Application of response surface methodology in the design of functionally graded plasma sprayed hydroxyapatite coatings

The highly complex process-property-structure relationship poses a major challenge in the optimization of plasma sprayed hydroxyapatite coatings. In addition, contradictions in relation to the ideal coating properties exist; a dense, highly crystalline coating is required for long term coating stability, whereas coatings with lower crystallinity dissolve more rapidly but have an improved osteogenic response in vivo. In this study, response surface methodology (RSM) is utilized to investigate the influences and interaction effects of current, gas flow rate, powder feed rate, spray distance and carrier gas flow rate on the roughness, crystallinity, purity, porosity and thickness of plasma sprayed HA coatings. Roughness related to the particle velocity and particle melting, and was highest at low gas flow rates and, due to the quadratic effect of current, at the central current value. High crystallinity resulted at high current and low spray distance due to the presence of bulk crystalline material and recrystallization of amorphous material. Purity was highest at low carrier gas flow rate and high gas flow rate, where particle temperature was reduced. Porosity was dependent on the degree of particle melting and was highest at low gas flow rate and powder feed rate and at high current and spray distance. Coating thickness was determined by the number of particles and the degree of flattening on impact, and was highest at high current, low gas flow rate, high powder feed rate and low spray distance. From this in-depth analysis, predictive process equations were developed and optimized to produce two distinct coatings; a stable coating and a bioactive coating, designed to form the base and surface layers of a functionally graded coating respectively, to provide enhanced osteogenesis, while maintaining long-term stability. Culture of osteoblast-like cells on the coatings demonstrated an increased osteogenic response on the bioactive coating compared to the other groups. Overall, this study identifies parameter effects and interactions leading to the development of optimized coatings with the potential to enhance the functional life of HA coated implants in vivo

Acylation des flavonoïdes par la lipase de candida antarctica (influence du donneur d'acyle sur la sélectivité et la cinétique de biotransformation)

L'objectif général de ce travail est l'étude et l'optimisation des réactions de synthèse enzymatique de nouveaux esters de flavonoide. Ce travail a été réalisé en présence de la lipase immobilisée de Candida antarctica et dans un milieu organique à faible teneur en eau (<300 ppm). Dans une première étape, une étude préliminaire des paramètres clef de la réaction a montré que la transestérification est moins performante que l'estérification directe car l'hydrolyse du donneur d'acyle prédomine la synthèse d'ester de flavonoide. La quantité d'eau du milieu présente au cours de la synthèse joue un rôle essentiel. Elle provoque un déplacement de l'équilibre vers l'hydrolyse, ce qui conduit à une diminution du rendement. Parmi les différents solvants testés, le méthyl-2-butanol 2 donne les meilleurs résultats. L'étude de l'effet de structure du donneur d'alcool et d'acyle sur la performance d'acylation montre que les meilleures vitesses initiales et rendements de conversion ont été obtenus avec la rutine (71 %, 3.1 [mu]mole.h-1) et l'estuline (80%,8. 7 [mu]mole.h-1) et les acides gras ayant une chaîne carbonée supérieure à C12 (87%, 15 [mu]mole.h-1). L'acylation des flavonoides mène uniquement à de monoesters et l'acylation a lieu au niveau du 6"-OH primaire de l'egcutine etdu 4"'-OH secondaire de la rutine. Cette étude a montré aussi que la synthèse d'ester aromatique de flavonoïde est faisable et le rendement d'acylation peut atteindre 75%. Une optimisation par la méthode de plan d'expériences a montré que la vitesse initiale de conversion et la séléctivité de la réaction dépend de la nature du solvant et des concentrations initiales des substratsThe general objective of this work is to study and to optimise the enzymatic synthesis of new esters of tlavonoide. Immobilized lipase of Candida antarctica was used as biocatalyst in an organic medium with low waler content (< 300 ppm). The obtained results showed that trans-esterification is less performant than direct esterification due to the fact that the hydrolytic reaction is predominant compared to the flavonoids ester synthesis. The water content of the medium along the time course of the reaction plays an essential role. Even if at a low level It provokes a drastic decrease of the conversion yield. Among, the various sol vents tested methyl- 2-butanol 2 gives the best results. The study of the effect of structure of the donors of alcohol and acyl on the performance of acylation shown that best initial rates and conversion yields were obtained with rutin (71 %, 3.1.[mu]ole.h-1 and the esculin (80%, 8.7 [mu]ole.h-1) in the presence of fatty acids with carbon chain higher than C12 (87%, 15 [mu]ole.h-1). The acylation of the flavonoides leads only to monoesters and the it takes place on the primary 6''-OH of the esculin and secondary 4''-OH of rotin. This study showed also that the aromatic ester synthesis of flavonoide is feasible and the conversion yield of this acylation can reach in some cases 75 %. The use of an experimental design showed that the initial rates of substrates conversion and the selectivity of the reaction depends on the nature ofsolvent and the initial concentrations of the substratesNANCY/VANDOEUVRE-INPL (545472102) / SudocSudocFranceF

Evaluation of cell behaviour on atmospheric plasma deposited siloxane and fluorosiloxane coatings

For developing functional biomaterials, an understanding of the biological response at material surfaces is of key importance. In particular, surface chemistry, roughness and cell type influence this response. Many previous reports in the literature have involved the study of single cell types and their adhesion to surfaces with a limited range of water contact angles. The objective of this study was to investigate the adhesion of five cell lines on surfaces with contact angles in the range of 20 to 115 . This range of water contact angles was obtained using siloxane and fluorosiloxane coatings deposited using atmospheric plasma deposition. These nm thick coatings were deposited by nebulizing liquid precursors consisting of poly(dimethylsiloxane) (PDMS) and a mixture of perfluorodecyl acrylate/ tetraethylorthosilicate (PPFDA/TEOS) into the atmospheric plasmas. Cell adhesion studies were carried out with the following cell types: Osteoblast, Human Embryonic Kidney (HEK), Chinese hamster ovary (CHO), Hepatocytes (HepZ) and THP1 leukemic cells. The study demonstrated that cell adhesion was significantly influenced by the type of cell line, water contact angle and coating chemistry. For example the sensitivity of cell lines to changes in contact angle was found to decrease in the following order: Osteoblasts >Hepatocytes> CHO. The HEK and THP-1 inflammatory cells in contrast were not found to be sensitive to changes in water contact angle.Science Foundation IrelandAuthor has checked copyrightAD 22/01/201