Structural manipulation of the gelatin/genipin network to inform the molecular transport of caffeine

Abstract

Low-solid gelatin hydrogels crosslinked with varied levels of genipin were examined to determine the effect of morphological properties on swelling and bioactive diffusion phenomena. FTIR analysis paired with WAXD showed the successful entrapment of caffeine and, when combined with the ninhydrin assay, confirmed the crosslinking of gelatin with genipin. Further investigation of the system with rheological profiling yielded a picture of the overall gel strength increasing with crosslinking and a change in the conformation of the gelatin chains with genipin addition. SEM micrographs were utilised to confirm the microstructural evaluation given by the Flory-Rehner theory from swelling studies. Further quantitative estimations of the gel crosslinking were also developed using this theory with increasing genipin concentration markedly changing the network density and mesh properties. Diffusive transport of caffeine was analysed for different proportions of genipin crosslinking with the denser crosslinked structures evidently hindering the free movement of bioactive molecules. The coupling parameter (ξ) between polymeric network and bioactive cargo, and the critical molecular weight between two crosslinks (M*c) were also determined to relate structural property to molecular diffusion.