purity of SX materials and possibly other enantiotropic pairs showing similar thermal behavior.

Albuterol↗