Study of the structural properties and control of degradation rate for biodegradable metallic stents using cold spray
Notice bibliographique
Résumé
AbstractThere is considerable interest in fabricating stents with degradable materials to avoid the disadvantages of permanent stents such as stent fracture. The focus of this thesis is on forming degradable materials consisting of mixtures of two metal powders and determining their rate of galvanic corrosion. To fabricate degradable coatings suitable for producing a stent, the cold gas dynamic spray technique is used to combine the two powders into a single low-porosity layer. Stainless steel (316L SS) and commercial purity iron (CP Fe) powders are mixed together and sprayed onto a metallic substrate in order to produce an amalgamate material. In terms of cold sprayability, spraying the single component 316L powder leads to a higher deposition efficiency (DE) as compared to CP Fe powder (72% vs. 33%), but the porosities remain low (about 1%). It is observed that spraying a mixture of 20wt% CP Fe and 80wt% 316L results in a DE of 43%. Increasing the percentage of CP Fe in the mixture to 50% does not change the DE significantly, although a further increase to 80% results in a DE of 66%. The porosities of the mixed coatings remain low in all cases. These observations may be related to differences in the hardness of the 316L and CP Fe powders. As-sprayed mixed coatings exhibit microhardness values between the range of microhardness of 316L and CP Fe coatings. Also, the effect of mixing does not result in any decrease in the shear strength of as-sprayed coatings as compared to the shear strength of as-sprayed 316L and CP Fe coatings. It is found that annealing the coating relieves work hardening by recrystallization, reduces porosity, and promotes sintering. Shear punch test results indicate that annealed mixed coatings attain shear strengths of that of 316L (455 MPa) with approximately 15% decrease in the reduction in area. Reduction of the work hardening in both 316L and CP Fe particles increases the coating ductility. The 20wt% Fe coatings exhibit 23% ductility, which is sufficient to be used for a degradable stent. Immersion and potentiodynamic polarization tests of the as-sprayed coatings indicate no significant difference in the corrosion rates of 100wt%Fe, 80wt%Fe and 50wt%Fe, which indicates that the corrosion rate of iron is increasing with increasing 316L in the composite material, assuming that iron is the only component which is corroding. This indicates that galvanic corrosion is accelerating the corrosion rate of iron in the mixed coatings. After heat treatment, the corrosion rate generally decreases primarily due to the reduction of pores, which reduces the surface area that is responsible for the higher corrosion rate of the as-sprayed coatings. X-ray diffraction (XRD) tests show that iron oxide forms after degradation. Energy dispersive X-Ray spectroscopy (EDS) also indicates the formation of iron oxides on the mixed coatings which reduces the corrosion rate with time. Considerable pitting is observed on the iron particles after the degradation tests, which indicates that chlorides are pitting the surface of mixed coatings. Overall, the use of the cold spray technique for forming an amalgamate material subject to galvanic corrosion appears to be a potential method for the fabrication of degradable stent. Further clinical investigations are required to validate the performance of such stents.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,001 | 0,000 |
| Méta-épidémiologie (sens large) | 0,001 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».