Rapid prototyping method for 3D PDMS microfluidic devices using a red femtosecond laser

A rapid prototyping technique is demonstrated which uses a red femtosecond laser to produce a metallic mould which is then directly used for the replica moulding of PDMS. The manufacturing process can be completed in less than 6 h making it a viable technique for testing new designs quickly. The technique is validated by creating a microfluidic device with channels of height and depth of 300 µm, with a ramp test structure where the height and width of the channels reduces to 100 µm to demonstrate the techniques 3D capabilities. The resulting PDMS device was easily removed from the metallic mould and closely replicated the shape aside the expected shrinkage during thermal curing. As the technique uses a single replica process, the surface roughness at the base of the channels corresponds to the un-ablated polished metal mould, resulting in a very low surface roughness of 0.361 nm. The ablated metallic mould surface corresponds to the top of the PDMS device, which is bonded to glass and does not affect the flow within the channels, reducing the need for optimisation of laser parameters. Finally, the device is validated by demonstrating laminar flow with the no-slip condition.

Biomechanical Performance of the Cemented Hip Stem with Different Surface Finish

The integrity of the cemented fixation interface is responsible for the long-term longevity of artificial hip prostheses. Metallic stems with roughened surfaces are considered to provide stronger adhesion with cement. However, clinical studies have reported that roughened stems show a lower survival rate than polished stems. These studies clearly reveal that the causes of artificial stem loosening are very complicated and multifaceted. Therefore, this study was conducted to investigate the mechanical effect of stem surface finish in cemented hip replacement. To accomplish this, a series of cement–metal specimens were tested configurations to assess the mechanical characteristics of the cement–metal interface specimens. A finite elemental model of cemented femoral prostheses was then created, in which the cement–stem interface was assumed to be in different bonding states according to the experimentally measured interface properties. The failure probabilities of the cement mantle and cemented interface under physiological loadings were evaluated. Experimental results indicate that the polished metal produced higher interfacial tensile and lower shearing strengths than the roughened metal. The polished stems were predicted to induce a lower failure probability of cement mantle and higher integrity of the cement–stem interface when compared to the roughened stem. Overall, current results provide significant evidence to support the clinical outcomes of cemented hip prostheses with different stem surface finishes.

Cementing a Polyethylene Cup into a Well Fixed Acetabular Metal-on-Metal Resurfacing Component? An Experimental Investigation

Introduction Adverse reactions to metal debris often indicate revision surgery in metal-on-metal (MoM) hip arthroplasty and an exchange of the MoM bearing into either a metal on polyethylene or a ceramic-on-polyethylene articulation. At the moment the removal of the entire implant system is the most reasonable method. In order to avoid bone loss caused by the removal of a well-fixed acetabular component, the purpose of this study was to measure the stability of a cemented polyethylene (PE) cup in an acetabular hip resurfacing component and to examine if such a method could be suitable for clinical use. Methods PE cups were cemented into 2 different hip resurfacing components and biomechanical tests were applied to measure failure torques under lever out and rotational load. Results In all cases failure of the interface between the resurfacing components and the cement layer occurred at a very low load (0.14 Nm-61.50 Nm). Discussion The early failure occurred due to lacking interdigitation of cement and the polished metal surface. Thus we warn against cementing a PE cup into acetabular hip resurfacing components for clinical use.

A method of comparing the wear resistance of various materials used for artificial teeth

OBJECTIVE: Abrasion resistance of three commercial brands of acrylic resin for artificial teeth, available on the domestic market (Biotone(r), Plus(r) and Vipi Dent Artiplus(r)) was evaluated by a new methodology called "Pirassununga Method ". METHODS: The Manufacturers produced the maxillary central incisor-shaped incisal resin specimens (n=27). These were embedded in chemically activated acrylic resin in an insulated metal matrix to fabricate test specimens, which were flattened on a lathe and refined manually with sandpaper. Wear testing was conducted in an experimental machine at the Vipi dental products factory. In the "Pirassununga Method" a polished metal sphere 4.8 mm in diameter, attached to a rotary device passes over the fixed specimens in programmable cycles, under 5N pressure, using distilled water as lubricant. In each sample, the groove caused by abrasion, was analyzed in two ways: Readout under a microscope to determine the breadth and depth of the groove caused by the ball, and by laser roughness meter readout, which obtained a value Rt. RESULTS: The nonparametric Kruskal Wallis test showed no statistically significant difference between the medians of brands evaluated in the cycles performed (p = 0.936). CONCLUSION: Artiplus(r) Brand showed a lower tendency to wear than commercial brands Biotone(r) and Plus(r) Vipi Dent, with the best performance shown for the IPN polymer.

Energy-dispersive X-ray diffraction mapping on a benchtop X-ray fluorescence system

A method for energy-dispersive X-ray diffraction mapping is presented, using a conventional low-power benchtop X-ray fluorescence spectrometer, the Seiko Instruments SEA6000VX. Hyper spectral X-ray maps with a 10 µm step size were collected from polished metal surfaces, sectioned Bi, Pb and steel shot gun pellets. Candidate diffraction lines were identified by eliminating those that matched a characteristic line for an element and those predicted for escape peaks, sum peaks, and Rayleigh and Compton scattered primary X-rays. The maps showed that the crystallites in the Bi pellet were larger than those observed in the Pb and steel pellets. The application of benchtop spectrometers to energy-dispersive X-ray diffraction mapping is discussed, and the capability for lower atomic number and lower-symmetry materials is briefly explored using multi-crystalline Si and polycrystalline sucrose.

New Approach to Fringe Pattern Analysis Obtained by Scanning Polished Metal Cylinders with Gaussian Beam

In laser-scanning measurement of cylindrical objects extremely complex interfering signals occur. They are due to superimposition of: reflected, unobstructed and scattered light. The proportions between these components vary in time and also the total intensity distribution changes. The considerations applying Fraunhofer theory are static and fragmentary, and may be concluded that the existing solutions for diffraction of 3D bodies do not fit to engineering applications. Having the above in view, the close analysis of detector signal was carried out. The obtained differential intensity characteristics allow to determine the important metrological qualities of diffraction field.

Flaw Detection Using Image Registration and Fusion Techniques

The inspection of polished metal contoured surfaces, such as silverware pieces, is much more difficult than for a flat surface, considering the complex curved surface, reflections, and shadows. It is hard to detect flaws when they overlap with shadows and specular reflections, which is typically the case. In this paper, this problem is solved using image registration and image fusion techniques. A continuous-inspection system is developed to take two images sequentially under different lighting conditions when the object is passing under the camera. Shadows and reflections shift, while the flaws do not. From the differences of these two images, flaws can be distinguished from shadows and reflections, and the lost information due to specular reflections can be made up. Fused images without specular reflections were obtained, and a new feature based image registration algorithm is developed to compare these two fused images to detect the surface flaws.

Investigation of the Formation and Applications of Ice Powder

Water ice powder constitutes a potentially important manufacturing tool. Availability and cleanliness of this powder constitute its major advantage. It was shown that the ice particles could be used as an abrasive in the course of waterjet machining. Although the erosion potential of ice particles is inferior to that of the conventional abrasives, the environmental soundness of ice enables us to expend the use of the ice abrasive jets on food industry, medicine, precision machining, etc. The principal issue in the use of the ice abrasives is particles formation. Analysis of various technologies showed that an effective avenue in particle production is integration of the water freezing and ice decomposition. As the results, the desired flow rate of ice particles at the desired temperature and size distribution can be generated. The objective of the present paper is the experimental investigation of the production of ice particles. An experimental setup was constructed and used for particles fabrication at controlled conditions. The acquired information was applied for the analysis of the phenomena leading to the particles formation. As a result a hypothetical mechanism of the ice decomposition was suggested and validated. The experiments involving the decontamination of the electronic devices, semiconductors, fabric, leather, food products, polished metal, soft plastics, rusted auto parts, etc., were carried out in order to demonstrate the potential application of the ice blasting.