PVDF nanocomposites are prepared through solution mixing of Au‐NPs or Au‐NSs with PVDF. The novel optical properties of Au‐NPs and ‐NSs are retained as confirmed from UV‐Vis spectra. Analysis of resulting nanocomposites by FT‐IR, XRD, and DSC shows an obvious polymorphism change from α‐ to β‐form compared to PVDF prepared under the same conditions. The β‐polymorph seems to be more prominent with higher concentration of Au‐NPs (0.5%) and even more so with Au‐NSs. Thermogravimetric analysis shows that both nanocomposites have better resistance toward thermal degradation. Combination of novel optical properties of Au‐NPs or Au‐NSs with induced ferroelectric‐active β‐polymorph in PVDF can lead to new design of optical, piezoelectric devices. magnified image

Abstract:Gold nanoshells (~160 nm in diameter) were encapsulated within a shell of temperature-responsive poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AA)) using a surface-bound rationally-designed free radical initiator in water for the development of a photothermally-induced drug-delivery system. The morphologies of the resultant hydrogel-coated nanoshells were analyzed by scanning electron microscopy (SEM), while the temperature-responsive behavior of the nanoparticles was characterized by dynamic light scattering (DLS). The diameter of the P(NIPAM-co-AA) encapsulated nanoshells decreased as the solution temperature was increased, indicating a collapse of the hydrogel layer with increasing temperatures. In addition, the optical properties of the composite nanoshells were studied by UV-visible spectroscopy. The surface plasmon resonance (SPR) peak of the hydrogel-coated nanoshells appeared at~800 nm, which lies within the tissue-transparent range that is important for biomedical applications. Furthermore, the periphery of the particles was conjugated with the model protein avidin to modify the hydrogel-coated nanoshells with a fluorescent-tagged biotin, biotin-4-fluorescein (biotin-4-FITC), for colorimetric imaging/monitoring.

Natural polymers are widely used as biodegradable matrices for the controlled release technology because they can improve the performance of the materials and make them environmentally friendly. In this work, the silk fibroin (SF)/gelatin hydrogel with chitosan (CS) was prepared by solvent casting aiming to reduce the rate of urea release from the hydrogels. Results from the Fourier transform infrared confirmed that no intermolecular interactions had taken place after the addition of CS into the SF/ gelatin. Furthermore, the increase of CS content in the SF/ gelatin blended hydrogels caused the decrease in their porosity that affected the increase in their crystallinity, degree of swelling, water solubility, and surface hydrophobicity. The rate of urea release from the hydrogels also depended on the content of CS of which its value of diffusion exponent characteristics (n) determined from the Korsmeyer-Peppas model for SF/gelatin/CS hydrogels were greater than 1.0. This indicated that the urea release from the SF/gelatin hydrogels with CS was a super case II transport type. Moreover, the urea release rate (k) of the SF/gelatin/CS hydrogels was lower than that of the SF/ gelatin hydrogel itself indicating an extension of the urea release from the SF/gelatin hydrogels by CS which could be utilized for controlled release applications.

Utilization of natural polymer as biodegradable matrix for the controlled releasing fertilizer can improve the performance of the materials and make them environmentally friendly. In this work, the effect of gelatin on the properties of hydrogels was investigated. The silk fibroin (SF)-gelatin hydrogels were prepared by solvent casting and β-crystallization of SF was promoted via methanol treatment. The secondary structure and the crystallinity of the blended hydrogels were investigated using Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction analysis (XRD), respectively. Moreover, the swelling ratio of the hydrogels and also their kinetics of nitrogen (N) release were also studied. Results from the FT-IR confirmed that no intermolecular interactions had taken place between SF and gelatin. Furthermore, the increase of gelatin content in the blended hydrogels caused the decrease of the SF crystallinity detected by XRD which corresponded to the swelling behavior of the hydrogel. The release rate of nitrogen (N) depends on the composition of SF and gelatin of which its value of diffusion exponent characteristics (n) determined from the Korsmeyer-Peppas model for all of the hydrogels are smaller than 0.5. This indicates that the release of N from the hydrogels is a quasi-Fickian diffusion. Moreover, the release rate (k) and diffusion coefficient (D) of the SF-gelatin hydrogels are lower than those of the SF itself indicating a potential to use the SF-gelatin hydrogel for nitrogen controlled release application.