Residual stress due to curing can initiate damage in porous bone cement: experimental and theoretical evidence

Residual stress due to shrinkage of polymethylmethacrylate bone cement after polymerisation is possibly one factor capable of initiating cracks in the mantle of cemented hip replacements. No relationship between residual stress and observed cracking of cement has yet been demonstrated. To investigate if any relationship exists, a physical model has been developed which allows direct observation of damage in the cement layer on the femoral side of total hip replacement. The model contains medial and lateral cement layers between a bony surface and a metal stem; the tubular nature of the cement mantle is ignored. Five specimens were prepared and examined for cracking using manual tracing of stained cracks, observed by transmission microscopy: cracks were located and measured using image analysis. A mathematical approach for the prediction of residual stress due to shrinkage was developed which uses the thermal history of the material to predict when stress-locking occurs, and estimates subsequent thermal stress. The residual stress distribution of the cement layer in the physical model was then calculated using finite element analysis. Results show maximum tensile stresses normal to the observed crack directions, suggesting a link between residual stress and preload cracking. The residual stress predicted depends strongly on the definition of the reference temperature for stress-locking. The highest residual stresses (4-7 MPa) are predicted for shrinkage from maximum temperature, in this case, magnitudes are sufficiently high to initiate cracks when the influence of stress raisers such as pores or interdigitation at the bone/cement interface are taken into account (up to 24 MPa when calculating stress around a pore according to the method of Harrigan and Harris (J. Biomech. 24(11) (1991) 1047-1058)). We conclude that the damage accumulation failure scenario begins before weight-bearing due to cracking induced by residual stress around pores or stress raisers. (C) 2002 Elsevier Science Ltd. All rights reserved.

Preparation and characterisation of cellulose nanofibres

Two different procedures were compared for the preparation of cellulose nanofibres from flax and microcrystalline cellulose (MCC). The first involved a combination of high energy ball milling, acid hydrolysis and ultrasound, whilst the second employed a high pressure homogenisation technique, with and without various pre-treatments of the fibrous feedstock. The geometry and microstructure of the cellulose nanofibres were observed by SEM and TEM and their particle size measured using image analysis and dynamic light scattering. Aspect ratios of nanofibres made by microfluidisation were orders of magnitude greater than those achieved by acid hydrolysis. FTIR, XRD and TGA were used to characterise changes to chemical functionality, cellulose crystallinity and thermal stability resulting from the approaches used for preparing the cellulose nanofibres. Hydrolysis using sulphuric acid gave rise to esterification of the cellulose nanofibres, a decrease in crystallinity with MCC, but an increase with flax, together with an overall reduction in thermal stability. Increased shear history of flax subjected to multiple passes through the microfluidiser, raised both cellulose nanofibril crystallinity and thermal stability, the latter being strongly influenced by acid, alkaline and, most markedly, silane pretreatment.

Proteomic profiling of human retinal pigment epithelium exposed to an advanced glycation-modified substrate

Purpose The retinal pigment epithelium (RPE) and underlying Bruch’s membrane undergo significant modulation during ageing. Progressive, age-related modifications of lipids and proteins by advanced glycation end products (AGEs) at this cell–substrate interface have been implicated in RPE dysfunction and the progression to age-related macular degeneration (AMD). The pathogenic nature of these adducts in Bruch’s membrane and their influence on the overlying RPE remains unclear. This study aimed to identify alterations in RPE protein expression in cells exposed to AGE-modified basement membrane (AGE-BM), to determine how this “aged” substrate impacts RPE function and to map the localisation of identified proteins in ageing retina. Methods Confluent ARPE-19 monolayers were cultured on AGE-BM and native, non-modified BM (BM). Following 28-day incubation, the proteome was profiled using 2-dimensional gel electrophoresis (2D), densitometry and image analysis was employed to map proteins of interest that were identified by electrospray ionisation mass spectrometry (ESI MS/MS). Immunocytochemistry was employed to localise identified proteins in ARPE-19 monolayers cultured on unmodified and AGE-BM and to analyze aged human retina. Results Image analysis detected altered protein spot densities between treatment groups, and proteins of interest were identified by LC ESI MS/MS which included heat-shock proteins, cytoskeletal and metabolic regulators. Immunocytochemistry revealed deubiquitinating enzyme ubiquitin carboxyterminal hydrolase-1 (UCH-L1), which was upregulated in AGE-exposed RPE and was also localised to RPE in human retinal sections. Conclusions This study has demonstrated that AGE-modification of basement membrane alters the RPE proteome. Many proteins are changed in this ageing model, including UCHL-1, which could impact upon RPE degradative capacity. Accumulation of AGEs at Bruch”s membrane could play a significant role in age-related dysfunction of the RPE.

A novel dual-fluorescence strategy for functionally validating microRNA targets in 3-prime untranslated regions: regulation of the inward rectifier potassium channel Kir2.1 by miR-212.

Gene targeting by microRNAs is important in health and disease. We developed a functional assay for identifying microRNA targets and applied it to the K+ channel Kir2.1 (KCNJ2) which is dysregulated in cardiac and vascular disorders. The 3'UTR was inserted downstream of the mCherry red fluorescent protein coding sequence in a mammalian expression plasmid. MicroRNA sequences were inserted into the pSM30 expression vector which provides enhanced green fluorescent protein as an indicator of microRNA expression. HEK293 cells were co-transfected with the mCherry-3'UTR plasmid and a pSM30-based plasmid with a microRNA insert. The principle of the assay is that functional targeting of the 3'UTR by the microRNA results in a decrease in the red/green fluorescence intensity ratio as determined by automated image analysis. The method was validated with miR-1, a known downregulator of Kir2.1 expression, and was used to investigate targeting of the Kir2.1 3'UTR by miR-212. Red/green ratio was lower in miR-212-expressing cells compared to non-targeting controls, an effect that was attenuated by mutating the predicted target site. MiR-212 also reduced inward rectifier current and Kir2.1 protein in HeLa cells. This novel assay has several advantages over traditional luciferase-based assays including larger sample size, amenability to time course studies and adaptability to high-throughput screening.

AdaBoost Multiple Feature Selection and Combination for Face Recognition

Gabor features have been recognized as one of the most successful face representations. Encouraged by the results given by this approach, other kind of facial representations based on Steerable Gaussian first order kernels and Harris corner detector are proposed in this paper. In order to reduce the high dimensional feature space, PCA and LDA techniques are employed. Once the features have been extracted, AdaBoost learning algorithm is used to select and combine the most representative features. The experimental results on XM2VTS database show an encouraging recognition rate, showing an important improvement with respect to face descriptors only based on Gabor filters.

Dealing with non-linearity in shape modelling of articulated objects

We address the problem of non-linearity in 2D Shape modelling of a particular articulated object: the human body. This issue is partially resolved by applying a different Point Distribution Model (PDM) depending on the viewpoint. The remaining non-linearity is solved by using Gaussian Mixture Models (GMM). A dynamic-based clustering is proposed and carried out in the Pose Eigenspace. A fundamental question when clustering is to determine the optimal number of clusters. From our point of view, the main aspect to be evaluated is the mean gaussianity. This partitioning is then used to fit a GMM to each one of the view-based PDM, derived from a database of Silhouettes and Skeletons. Dynamic correspondences are then obtained between gaussian models of the 4 mixtures. Finally, we compare this approach with other two methods we previously developed to cope with non-linearity: Nearest Neighbor (NN) Classifier and Independent Component Analysis (ICA).

Rao-blackwellized particle filter for human appearance and position tracking

In human motion analysis, the joint estimation of appearance, body pose and location parameters is not always tractable due to its huge computational cost. In this paper, we propose a Rao-Blackwellized Particle Filter for addressing the problem of human pose estimation and tracking. The advantage of the proposed approach is that Rao-Blackwellization allows the state variables to be splitted into two sets, being one of them analytically calculated from the posterior probability of the remaining ones. This procedure reduces the dimensionality of the Particle Filter, thus requiring fewer particles to achieve a similar tracking performance. In this manner, location and size over the image are obtained stochastically using colour and motion clues, whereas body pose is solved analytically applying learned human Point Distribution Models.

Monitoring the performance of aerodrome ground lighting

This article provides an overview of a novel prototype device that can be used to aid airports in monitoring their landing lighting. Known as Aerodrome Ground Lighting (AGL), the device is comprised of a camera that is capable of capturing images of landing lighting as aircraft approach the airport. AGL is designed to automatically examine landing lighting to assess if it is operating under uniform brightness standards (i.e., luminous intensity of luminares) that aviation governing bodies require. A detailed discussion of the hardware and software requirements of AGL -- currently under joint development by researchers at Queens University Belfast and Cobham Flight Inspection Limited -- is presented. Results from the research indicate that assessing the performance of both ground-based runway luminaries and elevated approach luminaries is possible, though further testing is needed for full validation.

TMAX – a Database System Integrating Tissue Biomarker & Genomic Data

Background: Popular approaches in human tissue-based biomarker discovery include tissue microarrays (TMAs) and DNA Microarrays (DMAs) for protein and gene expression profiling respectively. The data generated by these analytic platforms, together with associated image, clinical and pathological data currently reside on widely different information platforms, making searching and cross-platform analysis difficult. Consequently, there is a strong need to develop a single coherent database capable of correlating all available data types.

Method: This study presents TMAX, a database system to facilitate biomarker discovery tasks. TMAX organises a variety of biomarker discovery-related data into the database. Both TMA and DMA experimental data are integrated in TMAX and connected through common DNA/protein biomarkers. Patient clinical data (including tissue pathological data), computer assisted tissue image and associated analytic data are also included in TMAX to enable the truly high throughput processing of ultra-large digital slides for both TMAs and whole slide tissue digital slides. A comprehensive web front-end was built with embedded XML parser software and predefined SQL queries to enable rapid data exchange in the form of standard XML files.

Results & Conclusion: TMAX represents one of the first attempts to integrate TMA data with public gene expression experiment data. Experiments suggest that TMAX is robust in managing large quantities of data from different sources (clinical, TMA, DMA and image analysis). Its web front-end is user friendly, easy to use, and most importantly allows the rapid and easy data exchange of biomarker discovery related data. In conclusion, TMAX is a robust biomarker discovery data repository and research tool, which opens up the opportunities for biomarker discovery and further integromics research.

Treatment of age-related subfoveal neovascular membranes by teletherapy:a pilot study

This investigation was designed to determine whether low dose radiation to the macular region could influence the natural course of age-related subfoveal neovascularisation. Nineteen patients with subfoveal membranes due to age-related macular degeneration (ARMD) were treated with 10 or 15 Gy of 6 MV photons and seven patients who declined treatment were followed up as controls. Six controls and all treated patients had completed follow up times of at least 12 months. Visual acuity was maintained or improved in 78% and 63% of treated patients at their 6 and 12 month follow up examinations respectively. By contrast visual acuity showed steady deterioration in six of seven controls. Significant neovascular membrane regression, as measured by image analysis, was recorded in 68% and 77% of treated patients at 6 and 12 months post-radiation, whereas the membranes in all seven control patients showed progressive enlargement. This study suggests that low doses of radiation can maintain central vision and induce regression of subfoveal neovascular membranes of ARMD in a significant proportion of patients. We now believe it appropriate to proceed to a prospective randomised study to test this hypothesis further.

Methods to objectify reversibility of glaucomatous cupping

Lowering intraocular pressure in adults with glaucoma may be associated with an improvement in appearance of the optic nerve head. The stage of disease, the amount of intraocular pressure reduction, and the age of the patient probably influence the occurrence of this event. The clinical relevance of 'reversal' has not been established with certainty. The reversibility of glaucomatous cupping can be detected by subjective and qualitative means (examination of the patient or of fundus photographs) or by quantitative techniques such as photogrammetry, computerized image analysis, and scanning laser tomography. Clinical and experimental studies are providing new information about the behavior of the optic nerve head tissues in response to changes in intraocular pressure.

Landfill cap models under simulated climate change precipitation::Impacts of cracks and root growth

Desiccation crack formation is a key process that needs to be understood in assessment of landfill cap performance under anticipated future climate change scenarios. The objectives of this study were to examine: (a) desiccation cracks and impacts that roots may have on their formation and resealing, and (b) their impacts on hydraulic conductivity under anticipated climate change precipitation scenarios. Visual observations, image analysis of thin sections and hydraulic conductivity tests were carried out on cores collected from two large-scale laboratory trial landfill cap models (∼80 × 80 × 90 cm) during a year of four simulated seasonal precipitation events. Extensive root growth in the topsoil increased percolation of water into the subsurface, and after droughts, roots grew deep into low-permeability layers through major cracks which impeded their resealing. At the end of 1 year, larger cracks had lost resealing ability and one single, large, vertical crack made the climate change precipitation model cap inefficient. Even though the normal precipitation model had developed desiccation cracks, its integrity was preserved better than the climate change precipitation model.

The influence of high-temperature sintering on microstructure and mechanical properties of free-standing APS CeO-YO -ZrO coatings

In this study, ceria-yttria co-stabilized zirconia (CYSZ) free-standing coatings, deposited by air plasma spraying (APS), were isothermally annealed at 1315 °C in order to explore the effect of sintering on the microstructure and the mechanical properties (i.e., hardness and Young's modulus). To this aim, coating microstructure, before and after heat treatment, was analyzed using scanning electron microscopy, and image analysis was carried out in order to estimate porosity fraction. Moreover, Vickers microindentation and depth-sensing nanoindentation tests were performed in order to study the evolution of hardness and Young's modulus as a function of annealing time. The results showed that thermal aging of CYSZ coatings leads to noticeable microstructural modifications. Indeed, the healing of finer pores, interlamellar, and intralamellar microcracks was observed. In particular, the porosity fraction decreased from ~10 to ~5% after 50 h at 1315 °C. However, the X-ray diffraction analyses revealed that high phase stability was achieved, as no phase decomposition occurred after thermal aging. In turn, both the hardness and Young's modulus increased, in particular, the increase in stiffness (with respect to "as produced" samples) was equal to ~25%, whereas the hardness increased to up to ~60%. © 2010 Springer Science+Business Media, LLC.

Processing, microstructure and mechanical properties of air plasma-sprayed ceria-yttria co-stabilized zirconia coatings

Thermal barrier coatings (TBCs) are widely adopted to protect mechanical components in gas turbine engines operating at high temperature. Basically, the surface temperature of these components must be low enough to retain material properties within acceptable bounds and to extend component life. From this standpoint, air plasma-sprayed (APS) ceria and yttria co-stabilized zirconia (CYSZ) is particularly promising because it provides enhanced thermal insulation capabilities and resistance to hot corrosion. However, essential mechanical properties, such as hardness and Young's modulus, have been less thoroughly investigated. Knowledge of Young's modulus is of concern because it has a significant effect on strain tolerance and stress level and, hence, on durability. The focus of the present study was to determine the mechanical properties of APS CYSZ coatings. In particular, X-ray diffraction (XRD) is adopted for phase analysis of powders and as-sprayed coatings. In addition, scanning electron microscopy (SEM) and image analysis (IA) are employed to explore coating microstructure and porosity. Finally, the Young's modulus of the coating is determined using nanoindentation and a resonant method. The results obtained are then discussed and a cross-check on their consistency is carried out by resorting to a micromechanical model. © 2010 Blackwell Publishing Ltd.

Control of biofilm growth through photodynamic treatments combined with chemical inhibitors: in vitro evaluation methods

The rock/atmosphere interface is inhabited by a complex microbial community including bacteria, algae and fungi. These communities are prominent biodeterioration agents and remarkably influence the status of stone monuments and buildings. Deeper comprehension of natural biodeterioration processes on stone surfaces has brought about a concept of complex microbial communities referred to as "subaerial biofilms". The practical implications of biofilm formation are that control strategies must be devised both for testing the susceptibility of the organisms within the biofilm and treating the established biofilm. Model multi-species biofilms associated with mineral surfaces that are frequently refractory to conventional treatment have been used as test targets. A combination of scanning microscopy with image analysis was applied along with traditional cultivation methods and fluorescent activity stains. Such a polyphasic approach allowed a comprehensive quantitative evaluation of the biofilm status and development. Effective treatment strategies incorporating chemical and physical agents have been demonstrated to prevent biofilm growth in vitro. Model biofilm growth on inorganic support was significantly reduced by a combination of PDT and biocides