Rheological and low field NMR characterization of hydrophobically-modified PEG hydrogels for drug delivery

Supramolecular eutectogel as new oral paediatric delivery system to enhance benznidazole bioavailability

Benznidazole (BNZ) serves as the primary drug for treating Chagas Disease and is listed in the WHO Model List of Essential Medicines for Children. Herein, a new child-friendly oral BNZ delivery platform is developed in the form of supramolecular eutectogels (EGs). EGs address BNZ's poor oral bioavailability and provide a flexible twice-daily dose in stick-pack format. This green and sustainable formulation strategy relies on the gelation of drug-loaded Natural Deep Eutectic Solvents (NaDES) with xanthan gum (XG) and water. Specifically, choline chloride-based NaDES form stable and biocompatible 5 mg/mL BNZ-loaded EGs. Rheological and Low-field NMR investigations indicate that EGs are viscoelastic materials comprised of two co-existing regions in the XG network generated by different crosslink distributions between the biopolymer, NaDES and water. Remarkably, the shear modulus and relaxation spectrum of EGs remain unaffected by temperature variations. Upon dilution with simulated gastrointestinal fluids, EGs results in BNZ supersaturation, serving as the primary driving force for its absorption. Interestingly, after oral administration of EGs to rats, drug bioavailability increases by 2.6-fold, with a similar increase detected in their cerebrospinal fluid. The noteworthy correlation between in vivo results and in vitro release profiles confirms the efficacy of EGs in enhancing both peripheral and central BNZ oral bioavailability.

The Influence of Lyophilization Pretreatment and Whey Content on Whey and Gelatin-Based Hydrogels

Whey and gelatin, natural polymers within the protein category, find widespread use in hydrogel formulations applied across the food, medical, and pharmaceutical industries. This study presents new characteristics of hydrogels based on whey, gelatin, and copper sulfate as a consequence of the additional steps in the preparation method, specifically refrigeration and freezing storage followed by lyophilization. The water state in hydrogels prior to lyophilization impacts the morphological appearance, with refrigerated hydrogels exhibiting a more regular and dense pore distribution, as shown by the Scanning Electron Microscopy (SEM) images. This observation aligns with the higher mobility of polymer chains indicated by T2 distributions in 1H nuclear magnetic resonance (RMN) relaxometry measurements. Changes in the intensity and amide-specific wavenumbers of the FTIR spectra of whey and gelatin proteins are evident in the Fourier Transformed Infrared (FTIR) spectra of crosslinked and frozen hydrogels before lyophilization. Moreover, the reinforcing effect in the hydrogel matrix, noted in mechanical tests, is attributed to increased polymer chain content and copper sulfate crosslinking.

Ionic Strength Impacts the Physical Properties of Agarose Hydrogels

Agarose is a natural polysaccharide known for its ability to form thermoreversible hydrogels. While the effects of curing temperature and polysaccharide concentration on mechanical properties have been discussed in the literature, the role of ionic strength has been less studied. In the present manuscript, we investigate the effects of supporting salt concentration and the role of cation (i.e. Na+ or Li+, neighbors in the Hofmeister series), on the setting and performance of agarose hydrogels. Compressive and rheological measurements show that the supporting salts reduce the immediate elastic response of agarose hydrogels, with Li+ showing a stronger effect than Na+ at high ionic strength, while they significantly increase the extent of linear stress-strain response (i.e., linear elasticity). The presence of increasing amounts of added supporting salt also leads to a reduction in hysteresis during mechanical deformation due to loading and unloading cycles, which is more pronounced with Li+ than with Na+. The combination of rheological measurements and NMR relaxometry shows a mesh size in agarose hydrogels in the order of 6-17 nm, with a thickness of the water layer bound to the biopolymer of about 3 nm. Of note, the different structuring of the water within the hydrogel network due to the different alkali seems to play a role for the final performance of the hydrogels.