Kinetic studies of the photopolymerisation of acrylamide in aqueous solution:effects of bromoform as a Chain transfer agent

The effects of adding bromoform (CHBr3) as a potential chain transfer agent in the photopolymerisation of acrylamide (AM) in aqueous solution have been studied both in terms of influencing the rate of polymerisation and the molecular weight of the polyacrylamide (PAM) formed. Using 4,4′-azo-bis(4-cyanopentanoic acid) (ACPA) as photoinitiator, two different CHBr3 concentrations as chain transfer agent were compared: 0.5 and 2.0 mol % (relative to AM), the higher of which was determined by the limit of CHBr3 water solubility. The results showed that CHBr3 was an effective chain transfer agent that could regulate the molecular weight of the PAM formed without seriously affecting the polymerisation rate. It is concluded that chain transfer to CHBr3occurs by both Br and H atom transfer although Br transfer is the more favoured due to the weaker C-Br bond. Furthermore, Br transfer leads to Br-terminated chains in which the terminal C-Br bond can re-dissociate leading to re-initiation and re-propagation of the same chain, thereby maintaining the polymerisation rate. Continuing studies into how this mechanism can be exploited in order to synthesize water-soluble block copolymers of potential biomedical importance are currently in progress

Fabrication de micro/nano particules de polymère biodégradable et leur utilisation dans des applications cosmétiques et biomédicales

Biodegradable polymeric particles have attracted vast attention in cosmetic and biomedical fields because of its biocompatibility, non-toxicity, and degradability in natural environments. This study proposed the use of biodegradable polymers to fabricate the micro- and nanoparticles by several emulsification techniques. The first method was the fabrication of hollow nanoparticles which derived from poly(lactic acid-co-glycidyl methacrylate), P(LA-co-GMA) by one-step phase inversion emulsification. The influence of surfactant migration and evaporation rate play an important role in the hollow structure formation. The monodispersed hollow nanoparticles and good colloidal stability are obtained. These nanoparticles were applied to use as UV-shielding additives in cosmetic applications. The hollow nanoparticles showed high UVA&UVB shielding capability and low cytotoxicity. They also exhibited the stability under the UV exposure, and could be degraded under the hydrolysis system. The second one aimed to develop the thermoresponsive gating particles. Porous biodegradable micro/nanoparticles were prepared using Eudragit RS100 and poly(N-isopropylacrylamide) (PNIPAM) via a double emulsion solvent evaporation technique. The effect of initiator types on the polymerization of NIPAM monomer was influenced by the morphology, encapsulation efficiency, and loading capacity of the drug carriers. Temperature-sensitive particles possessed a swollen conformation to block the pores and prevent the diffusion of model drug at below the volume transition temperature (TVPT). In contrast, the crosslinked PNIPAM transformed to be a hydrophobicity and collapse, allowing the gate to open and release the encapsulated compound. These thermoresponsive particles remarkably showed a precise “on-off” switchable release mechanism which is easy to control drug delivery when triggered at the body temperature. Thus, these materials have a high potential for use as UV-shielding additives in cosmetic products, and drug delivery materials in biomedical and pharmaceutical applications.Les particules à base de polymères biodégradables ont attiré une grande attention dans le domaine cosmétique et biomédical en raison de leur biocompatibilité, de leur non-toxicité et de leur dégradabilité. Cette étude propose l'utilisation de polymères biodégradables pour fabriquer les micro- et nanoparticules par plusieurs techniques d'émulsification. La première méthode est la fabrication de nanoparticules poreuses dérivées du poly(acide lactique-co-méthacrylate de glycidyle), P(LA-co-GMA) par émulsification et par inversion de phase en une étape. L'influence de la migration des tensioactifs et de la vitesse d'évaporation joue un rôle important dans la formation de la structure poreuse. Les nanoparticules poreuses, monodisperses en taille et une présentant une bonne stabilité colloïdale sont obtenues. Ces nanoparticules ont été utilisées comme additifs de protection contre les UV dans des applications cosmétiques. Les nanoparticules poreuses ont montré une capacité de protection élevée contre les UVA et les UVB et une faible cytotoxicité. Elles présentaient également une bonne stabilité sous l'exposition aux UV et peuvent être dégradées via hydrolyse. Le second objectif vise à développer les particules thermosensibles. Des micro/nanoparticules poreuses biodégradables composées de Eudragit RS100 et de poly(N-isopropylacrylamide) (PNIPAM) ont été préparées via la technique double émulsion évaporation de solvant. L'effet de la nature d’amorceur sur la polymérisation du monomère NIPAM a été influencé par la morphologie, l'efficacité d'encapsulation et le taux d’encapsulation de la molécule active. En dessous de la température de transition de phase volumique (TVPT), Le PNIPAM sensibles à la température contenu dans les particules, possède une conformation expansée obstruant les pores et empêchant ainsi la diffusion du médicament modèle à l'extérieur. En revanche, le PNIPAM réticulé s'est transformé en polymère rétracté et hydraté, permettant ainsi l’ouverture des cavités réservoirs et la libération du composé encapsulé. Ces particules thermosensibles ont remarquablement montré un mécanisme de libération de molécule active commutable "marche-arrêt" précis est contrôlable. Ainsi, ces matériaux ont un fort potentiel d'utilisation comme additifs de protection contre les UV dans les produits cosmétiques et comme matériaux d'administration de molécules actives dans les applications biomédicales et pharmaceutiques

Fabrication de micro/nano particules de polymère biodégradable et leur utilisation dans des applications cosmétiques et biomédicales

Les particules à base de polymères biodégradables ont attiré une grande attention dans le domaine cosmétique et biomédical en raison de leur biocompatibilité, de leur non-toxicité et de leur dégradabilité. Cette étude propose l'utilisation de polymères biodégradables pour fabriquer les micro- et nanoparticules par plusieurs techniques d'émulsification. La première méthode est la fabrication de nanoparticules poreuses dérivées du poly(acide lactique-co-méthacrylate de glycidyle), P(LA-co-GMA) par émulsification et par inversion de phase en une étape. L'influence de la migration des tensioactifs et de la vitesse d'évaporation joue un rôle important dans la formation de la structure poreuse. Les nanoparticules poreuses, monodisperses en taille et une présentant une bonne stabilité colloïdale sont obtenues. Ces nanoparticules ont été utilisées comme additifs de protection contre les UV dans des applications cosmétiques. Les nanoparticules poreuses ont montré une capacité de protection élevée contre les UVA et les UVB et une faible cytotoxicité. Elles présentaient également une bonne stabilité sous l'exposition aux UV et peuvent être dégradées via hydrolyse. Le second objectif vise à développer les particules thermosensibles. Des micro/nanoparticules poreuses biodégradables composées de Eudragit RS100 et de poly(N-isopropylacrylamide) (PNIPAM) ont été préparées via la technique double émulsion évaporation de solvant. L'effet de la nature d’amorceur sur la polymérisation du monomère NIPAM a été influencé par la morphologie, l'efficacité d'encapsulation et le taux d’encapsulation de la molécule active. En dessous de la température de transition de phase volumique (TVPT), Le PNIPAM sensibles à la température contenu dans les particules, possède une conformation expansée obstruant les pores et empêchant ainsi la diffusion du médicament modèle à l'extérieur. En revanche, le PNIPAM réticulé s'est transformé en polymère rétracté et hydraté, permettant ainsi l’ouverture des cavités réservoirs et la libération du composé encapsulé. Ces particules thermosensibles ont remarquablement montré un mécanisme de libération de molécule active commutable "marche-arrêt" précis est contrôlable. Ainsi, ces matériaux ont un fort potentiel d'utilisation comme additifs de protection contre les UV dans les produits cosmétiques et comme matériaux d'administration de molécules actives dans les applications biomédicales et pharmaceutiques.Biodegradable polymeric particles have attracted vast attention in cosmetic and biomedical fields because of its biocompatibility, non-toxicity, and degradability in natural environments. This study proposed the use of biodegradable polymers to fabricate the micro- and nanoparticles by several emulsification techniques. The first method was the fabrication of hollow nanoparticles which derived from poly(lactic acid-co-glycidyl methacrylate), P(LA-co-GMA) by one-step phase inversion emulsification. The influence of surfactant migration and evaporation rate play an important role in the hollow structure formation. The monodispersed hollow nanoparticles and good colloidal stability are obtained. These nanoparticles were applied to use as UV-shielding additives in cosmetic applications. The hollow nanoparticles showed high UVA&UVB shielding capability and low cytotoxicity. They also exhibited the stability under the UV exposure, and could be degraded under the hydrolysis system. The second one aimed to develop the thermoresponsive gating particles. Porous biodegradable micro/nanoparticles were prepared using Eudragit RS100 and poly(N-isopropylacrylamide) (PNIPAM) via a double emulsion solvent evaporation technique. The effect of initiator types on the polymerization of NIPAM monomer was influenced by the morphology, encapsulation efficiency, and loading capacity of the drug carriers. Temperature-sensitive particles possessed a swollen conformation to block the pores and prevent the diffusion of model drug at below the volume transition temperature (TVPT). In contrast, the crosslinked PNIPAM transformed to be a hydrophobicity and collapse, allowing the gate to open and release the encapsulated compound. These thermoresponsive particles remarkably showed a precise “on-off” switchable release mechanism which is easy to control drug delivery when triggered at the body temperature. Thus, these materials have a high potential for use as UV-shielding additives in cosmetic products, and drug delivery materials in biomedical and pharmaceutical applications

Biodegradable porous micro/nanoparticles with thermoresponsive gatekeepers for effective loading and precise delivery of active compounds at the body temperature

International audienceAbstract Stimuli-responsive controlled delivery systems are of interest for preventing premature leakages and ensuring precise releases of active compounds at target sites. In this study, porous biodegradable micro/nanoparticles embedded with thermoresponsive gatekeepers are designed and developed based on Eudragit RS100 (PNIPAM@RS100) and poly(N-isopropylacrylamide) via a double emulsion solvent evaporation technique. The effect of initiator types on the polymerization of NIPAM monomer/methylene-bis-acrylamide (MBA) crosslinker was investigated at 60 °C for thermal initiators and ambient temperature for redox initiators. The crosslinked PNIPAM plays a key role as thermal-triggered gatekeepers with high loading efficiency and precise release of a model active compound, Nile Blue A (NB). Below the volume phase transition temperature (T VPT ), the gatekeepers possess a swollen conformation to block the pores and store NB within the cavities. Above its T VPT , the chains rearrange, allowing gate opening and a rapid and constant release rate of the compound until completion. A precise “on–off” switchable release efficiency of PNIPAM@RS100 was demonstrated by changing the temperatures to 4 and 40 °C. The materials are a promising candidate for controlled drug delivery systems with a precise and easy triggering mechanism at the body temperature for effective treatments

Preparation of Eumelanin-Encapsulated Stereocomplex Polylactide Nano/Microparticles for Degradable Biocompatible UV-Shielding Products

The role of eumelanin as a natural pigment in protecting human skin from ultraviolet (UV) light has drawn vast interest in the research and industrial community. Encapsulation of the compound by various shell materials has been extensively studied to optimize and prolong its shielding efficiency from UV penetration through the skin. Polylactide (PLA)-based copolymers have been widely used in the encapsulation of various active compounds due to their biocompatibility and biodegradability that facilitate sustained release of the active compounds. In this work, stereocomplex PLA (sc-PLA) derived from mixtures of poly(D-lactide-caprolactone-D-lactide), P(DLA-b-CL-b-DLA), a triblock copolymer with linear poly(L-lactide), and PLLA are employed to encapsulate eumelanin by an oil-in-water emulsion (O/W) technique. The effect of eumelanin distribution in PLA’s enantiomers and ultrasonication on the physicochemical properties, encapsulation efficiency, and release behavior of the nano/microparticles were evaluated. The potential application of the resulting particles for sunscreen products was assessed in terms of UV absorbance and in vitro sun protection factor (SPF). The nano/microparticles show a hollow spherical structure, whose size can be controlled by ultrasonication. The distribution of eumelanin and the ultrasonication process play a key role in the growth of sc-PLA and the crystalline structure of the particles. The highest encapsulation efficiency of 46.6% was achieved for sc-PLA2U particles. The high content of eumelanin and the hollow structure with a large surface area lead to improvement in the UV absorbance and sunscreen performance of the particles, as revealed by the increase in the SPF value from 9.7 to 16.5. The materials show high potential for various applications, especially in cosmetic and pharmaceutical fields, as UV-shielding products