In Chul Um

Structural characteristics and properties of the regenerated silk fibroin prepared from formic acid.

Structural characteristics and thermal and solution properties of the regenerated silk fibroin (SF) prepared from formic acid (FU) were compared with those of SF from water (AU). According to the turbidity and shear viscosity measurement, SF formic acid solution was stable and transparent, no molecular aggregations occurred. The sample FU exhibited the beta-sheet structure, while AU random coil conformation using Fourier transform infrared (FTIR), X-ray diffraction (XRD), and differential scanning calorimetry. The effects of methanol treatment on samples were also examined. According to the measurement of crystallinity (XRD) and crystallinity index (FTIR), the concept of long/short-range ordered structure formation was proposed. Long-range ordered crystallites are predominantly formed for methanol treated SF film while SF film cast from formic acid favors the formation of short-range ordered structure. The relaxation temperatures of SF films measured by dynamic thermomechanical analysis supported the above mechanism due to the sensitivity of relaxation temperature on the short-range order.

Structural and thermal characteristics of Antheraea pernyi silk fibroin/chitosan blend film

Abstract Antheraea pernyi silk fibroin (SF)/chitosan blend films were prepared by mixing aqueous solution of A. pernyi SF and acetic acid solution of chitosan. The conformation of A. pernyi SF in blend films was revealed to be a β-sheet structure, mainly due to the effect of acetic acid used as a mixing solvent. According to the Fourier transform infrared (FTIR) spectra, NH groups of SF and C O and NH2 groups of chitosan might have participated in a specific intermolecular interaction among themselves. The exotherm of SF was not exhibited in blend films due to the precrystallization of SF induced by acetic acid. The blend films showed two distinct maximum decomposition temperatures at around 294 (chitosan component) and 369°C (A. pernyi component), which could be indirect evidences of a phase separation. Scanning electron microscopy (SEM) results confirmed that the phase separation occurred in A. pernyi SF/chitosan blend film. Blending with A. pernyi SF can enhance the thermal decomposition stability of chitosan.

Thermal behavior of regenerated Antheraea pernyi silk fibroin film treated with aqueous methanol

The regenerated Antheraea pernyi silk fibroin films prepared from calcium nitrate solution were treated with 80% aqueous methanol. The thermal and dynamic thermomechanical behaviors of the films were investigated through TGA, DSC and DMTA. IR spectroscopy was used for the conformational changes with methanol treatments. The treatment time of aqueous methanol highly influenced the thermal behavior of regenerated films. As the methanol treatment time increased up to 60 min, the thermal decomposition behavior did not differ significantly compared with untreated films while the endo/exo transition was gradually decreased, with the exotherm finally disappearing. The dynamic mechanical thermal behavior was also affected by the treatment time of aqueous methanol. The onset temperature of storage modulus drop or damping peak shifted to a higher temperature due to the increase in crystallinity induced by the methanol treatment. The thermal transition was strongly dependent on the formation of β-sheet crystal conformation of the regenerated films upon methanol treatment.

Antihyperlipidemic and body fat-lowering effects of silk proteins with different fibroin/sericin compositions in mice fed with high fat diet.

The effect of silk protein with different fibroin/sericin compositions on body weight and lipid metabolism in high fat-fed mice was investigated. The animals were given experimental diets for 6 weeks: normal control (NC), high fat (HF) and high fat diet supplemented with F100 (pure fibroin, HF-F100), F81 (81:19 fibroin/sericin, w/w, HF-F81) or F50 (50:50 fibroin/sericin, w/w, HF-F50). The silk protein-fed mice showed markedly reduced body weight and enhanced lipid profile relative to the HF group. In general, the amount of body fat, triglyceride and total plasma cholesterol levels, atherogenic index and free fatty acid level tended to decrease, while the HDL-cholesterol level increased, with increased amount of sericin in the diet. This hypolipidemic effect was partly due to increased fecal lipid excretion, inhibition of lipogenesis and regulation of adipokine production. These findings illustrate that silk protein, particularly sericin, may be beneficial in the prevention of high fat diet-induced hyperlipidemia and obesity.

Antihyperglycemic and Antioxidative Effects of Hydroxyethyl Methylcellulose (HEMC) and Hydroxypropyl Methylcellulose (HPMC) in Mice Fed with a High Fat Diet

The effect of dietary feeding of hydroxyethyl methylcellulose (HEMC) and hydroxypropyl methylcellulose (HPMC) on the glucose metabolism and antioxidative status in mice under high fat diet conditions was investigated. The mice were randomly divided and given experimental diets for six weeks: normal control (NC group), high fat (HF group), and high fat supplemented with either HEMC (HF+HEMC group) or HPMC (HF+HPMC group). At the end of the experimental period, the HF group exhibited markedly higher blood glucose and insulin levels as well as a higher erythrocyte lipid peroxidation rate relative to the control group. However, diet supplementation of HEMC and HPMC was found to counteract the high fat-induced hyperglycemia and oxidative stress via regulation of antioxidant and hepatic glucose-regulating enzyme activities. These findings illustrate that HEMC and HPMC were similarly effective in improving the glucose metabolism and antioxidant defense system in high fat-fed mice and they may be beneficial as functional biomaterials in the development of therapeutic agents against high fat dietinduced hyperglycemia and oxidative stress.

Hemicellulose Removal and Crystalline Structure Transition of Flax Fiber with Alkali Treatment

In this study, delignified flax fiber was treated with a NaOH aqueous solution. XRD diffractometry and FTIR spectroscopy were utilized to examine the structural transition of the alkali-treated flax fibers. Also, the effect of the hemicellulose removal on the structural change of flax fibers was discussed. XRD measurement revealed that the crystallinity of cellulose I increased at low NaOH concentration (3%) due to the elimination of amorphous hemicellulose. The structural transition from cellulose I to cellulose II occurred in a NaOH concentration range of 12~15%. Considering most hemicellulose in flax fiber is removed at 12% NaOH, it can be assumed that the presence of hemicellulose in flax fiber has a role in preventing the structural change of flax cellulose. IR absorbance ratios ( and ) were utilized as a barometer of cellulose I crystalline exhibiting a similar result with the cellulose I crystallinity from XRD. Another absorbance ratio () reflected the cellulose II crystalline showing almost the same trend as cellulose II crystallinity. On the whole, the total crystallinity of flax fiber was increased at low NaOH concentration (3%) and decreased at 12% due to the reduction of cellulose I content and increased again at 15% attributed to the formation of cellulose II content.