Impact of Hard Machining on Zirconia Based Ceramics for Dental Applications

Since the late 90s the use of zirconia based all-ceramic restorations increases. Many manufacturing steps are necessary, like pre-sintering, soft machining (pre-sintered condition), sintering and hard machining (fully sintered) in combination with a final staining or veneering step. All these techniques, especially hard machining, are associated with the production of flaws in different scales, in conjunction with thermal and residual stresses and phase transformations. These are inter alia capable to induce failure. This work investigates the impact of hard machining on the material properties and attempts to establish a correlation to failure. © 2016 Published by Elsevier B.V

Analysis of flow induced texturing in complex fluids with Brillouin Rheology - a proof of concept

The aim of this work is to study the flow induced texturing of molecules (complex fluids) in a shear field. This is done by measuring phonons with photons [1] in a commercially available rotational rheometer. The optical experimental method of transferring momentum and energy between phonons and photons is generally known as Inelastic Light Scattering (ILS) [2]. Brillouin Light Scattering (BLS) [3] has a quite small energy transfer compared to Raman spectroscopy [4] but with a high performance multi-pass Vernier tandem Fabry-Perot interferometer [5] and a sophisticated optical set-up, it is possible to achieve information about the texture (like entanglement of molecules) of complex fluids inside a rheometer gap while shearing. This can be acquired for any position in the sample, in contrast to the rheological experiments were an average over a whole sample is used. Here we successfully demonstrate an optical set-up that couples a BLS with rotational rheology in order to simultaneously measure the high-frequency longitudinal elastic modulus in a classical rheometer along with the zero-shear viscosity during the flow of complex fluids. BLS gives the possibility for contactless determination of local elastic properties, while the designed optical set-up is introduced as boundary conditions to control temperature gradients in the sample, and the position and dimension of the scattering volume. This method was tested for a range of temperatures, and well as for an applied shear field and different radial positions of the scattering volume in the sample using a plate-plate rheometer geometry. Measurements of a dilute polymer system suggest a homogeneous orientation of polymer molecules throughout the sample as soon as a critical shear rate has been reached at one spatial position

Brillouin light scattering during shearing of complex fluids

A setup for the optical measurement of elastic properties during the flow of complex fluids is presented. Brillouin light scattering and rotational rheology are combined in order to simultaneously measure the high-frequency longitudinal elastic modulus in a classical rheometer along with the zero-shear viscosity. Brillouin light scattering allows for the contactless determination of local elastic properties. First measurements of a diluted polymer system suggest a homogeneous orientation of polymer molecules throughout the sample as soon as a critical shear rate has been reached at one spatial position

Determination of the rheological properties of Matrigel for optimum seeding conditions in microfluidic cell cultures

Hydrogels are increasingly used as a surrogate extracellular matrix in three-dimensional cell culture systems, including microfluidic cell culture. Matrigel is a hydrogel of natural origin widely used in cell culture, particularly in the culture of stem cell-derived cell lines. The use of Matrigel as a surrogate extracellular matrix in microfluidic systems is challenging due to its biochemical, biophysical, and biomechanical properties. Therefore, understanding and characterising these properties is a prerequisite for optimal use of Matrigel in microfluidic systems. We used rheological measurements and particle image velocimetry to characterise the fluid flow dynamics of liquefied Matrigel during loading into a three-dimensional microfluidic cell culture device. Using fluorescence microscopy and fluorescent beads for particle image velocimetry measurements (velocity profiles) in combination with classical rheological measurements of Matrigel (viscosity versus shear rate), we characterised the shear rates experienced by cells in a microfluidic device for three-dimensional cell culture. This study provides a better understanding of the mechanical stress experienced by cells, during seeding of a mixture of hydrogel and cells, into three-dimensional microfluidic cell culture devices. (C) 2018 Author(s)