Probing the Cr3+ luminescence sensitization in ß-Ga2O3 with ion-beam-induced luminescence and thermoluminescence.

Ion-beam-induced luminescence (IBIL) measurements were performed in Cr-doped ß-Ga2O3 using both protons and helium ions, showing a strong enhancement of the Cr3+ luminescence upon ion irradiation. Theoretical modelling of the IBIL intensity curves as a function of the fluence allowed estimating the effective cross-sections associated with the defect-induced IBIL enhancement and quenching processes. The results suggest that sensitizing the Cr3+ luminescence is more efficient for H+ than for He+ irradiation. Thermoluminescence (TL) studies were performed in the pristine sample, with no TL signal being observed in the spectral region corresponding to the Cr3+ emission. In agreement with the IBIL study, upon ion irradiation (with either protons or helium ions), this TL emission is activated. Moreover, it can be quenched by annealing at 923 K for 10 s, thus revealing the role played by the defects induced by the irradiation. These results show that the irradiation-induced defects play a major role in the activation of the Cr3+ luminescence, a fact that can be exploited for radiation sensing and dosimetry.

Fracture characterization of human cortical bone under mode II loading using the end-notched flexure test.

Fracture characterization of human cortical bone under mode II loading was analyzed using a miniaturized version of the end-notched flexure test. A data reduction scheme based on crack equivalent concept was employed to overcome uncertainties on crack length monitoring during the test. The crack tip shear displacement was experimentally measured using digital image correlation technique to determine the cohesive law that mimics bone fracture behavior under mode II loading. The developed procedure was validated by finite element analysis using cohesive zone modeling considering a trapezoidal with bilinear softening relationship. Experimental load-displacement curves, resistance curves and crack tip shear displacement versus applied displacement were used to validate the numerical procedure. The excellent agreement observed between the numerical and experimental results reveals the appropriateness of the proposed test and procedure to characterize human cortical bone fracture under mode II loading. The proposed methodology can be viewed as a novel valuable tool to be used in parametric and methodical clinical studies regarding features (e.g., age, diseases, drugs) influencing bone shear fracture under mode II loading.

Mixed-mode I+II fracture characterization of human cortical bone using the Single Leg Bending test.

Mixed-mode I+II fracture characterization of human cortical bone was analyzed in this work. A miniaturized version of the Single Leg Bending test (SLB) was used owing to its simplicity. A power law criterion was verified to accurately describe the material fracture envelop under mixed-mode I+II loading. The crack tip opening displacements measured by digital image correlation were used in a direct method to determine the cohesive law mimicking fracture behavior of cortical bone. Cohesive zone modeling was used for the sake of validation. Several fracture quantities were compared with the experimental results and the good agreement observed proves the appropriateness of the proposed procedure for fracture characterization of human bone under mixed-mode I+II loading.

Bone fracture characterization under mixed-mode I+II loading using the single leg bending test.

Fracture under mixed-mode I+II was induced in bovine cortical bone tissue using a developed miniaturized version of the single leg bending test (SLB). Due to the difficulty in crack length monitoring in the course of the test, an equivalent crack method based on specimen compliance and beam theory was adopted as a data reduction scheme. The method was applied to the experimental results in order to obtain the Resistance curves in each loading mode. The determined fracture energy is well described by an energetic power law whose exponent is below one, which means that the linear energetic criterion is not applicable to this material. The proposed procedure was numerically validated by means of a cohesive mixed-mode I+II damage model with bilinear softening. It was concluded that the miniaturized version of the SLB test is adequate for mixed-mode I+II fracture characterization of bone for a constant mode ratio.

Bone fracture characterization using the end notched flexure test.

A miniaturized version of the end notch flexure test was used in the context of pure mode II fracture characterization of bovine cortical bone. To overcome the difficulties intrinsic to crack length monitoring during its propagation an equivalent crack method was employed as data reduction scheme. The proposed method was validated numerically by means of a finite element analysis including a cohesive zone modeling and subsequently applied to experimental results to determine the fracture energy of bone under pure mode II loading. Finally, a cohesive law representative of fracture behavior of each specimen was determined employing an inverse method, considering a trapezoidal shape for the softening law. The consistency of the obtained results leads to the conclusion that the trapezoidal law is adequate to simulate fracture behavior of bone under mode II loading. The proposed testing setup and the employed data reduction scheme constitute powerful tools in which concerns fracture characterization of bone under pure mode II loading and can be viewed as the main outcomes of this work.

Fracture characterization of bone under mode II loading using the end loaded split test.

Fracture energy release rate under mode II loading of bovine cortical bone is determined using a miniaturized testing device of the end loaded split test. The energy release rate is evaluated by means of a data reduction scheme based on specimen compliance, beam theory and crack equivalent concept. Experimental tests were carried out to evaluate the Resistance curve which provides a successful method to characterize fracture behavior of quasi-brittle materials like bone. A numerical analysis including a cohesive damage model was used to validate the procedure. It was demonstrated that the end loaded split test and proposed data reduction scheme provide a valuable solution for mode II fracture characterization of bone.

The double cantilever beam test applied to mode I fracture characterization of cortical bone tissue.

The primary objective of this work was to analyse the adequacy of the Double Cantilever Beam (DCB) test in determining fracture toughness under pure mode I loading of cortical bone tissue. A new data reduction scheme based on specimen compliance and the crack equivalent concept was used to overcome the difficulties inherent in crack monitoring during its growth. It provides a complete resistance curve, which is fundamental in estimating the fracture energy. A cohesive zone model was used to simulate damage initiation and propagation, thus assessing the efficacy of the proposed testing method and data reduction scheme. Subsequently, the DCB test was applied to evaluate the mode I fracture energy of hydrated and thermally dehydrated cortical bone tissue from young bovine femur, in the tangential-longitudinal propagation system. The results obtained demonstrate the efficacy of the DCB test and the proposed data reduction scheme on the bone fracture characterization under mode I loading.

Modified model of sub-critical size cranial defect in the rabbit / Modelo modificado de defecto craneal de tamaño subcrítico de conejo

In medical sciences, any experimental animal model should be reproducible and adequate to the purpose of simulated human physiological response. In bone injury response research, when bone substitutes are in use, it is of primary importance that studied defects fail to heal unless treated with the tissue engineering therapy under study. This failure defines the concept of "critical size defect" (CSD) wich has different limits according to the animal species used and the location of the defect. Although this is a basic concept, when the aim of the study is to investigate the interface Bone-Biomaterial, it is of primary importance to obtain as much contact area as possible. In order to do so, we propose a modified surgical approach to the classical bi-parietal round sub-critical defect model in rabbit vault.

En las ciencias médicas, cualquier modelo animal de experimentación debe ser reproducible y ajustado al propósito de simular la respuesta fisiológica humana. En la investigación de la respuesta a la lesión ósea, cuando son utilizados sustitutos óseos, es de gran importancia el estudio de defectos que no logran sanar, a menos que sean tratados con terapia de ingeniería de tejidos. Este fracaso define el concepto de "defecto de tamaño crítico" (CDS) el cual tiene límites diferentes según la especie animal utilizada y la ubicación del defecto. Aunque se trata de un concepto básico, cuando el objetivo del estudio es investigar la interfaz hueso-biomaterial, es de primordial importancia obtener la máxima superficie de contacto que sea posible. Para ello, se propone una modificación en el enfoque quirúrgico del modelo clásico de defecto de tamaño subcrítico biparietal en la bóveda de conejo.

Evaluation of microbiological quality of medicinal plants used in natural infusions.

Consumption of preparations of medicinal plants has been increasing during the last decades in occidental societies. However, there are no effective sanitary controls of these products. To evaluate the nature and content of microbiological contamination, 62 samples of seven medicinal plants (chamomile, leaves of orange tree, flowers of linden, corn silk, marine alga, pennyroyal mint and garden sage) were studied, using conventional microbiological methods. Practically all samples (96.8%) were contaminated with Bacillus cereus; 19.2% of them with levels higher than 10(3) spores/g. The highest levels were found in corn silk samples (> 10(7) spores/g). Spores of Clostridium perfringens were detected in 83.9% of samples, but only 19.2% had levels greater than 10(3)/g. The mean level of fungal population was 10(5.5) cfu/g. Corn silk samples were the most contaminated, with levels above 10(6) cfu/g. Fusarium spp., Penicillium spp., Aspergillus flavus and Asp. niger were predominant in all samples with the exception of garden sage samples. Many yeasts were found in chamomile, flowers of linden, corn silk, pennyroyal mint and garden sage. Predominant species were Cryptococcus laurentii (28.1%) and Rhodotorula mucilaginosa (22.8%). The mean level of Crypt. laurentii contamination in corn silk was greater than 10(4) cfu/g.