effect of porosity and cell topology on elastic plastic behavior of cellular structures

Abstract In this work we study the mechanical behavior of Ti6Al4V cellular structures by varying the randomness in the cell topology from regular cubic to completely random and the porosity of the structure. The porosity of the structure is altered by changing the strut thickness and the pore size to obtain a stiffness value between 0.5-12Gpa. The geometrical deviation in the structures from the as-designed values is studied by morphological characterization. The samples are subjected to compression and tensile loading to obtain the stiffness and the elastic-plastic behavior of the samples. Finite element modelling (FEM) is carried out on the as-designed structures for both tensile and compressive loading to study the effect of deviation between the as-designed and as-built structures. FEM is also carried out for as-built regular structures, by introducing the geometrical deviation to match the porosity of the as-built structures. Comparison of FEM and experimental results indicated that the effect of cell topology depends on the porosity values. Simulation results of as-built structures demonstrated the importance of defects in the structure

Tensile and compression properties of variously arranged porous Ti-6Al-4V additively manufactured structures via SLM

Abstract Additively manufactured porous structures find increasing applications in the biomedical context to produce orthopedic prosthesis and devices. In comparison with traditional bulk metallic implants, they permit to tailor the stiffness of the prosthesis to that of the surrounding bony tissues, thus limiting the onset of stress shielding and resulting implant loosening, and to favor the bone in-growth through the interconnected pores. Mechanical and biological properties of these structures are strongly influenced by the size and spatial arrangement of pores and struts. In the present work irregular and regular cellular as well as fully random porous structures are investigated through tensile and compression uniaxial tests. Specific point of novelty of this work is that, beside classical compressive tests, which are standard characterization methods for porous/ cellular materials, tensile tests are carried out. Mechanical tests are complemented with morphological analysis and porosity measurements. An attempt is made to find correlations between cell arrangements, porosity and mechanical properties

Anticipatory Corticosteroid Administration to Asymptomatic Women with a Short Cervix.

OBJECTIVE:  A short cervix is an important risk factor for spontaneous preterm birth. There is substantial evidence that antenatal exposure to corticosteroids significantly benefits infants that are born when delivery occurs between 24 and 34 weeks\u27 gestation and after 48 hours but within 7 days of their administration. Our study was to evaluate whether asymptomatic women who are given a course of antenatal corticosteroids (ACS) at the time a short cervix is identified deliver within the window of proven steroid benefit. STUDY DESIGN:  This was a retrospective chart review of patients who had a cervical length of \u3c 2.5 cm between 23 and 34 weeks and who did not have cervical dilation or significant symptoms of preterm labor. RESULTS:  Of 367 asymptomatic patients with a short cervix, only two (0.5%) delivered within 7 days of the time a short cervix was identified. With a policy of giving ACS at the time an ultrasound shows a short cervix, 184 patients would have to be treated for each one who realizes a steroid benefit by delivering within 7 days. CONCLUSION:  We conclude that unless future studies show that neonates benefit from ACS given more than 7 days before delivery, giving ACS to asymptomatic women solely because the cervix is short is not advised

Efficient optimization framework for L-PBF fatigue enhanced Ti6Al4V lattice component

Industries today face challenges in incorporating metallic additively manufactured lattice structures in critical components subjected to fatigue loading. This work explores the relationship between fatigue properties and the printing orientation of Laser-Powered Bed Fusion (LPBF) lattice structures. This relation is at the base of a cost-effective and time-efficient optimization workflow able to determine the optimal lattice printing orientation for improved fatigue life. Fatigue resistance is tested under uniaxial conditions on miniaturized specimens that mimic the lattice sub-unit elements: struts and nodes. The collected data is used as input for the optimization algorithm to determine the specimen orientation that maximizes fatigue life. The optimized specimens are manufactured, tested under three-point-bending conditions, and analysed using metrological x-ray computed tomography to verify the improvement. The proposed workflow is able to produce a 24 % increase in specimen fatigue life by simply adjusting the orientation on the printing plane

Comparative metrological characterization of Ti6Al4V lattice structures produced by laser powder bed fusion

The advancement of Additive Manufacturing (AM) technologies, such as Laser Powder Bed Fusion (LPBF), enables the fabrication of metallic lattice materials with a wide range of topologies and size scales. The possibility to manufacture these materials into complex shapes with good property-to-weight ratio stimulates a growing interest in several industrial sectors, including biomedical, aerospace, and automotive. Nevertheless, such structural features printed at a small-scale often suffer from a wide range of morphological defects that can lead to a marked deviation from the nominal geometry and consequently impact the mechanical, transport and thermal properties. An accurate metrological characterization of the lattice is thus of paramount importance for a more reliable prediction of the properties of the lattice. The most common characterization techniques used for as-built lattice materials are scanning electron microscopy (SEM), optical microscopy (OM) and X-ray computed tomography (CT). CT, contrary to the other methods, provides full 3D data including inaccessible geometries and features, in a non-destructive way, but it requires expensive equipment and considerable expertise. SEM and OM can be faster and less expensive, but can be non-destructive only when limited to the outer surface of the lattice. When combined with metallographic analysis, instead, they require destructive, careful and time-consuming specimen preparation, and the analysis is confined to selected sections. In this work, the three above-mentioned techniques are applied to the metrological characterization of LBPF Ti6Al4V regular cubic lattices of 4 mm unit cell size and struts with circular cross-section of diameter 0.760 mm. The results in terms of strut cross-section parameters and junction fillet radius are compared and the effect of the size of the analysis domain on the accuracy of the results is investigated by comparing lattice sub-volumes of different size. Via a thorough statistical analysis it is shown that CT and metallographic characterization are compatible, while microscope imaging can lead to an overestimation of the strut thickness

Proton tree-dimensional radiotherapy and radiosurgery of intracranial targets at the Dubna.

Proton tree-dimensional radiotherapy and radiosurgery of intracranial targets at the Dubna. S.V. Shvidkij, A.V. Agapov, A.V. Iglin, Ye.I. Luchin, G.V. Mytsin, A.G. Molokanov, K.N Shipulin Joint Institute for Nuclear Research, 141980, Dubna, Russia Stereotactic radiosurgery with the usage of different kinds of radiation has been of great importance in the treatment of non-operating arteriovenous malformation (AVM) of the brain for the last three decades. Proton beams have unique physical properties that are favorable for stereotactic radiosurgery or conformal radiation therapy: small lateral divergence, sharp lateral penumbra, final and easy controlled range in tissue, depending of beam energy and tissue density, increasing of dose deposition at the end of range, so called Bragg peak. Modern and up-to-date technology of three-dimensional proton radiosurgery AVM of the brain which allows irradiating accurately AVM of the brain of any size, shape and location, was worked out and clinically approved in Medical Technical Complex after 2001 year. International report was used for the treatment of patients, according to it the target of irradiation was included into 70-80% isodose. The absorbed doses made 25 Gy-equivalent in the isocenter point (1 Grey-equivalent equals 1 Gy physical, multiplied by the relative biological effectiveness of the proton, which is 1.1). Irradiation treatment was conducted within 2 session for the two successive days. Proton radiosurgery based on this new technology was conducted on 39 patients suffering from AVM of the brain. The volume of the targets of irradiation was from 1.5 to 82.1 cm3 . Early result demonstrated that developed technique of proton irradiation allows to deliver proton dose to the target volume precisely

Cyclooxygenase-2 inhibitors prevent the development of chemoresistance phenotype in a breast cancer cell line by inhibiting glycoprotein p-170 expression.

Breast cancer cells are usually sensitive to several chemotherapeutic regimens, but they can develop chemoresistance after prolonged exposure to cytotoxic drugs, acquiring a more aggressive phenotype. Drug resistance might involve the multi-drug resistance (MDR) 1 gene, encoding a transmembrane glycoprotein p-170 (P-gp), which antagonizes intracellular accumulation of cytotoxic agents, such as doxorubicin. We previously demonstrated that type 2 cyclooxygenase (COX-2) inhibitors can reverse the chemoresistance phenotype of a medullary thyroid carcinoma cell line by inhibiting P-gp expression and function. The aim of our study was to investigate the role of COX-2 inhibitors in modulating chemoresistance in a human breast cancer cell line, MCF7. MCF7 cells, expressing COX-2 but not MDR1, were treated with increasing doses of doxorubicin, and they became chemoresistant after 10 days of treatment, in association with MDR1 expression induction. This effect was reversed by doxorubicin withdrawal and prevented by co-incubation with N-[2-(cyclohexyloxy)4-nitrophenyl]-methanesulfonamide (NS-398), a selective COX-2 inhibitor. Treatment with NS-398 alone did not influence cell viability of a resistant MCF7 cell clone (rMCF7), but sensitized rMCF7 cells to the cytotoxic effects of doxorubicin. Moreover, treatment with NS-398 significantly reduced MDR1 expression in rMCF7 cells. Doxorubicin-induced membrane P-gp expression and function was also greatly impaired. Our data therefore support the hypothesis that COX-2 inhibitors can prevent or reduce the development of the chemoresistance phenotype in breast cancer cells by inhibiting P-gp expression and function