M.F. Vaz

Chronic arthritis leads to disturbances in the bone collagen network

IntroductionIn this study we used a mice model of chronic arthritis to evaluate if bone fragility induced by chronic inflammation is associated with an imbalance in bone turnover and also a disorganization of the bone type I collagen network.MethodsSerum, vertebrae and femur bones were collected from eight-month-old polyarthritis SKG mice and controls. Strength of the femoral bones was evaluated using three-point bending tests and density was assessed with a pycnometer. Bone turnover markers carboxy-terminal collagen cross-linking telopeptides (CTX-I) and amino-terminal propeptide of type I procollagen (PINP) were measured in serum. The organization and density of bone collagen were analyzed in vertebrae using second-harmonic generation (SHG) imaging with a two-photon microscope and trabecular bone microstructure was assessed by scanning electron microscope (SEM).ResultsFemoral bones of SKG mice revealed increased fragility expressed by deterioration of mechanical properties, namely altered stiffness (P = 0.007) and reduced strength (P = 0.006), when compared to controls. Accordingly, inter-trabecular distance and trabecular thickness as observed by SEM were reduced in SKG mice. PINP was significantly higher in arthritic mice (9.18 ± 3.21 ng/ml) when compared to controls (1.71 ± 0.53 ng/ml, P < 0.001). Bone resorption marker CTX-I was 9.67 ± 3.18 ng/ml in arthritic SKG mice compared to 6.23 ± 4.11 ng/ml in controls (P = 0.176). The forward-to-backward signal ratio measured by SHG was higher in SKG animals, reflecting disorganized matrix and loose collagen structure, compared to controls.ConclusionsWe have shown for the first time that chronic arthritis by itself impairs bone matrix architecture, probably due to disturbed bone remodeling and increased collagen turnover. This effect might predispose patients to bone fragility fractures.

Rheumatoid Arthritis Bone Fragility Is Associated With Upregulation of IL17 and DKK1 Gene Expression

Our aim was to compare bone gene expression in rheumatoid arthritis (RA) and primary osteoporosis (OP) patients. Secondary aims were to determine the association of gene expression of the Wnt/β-catenin signaling pathway with inflammatory cytokines in the bone microenvironment and to assess the serum levels of Wnt/β-catenin proteins in both groups. RA patients referred for hip replacement surgery were recruited. Primary OP patients were used as controls. Gene expression of Wnt pathway mediators, matrix proteins, and pro-inflammatory cytokines were analyzed in bone samples. Bone turnover markers, inflammatory cytokines, and Wnt mediators were measured in serum. Twenty-two patients were included: 10 with RA and 12 with primary OP. The expressions of Wnt10b (p = 0.034), its co-receptor LRP6 (p = 0.041), and its negative regulator DKK1 (p = 0.008) were upregulated in RA bone. IL17 gene expression in bone was upregulated in RA patients (p = 0.031) and correlated positively with Wnt10b (r = 0.810, p = 0.015), DKK2 (r = 0.800, p = 0.010), and RANKL/OPG ratio (r = 0.762, p = 0.028). DKK2 (p = 0.04) was significantly decreased in RA serum compared with primary OP. In conclusion, bone fragility in RA patients is induced by an unbalanced bone microenvironment and is associated with a specific gene expression pattern, namely, the upregulation of IL17 and DKK1, suggesting that the modulation of these two pathways might prevent RA systemic bone loss.

Low osteocalcin/collagen type I bone gene expression ratio is associated with hip fragility fractures

INTRODUCTION Osteocalcin (OC) is the most abundant non-collagenous bone protein and is determinant for bone mineralization. We aimed to compare OC bone expression and serum factors related to its carboxylation in hip fragility fracture and osteoarthritis patients. We also aimed to identify which of these factors were associated with worse mechanical behavior and with the hip fracture event. METHODS In this case-control study, fragility fracture patients submitted to hip replacement surgery were evaluated and compared to a group of osteoarthritis patients submitted to the same procedure. Fasting blood samples were collected to assess apolipoproteinE (apoE) levels, total OC and undercarboxylated osteocalcin (ucOC), vitamin K, LDL cholesterol, triglycerides and bone turnover markers. The frequency of the apoε4 isoform was determined. Femoral epiphyses were collected and trabecular bone cylinders drilled in order to perform compression mechanical tests. Gene expression of bone matrix components was assessed by quantitative RT-PCR analysis. RESULTS 64 patients, 25 submitted to hip replacement surgery due to fragility fracture and 39 due to osteoarthritis, were evaluated. Bone OC/collagen expression (OC/COL1A1) ratio was significantly lower in hip fracture compared to osteoarthritis patients (p<0.017) adjusted for age, gender and body mass index. Moreover, OC/COL1A1 expression ratio was associated with the hip fracture event (OR ~0; p=0.003) independently of the group assigned, or the clinical characteristics. Apoε4 isoform was more frequent in the hip fracture group (p=0.029). ucOC levels were higher in the fracture group although not significantly (p=0.058). No differences were found regarding total OC (p=0.602), apoE (p=0.467) and Vitamin K (p=0.371). In hip fracture patients, multivariate analysis, adjusted for clinical characteristics, serum factors related to OC metabolism and gene expression of bone matrix proteins showed that low OC/COL1A1 expression ratio was significantly associated with worse trabecular strength (β=0.607; p=0.013) and stiffness (β=0.693; p=0.003). No association was found between ucOC and bone mechanics. Moreover, in osteoarthritis patients, the multivariate analysis revealed that serum total OC was negatively associated with strength (β=-0.411; p=0.030) and stiffness (β=-0.487; p=0.009). CONCLUSION We demonstrated that low bone OC/COL1A1 expression ratio was an independent predictor of worse trabecular mechanical behavior and of the hip fracture event. These findings suggest that in hip fracture patients the imbalance of bone OC/COL1A1 expression ratio reflects disturbances in osteoblast activity leading to bone fragility.

Arthritis Induces Early Bone High Turnover, Structural Degradation and Mechanical Weakness

Background We have previously found in the chronic SKG mouse model of arthritis that long standing (5 and 8 months) inflammation directly leads to high collagen bone turnover, disorganization of the collagen network, disturbed bone microstructure and degradation of bone biomechanical properties. The main goal of the present work was to study the effects of the first days of the inflammatory process on the microarchitecture and mechanical properties of bone. Methods Twenty eight Wistar adjuvant-induced arthritis (AIA) rats were monitored during 22 days after disease induction for the inflammatory score, ankle perimeter and body weight. Healthy non-arthritic rats were used as controls for compar-ison. After 22 days of disease progression rats were sacrificed and bone samples were collected for histomorphometrical, energy dispersive X-ray spectroscopical analysis and 3-point bending. Blood samples were also collected for bone turnover markers. Results AIA rats had an increased bone turnover (as inferred from increased P1NP and CTX1, p = 0.0010 and p = 0.0002, respectively) and this was paralleled by a decreased mineral content (calcium p = 0.0046 and phos-phorus p = 0.0046). Histomorphometry showed a lower trabecular thickness (p = 0.0002) and bone volume (p = 0.0003) and higher trabecular sepa-ration (p = 0.0009) in the arthritic group as compared with controls. In addition, bone mechanical tests showed evidence of fragility as depicted by diminished values of yield stress and ultimate fracture point (p = 0.0061 and p = 0.0279, re-spectively) in the arthritic group. Conclusions We have shown in an AIA rat model that arthritis induc-es early bone high turnover, structural degradation, mineral loss and mechanical weak-ness.

Chronic Hyperglycemia Modulates Rat Osteoporotic Cortical Bone Microarchitecture into Less Fragile Structures

There is controversy concerning the diabetes impact on bone quality, notorious in type 2 diabetic postmenopausal women. One pointed cause might be uncontrolled glycemia. In this study, the effect of chronic hyperglycemia in bone turnover, morphology, and biomechanics was evaluated in female Wistar rats in the presence/absence of estrogens (ovariectomy). Animals (n = 28) were divided into sham, ovariectomized (OVX), hyperglycemic (streptozotocin 40 mg/kg, single-dose i.p.-STZ), and hyperglycemic-ovariectomized (STZ + OVX) animals. Blood biomarkers were estimated 60 days postovariectomy. Body weight, vertebral microarchitecture (L4-histomorphometry), femur biomechanical properties (bending tests), tibia ultrastructure (scanning electron microscopy), and femur and urinary calcium (atomic absorption) were also evaluated. The increased PINP/CTX ratio of hyperglycemic animals and the similar ratio between STZ + OVX and healthy animals contrasting with the lower ratio of OVX (in line with its histomorphometric data) suggest a tendency for improved bone formation in hyperglycemic-ovariectomized animals. The increased tibia medullar canal, which contrasts with the unaffected cortical thickness of both hyperglycemic groups while that of OVX decreased, was associated to the increased stiffness and strength of STZ + OVX bones compared to those of OVX, in line with the observed ultrastructure. Concluding, chronic hyperglycemia in ovariectomized female rats causes bone morphological changes that translate positively in the ultrastructure and mechanical properties of cortical bones.

Effect of the Strain Rate on the Twisting of Trabecular Bone from Women with Hip Fracture

As one of the major functions of bone is to provide structural support for the musculoskeletal system, it is important to evaluate its mechanical strength. Bones may be subjected to multiaxial stresses due to bone pathologies, accidental loads which may lead to hip, wrist fracture, or to a prosthetic joint replacement. Twist loading may lead to fractures, especially involving long bones from lower limbs. The aim of this work was to study the effect of the strain rate on the shear properties of trabecular bone samples from women with hip fracture (from 65 to 100 years). Cylindrical samples were core drilled from human femoral heads along the primary trabecular direction. The cylinders ends were polished and embedded in blocks of polymeric material which fit the grips of the testing device. Deformation rates of 0.005, 0.01, 0.015, and 0.05 s⁻¹ were applied. Twisting tests were conducted with or without an applied axial load of 500 N. From the torque-angular displacement curves, the shear stress-strain curves were obtained. The maximum shear strength and the shear modulus (i.e. the slope of the linear region) were determined. A large scatter of the results of the shear strength and the shear modulus was found, which is probably related to the heterogeneity of nonhealthy human bone samples. There is no significant effect of the strain rate on the maximum shear stress and the shear modulus, either in tests undertaken with or without the application of an axial load. The effect of strain rate on nonhealthy bone trabecular twisting properties did not follow the trend observed on the effect of strain rate in healthy bone, where an increase is detected.

Effect of the Conservation Treatment of Historical Ceramic Tiles on the Tensile Adhesion Strength

The present work describes some preliminary results of a first attempt to study the effect of a conservation treatment on the adhesion strength of ancient ceramic tiles. Several tiles from the 16th through 20th centuries were submitted to a conservation treatment. The treatment involves the impregnation with Paraloid B-72 using a protocol widely used in most museum restoration departments. Treated and untreated tiles were attached to a brick surface with a bonding mortar. After 3 months, pull-off tests were performed in treated and untreated samples and the tensile adhesion strength was determined. Although a small number of samples was analyzed, the adhesion strength was found to increase for treated tiles in comparison with the pull-off strength of untreated samples.

Quadruple Semitendinosus Graft Construct With Double Cortical Suspensory Fixation for Anterior Cruciate Ligament Reconstruction: A Biomechanical Study

The purpose of this study was to evaluate the biomechanical properties of a graft construct with quadrupled Semitendinosus and two cortical buttons with adjustable loops concerning elongation, stiffness and resistance. A total of 15 fresh human cadaveric semitendinosus tendons were quadrupled over the two adjustable loops and stitched at the tibial tip with a cerclage type suture. They underwent pre-tensioning at 300 N for 2 minutes followed by cyclic loading (1000 cycles between 50–250 N) and finally a load-to-failure test. Statistical analysis was performed using SPSS Statistics software and groups were compared using a paired t-test, with a significance level set at α = 0.05. Graft construct elongation after pre-tensioning at 300 N was 12.8 mm (9.3 mm–16.5 mm) and mean cyclic elongation 0.4 mm (0.2 mm–0.9 mm), considered significant (p < 0,001). The resistance and stiffness values were respectively 849.46 N (649.30 N-1027.90 N) and 221.49 N (178,30 N – 276.10 N). Quadruple ST graft construct using two cortical buttons and adjustable loops showed a high stiffness and resistance with a very low elongation after cycling.

Study of the influence of 3D printing parameters on the mechanical properties of PLA

This paper aims to determine the influence of 3D printing parameters, such as Infill Density, Extrusion Temperature, Raster Angle and Layer Thickness, on mechanical properties, namely Ultimate Tensile Strength, Yield Strength, Modulus of Elasticity and Elongation at Break, in the case of polylactic acid (PLA), after it goes through the manufacturing process. Another objective is to study water absorption by the PLA, with a goal to minimize it by means of a coating agent. The influence of each printing parameter on each mechanical property is evaluated by using analysis of variance (ANOVA).

Mechanical properties and water absorption of surface modified ABS 3D printed by fused deposition modelling

Purpose The purpose of this paper is to investigate the effect of a sealing protective treatment on the water absorption and mechanical properties of acrylonitrile butadiene styrene (ABS)-printed parts by fused deposition modelling. Protective products include aqueous acetone solutions with different concentrations, polyurethane wood sealer and aqueous acrylic-based varnish. Design/methodology/approach Open porosity was estimated by the absorption coefficient and the total amount of water retained, obtained from water absorption tests. Mechanical characterization was performed by compressive and tensile tests. Different specimens with different build directions and raster angles were used. Findings The treatments with acetone solutions were not effective in reducing the porosity of ABS parts, as the amount of acetone that reduces effectively the porosity will also affect the sample dimensional stability. The polyurethane treatment was found to reduce the absorption coefficient, but the maximum water content and the open porosity remain almost unchanged in comparison with the ones obtained for untreated specimens. The treatment with an acrylic-based varnish was found to preserve the dimensional stability of the specimens, to reduce the open porosity and to maintain the compression and tension properties of the specimens in different build directions and raster angles. Originality/value Surface modification for water tight applications of ABS 3D printing parts enables new designs where both sealing and the preservation of mechanical properties are important. As per the knowledge of the authors, the water absorption and the mechanical behaviour of ABS 3D printed parts, before and after treatment, were not previously investigated.