Contact mechanics and friction for transversely isotropic viscoelastic materials

Transversely isotropic materials are an unique group of materials whose properties are the same along two of the principal axes of a Cartesian coordinate system. Various natural and artificial materials behave effectively as transversely isotropic elastic solids. Several materials can be classified as transversely isotropic materials including crystals, rocks, piezoelectrics, some biological tissues such as muscles, skin, cartilage tissue or brainstem and fibrous composites. In this study, the theory of contact mechanics developed by Persson is extended in such a way that it can model the contact and friction of a transversely isotropic viscoelastic solid in contact with a rigid rough surface. Numerical results show that anisotropy should be taken into account when dealing with transversely isotropic materials. The hysteresis friction between a transversely isotropic viscoelastic rubber, reinforced unidirectionally by fibers and two rough counter surfaces are measured by a pin-on-disk setup. The experimental results validate the theory

Compatibility of Zr2AlCZr_{2}AlC MAX phase-based ceramics with oxygen-poor, static liquid lead-bismuth eutectic

This work investigates the compatibility of $Zr_{2}AlC$ MAX phase-based ceramics with liquid LBE, and proposes a mechanism to explain the observed local $Zr_{2}AlC$/LBE interaction. The ceramics were exposed to oxygen-poor ($C_{O}\le2.2 \cdot10^{-10}$ mass%), static liquid LBE at 500{\deg}C for 1000 h. A new $Zr_{2}(Al,Bi,Pb)C$ MAX phase solid solution formed in-situ in the LBE-affected $Zr_{2}AlC$ grains. Out-of-plane ordering was favorable in the new solid solution, whereby $\textit{A}$-layers with high and low-Bi/Pb contents alternated in the crystal structure, in agreement with first-principles calculations. Bulk $Zr_{2}(Al,Bi,Pb)C$ was synthesized by reactive hot pressing to study the crystal structure of the solid solution by neutron diffraction

Chromoendoscopy versus autofluorescence imaging for neoplasia detection in patients with longstanding ulcerative colitis (FIND-UC): an international, multicentre, randomised controlled trial

Background: Patients with longstanding ulcerative colitis (UC) undergo regular dysplasia surveillance because of increased colorectal cancer risk. Previous studies demonstrated that autofluorescence imaging (AFI) and chromoendoscopy (CE) increased dysplasia detection. The aim of this study was to determine whether AFI should be further studied as an alternative method for dysplasia surveillance in patients with longstanding UC. Methods: In this prospective international, randomised trial, 210 patients undergoing colonoscopy surveillance for longstanding UC were randomised between 1 August 2013 and 10 March 2017 for inspection with either AFI or CE (105:105). Randomisation was minimised for a previous history of dysplasia and a previous history of primary sclerosing cholangitis. The main outcome was the relative dysplasia detection rate calculated by the ratio of AFI versus CE. This relative dysplasia detection rate was determined for the proportion of UC patients in which at least one dysplastic lesion was detected and for the mean number of dysplastic lesions per patient. The relative dysplasia detection rate needed to be above 0·67 for both outcomes to support performing a subsequent large non-inferiority trial, using an 80% confidence interval. Analysis was performed per protocol. The trial is registered at Netherlands Trial Register (NTR4062). Findings: AFI detected dysplasia in 13 (12·4%) patients, compared to 20 patients (19·1%) with CE. The relative dysplasia detection rate of CE versus AFI for the proportion of UC patients with at least one dysplastic lesion was 0·65 (80% CI; 0·43-0·99). The mean number of detected dysplastic lesions per patient was 0·13 for AFI compared to 0·37 for CE (relative dysplasia detection rate 0·36, 80% CI; 0·21-0·61). Two patients experienced an adverse event (intraprocedural mild bleeding = 1, abdominal pain = 1) in the AFI-arm and three patients (intraprocedural mild bleeding = 2, perforation = 1) in the CE-arm. Interpretation: In this randomised study comparing AFI with CE for dysplasia surveillance in patients with longstanding UC, AFI did not meet criteria for proceeding to a large non-inferiority trial. Therefore, current AFI technology should not be further investigated as an alternative dysplasia surveillance method. Funding: Olympus Europe and Olympus Keymed, Oxford and Nottingham NIHR biomedical research centres

Bone Tissue Response to Porous and Functionalized Titanium and Silica Based Coatings

Background: Topography and presence of bio-mimetic coatings are known to improve osseointegration. The objective of this study was to evaluate the bone regeneration potential of porous and osteogenic coatings. Methodology: Six-implants [Control (CTR); porous titanium coatings (T1, T2); thickened titanium (Ti) dioxide layer (TiO2); Amorphous Microporous Silica (AMS) and Bio-active Glass (BAG)] were implanted randomly in tibiae of 20-New Zealand white rabbits. The animals were sacrificed after 2 or 4 weeks. The samples were analyzed histologically and histomorphometrically. In the initial bone-free areas (bone regeneration areas (BRAs)), the bone area fraction (BAF) was evaluated in the whole cavity (500 mm, BAF-500), in the implant vicinity (100 mm, BAF-100) and further away (100–500 mm, BAF-400) from the implant. Bone-to-implant contact (BIC-BAA) was measured in the areas where the implants were installed in contact to the host bone (bone adaptation areas (BAAs)) to understand and compare the bone adaptation. Mixed models were used for statistical analysis. Principal Findings: After 2 weeks, the differences in BAF-500 for different surfaces were not significant (p.0.05). After 4 weeks, a higher BAF-500 was observed for BAG than CTR. BAF-100 for AMS was higher than BAG and BAF-400 for BAG was higher than CTR and AMS. For T1 and AMS, the bone regeneration was faster in the 100-mm compared to the 400-mm zone. BIC-BAA for AMS and BAG was lower after 4 than 2 weeks. After 4 weeks, BIC-BAA for BAG was lower than AMS and CTR. Conclusions: BAG is highly osteogenic at a distance from the implant. The porous titanium coatings didn’t stimulate bone regeneration but allowed bone growth into the pores. Although AMS didn’t stimulate higher bone response, it has a potential of faster bone growth in the vicinity compared to further away from the surface. BIC-BAA data were inconclusive to understand the bone adaptation.status: publishe