Zinc oxide doped with copper and nitrogen exhibits photocatalytic antibacterial activity under light from common fluorescent tubes

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Développement de biocomposites poreux pour des applications biomédicales

Over the last decades, porous matrices, called scaffolds, have increasingly gained in importance for bone regeneration. These matrices have been tailored to support and control the spatial organization of stem cells. Even though various materials have been proposed for their conception, their in vivo assessments have highlighted their lack of bioactivity and integration. In this context, this thesis focused on the development of biodegradable scaffolds with surface properties specifically designed to promote bone regeneration by a sustained local delivery of growth factors. The first part was devoted to the optimization of calcium phosphate ceramics in order to obtain inorganic matrices with well-defined composition and textural properties in contrast to commercially available materials. In this context, two methods of ceramic preparation were compared: wet precipitation method and sol-gel process. The resulting powders were processed into disks via a press-molding process and into tridimensional matrices via a sponge replication technique. Their resistance to post-treatments, i.e. calcination and sterilization, was also assessed. The second, third, and fourth parts of this work focused on the functionalization and the texturing of silica, selected as material for the surface modification of calcium phosphate ceramics, to promote the local sustained delivery of growth factors. The textural and chemical properties of silica were tuned to control the encapsulation and the release of a model protein of these growth factors. More specifically, three different strategies were investigated to adjust the protein loading and its release kinetics: (i) the protein encapsulation method, (ii) the addition of functionalized organosilanes, and (iii) the structuration of the silica texture. In the second part, the influence of the encapsulation method on the release kinetics and activity of protein was examined via the impregnation of silica gels with a protein solution and the direct incorporation of the protein during the synthesis of the silica gel. The results showed that a continuous protein release over 80 days could be obtained. The third part focused on the modification of the silica surface composition and textural properties via the use of different functionalized organosilanes (i.e. containing amine, ethylene diamine, or phenyl groups) and silica precursors (i.e. containing methoxy or ethoxy groups) in order to modulate the release rate of the protein. The results highlighted the preponderant role of the matrix hydrophilicity on the protein encapsulation and release compared to its surface charge. The fourth part studied the influence of the structuration of mesoporous silica on the protein encapsulation and release. SBA-15 type silica with large mesopores were synthesized using different silica precursors (i.e. containing or not phenyl groups) to offer a greater control of the material composition and textural properties. The results demonstrated that the structuration of silica allowed a regulation of the protein release over a longer period than the absence of structure. In the last part of this work, the surface modification of calcium phosphate scaffolds was investigated through the deposition of a composite made of silica particles dispersed in agarose. Specifically, this part consisted in an exploratory study focusing on the production and the characterization of the silica/agarose composite. The promising results of this part highlighted that agarose was not a barrier to the protein diffusion, suggesting that agarose could be adopted as a matrix to disperse silica for drug delivery applications

Encapsulation of proteins via sol-gel process for bone reconstruction application

Ces dernières années, l’ingénierie tissulaire est devenue une des techniques les plus prometteuse pour le maintien et la reconstruction de tissus humains, voire même d’organes entiers. Cette solution est fréquemment basée sur la réalisation de matrices poreuses, appelées « scaffolds ». De nombreux matériaux ont été proposés pour la conception de scaffolds, comme les biocéramiques (e.g. hydroxyapatite, β-tricalcium phosphate). Cependant, de nombreuses études ont montré que un manque de propriétés d'ostéoinduction, d’ostéogenèse et d’ostéointégrité. Cette étude vise à ajuster les propriétés de surface de biocéramiques par l’ajout d’un revêtement sol-gel de silice dans lequel seront encapsulées des protéines. Dans cette optique, l’étude de l’influence des paramètres d’encapsulation sur la cinétique de libération des protéines est une étape cruciale. L’encapsulation d’une protéine modèle (Soybean Trypsin Inhibitor) a été étudiée via deux méthodes : (1) l'imprégnation de gels de silice préalablement synthétisés, par une solution de protéine : méthode ex situ, (2) l'incorporation de la protéine lors de la synthèse du gel de silice : méthode in situ. Pour la méthode ex situ, le tétraéthylorthosilicate (TEOS) a été utilisé comme précurseur principal de la silice et le 3-(2-aminoéthylamino)propyltriméthoxysilane (EDAS) comme agent nucléant en milieu alcoolique et à pH basique. Les gels formés ont ensuite été séchés et/ou calcinés à différentes températures. Le type de traitement et la durée d'imprégnation ont été étudiés. Pour la méthode in situ, le tétraméthylorthosicilate (TMOS) a servi de précurseur au gel de silice après hydrolyse en pH acide. Les propriétés texturales des gels de silice ont été caractérisées par adsorption-désorption d'azote et porosimétrie au mercure. La cinétique de libération de la protéine a été analysée in vitro sur une durée de 4 semaines. Les résultats de porosimétrie au mercure et d’adsorption-désorption d’azote montrent que les gels ex situ présentent une structure poreuse en forme d'entonnoir (micro, méso et macropores) tandis que le gel in situ présente une structure microporeuse. Concernant la méthode ex-situ, les résultats montrent un « burst » après seulement 24 h suivi de l’établissement d’un plateau. Le pourcentage de protéine libérée après 7 jours d’incubation augmente lorsque la quantité de groupements aminés présents dans la silice diminue (i.e. augmentation de la température de calcination). L’effet du temps d’imprégnation ne se marque que dans le cas des gels contenant des fonctions amines avec une augmentation de la quantité de protéines absorbées avec le temps d’imprégnation. Pour la méthode in situ, un « burst » plus faible a été observé durant les premières 24 h, suivi par une libération continue de la protéine sur une période de 7 jours. Tilkin Rémi et Régibeau Nicolas bénéficie d’une bourse FRIA octroyée par le F.R.S.-FNRS. S. D. Lambert remercie également le FRS-FNRS pour sa position de Maître de Recherches

Influence of nucleating agent addition on the textural and photo-Fenton properties of Fe(III)/SiO2 catalysts

Two Fe-based/SiO2 catalysts have been prepared by a sol–gel method, with or without co-gelation with a modified silicon alkoxide, 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS). The aim was to compare these two materials and to study the influence of EDAS on the catalyst texture and photo-Fenton activity. Physico-chemical characterization showed that when EDAS was used, the iron was located inside the silica nanoparticles and was partially arranged in iron oxide clusters. As EDAS is a nucleating agent for silica, the reaction time was shorter in its presence, leading to larger silica nanoparticles. Studies of their behavior in aqueous media showed that the catalyst without EDAS released iron, whereas the catalyst with EDAS did not. This iron release influenced the photo-Fenton activities of the catalysts. p-Nitrophenol was degraded more rapidly with the catalyst without EDAS due to the greater availability of iron. Finally, both Fe/SiO2 catalysts displayed stable catalytic activity for 72 h of operation

Functionalization of silica synthesized by sol-gel process with PDLLA via "grafting to" method

Due to its properties of biodegradability and biocompatibility, polylactide has been first designed for the medical field, in particular for tissue reconstruction by tissue engineering. However, for this kind of application, its mechanical properties are too low. The addition of silica has been proposed to reinforce the mechanical strength of this biopolymer. The main challenging aspect to realize this nanocomposite is to achieve a good dispersion of nanofillers in the polymer matrix. An effective method to improve compatibility between inorganic particles and polymer matrix relies upon the preparation of PLA grafted silica nanoparticles. To form a network structure with PLA matrix, molecular weight of these grafted chains has to be superior to the critical entanglement molecular weight (CEMW) of 8.5 kDa [1]. This work is dedicated to the functionalization of sol-gel silica by the “grafted to” method. A recurrent problem with this method is the great dependence of the grafting density on the molecular weight of the PDLLA chains. When weight is above the CEMW, grafting densities greater than 0.001 chains/nm2 of silica are difficult to achieve [1]. To increase grafting density of PDLLA chains, these chains were firstly synthesized via ring opening polymerization with Sn(oct)2 as catalyst and with a organosilane (alkoxyde XSi(OR)3), the (3-Aminopropyl)triethoxysilane (APTES) as initiator, instead of a classic protic compound. This process led to the formation of PDLLA capped with three terminal functions Si-O-CH2-CH3. The resulting polyester was then dissolved in tetrahydrofuran under inert atmosphere to prevent hydrolysis of Si-OR functions. After dissolution, silica was synthesized by sol-gel reaction by mixing prehydrolysed tetramethyl orthosilicate (TMOS), dissolved polymer, water and APTES followed by three days of gelation at 65°C. Finally, these nanoparticles were washed several time with methylene chloride and cycle of centrifugation to remove unbound PDLLA and APTES. GPC and 1H NMR have confirmed the targeted molecular weight of PDLLA of 11 kDa with a monomer conversion closed to 100%. FTIR measurement and solid 29Si NMR have confirmed the covalent attachment of PDLLA chains on silica surface. BET analysis, performed after calcination of silica at 400°C, gave a specific surface of 350 m2/g. Finally, TGA allowed us to calculate a grafting yield of 25 % and a grafting density of 0.035 chains/nm2 in a reproducible and manner. As a conclusion, our chemical strategy has been demonstrated successful to increase significantly the grafting density of polyester chains on silica according to a reproducible methodology easier to apply compared to former publications [1][2]

Optimization of calcium phosphate ceramic

During the past few years, tissue engineering has become one of the most promising techniques to maintain, improve, or reconstruct human tissue, even complete human organs. This solution is frequently based on the realization of temporary porous matrices, also called "scaffolds". These materials are highly porous matrices designed to structure the development of cells, but also to guarantee the function of the implant during the regeneration process. Several materials have been proposed for the conception of scaffolds, including calcium phosphate ceramics. Among these materials, the bioceramic class is composed of hydroxyapatite (HA), Ca5(PO4)3(OH), and β-tricalcium phosphate (TCP), β-Ca3(PO4)2. These two products are frequently used, because of their chemical and structural similarity to human bones. These similarities explain good scores observed in vitro and in vivo in terms of biocompatibility and cell colonization