The role of Eudragit® as a component of hydrogel formulations for medical devices.

Over the last decade, significant progress has been made in developing hydrogels as medical devices. By physically cross-linking pharmaceutically approved polymers into three-dimensional matrices, we can ensure their biocompatibility and facilitate their seamless transition from the laboratory to clinical applications. Moreover, the reversible nature of their physical cross-links allows hydrogels to dissolve in the presence of external stimuli. Particularly, their high degree of hydration, high molecular weight, and superior flexibility of the polymer chains facilitate their interaction with complex biological barriers (e.g., mucus layer), making them ideal candidates for mucosal drug delivery. However, fine-tuning the composition of the hydrogel formulations is of great importance to optimize the performance of the medical device and its therapeutic cargo. Herein, we investigated the influence of different Eudragits® on the properties of hydrogels based on polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), and polyethylene glycol (PEG), which were originally proposed as ocular inserts in previous reports. Our research aims to determine the effects that including different Eudragits® have on the structure and protein ocular delivery ability of various hydrogel formulations. Properties such as matrix stability, protein encapsulation, release kinetics, mucoadhesion, and biocompatibility have been analyzed in detail. Our study represents a guideline of the features that Eudragits® have to exhibit to endow hydrogels with good adhesion to the eye's conjunctiva, biocompatibility, and structural strength to cope with the ocular biointerface and allow sustained protein release. This work has important implications for the design of new hydrogel materials containing Eudragits® in their composition, particularly in mucosal drug delivery.

Effect of Light Intensity on the Aggregation Behavior of Primary Particles during In Situ Photochemical Synthesis of Gold/Polymer Nanocomposites.

Metal/polymer nanocomposites have attracted much attention in recent years due to their exceptional properties and wide range of potential applications. A key challenge to obtain these materials is to stabilize the metal nanoparticles in the matrix, avoiding uncontrolled aggregation processes driven by the high surface free energy of nanosized particles. Here, we investigate the aggregation mechanism of primary particles in gold-epoxy nanocomposites prepared via light-assisted in situ synthesis, under different irradiation conditions. The growth and aggregation of gold nanoparticles were monitored in situ by time-resolved small-angle X-ray scattering experiments, whereas spectroscopic measurements were performed to interpret how matrix polymerization influences the aggregation process. It was found that light intensity has a greater influence on the reduction rate than on the polymerization rate. Under irradiation, gold nanostructures evolve through five time-defined stages: nuclei-mass fractals-surface fractals-spherical nanoparticles-aggregates. If the maximum in the polymerization rate is reached before the aggregation step, individual primary nanoparticles will be preserved in the polymer matrix due to diffusional constraints imposed by the reaction medium. Because the light intensity has a different influence on the reduction rate than on the polymerization rate, this parameter can be used as a versatile tool to avoid aggregation of gold nanoparticles into the polymer matrix.

Core-crystalline nanoribbons of controlled length via diffusion-limited colloid aggregation.

It has been previously reported that poly(ethylene) (PE)-based block copolymers self-assemble in certain thermosetting matrices to form a dispersion of one-dimensional (1D) nanoribbons. Such materials exhibit exceptional properties that originate from the high aspect ratio of the elongated nano-objects. However, the ability to prepare 1D assemblies with well-controlled dimensions is limited and represents a key challenge. Here, we demonstrate that the length of ribbon-like nanostructures can be precisely controlled by regulating the mobility of the matrix during crystallization of the core-forming PE block. The selected system to prove this concept was a poly(ethylene-block-ethylene oxide) (PE-b-PEO) block copolymer in an epoxy monomer based on diglycidyl ether of bisphenol A (DGEBA). The system was activated with a dual thermal- and photo-curing system, which allowed us to initiate the epoxy polymerization at 120 °C until a certain degree of conversion, stop the reaction by cooling to induce crystallization and micellar elongation, and then continue the polymerization at room temperature by visible-light irradiation. In this way, crystallization of PE blocks took place in a matrix whose mobility was regulated by the degree of conversion reached at 120 °C. The mechanism of micellar elongation was conceptualized as a diffusion-limited colloid aggregation process which was induced by crystallization of PE cores. This assertion was supported by the evidence obtained from in situ small-angle X-ray scattering (SAXS), in combination with differential scanning calorimetry (DSC) and transmission electron microscopy (TEM).