Influence of spark plasma sintering and baghdadite powder on mechanical properties of hydroxyapatite

AbstractSince hydroxyapatite-based materials have similar composition and crystallinity as natural calcified tissues, can be used for bone/tissue engineering. In the present study a novel nanocomposite based on bioceramics such as Natural Hydroxyapatite (NHA) and Baghdadite (BAG), was sintered by spark plasma sintering (SPS) technique. The prepared composite was characterized using scanning electron microscopy (SEM), X-ray diffractometer (XRD) and Brunauer–Emmett–Teller (BET) techniques. The porosity of the samples was measured by Archimedes method. The cold crushing strength (CCS) test was applied to evaluate their mechanical properties. Our results demonstrated that NHA-30wt. %BAG nanocomposite specimens have the lower CCS in comparison with other examined composites. Consequently, NHA/BAG samples exhibited acceptable mechanical properties and could be suitable candidates for bone tissue engineering applications especially orthopaedic fields

Digital image correlation and finite element analysis applied to fiber-reinforced composites at the micro-scale

© 2015 International Committee on Composite Materials. All rights reserved. Digital image correlation (DIC) is a widely employed technique to study deformation of fiber-reinforced composites at the macro and meso-levels. It is, however, rarely applied at the micro-level although deformation analysis of the microstructure is of great interest in the field of composites. This is mainly attributed to practical difficulties related to creation of a nano-scale speckle pattern as well as the experimental set-up. The challenge is to combine DIC with SEM, where imaging involves noise, the gray intensity level of microstructure can be uniform over large areas, and it is difficult to maintain the observation window fixed during loading. The current study aims to address these challenges and enhance the methodology for real-time strain mapping of composites at the micro-scale. A large effort of the work is dedicated to deposition of a high-quality nano-scale random speckle pattern, of which the adequacy is assessed through a strain deviation analysis. The DIC parameters are optimized for the study zone. The methodology is applied to a fiber-reinforced composite loaded under transverse three-point bending inside an ESEM. The innovations in this methodology necessitate its validation against more reliable methods. For this, a finite element model of the study zone is created with boundary conditions taken from the experiment. An acceptable level of agreement was observed between experimentally measured and numerically predicted displacement/strain maps. For the studied case, DIC could correctly capture the mean strain, display the effect of microstructure heterogeneity, show the lowest strains inside fibers, and finally detect some of the strain concentrations in the matrix between fibers. Some small-scale strain concentrations e.g. those in between touching fibers, however, could not be detected. Overall, it was concluded that the methodology can be considered as a promising and dependable technique for strain mapping at the micro-scale.status: publishe

Effect of exercise and gait retraining on knee adduction moment in people with knee osteoarthritis

The knee adduction moment represents the medial knee joint load, and greater value is associated with higher load. In people with knee osteoarthritis, it is important to apply proper treatment with the least side effects to reduce knee adduction moment and, consequently, reduce medial knee joint load. This reduction may slow the progression of knee osteoarthritis. The research team performed a literature search of electronic databases. The search keywords were as follows: knee osteoarthritis, knee adduction moment, exercise program, exercise therapy, gait retraining, gait modification and knee joint loading. In total, 12 studies were selected, according to the selection criteria. Findings from previous studies illustrated that exercise and gait retraining programs could alter knee adduction moment in people with knee osteoarthritis. These treatments are noninvasive and nonpharmacological which so far have no or few side effects, as well as being low cost. The results of this review revealed that gait retraining programs were helpful in reducing the knee adduction moment. In contrast, not all the exercise programs were beneficial in reducing knee adduction moment. Future studies are needed to indicate best clinical exercise and gait retraining programs, which are most effective in reducing knee adduction moment in people with knee osteoarthritis

Detailed experimental validation and benchmarking of six models for longitudinal tensile failure of unidirectional composites

Longitudinal tensile failure of unidirectional fibre-reinforced composites remains difficult to predict accurately. The key underlying mechanism is the tensile failure of individual fibres. This paper objectively measured the relevant input data and performed a detailed experimental validation of blind predictions of six state-of-the-art models using high-resolution in-situ synchrotron radiation computed tomography (SRCT) measurements on two carbon fibre/epoxy composites. Models without major conservative assumptions regarding stress redistributions around fibre breaks significantly overpredicted failure strains and strengths, but predictions of models with at least one such assumption were in better agreement for those properties. Moreover, all models failed to predict fibre break (and cluster) development accurately, suggesting that it is vital to improve experimental methods to characterise accurately the in-situ strength distribution of fibres within the composites. As a result of detailed measurements of all required input parameters and advanced SRCT experiments, this paper establishes a benchmark for future research on longitudinal tensile failure