Design, development and validation of iron-based composites for biodegradable implant applications

"Thèse en cotutelle : Doctorat en génie des matériaux et de la métallurgie, Université Laval, Québec, Canada, Philosophiæ doctor (Ph. D.) et Politecnico di Milano, Milano, Italie."Récemment, le Fe et ses alliages ont montré leur potentiel en tant que matériaux dégradables pour des applications biomédicales. Néanmoins, la vitesse de corrosion lente limite leurs performances dans certaines situations. Les matériaux composites à matrice de fer représentent une approche possible, non seulement pour améliorer leurs propriétés mécaniques, mais aussi pour accélérer et ajuster la vitesse de corrosion dans un environnement physiologique. Dans ce travail, des composites à base de Fe renforcés par des particules Mg2Si ont été proposés. Les poudres initiales ont été préparées par différentes combinaisons de procédés de mélange et de broyage, et finalement consolidées par laminage à chaud. L'influence de la microstructure sur les propriétés mécaniques et le comportement à la corrosion de Fe/Mg2Si a été étudiée. Les échantillons contenant des particules Mg2Si plus petites présentaient une distribution plus homogène du renforcement. Le rendement et l’état limite ultime à la traction ont augmenté par rapport à ceux du Fe pur. La présence des particules de renforcement a joué un rôle crucial dans la susceptibilité à l'attaque de corrosion localisée dans les composites à base de Fe. L'initiation de la corrosion et son développement ont été systématiquement suivis pour étudier le mécanisme de corrosion. L'importance des particules de Mg2Si dans le déclenchement des processus de corrosion a été expliquée. Des mesures électrochimiques et des tests d'immersion statique ont indiqué que l'ajout de Mg2Si pourrait augmenter le taux de corrosion du Fe. Il a été constaté que la taille et la distribution des particules de renfort jouaient un rôle crucial à l'uniformité de l'attaque de corrosion. Après, une série de tests d'immersion à différents intervalles d'exposition (20, 50 et 100 jours) à la solution modifiée de Hanks a été réalisée à fin d’évaluer le comportement de dégradation des composites Fe/Mg2Si et Fe pur préparés par différentes techniques de métallurgie des poudres. Les résultats ont révélé l’importance du Mg2Si dans la composition et la stabilité des films protecteurs formés lors des expériences de corrosion statique. Les composites Fe/Mg2Si présentaient des taux de dégradation plus élevés que le Fe pur à toutes les étapes du test d'immersion. Les taux de dégradation à des intervalles d'exposition distincts dépendaient fortement de la composition et de la stabilité des films protecteurs d'oxyde, d'hydroxyde, de carbonate et de phosphate formés sur les surfaces dégradées. La libération d'ions Fe dans la solution aux stades ultérieurs de l'expérience était limitée en raison de l'effet de barrière dû au dépôt insoluble. Cette étude fondamentale a servi de base aux processus de formation de film protecteur dans la solution de Hanks modifiée, permettant une identification détaillée de leurs caractéristiques.Fe-based alloys have shown a potential as a degradable material for biomedical applications. Nevertheless, the slow corrosion rate limits their performance as a biodegradable implant. One approach to control and modify their corrosion properties is the reinforcement addition, to create metal matrix composites in which the second phase is aimed at tuning not only the mechanical properties but also the corrosion mode and rate in a physiological environment. This thesis presents an original and thorough contribution on a very pertinent topic, the design, development, and validation of a new Fe/Mg2Si composites prepared powder metallurgy. The initial powders were prepared by different combinations of mixing and high energy ball milling processes and finally consolidated by hot rolling. Mechanical properties, microstructural features, as well as the corrosion performance, were extensively investigated in relation to the reinforcement size and distribution. The composites made of small size reinforcement particles showed a general increase in tensile strength. For instance, high energy ball milled samples exhibited better tensile performances (YS = 523 MPa, UTS = 630 MPa) while having the lower ductility (around 4%). A fundamental understanding of corrosion initiation, protective film formation, and growth on Fe-based materials and leads to a design of smarter and surface responsive biomaterials with modulable degradation rates, at distinct stages of the corrosion process. Here, the corrosion performance of Fe/Mg2Si composites varied with the reinforcement size and distribution. The predominant localized pitting corrosion in Fe/Mg2Si prepared by mixing was replaced by a more uniform pattern found in samples produced by mechanical milling. Further, it was found that Mg2Si plays a significant role in the composition and stability of the protective films formed during the static corrosion experiments. Fe/Mg2Si showed a higher corrosion rate compared to that of pure Fe at all stages of the corrosion experiment (1, 10, 20, 50 and 100 days). Moreover, the final degradation products varied with the substrate chemical composition and microstructure. In case of pure Fe, low solubility (Fe3(PO4)2) covered the entire surface, while Fe/Mg2Si exhibited the presence of carbonates at the latest stages of the test. The details about the degradation behaviour during long-term exposure times to the physiological environment highlighted in this work add a new knowledge on corrosion mechanism of degradable implant materials. In particular, the ability to tune mechanical and corrosion behavior of the composites as a function of reinforcement properties and manufacturing method was experimentally verified, highlighting the microstructure-corrosion property relationship.I biomateriali in ferro puro e in leghe a base di ferro presentano una combinazione interessante di proprietà meccaniche, elettrochimiche e biologiche; per questo motivo, questa classe di materiali metallici possono trovare utilizzo in applicazioni di tipo impiantistico biomedicale. Malgrado ciò, nonostante le sue soddisfacenti proprietà meccaniche, questo elemento impiegato allo stato puro mostra un inconveniente rilevante - un basso tasso di degradazione. L’oggetto di questa tesi è lo studio di un nuovo gruppo di materiali biodegradabili compositi a matrice ferrosa (Fe/Mg2Si), in cui il Fe costituisce la matrice e il Mg2Si è impiegato come rinforzo; questi materiali sono stati sviluppati con tecniche di metallurgia delle polveri, e presentano un, alta resistenza meccanica come caratteristica principale. Le polveri che costituiscono i materiali di partenza sono stati preparati con diverse combinazioni di procedure oltre al semplice mescolamento e/o high energy ball milling (macinatura in mulino a sfere a alta energia). Tutte le formulazioni preparate sono state compattate attraverso laminazione a caldo. Le proprietà meccaniche, le caratteristiche microstrutturali, la composizione delle fasi e le prestazioni in termini di corrosione sono state studiate dettagliatamente, in relazione alla dimensione delle particelle di rinforzo e della loro distribuzione. Lavori precedenti hanno confermato l’efficacia dell’aggiunta di una seconda fase, soprattutto se finemente dispersa, per aumentare il tasso di degradazione di materiali metallici per applicazioni biomedicali a base Fe: gli esperimenti condotti in questo lavoro hanno confermato che i compositi Fe/Mg2Si hanno mostrato, rispetto al Fe puro che compone la matrice, non solo una resistenza meccanica più elevata, ma anche un tasso di degradazione più alto negli esperimenti di laboratorio in vitro. Infine, i materiali ottenuti tramite high energy ball milling, presentano una resistenza alla trazione migliore (carico di snervamento= 523 MPa, resistenza alla trazione = 630 MPa), ma contemporaneamente una ridotta duttilità (circa 4%). Una attenzione particolare è stata posta nello studio degli effetti della presenza di Mg2Si sui meccanismi di corrosione.Tutti i compositi studiati hanno mostrato un tasso di degradazione più elevato rispetto alla matrice fabbricata con la stessa procedura; inoltre, la formazione del film di prodotti di degradazione sulla superficie del materiale cambiava in maniera rilevante in funzione della composizione chimica del substrato e della sua microstruttura. Nel caso del Fe puro, cristalli isolati di vivianite (Fe3(PO4)2) erano presenti su tutta la superficie, mentre carbonati di Fe si formavano principalmente sulla superficie dei compositi, specialmente negli ultimi stadi del processo di degradazione

Identification of genetic variants associated with Huntington's disease progression: a genome-wide association study

Background Huntington's disease is caused by a CAG repeat expansion in the huntingtin gene, HTT. Age at onset has been used as a quantitative phenotype in genetic analysis looking for Huntington's disease modifiers, but is hard to define and not always available. Therefore, we aimed to generate a novel measure of disease progression and to identify genetic markers associated with this progression measure. Methods We generated a progression score on the basis of principal component analysis of prospectively acquired longitudinal changes in motor, cognitive, and imaging measures in the 218 indivduals in the TRACK-HD cohort of Huntington's disease gene mutation carriers (data collected 2008–11). We generated a parallel progression score using data from 1773 previously genotyped participants from the European Huntington's Disease Network REGISTRY study of Huntington's disease mutation carriers (data collected 2003–13). We did a genome-wide association analyses in terms of progression for 216 TRACK-HD participants and 1773 REGISTRY participants, then a meta-analysis of these results was undertaken. Findings Longitudinal motor, cognitive, and imaging scores were correlated with each other in TRACK-HD participants, justifying use of a single, cross-domain measure of disease progression in both studies. The TRACK-HD and REGISTRY progression measures were correlated with each other (r=0·674), and with age at onset (TRACK-HD, r=0·315; REGISTRY, r=0·234). The meta-analysis of progression in TRACK-HD and REGISTRY gave a genome-wide significant signal (p=1·12 × 10−10) on chromosome 5 spanning three genes: MSH3, DHFR, and MTRNR2L2. The genes in this locus were associated with progression in TRACK-HD (MSH3 p=2·94 × 10−8 DHFR p=8·37 × 10−7 MTRNR2L2 p=2·15 × 10−9) and to a lesser extent in REGISTRY (MSH3 p=9·36 × 10−4 DHFR p=8·45 × 10−4 MTRNR2L2 p=1·20 × 10−3). The lead single nucleotide polymorphism (SNP) in TRACK-HD (rs557874766) was genome-wide significant in the meta-analysis (p=1·58 × 10−8), and encodes an aminoacid change (Pro67Ala) in MSH3. In TRACK-HD, each copy of the minor allele at this SNP was associated with a 0·4 units per year (95% CI 0·16–0·66) reduction in the rate of change of the Unified Huntington's Disease Rating Scale (UHDRS) Total Motor Score, and a reduction of 0·12 units per year (95% CI 0·06–0·18) in the rate of change of UHDRS Total Functional Capacity score. These associations remained significant after adjusting for age of onset. Interpretation The multidomain progression measure in TRACK-HD was associated with a functional variant that was genome-wide significant in our meta-analysis. The association in only 216 participants implies that the progression measure is a sensitive reflection of disease burden, that the effect size at this locus is large, or both. Knockout of Msh3 reduces somatic expansion in Huntington's disease mouse models, suggesting this mechanism as an area for future therapeutic investigation

En studie av samarbeid mellom kommune og frivillig sektor. Hvilke former for samspill med frivillige organisasjoner benytter kasus kommunen i samarbeidet med frivillige organisasjoner?

Med årenes løp har jeg fått større forståelse for utfordringer som offentlig sektor står overfor i forhold til ytelsen av velferdstjenester til innbyggere og betydningen av frivillig sektor i denne sammenhengen. Derfor har jeg valgt å studere denne problemstillingen gjennom kasus kommunens samhandling med frivillige organisasjonene. Jeg ønsket å finne ut hvilke samarbeidsmodeller: vertskap, partnerskap eller samskaping dominerer i den kommunale samhandlingen med frivillige organisasjoner og om kasus kommunen har fokus på samskaping og tilrettelegger for den. Samskaping i offentlig sektor er den mest innovative formen for samhandling og handler om at kommunen skal legge til rette for samskaping av velferdssamfunnet sammen med sivilsamfunnet. Samskaping kan være en av løsninger på kommunale problemer og dilemmaer siden den tradisjonelle rollen til kommunen som tjenesteleverandør er i dag under omstilling. Det er ønskelig fra statlig hold at kommunen skal være en tilrettelegger av velferdssamfunnet og skal inkludere sivilsamfunnet i offentlig problemløsning. Gjennom arbeidet med oppgaven fikk jeg mulighet til å bli bedre kjent med disse tre samarbeidsformene og hvordan samhandling med frivillige organisasjonene foregår i en gjennomsnittlig kommune som ikke har utarbeidet frivillig politikk. Målet med studien var å finne ut om teorien til Guribye og Holdt om samarbeidsformer stemmer overens med den kommunale virkeligheten, og om mine funn kommer til å forsterke denne gjeldende forskningen eller kommer jeg til å finne noe nytt i forhold til den. Resultatene fra studien bekrefter etter min mening paralleller mellom oppgavens funn og teorien til Holdt og Guribye og understøtter kommunens behov for mer innovative samarbeidsformer med frivillig sektor

Circadian Plasticity of Mammalian Inhibitory Interneurons

Inhibitory interneurons participate in all neuronal circuits in the mammalian brain, including the circadian clock system, and are indispensable for their effective function. Although the clock neurons have different molecular and electrical properties, their main function is the generation of circadian oscillations. Here we review the circadian plasticity of GABAergic interneurons in several areas of the mammalian brain, suprachiasmatic nucleus, neocortex, hippocampus, olfactory bulb, cerebellum, striatum, and in the retina

Bio-Based Waste’ Substrates for Degraded Soil Improvement—Advantages and Challenges in European Context

The area of degraded sites in the world is constantly expanding and has been a serious environmental problem for years. Such terrains are not only polluted, but also due to erosion, devoid of plant cover and organic matter. The degradation trends can be reversed by supporting remediation/reclamation processes. One of the possibilities is the introduction of biodegradable waste/biowaste substrates into the soil. The additives can be the waste itself or preformed substrates, such composts, mineral-organic fertilizers or biochar. In EU countries average value of compost used for land restoration and landfill cover was equal 4.9%. The transformation of waste in valuable products require the fulfillment of a number of conditions (waste quality, process conditions, law, local circumstances). Application on degraded land surface bio-based waste substrates has several advantages: increase soil organic matter (SOM) and nutrient content, biodiversity and activity of microbial soil communities and change of several others physical and chemical factors including degradation/immobilization of contaminants. The additives improve the water ratio and availability to plants and restore aboveground ecosystem. Due to organic additives degraded terrains are able to sequestrate carbon and climate mitigate. However, we identified some challenges. The application of waste to soil must comply with the legal requirements and meet the end of use criteria. Moreover, shorter or long-term use of bio-waste based substrate lead to even greater soil chemical or microbial contamination. Among pollutants, “emerging contaminants” appear more frequently, such microplastics, nanoparticles or active compounds of pharmaceuticals. That is why a holistic approach is necessary for use the bio-waste based substrate for rehabilitation of soil degraded ecosystems

Effect of Associative Learning on Memory Spine Formation in Mouse Barrel Cortex

Associative fear learning, in which stimulation of whiskers is paired with mild electric shock to the tail, modifies the barrel cortex, the functional representation of sensory receptors involved in the conditioning, by inducing formation of new inhibitory synapses on single-synapse spines of the cognate barrel hollows and thus producing double-synapse spines. In the barrel cortex of conditioned, pseudoconditioned, and untreated mice, we analyzed the number and morphological features of dendritic spines at various maturation and stability levels: sER-free spines, spines containing smooth endoplasmic reticulum (sER), and spines containing spine apparatus. Using stereological analysis of serial sections examined by transmission electron microscopy, we found that the density of double-synapse spines containing spine apparatus was significantly increased in the conditioned mice. Learning also induced enhancement of the postsynaptic density area of inhibitory synapses as well as increase in the number of polyribosomes in such spines. In single-synapse spines, the effects of conditioning were less pronounced and included increase in the number of polyribosomes in sER-free spines. The results suggest that fear learning differentially affects single- and double-synapse spines in the barrel cortex: it promotes maturation and stabilization of double-synapse spines, which might possibly contribute to permanent memory formation, and upregulates protein synthesis in single-synapse spines

Increases in the Numerical Density of GAT-1 Positive Puncta in the Barrel Cortex of Adult Mice after Fear Conditioning

<div><p>Three days of fear conditioning that combines tactile stimulation of a row of facial vibrissae (conditioned stimulus, CS) with a tail shock (unconditioned stimulus, UCS) expands the representation of “trained” vibrissae, which can be demonstrated by labeling with 2-deoxyglucose in layer IV of the barrel cortex. We have also shown that functional reorganization of the primary somatosensory cortex (S1) increases GABAergic markers in the hollows of “trained” barrels of the adult mouse. This study investigated how whisker-shock conditioning (CS+UCS) affected the expression of puncta of a high-affinity GABA plasma membrane transporter GAT-1 in the barrel cortex of mice 24 h after associative learning paradigm. We found that whisker-shock conditioning (CS+UCS) led to increase expression of neuronal and astroglial GAT-1 puncta in the “trained” row compared to controls: Pseudoconditioned, CS-only, UCS-only and Naïve animals. These findings suggest that fear conditioning specifically induces activation of systems regulating cellular levels of the inhibitory neurotransmitter GABA.</p></div

Albumins inhibit the corrosion of absorbable Zn alloys at initial stages of degradation

Understanding the surface interactions and reactivity of zinc (Zn)-based biomaterials with constituents of physiological fluids such as proteins and ions is essential for an accurate evaluation of biomaterial corrosion initiation and progression. In this paper, the effect of the albumin addition on the corrosion behavior of pure Zn and Zn–4Ag alloy is discussed. The corrosion behavior of Zn-based materials was studied using potentiodynamic polarization, electrochemical impedance spectroscopy, immersion tests and X-ray photoelectron spectroscopy. It was found that the addition of albumins largely affects the chemical composition, morphology and compactness of the protective films formed on biomaterials. A shift of the corrosion regime from localized to more general was observed in the protein-containing electrolytes. The proteins acted as corrosion inhibitors, reducing the corrosion current density and promoting passivation of the metallic surfaces. The increase in the corrosion resistance of the Zn–4Ag alloy is attributed to a selective Zn ion leaching that leaves the metal surface enriched with electrochemically more stable alloying element