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Biomedical subjects

Ludwig J Gauckler

Publications and source records attributed to Ludwig J Gauckler.

14 recordsLinked to original sources
PubMed2006

Stabilization of foams with inorganic colloidal particles.

Wet foams are used in many important technologies either as end or intermediate products. However, the thermodynamic instability of wet foams leads to undesired bubble coarsening over time. Foam stability can be drastically improved by using particles instead of surfactants as foam stabilizers, since particles tend to adsorb irreversibly at the air-water interface. Recently, we presented a novel method for the preparation of high-volume particle-stabilized foams which show neither bubble growth nor drainage over more than 4 days. The method is based on the in-situ hydrophobization of initially hydrophilic particles to enable their adsorption on the surface of air bubbles. In-situ hydrophobization is accomplished through the adsorption of short-chain amphiphiles on the particle surface. In this work, we illustrate how this novel method can be applied to particles with various surface chemistries. For that purpose, the functional group of the amphiphilic molecule was tailored according to the surface chemistry of the particles to be used as foam stabilizers. Short-chain carboxylic acids, alkyl gallates, and alkylamines were shown to be appropriate amphiphiles to in-situ hydrophobize the surface of different inorganic particles. Ultrastable wet foams of various chemical compositions were prepared using these amphiphiles. The simplicity and versatility of this approach is expected to aid the formulation of stable wet foams for a variety of applications in materials manufacturing, food, cosmetics, and oil recovery, among others.

Journal Article↗
PubMed2006

Cyclic fatigue in water of veneer-framework composites for all-ceramic dental bridges.

OBJECTIVES: Ceramic materials applied in dentistry may exhibit significant subcritical crack growth due to the severe cyclic loading in the aqueous environment encountered in the mouth during mastication. The authors report on the subcritical crack growth behavior of three dental restoration systems (Empress 2/IPS Eris, TZP/Cercon S and Inceram-Zirconia/Vita VM7) under cyclic loading in water, in order to establish guidelines for the use and design of long-lifetime all-ceramic posterior bridges. METHODS: Inert strength and lifetime tests under cyclic loading in an aqueous environment were performed in a mechanical bending apparatus and evaluated with Weibull statistics. RESULTS: Subcritical crack growth occurred predominantly in the outer veneer layer of the veneer-framework composites. The apatite-based veneer (IPS Eris) was more susceptible to subcritical crack propagation compared to the feldspathic glass veneers (Cercon S and Vita VM7). SIGNIFICANCE: Dental restoration systems containing apatite-based veneers and weak frameworks (Empress 2/IPS Eris) are not recommended for the fabrication of all-ceramic bridges in the molar region. Conversely, veneer-framework systems consisting of feldspathic glass veneers and tough zirconia-based frameworks (TZP/Cercon S and Inceram-Zirconia/Vita VM7) may exhibit lifetimes longer than 20 years if the bridge connector is properly designed.

Aluminum Oxide↗
PubMed2006

Fatigue of zirconia under cyclic loading in water and its implications for the design of dental bridges.

OBJECTIVES: The aim of this study was to evaluate the cyclic fatigue behavior of zirconia (3Y-TZP) in water and derive guidelines for the design of zirconia-based dental bridges with extended lifetime. METHODS: The subcritical crack growth parameters under aqueous and cyclic loading conditions were determined from Weibull distributions of the initial mechanical strength and of the lifetime of TZP specimens. The strength and lifetime data were obtained using a specially designed bending machine under simple and oscillatory loading conditions, respectively. RESULTS: The TZP components submitted to cyclic loading in water exhibited subcritical crack propagation at stress levels significantly ( approximately 50%) lower than the critical stress intensity factor (K(IC)=5.6 MPam(1/2)). In spite of this susceptibility to subcritical crack growth, calculations based on the fatigue parameters and on the stress applied on the prosthesis indicate that posterior bridges with zirconia frameworks can exhibit lifetimes longer than 20 years if the diameter of the bridge connector is properly designed. SIGNIFICANCE: This in vitro study indicates that partially stabilized zirconia (3Y-TZP) can withstand the severe cyclic loading and wet conditions typically applied in the molar region of the mouth and is therefore an appropriate material for the fabrication of all-ceramic multi-unit posterior bridges.

Ceramics↗
PubMed2006

Mechanical and fracture behavior of veneer-framework composites for all-ceramic dental bridges.

OBJECTIVES: High-strength ceramics are required in dental posterior restorations in order to withstand the excessive tensile stresses that occur during mastication. The aim of this study was to investigate the fracture behavior and the fast-fracture mechanical strength of three veneer-framework composites (Empress 2/IPS Eris, TZP/Cercon S and Inceram-Zirconia/Vita VM7) for all-ceramic dental bridges. METHODS: The load bearing capacity of the veneer-framework composites were evaluated using a bending mechanical apparatus. The stress distribution through the rectangular-shaped layered samples was assessed using simple beam calculations and used to estimate the fracture strength of the veneer layer. Optical microscopy of fractured specimens was employed to determine the origin of cracks and the fracture mode. RESULTS: Under fast fracture conditions, cracks were observed to initiate on, or close to, the veneer outer surface and propagate towards the inner framework material. Crack deflection occurred at the veneer-framework interface of composites containing a tough framework material (TZP/Cercon S and Inceram-Zirconia/Vita VM7), as opposed to the straight propagation observed in the case of weaker frameworks (Empress 2/IPS Eris). SIGNIFICANCE: The mechanical strength of dental composites containing a weak framework (K(IC)<3 MPam(1/2)) is ultimately determined by the low fracture strength of the veneer layer, since no crack arresting occurs at the veneer-framework interface. Therefore, high-toughness ceramics (K(IC)>5 MPam(1/2)) should be used as framework materials of posterior all-ceramic bridges, so that cracks propagating from the veneer layer do not lead to a premature failure of the prosthesis.

Aluminum Oxide↗
PubMed2006

Prospective clinical study of zirconia posterior fixed partial dentures: 3-year follow-up.

OBJECTIVES: The purpose of this prospective clinical cohort study was to determine the success rate of 3- to 5-unit posterior fixed partial dentures (FPDs) with zirconia frameworks after 3 years of function. METHOD AND MATERIALS: Forty-five patients in need of at least 1 FPD to replace 1 to 3 posterior teeth were included. The frameworks were produced by means of a prototype computer-assisted manufacture system. They were milled with a precisely calculated increase in size out of presintered zirconia blanks and subsequently shrunk to the required size. Fifty-seven FPDs were cemented using either Variolink or Panavia TC cement. Clinical and radiographic examinations were performed at baseline, 12, 24, and 36 months after cementation. Statistical analysis was performed by descriptive statistics and the Kaplan-Meier survival analysis. Comparisons of probing depth, Plaque Index, and bleeding on probing between test (abutment) and control (contralateral) teeth were done with the McNemar test. RESULTS: Thirty-six patients with 46 FPDs were available for examination after 36 months. No fractures occurred, rendering a 100% success rate of the zirconia frameworks. Seven FPDs had to be replaced because of biologic and technical problems. The survival rate, therefore, was 84.8%. Secondary caries was found in 10.9% of the FPDs, and chipping of the veneering ceramic was found in 13.0%. There were no significant differences regarding the probing depth in test and control teeth. CONCLUSION: Zirconia frameworks demonstrated sufficient stability for replacement of posterior teeth. However, the high rates of technical problems should be reduced by further developments of the prototype processing technology.

Cementation↗
PubMed2005

A prediction method for the isoelectric point of binary protein mixtures of bovine serum albumin and lysozyme adsorbed on colloidal titania and alumina particles.

Bovine serum albumin and lysozyme mixtures of different mole fractions were adsorbed to colloidal alumina (116 nm) and titania particle (271 nm) suspensions of 2 vol % solid content for 16 h at pH 7.5. The total protein amount normalized to the powder surface area was 1000 ng/cm2. The zeta potential of the protein-treated suspensions was measured as a function of pH and the isoelectric point (IEP) obtained. A simple prediction model in two refinement steps was derived and evaluated for the obtained IEPs. The best model fit which takes into account moles of protein and surface fractions yielded an average prediction error of 7.5% and a maximum error of 16.7%.

Adsorption↗
PubMed2005

Lysozyme and bovine serum albumin adsorption on uncoated silica and AlOOH-coated silica particles: the influence of positively and negatively charged oxide surface coatings.

The adsorption of lysozyme and bovine serum albumin on silica and AlOOH-coated silica particles-representing negatively and positively charged oxide surfaces-was investigated. The protein-treated uncoated and completely AlOOH-coated silica particles were characterized by zeta potential analysis and UV/VIS spectroscopy. It was found that at pH 7 a protein oppositely charged to the oxide surface adsorbs in significantly higher amounts. In contrast, proteins of the same charge did not or only in very low amounts adsorbed on an oxide surface. As both oxide surfaces were measured to be very hydrophilic it can be concluded that electrostatic interactions dominate the adsorption process at the investigated experimental conditions. The pH regions where the proteins interact via attractive and repulsive coulomb interaction with the particular oxide surfaces were calculated and outlined.

Adsorption↗
PubMed2005

Strength and reliability of four-unit all-ceramic posterior bridges.

OBJECTIVES: The purpose of this study was to determine the in vitro load bearing capacity of four-unit posterior frameworks made of glass ceramic with lithium-disilicate crystals (E2), of zirconia-reinforced glass-infiltrated alumina (ICZ) and of zirconia stabilized with 3 mol% yttria (CEZ). METHODS: All frameworks mimicked a four-unit posterior situation with 7.3 mm2 interdental cross-sections and possessed exactly the same dimensions. The load bearing capacity was measured on a special bridge test setup with 15 specimens for each of the materials. The data were analyzed with Weibull statistics giving the characteristic load bearing capacity F0 at 63% failure probability and the Weibull modulus m as indicator for the reliability and reproducibility. RESULTS: For the E2 frameworks the average load bearing capacity and the SD was 260 (+/-53) N, the characteristic load F0 282 N and the reliability m = 5.7. For the ICZ frameworks the average load bearing capacity was 470 (+/-101) N, F0 518 N and m = 4.5. CEZ frameworks revealed the highest average load bearing capacity of 706 (+/-123) N, the highest characteristic load bearing capacity F0 = 755 N and the best reliability m = 7.0. SIGNIFICANCE: CEZ frameworks showed the best mechanical properties as demonstrated by the high values of average load bearing capacity, reliability and characteristic load bearing capacity with respect to the other ceramics studied. However, for four-unit posterior CEZ frameworks the connector size of 7.3 mm2 is insufficient to withstand occlusal forces reported in the literature. Four-unit posterior frameworks require a connector size larger than 7.3 mm2.

Aluminum Oxide↗
PubMed2004

Bovine serum albumin adsorption onto colloidal Al2O3 particles: a new model based on zeta potential and UV-vis measurements.

We investigated the adsorption of bovine serum albumin (BSA) on colloidal Al2O3 particles in an aqueous environment. Changes in the zeta potential of the Al2O3 particles upon the adsorption of BSA were measured using an electro-acoustic technique. The mass of protein adsorbed was determined by using UV-vis spectroscopy. The change of the isoelectric point of the Al2O3 powder-protein suspension was found to be a function of adsorbed protein mass. It was shown that approximately one monolayer of BSA was needed to fully mask the surface and to compromise the charge of Al2O3. From titration experiments it follows that about 30-36% of the negatively charged groups of the protein form bonds with the protonated and charged Al2O3 surface. On the basis of our observations we introduced a new adsorption model for BSA on Al2O3 particles.

Adsorption↗
PubMed2004

Relation between microstructure and mechanical behavior of concentrated silica gels.

We produce concentrated (40 vol%) gels of uniformly sized silica particles by an in situ process, based on the enzyme-catalyzed hydrolysis of urea in the liquid phase of electrostatically stabilized suspensions. Two different methods are used: Either the pH of the suspensions is shifted toward the isoelectric point of the particles (delta pH method), or the ionic strength is continuously increased at constant pH (deltaI method). We compare the two kinds of gels in terms of elastic and yield behavior as well as microstructure by using rheological measurements in oscillation and high-pressure freezing in combination with cryo-SEM, respectively. Results suggest a strong increase of elastic and yield properties in concentrated particle gels with decreasing homogeneity of their microstructures.

Journal Article↗
PubMed2004

Small-angle static light scattering of concentrated silica suspensions during in situ destabilization.

The aggregation of concentrated aqueous silica suspensions is characterized by means of static light scattering. We use an in situ destabilization mechanism based on the enzyme-catalyzed hydrolysis of urea. This method enables us to continuously and homogeneously change the interparticle potential from repulsive to attractive without disturbing the aggregation process. Moreover, our electrostatically stabilized suspensions can be destabilized by two different methods. In the first method, the pH is shifted toward the isoelectric point of the particles ( Delta pH method), thereby leading to a decrease of their surface charge. In the second method, the ionic strength is continuously increased at constant pH ( Delta I method), leading to a compression of the electrical double layer around the charged particles. A laboratory-built flat-cell light-scattering instrument is used, which allows fast data acquisition and an adjustment of the sample cell thickness. To circumvent multiple scattering effects, we use a very small sample thickness ( approximately 13 microm). In addition, the refractive index difference between the aqueous phase and the particles is reduced by adding sucrose to the liquid phase of our suspensions. We are able to characterize the structural changes at the very early stages of the destabilization process, where no significant effects are yet detected in macroscopic rheological measurements. While during the Delta pH destabilization, the scattering curve shows significant changes only after some characteristic delay time, it changes continuously during the Delta I destabilization. The latter is attributed to the formation of a weak pre-gel structure in the suspensions, as a shallow secondary minimum appears in the interparticle potential. Data are evaluated by using a HMSA square-well structure factor model. Results are in good agreement with those predicted from DLVO theory.

Journal Article↗
PubMed2002

Quantification of microstructures in stable and gelated suspensions from Cryo-SEM.

It is shown that the microstructures of concentrated suspensions can be analyzed in a quantitative way from cryo-SEM images of high-pressure frozen samples, both in the electrostatically stabilized and in the flocculated state. Suspensions of spherical silica particles (40 vol%) in an aqueous solution were used. The average particle radius was 525 nm with a polydispersity of below 7%. The suspensions were high-pressure frozen, which resulted in a quenching of the configuration without apparent change in volume or crack formation. After fracturing the samples at liquid nitrogen temperature, the fracture surface was etched by controlled sublimation of the frozen aqueous phase, coated with 8 nm of platinum, and examined by stereo-cryo-SEM. The 3-dimensional positions of all the visible particles were determined from the SEM images. Assuming an isotropic particle configuration in the sample before cracking, it is possible to extract the 3-dimensional pair correlation function from the particle positions on the fracture surface. A comparison to recent results from Brownian Dynamics simulations shows good agreement between our experiments and the simulations.

Journal Article↗
PubMed2002

Rheological behavior of aqueous suspensions of hydroxyapatite (HAP).

The aim of this study is to characterize the influence of organic dispersants on the stability of hydroxyapatite (HAP) dispersions, using viscosity measurements, electrokinetic sonic amplitude (ESA) measurements and adsorption isotherms. Colloidal stability of aqueous suspensions of HAP as a function of solids loading and of the type and concentration of deflocculant has been studied. The interaction between particles and dispersant molecules was characterized. Adsorption measurements of the amount of dispersants on the particles surface, viscosity and electrophoretic measurements as a function of the dispersant concentration are correlated. Suspension parameters have been adjusted in order to obtain a high solids loading slurry with a plastic viscosity which will allow its use in colloidal processing.

Journal Article↗