RESUMEN
This work examines the relationship between microstructural properties of hot-moulded chitosan networks, crosslinked with trisodium phosphate, and diffusive behaviour from these networks. Analysis through infrared spectroscopy (FTIR) confirmed successful crosslinking of the polymer chains and bioactive entrapment, while X-ray diffraction (WAXD) and dynamic oscillation in-shear elucidated the higher order structural properties of each matrix, as they transitioned from solutions to amorphous gels to semi-crystalline matrices. The picture of molecular motion observed in these systems and consequent application of the Flory-Rehner theory further indicated that different extents of chitosan crosslinking yielded a distinct water infusion functionality seen in the levels of swelling. Diffusion of caffeine from these delivery vehicles showed that network structural properties (governed by crosslinker concentration) had a significant effect on the release kinetics of the entrapped bioactive. The relationship between network mesh characteristics and diffusion properties were further confirmed by correlating caffeine release rates and molecular pore size.
Asunto(s)
Quitosano , Cafeína , Quitosano/química , Reactivos de Enlaces Cruzados/química , Difusión , Cinética , Fosfatos , Espectroscopía Infrarroja por Transformada de Fourier , Difracción de Rayos XRESUMEN
Crosslinking of hydroxypropyl methyl cellulose (HPMC) and acrylic acid (AAc) was carried out at various compositions to develop a high-solid matrix with variable glass transition properties. The matrix was synthesized by the copolymerisation of two monomers, AAc and N,N'-methylenebisacrylamide (MBA) and their grafting onto HMPC. Potassium persulfate (K2S2O8) was used to initiate the free radical polymerization reaction and tetramethylethylenediamine (TEMED) to accelerate radical polymerisation. Structural properties of the network were investigated with Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), modulated differential scanning calorimetry (MDSC), small-deformation dynamic oscillation in-shear, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The results show the formation of a cohesive macromolecular entity that is highly amorphous. There is a considerable manipulation of the rheological and calorimetric glass transition temperatures as a function of the amount of added acrylic acid, which is followed upon heating by an extensive rubbery plateau. Complementary TGA work demonstrates that the initial composition of all the HPMC-AAc networks is maintained up to 200 °C, an outcome that bodes well for applications of targeted bioactive compound delivery.
Asunto(s)
Acrilamidas/química , Derivados de la Hipromelosa/química , Acrilatos/química , Rastreo Diferencial de Calorimetría , Vidrio , Ensayo de Materiales , Microscopía Electrónica de Rastreo , Polimerizacion , Espectroscopía Infrarroja por Transformada de Fourier , Termogravimetría , Vitrificación , Difracción de Rayos XRESUMEN
High-solid chitosan matrices were prepared to investigate the effect of their swelling on structural relaxation and glass transition. Degree of crosslinking in genipin-crosslinked chitosan networks was measured with a ninhydrin assay and a suitable crosslinker concentration was determined for gels used in swelling and thermomechanical analysis. Fourier transform infrared spectroscopy and wide angle X-ray diffraction examined the intermolecular interactions, crystallinity and amorphicity of the biopolymer networks. Swelling characteristics following immersion in water included approximate equilibrium values of the average molecular weight between crosslinks and network mesh size, e.g. 902 g mol-1 and 110 nm for the preparation with an initial solids content of 60% (w/w) after 80 min of swelling, which were quantified with the modified Flory-Rehner theory. Thermal glass transition temperature was observed in the condensed crosslinked networks (≥ 70% w/w total solids) during differential scanning calorimetry experiments. Time-temperature superposition of rheological measurements, obtained with dynamic oscillation in-shear, generated a master curve describing the viscoelastic behaviour of the system, moving through the rubbery, glass transition region and glassy state. Combined analysis using the modified Arrhenius and William-Landel-Ferry theories determined mechanical glass transition temperatures in the range of -68 to -8 °C for the crosslinked biopolymer at intermediate-solid concentrations (40 to 60% w/w solids). An understanding of the effect of swelling on molecular network characteristics was achieved, which is crucial for greater control in the design of systems for the targeted delivery of bioactive compounds.
Asunto(s)
Quitosano/química , Iridoides/química , Rastreo Diferencial de Calorimetría , Peso Molecular , Transición de Fase , Reología , Espectroscopía Infrarroja por Transformada de Fourier , Propiedades de Superficie , Vitrificación , Difracción de Rayos XRESUMEN
Structural relaxation and glass transition were examined in the swelling behaviour of a high-solid biopolymer matrix; genipin-crosslinked gelatin. Degree of swelling was quantified by the Flory-Rehner theory that furnishes estimates of average molecular weight between crosslinks and network mesh size. Fourier transform infrared spectroscopy and wide angle X-ray diffraction described intermolecular interactions and the extent of amorphicity in the crosslinked matrix. Micro differential scanning calorimetry provided evidence of the changing thermodynamic characteristics of the gelatin network in the presence of the crosslinker. Modulated differential scanning calorimetry and small deformation oscillatory rheology unveiled the vitrification properties of the system. Experimental measurements were treated with the time-temperature superposition principle to unveil an extensive master curve through the rubbery, glass transition and glassy states. Viscoelastic behaviour was modelled with the combined predictions of the modified Arrhenius and William-Landel-Ferry theories to pinpoint the mechanical glass transition temperature that was compared with predictions from calorimetry. Comprehensive understanding of polymeric behaviour during swelling affords greater control in the design of targeted delivery matrices for drugs and other bioactive compounds.