AN INVESTIGATION INTO SURFACE FINISH IMPROVEMENT OF SMALL PLASTIC PARTS MANUFACTURED THROUGH ADDITIVE MANUFACTURING

Published ThesisNowadays, Additive Manufacturing (AM), also known as 3D printing finds wide application in automotive, aerospace and medical fields. Functional additive manufactured parts must satisfy dimensional accuracy as well as to provide an acceptable quality of surface finish. However the dimensional accuracy of additive manufactured parts are affected by many process variables including accuracy of tessellation from Computer Aided Design (CAD) model, slicing algorithm, data transfer, device motion resolution, powder granulometry, beam offset, process parameters and shrinkage. The surface finish of additive manufactured parts is often poor due to the layer-by-layer manufacturing process of AM. The degree of this so called “stairstepping” is dependent on the type of AM process and layer thickness used. Different post processing techniques can be used to improve the surface finish. Six post processing techniques were investigated in this study to improve the surface finish of small test pieces that were additive manufactured in nylon polyamide, Alumide® and Acrylonitrile Butadiene Styrene (ABS) plastic materials. The techniques include tumbling, shot peening, Computer Numerical Control (CNC) machining, spray painting, undercoat and hand finishing and chemical treatment by dissolving the surface of the test pieces. A Laser Sintering (LS) process was used to manufacture the nylon polyamide and Alumide® test pieces while Fused Deposition Modelling (FDM) was used for the ABS test pieces. A Coordinate Measuring Machine (CMM) also known as Touch probe scan machine was used for assessment of the dimensional accuracy of post processed test pieces compared to the geometry of the “as built” test pieces. The Chisquare test ( 2 ) and the test for differences in deviation range proportions were used to establish the level of significance of differences between ‘“as built” and each post processing technique. It was shown that there exists a significant difference between deviation range proportions as one compares the “as built” to any one of the six considered post processing techniques. For all the three investigated materials, hand finishing technique produced the best improvement of surface finish though this technique was generally characterized by a lack of consistency in distribution of uniform deviation ranges across individual surfaces as well as across entire test pieces. The spray painting improved the surface finish and was found to be consistent in distribution of uniform deviation ranges across individual surfaces as well as across entire test pieces. However this technique led to significant positive deviation ranges from the geometry of the “as built” test piece, thus affecting negatively the dimensional accuracy of the “as built” test piece. On one hand, despite the rounding of the sharp corners and the removal of small protrusions, tumbling and shot peening techniques, without affecting negatively the dimensional accuracy of the test piece, it was found that tumbling and shot peening are the optimal post processing techniques to improve the surface finish of relatively wide surfaces of Laser Sintered nylon and Alumide® test pieces. On the other hand, it was realized that tumbling or shot peening technique should not be applied to ABS test pieces as, in addition to the negative effects of the two techniques on nylon and Alumide® test pieces, tumbling and shot peening damage heavily the surfaces of ABS pieces. Chemical treatment by immersion into acetone bath was found to be the optimal technique for improvement of the surface finish of Fused Deposition Modelled ABS test pieces. Though through CNC machining the surface finish of nylon, Alumide® and ABS test pieces was improved, a relatively high standard deviation in surface finish across the entire test piece was observed. In addition to this, excessive negative deviation ranges were observed on the machined surfaces. This can be attributed to a single error during the calibration of the machine or the setting of the cutting parameters which led to the excessive negative deviation ranges from the geometry of the “as built” test piece. The consideration of individual cutting parameters for each surface inclination angle would reduce the standard deviation and eliminate the risk of excessive negative deviation ranges across the entire test piece. However, this approach would lead to excessive machining time, thus increasing the cost of the process. Finally, it was realized that CNC machining is not an appropriate technique to improve the surface finish of small plastic parts with complex shapes in the form of various inclination angles and small entities such as small conical features, round cavities and protrusions

State of the art of Additive Manufacturing for polymeric medical implants

Published Conference ProceedingsAdditive Manufacturing (AM) commonly known as 3D printing has found many applications in the automotive, aerospace and medical industries. The flexibility to fabricate 3D objects of any complexity displayed by AM technologies such as Selective Laser Sintering (SLS), Stereolithography (SLA), Fused Deposition Modeling (FDM), PolyJet printing and electrospinning, has been used to improve the lives of many patients through the provision of polymeric implants, scaffolds and devices for drug delivery. The common limitation of such applications is the biocompatibility of the AM material with the human body and systems. An ideal non degradable implant would not invoke an inflammatory or toxic response whereas for a degradable implant, the degradants must also be metabolized in the body after fulfilling its purpose, thus leaving no trace. Furthermore, inertness, weight similar to human bone or even lighter, capability to generate no artifacts on Computer Tomography (CT) and Magnetic Resonance Imaging (MRI) scans, sufficient strength to resist functional stresses for load bearing implants, low and no thermal conductivity, easy sterilization and low cost of manufacturing are the desired characteristics for the acceptance of the use of an implant in a human body. Metallic and ceramic implants have been extensively used for medical implants. However the possible need for a second surgery to remove metallic implants, the stress shielding effect, the radio-opacity of the metal and long-term presence of metallic ions in vivo are major disadvantages of metallic implants which can be overcome by the use of their counterparts manufactured from polymeric materials. Building on the already established AM powder based technologies; a transition from micro to nanosized powder particles to improve the mechanical properties of SLS polymeric implants is a new trend of development. The optimum ratio of Hydroxyapatite (HA) to polymer composites and the establishment of measuring standards to meet the requirement of a medical implant are the actual challenges of AM for polymeric medical implants

Silencing of Mg-pat-10 and Mg-unc-87 in the plant parasitic nematode Meloidogyne graminicola using siRNAs

Until recently, the standard method for RNA interference (RNAi)-based reverse genetics in plant parasitic nematodes (PPNs) was based on the use of long double-stranded RNA (dsRNA). This increased the chance of off-target gene silencing through interactions between different short interfering RNAs (siRNAs) and non-cognate mRNA targets. In this work, we applied gene-specific knockdown of Mg-pat-10 and Mg-unc-87 of the root knot nematode Meloidogyne graminicola, using discrete 21 bp siRNAs. The homologue of Mg-pat-10 in C. elegans encodes body wall troponin C, which is essential for muscle contraction, whereas the homologue of Mg-unc-87 encodes two proteins involved in maintenance of the structure of myofilaments in the body wall muscle of C. elegans. The knockdown at the transcript level, as seen by semi-quantitative RT-PCR analysis, indicates that the Mg-pat-10 gene was silenced after soaking the nematodes in a specific siRNA for 48 h. At 72 h post-soaking, the Mg-pat-10 mRNA level was similar to the control, indicating the recovery of expression between 48 h and 72 h post-soaking. For Mg-unc-87 the nematodes started to recover from siRNA silencing 24 h after thorough washing. A migration assay showed that for the nematodes that were soaked in the control (siRNA of β-1,4-endoglucanase), 77% of the nematodes completed migration through the column in a 12 h period. By comparison with the control, nematodes incubated in the siRNA of pat-10 or unc-87 were significantly inhibited in their motility. After 12 h, only 6.3% of the juveniles incubated in the Mg-pat-10 siRNA and 9.3% of those incubated in Mg-unc-87 siRNA had migrated through the column, representing 91.8% and 87.9% inhibition respectively compared to the control. In the present work, we demonstrated that M. graminicola is readily susceptible to siRNAs of two genes involved in nematode motility. This is an important contribution to the progressive use of siRNA for functional analysis. Moreover, the application of RNAi in PPNs opens the way for environmentally friendly control of M. graminicola

Effects of hospital facilities on patient outcomes after cancer surgery: an international, prospective, observational study

Background Early death after cancer surgery is higher in low-income and middle-income countries (LMICs) compared with in high-income countries, yet the impact of facility characteristics on early postoperative outcomes is unknown. The aim of this study was to examine the association between hospital infrastructure, resource availability, and processes on early outcomes after cancer surgery worldwide.Methods A multimethods analysis was performed as part of the GlobalSurg 3 study-a multicentre, international, prospective cohort study of patients who had surgery for breast, colorectal, or gastric cancer. The primary outcomes were 30-day mortality and 30-day major complication rates. Potentially beneficial hospital facilities were identified by variable selection to select those associated with 30-day mortality. Adjusted outcomes were determined using generalised estimating equations to account for patient characteristics and country-income group, with population stratification by hospital.Findings Between April 1, 2018, and April 23, 2019, facility-level data were collected for 9685 patients across 238 hospitals in 66 countries (91 hospitals in 20 high-income countries; 57 hospitals in 19 upper-middle-income countries; and 90 hospitals in 27 low-income to lower-middle-income countries). The availability of five hospital facilities was inversely associated with mortality: ultrasound, CT scanner, critical care unit, opioid analgesia, and oncologist. After adjustment for case-mix and country income group, hospitals with three or fewer of these facilities (62 hospitals, 1294 patients) had higher mortality compared with those with four or five (adjusted odds ratio [OR] 3.85 [95% CI 2.58-5.75]; p<0.0001), with excess mortality predominantly explained by a limited capacity to rescue following the development of major complications (63.0% vs 82.7%; OR 0.35 [0.23-0.53]; p<0.0001). Across LMICs, improvements in hospital facilities would prevent one to three deaths for every 100 patients undergoing surgery for cancer.Interpretation Hospitals with higher levels of infrastructure and resources have better outcomes after cancer surgery, independent of country income. Without urgent strengthening of hospital infrastructure and resources, the reductions in cancer-associated mortality associated with improved access will not be realised

Socializing One Health: an innovative strategy to investigate social and behavioral risks of emerging viral threats

In an effort to strengthen global capacity to prevent, detect, and control infectious diseases in animals and people, the United States Agency for International Development’s (USAID) Emerging Pandemic Threats (EPT) PREDICT project funded development of regional, national, and local One Health capacities for early disease detection, rapid response, disease control, and risk reduction. From the outset, the EPT approach was inclusive of social science research methods designed to understand the contexts and behaviors of communities living and working at human-animal-environment interfaces considered high-risk for virus emergence. Using qualitative and quantitative approaches, PREDICT behavioral research aimed to identify and assess a range of socio-cultural behaviors that could be influential in zoonotic disease emergence, amplification, and transmission. This broad approach to behavioral risk characterization enabled us to identify and characterize human activities that could be linked to the transmission dynamics of new and emerging viruses. This paper provides a discussion of implementation of a social science approach within a zoonotic surveillance framework. We conducted in-depth ethnographic interviews and focus groups to better understand the individual- and community-level knowledge, attitudes, and practices that potentially put participants at risk for zoonotic disease transmission from the animals they live and work with, across 6 interface domains. When we asked highly-exposed individuals (ie. bushmeat hunters, wildlife or guano farmers) about the risk they perceived in their occupational activities, most did not perceive it to be risky, whether because it was normalized by years (or generations) of doing such an activity, or due to lack of information about potential risks. Integrating the social sciences allows investigations of the specific human activities that are hypothesized to drive disease emergence, amplification, and transmission, in order to better substantiate behavioral disease drivers, along with the social dimensions of infection and transmission dynamics. Understanding these dynamics is critical to achieving health security--the protection from threats to health-- which requires investments in both collective and individual health security. Involving behavioral sciences into zoonotic disease surveillance allowed us to push toward fuller community integration and engagement and toward dialogue and implementation of recommendations for disease prevention and improved health security

Au cœur des identités culturelles : lecture croisée d’un conte de Birago Diop et d’une fable de La Fontaine

Nsengimana Joseph. Au cœur des identités culturelles : lecture croisée d’un conte de Birago Diop et d’une fable de La Fontaine. In: Le Fablier. Revue des Amis de Jean de La Fontaine, n°4, 1992. Actes de la journée : La Fontaine en Sorbonne (1er février 1992) pp. 43-47

Investigating the effect of process parameters on the degree of fusion of two adjacent tracks produced through fused deposition modelling of acrylonitrile butadiene styrene

This study was conducted to investigate the effects of different process parameters on the degree of fusion of two adjacent tracks produced by fused deposition modelling of acrylonitrile butadiene styrene. Incorrectly defined process parameters adversely influence the geometrical accuracy, surface roughness, and mechanical properties of the printed parts. Therefore, numerous studies have been conducted to this effect, but few investigations have focused on the defects of tracks, monolayers, double, or few layers despite significantly influencing the shape of the entire component and causing other printing defects. In this respect, the current study assesses the fusion of two adjacent tracks when printed using different key process parameters (layer thickness, infill density, printing speed, air gap, and extrusion temperature). The printed adjacent double track parts were examined using a scanning electron microscope and their degree of fusion calculated as a ratio of the height of the neck (h) and diameter of adjacent double tracks (d) after fusion and cooling. It was concluded that the highest degree of fusion of two adjacent tracks of acrylonitrile butadiene styrene material was obtained at 0.25 mm, 40 mm/s, −0.10 mm, and 255 °C layer thickness, printing speed, air gap, and extrusion temperature, respectively

DECLARATION DU COMITE EXECUTIF DU CONSEIL DE CONCERTATION DES ORGANISATIONS D'APPUI AUX INIATIVES DE BASE "CCOAIB"

UT Librarie

Global variation in postoperative mortality and complications after cancer surgery: a multicentre, prospective cohort study in 82 countries

Background: 80% of individuals with cancer will require a surgical procedure, yet little comparative data exist on early outcomes in low-income and middle-income countries (LMICs). We compared postoperative outcomes in breast, colorectal, and gastric cancer surgery in hospitals worldwide, focusing on the effect of disease stage and complications on postoperative mortality. Methods: This was a multicentre, international prospective cohort study of consecutive adult patients undergoing surgery for primary breast, colorectal, or gastric cancer requiring a skin incision done under general or neuraxial anaesthesia. The primary outcome was death or major complication within 30 days of surgery. Multilevel logistic regression determined relationships within three-level nested models of patients within hospitals and countries. Hospital-level infrastructure effects were explored with three-way mediation analyses. This study was registered with ClinicalTrials.gov, NCT03471494. Findings: Between April 1, 2018, and Jan 31, 2019, we enrolled 15 958 patients from 428 hospitals in 82 countries (high income 9106 patients, 31 countries; upper-middle income 2721 patients, 23 countries; or lower-middle income 4131 patients, 28 countries). Patients in LMICs presented with more advanced disease compared with patients in high-income countries. 30-day mortality was higher for gastric cancer in low-income or lower-middle-income countries (adjusted odds ratio 3·72, 95% CI 1·70–8·16) and for colorectal cancer in low-income or lower-middle-income countries (4·59, 2·39–8·80) and upper-middle-income countries (2·06, 1·11–3·83). No difference in 30-day mortality was seen in breast cancer. The proportion of patients who died after a major complication was greatest in low-income or lower-middle-income countries (6·15, 3·26–11·59) and upper-middle-income countries (3·89, 2·08–7·29). Postoperative death after complications was partly explained by patient factors (60%) and partly by hospital or country (40%). The absence of consistently available postoperative care facilities was associated with seven to 10 more deaths per 100 major complications in LMICs. Cancer stage alone explained little of the early variation in mortality or postoperative complications. Interpretation: Higher levels of mortality after cancer surgery in LMICs was not fully explained by later presentation of disease. The capacity to rescue patients from surgical complications is a tangible opportunity for meaningful intervention. Early death after cancer surgery might be reduced by policies focusing on strengthening perioperative care systems to detect and intervene in common complications. Funding: National Institute for Health Research Global Health Research Unit