Emmanuel Richaud

Poly(N-isopropylacrylamide) (PNIPAm)-based polymers are undoubtedly a promising solution for controlled drug delivery. This study presents the potential of such hydrogels in terms of stability for drug delivery property. Aging under thermal oxidative aging at 120°C for 2 months is performed and its consequences on drug delivery are investigated. First, two active pharmaceutical ingredients (API) (metronidazole, MTZ and orbifloxacin, ORBI) and PNIPAm-based polymers are fully characterized. Linear poly(N-isopropylacrylamide) demonstrates an immediate release of antibiotic-type active pharmaceutical ingredients (MTZ and ORBI) at 25°C and 37°C with over 90% API release after 1-hour period. For more complex systems, such as cross-linked networks and copolymers, controlled release of ORBI at 25°C and 37°C is achieved over a 24-hour period and only 80% API release with an initial burst release phase. Results showed a slight increase in glass transition after aging at 120°C for 2 months with a decrease in the macromolecular mobility of the polymer. Structural modifications induced by aging lead to variations in the release behavior of APIs. Over time, the release slows down, and the overall efficacy of the system diminishes drastically. 19F is used as a probe to monitor ORBI release by quantitative NMR spectrometry, and diffusion coefficients are determined by Diffusion Ordered SpectroscopY (DOSY) to characterize API-Hydrogels interactions. This work extends our understanding of the stability of poly(N-isopropylacrylamide)-based polymers, enabling a rational approach of their use as pharmaceutical excipients.

Fluorescence spectroscopy is a powerful tool for polymer characterization; however, the use of commercial probes is frequently hindered by the UV-visible opacity of the matrices. To circumvent this limitation, a novel reactive push-pull probe was designed, combining a triphenylamine core with a pyridinium and amine group (NH₂-TPA-Py⁺). Through its amine functionality, the probe is covalently grafted within an epoxy-amine network (DGEBA-DDM), thereby eliminating sublimation risks and mitigating self-aggregation (AIE phenomena). This work presents the synthesis and characterization of this probe. It exhibits an intense, red-shifted dual fluorescence (LE and TICT states), which bypasses the internal filter effects of the matrix. After deconvolving the various fluorescence emission signals from the isolated probe and aggregates in different solvents, the use of absorbance and LE and TICT states enables the solvatochromic behaviour of the probe using the Kamlet-Abboud-Taft multiparameter model. This approach was successfully applied to characterize the local polarity (\pi^\ast), acidity (\alpha), and basicity (\beta) of the network. This method provides a highly sensitive in situ analytical tool for probing the molecular physicochemical environment of thermosetting polymers.

Industrial polymeric materials often rely on antioxidants to achieve long‐term reliability. Previous studies have frequently discussed the stabilization effect in the presence of macroscopic additive migration. However, the micro‐ to mesoscale coupling between polymer dynamics and antioxidant molecular dynamics remains insufficiently understood. In this study, we extend a polymer dynamics simulation framework that can account for oxidative aging. We also update the model so that it can explicitly incorporate antioxidant molecules into the simulation. As a result, the framework enables us to quantify how the molecular architecture of antioxidants affects oxidation kinetics, which has previously been inferred only indirectly from apparent changes in reaction rates. It also allows us to evaluate the effects of antioxidant concentration and molecular architecture on the spatial heterogeneity of oxidative aging.

Epoxy diamine systems were thermally oxidized at 110°C under air. Ageing was monitored using DMA in multi‐frequency multi‐temperature mode. The analysis led to the conclusion that the crosslinking predominates. Data were exploited using classical VTFH and WLF theories for estimating the changes of free volume‐related parameters with ageing.

This study reports the impact of temperature, oxygen, and humidity ageing on the mechanical properties of a crosslinked hydroxy‐terminated polybutadiene (HTPB) network. Its mechanical behavior is described using a classical Mooney‐Rivlin model and shows a slight crosslinking reaction possibly due to oxidation of HTPB. Water presence is shown to have negligible effect during ageing and during the post ageing preconditioning step prior to mechanical tests.