Control of morphology and nanostructure of copper and cobalt oxalates: Effect of complexing ions, polymeric additives and molecular weight

Precipitated oxalates are often nanostructured and can be used as precursors for nanostructured oxides for different applications. The modification of the particle shape and nanostructures of both copper and cobalt oxalates has been demonstrated using polymeric additives or complexing counter-ions. In the case of cobalt oxalate the characteristic elongated rod particle shape (axial ratio of 10) can be modified by using polymethymethacrylate (PMMA) to produce particles with lower axial ratios of 2, through cubes all the way to platelets (axial ratio 0.2). The PMMA inhibits the growth of the particles along the [101] direction more and more strongly as the concentration of the polymer increases. The crystallite size from XRD line broadening is not modified by the PMMA indicating that the PMMA does not influence the nucleation and growth but modifies the aggregation kinetics. Copper oxalates precipitated in the presence of different cellulose derived polymers with different molecular weights and functional groups (methyl and propyl) showed sensitivity to both molecular weight and functional group. Higher molecular weights did not influence the copper oxalate particle shape, whereas methyl cellulose gave elongated particles and propyl celluloses gave platelet like particles. Copper oxalate precipitated in the presence of acetate counter ions gave platelets with an axial ratio of 0.15 compared to the cushion-like morphology (axial ratio 0.5). The primary crystallites were more elongated along the [001] direction in the presence of acetate, modifying the proportion of the hydrophobic and hydrophilic surfaces and hence influencing the aggregation kinetics and particle shape. The copper and cobalt oxalate particle formation seems to be dominated by the primary particle aggregation with the different additives interacting specifically with different crystallographic faces of the primary particles. By tuning this interaction particles with different shapes and substructures can be formed

Etude par microscopie électronique de particules nanostructurées d'oxalate de cobalt précipitées en milieu aqueux

The understanding of material self-assembling and self-organization mechanisms, at mesoscale, is crucial for nanotechnologies development. Such structures, hierarchically organized in superlattices or colloïdal crystals, are observed in inorganic or organo-metallic precipitates. The classical characterization, using electron microscopy and X-ray diffraction, of a synthesized powder is inadequate to describe the hierarchically organized polycrystalline structure of the final particles. Here, we have highlighted the successive steps that lead to the spontaneous formation of a cobalt oxalate dihydrate (COD) colloïdal crystals that precipitate in aqueous media. The characterization of the final particles, made by X-ray and electronic diffraction, has allowed us to determine the controversial crystalline phase of the precipitated COD. The β and γ COD phases has been discriminated by comparing experimental results with simulations of X-ray diffractogram and electron diffraction patterns for these both structures. The precipitated COD corresponds to the γ phase indicating that it comes from solid dehydration of cobalt oxalate tetrahydrate. The final powder characterization, performed by X-ray diffraction (XRD), atomic force microscopy (AFM), low voltage high resolution scanning electron microscopy (LVHRSEM) and transmission electron microscopy (TEM), gives some diverging results about monocrystalline or polycrystalline nature of the precipitates. XRD and AFM analysis show a polycrystalline structure of particles whereas LVHRSEM, TEM and electron diffraction observations indicate a monocrystalline structure. This apparent contradiction has led us to elaborate a new characterization method allowing to follow the growth and the structural evolution of the precipitate as a function of time. The cryo- preparation techniques are well adapted as they allow freezing and direct observation of solid state suspension by electron microscopy. The freeze/drying method has been modified and used for both SEM and TEM, and has allowed us to study the morphological and structural evolution of the COD precipitate from nanoscale to mesoscale. In addition, TEM analysis of samples prepared by classical techniques has been performed to complement cryo-electron microscopy observations. The combination of these two methods show that COD precipitation is a complex multi-step process leading to the formation of a core/shell heterostructure. The anisotropic core is porous and partially crystalline. It is formed by agglomeration of isolated primary particles and agregated ones (15-20 nm sized secondary particles). The crystalline shell corresponds to the final particles faces and is made up by the layer by layer self-assembling and alignment of 5-7 nm sized crystalline primary particles. These nanoparticles are aligned and perfectly ordered in strings of nanograins in the layer structure. The self-assembling occurs in the last step of growth where we have a lower ionic strength and supersaturation inducing slower kinetics of growth and aggregation. Moreover, the crystalline order in the primary and secondary particles increase with the time of reaction consistent with a continuous process of primary particle nucleation and growth. Our results show that self-assembling occurs layer by layer with terraces, kinks and steps that are present on the faces. This reminds the layer by layer crystalline growth models but in this case, the buiding blocks are colloïdal instead of atomic or molecular. Based on these different results, we propose an original model describing the COD precipitate growth. In addition, we have studied the poly(methacrylic acid-sodium salt) effect on the COD precipitation. This additive (PMMA) appeared to be a very good growth inhibitor. The PMMA effect on the final particles morphology is dramatic. Its concentration variation in solution slows down the nanoparticles aggregation rates along a [101] preferential direction. The crystal habit can then be controlled and we have synthesized platelets, cubes and rods with tailored length. The use of cryogenic electron microscopy has been shown to be a powerful tool for the understanding of time dependent aspects of particle growth. The use of such techniques for the study of other systems, where the final precipitate appearance may hide particle substructures, will help to elucidate growth mechanisms and allow finer control of nanostructured materials for many applications. The complex self-assembling and self-organization processes could then be highlighted and studied on a nanometer to micrometer scale

Sectioning of the anterior intermeniscal ligament changes knee loading mechanics

International audienceIntroduction: The aim of this cadaver research project was to describe the biomechanical consequences of AIML resection on menisci function under load conditions in full extension and 60° flexion. Methods: Ten unpaired fresh frozen cadaveric knees were dissected leaving the knee joint intact with its capsular and ligamentous attachments. The femur and tibia were sectioned 15 cm from the joint line and mounted onto loading plateform. A linear motion x-y table allows the tibial part of the joint to freely translate in anterior-posterior direction. K-scan sensors, were used to define contact area, contact pressure and position of pressure center of application (PCOA). Two series of analysis were planed: before and after AIML resection, mechanical testing were performed with specimens in full extension and 60° of flexion to approximate heel strike and foot impulsion during the gait. A standard compression load of 1400 N at full extension and 700N at 60° flexion was applied. Results: Sectioning of the AIML produced mechanical variations bellow the two menisci when specimens were at full extension and loaded to 1400N: increasing of mean contact-pressure (delta 0.4+/-0.2MPa, + 15% variation p=0.008) and maximum contact-pressure (delta 1.50+/-0.8MPa, 15% variation p<0.0001), decreasing of tibio-femoral contact area (delta 71+/-51mm2,-15% variation p<0.0001) and PCOA (delta 2.1+/0.8mm). At 60° flexion, significant differences regarding lateral meniscus mechanical parameters was observed before and after AIML resection : mean contact pressure increasing (delta 0.06+/-0.1MPa, +21% variation p=0.001), maximal contact-pressure increasing (delta 0.17+/-0.9MPa, +28% variation p=0.001), mean contact area decreasing (delta 1.84+/-8mm2 4% variation p=0.3), PCOA displacement to the joint-center (mean displacement 0.6+/-0.5mm). Conclusion: The section of the intermeniscal ligament leads to substantial changes in knee's biomechanics, increasing femoro-tibial contact pressures, decreasing contact areas and finally moving force center of application which becomes more central inside of the joint

Recent advances in ligamentous, meniscal and joint-preserving knee surgery: Pushing the limits

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Analysis of the trends in arthroscopic meniscectomy and meniscus repair procedures in France from 2005 to 2017

International audienceIntroduction: In 2008, the French National Authority for Health (HAS) recommended that "conservative" treatments be adopted for meniscal lesions. This recommendation and the lack of superiority of menis-cectomy over non-operative treatment for meniscus degeneration have modified the treatment pathway. However, the impact of these findings on French clinical practice is not known. The objective of this study was to evaluate the change over time in the number of alternative surgical procedures (meniscectomy and meniscus repair) and regional variation in France using data from the French agency for information on hospital care (ATIH). Hypothesis: We hypothesized that the number of meniscectomy procedures will decrease, and the number of repair procedures will increase over time at various healthcare facilities. Patients and methods: Between 2005 and 2017, the number of hospitalizations in the Medicine-Surgery-Obstetrics wards for meniscectomy (NFFC003 and NFCC004) or meniscus repair (NFEC001 and NFEC002) was evaluated overall and then based on whether the stay occurred in public or private sector hospitals in France. Data were extracted from the ATIH database and the findings were (1) related to French demographics during the period in question; (2) separated into public or private sector hospitals; (3) distributed into various regions in France and; (4) stratified by patient age

Sectioning of the anterior intermeniscal ligament changes knee loading mechanics

International audienceIntroduction: The aim of this cadaver research project was to describe the biomechanical consequences of AIML resection on menisci function under load conditions in full extension and 60° flexion. Methods: Ten unpaired fresh frozen cadaveric knees were dissected leaving the knee joint intact with its capsular and ligamentous attachments. The femur and tibia were sectioned 15 cm from the joint line and mounted onto loading plateform. A linear motion x-y table allows the tibial part of the joint to freely translate in anterior-posterior direction. K-scan sensors, were used to define contact area, contact pressure and position of pressure center of application (PCOA). Two series of analysis were planed: before and after AIML resection, mechanical testing were performed with specimens in full extension and 60° of flexion to approximate heel strike and foot impulsion during the gait. A standard compression load of 1400 N at full extension and 700N at 60° flexion was applied. Results: Sectioning of the AIML produced mechanical variations bellow the two menisci when specimens were at full extension and loaded to 1400N: increasing of mean contact-pressure (delta 0.4+/-0.2MPa, + 15% variation p=0.008) and maximum contact-pressure (delta 1.50+/-0.8MPa, 15% variation p<0.0001), decreasing of tibio-femoral contact area (delta 71+/-51mm2,-15% variation p<0.0001) and PCOA (delta 2.1+/0.8mm). At 60° flexion, significant differences regarding lateral meniscus mechanical parameters was observed before and after AIML resection : mean contact pressure increasing (delta 0.06+/-0.1MPa, +21% variation p=0.001), maximal contact-pressure increasing (delta 0.17+/-0.9MPa, +28% variation p=0.001), mean contact area decreasing (delta 1.84+/-8mm2 4% variation p=0.3), PCOA displacement to the joint-center (mean displacement 0.6+/-0.5mm). Conclusion: The section of the intermeniscal ligament leads to substantial changes in knee's biomechanics, increasing femoro-tibial contact pressures, decreasing contact areas and finally moving force center of application which becomes more central inside of the joint

Mid-term survivorship of Mini-keel (TM) versus Standard keel in total knee replacements: Differences in the rate of revision for aseptic loosening

International audienceIntroduction: To reduce the size of the surgical incision, modular mini-keel tibial components have been developed with or without extensions for the Nexgen (TM) MIS Tibial Component. Although a smaller component could theoretically result in defective fixation, this has never been evaluated in a large comparative series. Thus, we performed the following case control study to: (1) evaluate intermediate-term survival of a modular ``mini-keel'' tibial component compared to a reference standard keel component from the same line of products (Nexgen LPS-Flex Tibial Component, Zimmer); (2) to identify any eventual associated factors if the frequency of loosening was increased. Hypothesis: The rate of revision for aseptic tibial loosening is comparable for both components. Materials and methods: This comparative, retrospective, single center series of 459 consecutive total knee arthroplasties (TKA) was performed between 2007 and 2010: with 212 modular ``mini-keel'' (MK) tibial components and 247 ``standard'' (S) components. Survival, rate of revision for aseptic tibial loosening and identification of a radiolucent line were analyzed at the final follow-up. Results: After a median follow-up of 5years, the rate of revision for tibial aseptic loosing was significantly higher in the MK group with 12 cases (5.7%) and 4 cases in the S group (1.6%) (P=0.036). The use of the MK component appears to be a prognostic factor for surgical revision (hazard ratio=3.86 (1.23-11.88), P=0.02) but not for the development of a radiolucent line (HR=1.75 (0.9-3.4), P=0.097). The mean delay before revision was 38months (8-64) in the MK group and 15.2months (8-22) in the S group (P=0.006). Individual factors, such as gender, body mass index (BMI) and pre- or postoperative alignment were not prognostic factors for revision or radiolucent lines. Conclusion: The modular ``mini-keel'' tibial component was associated with a greater risk of revision for tibial component loosening. (C) 2016 Elsevier Masson SAS. All rights reserved

Starch-induced implant periapical lesion: A case report

This paper reports an implant periapical lesion (IPL) with a previously unreported etiology. The presence of an osteolytic area around the apex and around the middle portion of a stable Straumann hollow-screw implant was found on periapical radiographs 3.5 years after implant placement. Case management involved curettage of the soft tissue surrounding the implant apex as well as resection of the nonosseointegrated portion of the implant. Histopathologic examination revealed a connective fibrous tissue containing a dense chronic inflammatory infiltrate with a foreign-body material. Polarized light microscopy and Fourier transform infrared microspectroscopy identified the foreign-body material as starch particles. Etiology of this IPL was thus related to a foreign-body reaction to starch particles. This exogenous contamination probably originated from starch-coated gloves during the surgical procedure. This case report suggests that IPL may successfully be treated by debridement and implant resection instead of implant removal. Peri-implant apical soft tissue should be systematically submitted for histopathologic examination