Structural characterization and properties of polyols plasticized chitosan films.

In this study, the influence of different polyols such as glycerol, xylitol and maltitol on the crystalline structure and thermal properties of chitosan films were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The concentration of polyol was fixed at 20 wt%. FTIR result showed that the addition of polyols weakened the hydrogen bonding between chitosan molecules, whereas the electrostatic interactions remained nearly unchanged. Structural analysis revealed that the plasticizer which promoted the crystallization of chitosan was moisture rather than polyol contained in the polymer films. DSC result indicated that glycerol plasticized film had a lower glass transition temperature (Tg) and lower melting temperature (Tm). The low thermal transition temperatures suggested that the moisture content is higher in glycerol plasticized film, which was evidenced by TGA result. In addition, the polyols incorporation resulted in a decrease of the tensile strength of chitosan films, while their ductility was improved. These observations indicate that the addition of polyols as plasticizers could regulate the microstructure as well as the properties of chitosan films, which is essential for their usage in food industry.

Effect of hydration on water state, glass transition dynamics and crystalline structure in chitosan films.

The influence of water uptake on water state, glass transition dynamics and crystalline structure in chitosan films was investigated by differential scanning calorimetry (DSC), X-ray diffraction and infrared spectroscopy (FTIR) techniques. DSC result indicated that two types of water, i.e., non-freezable water and freezable water, appeared in turn with the gradual increase of water content. Only the non-freezable water was responsible for the reduction of glass transition temperature (Tg), which leveled off at higher hydration levels. Structural analysis revealed that moisture could bring about a slight increase in the crystallinity of polymer due to alignment of hydrated and relaxed chitosan chains in the amorphous region. FTIR result showed that the hydrogen bonds and electrostatic forces existing in chitosan films varied slightly with water content. These observations suggest that changing the water content in such systems offers the possibility to control the microstructure as well as properties of polymers.

Effect of sorbitol content on microstructure and thermal properties of chitosan films.

In this work, the influence of sorbitol content on the microstructure and thermal properties of chitosan films was investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Thermogravimetric analysis (TGA) and Differential scanning calorimetry (DSC). It showed that the addition of sorbitol weakened the hydrogen bonding between chitosan molecules as well as the electrostatic interactions existed in chitosan films. Structural analysis revealed that a small amount of sorbitol (~10 wt%) could facilitate the crystallization of chitosan, whereas it was seriously hindered at high content of sorbitol (~50 wt%). The thermal behavior of composite films indicated that the sorbitol addition did not reduce the thermal stability of polymer films. When the sorbitol content rose to above 30 wt%, phase separation may occur and two glass transitions presented in composite films. The lower temperature transition was associated with the glass-rubber transition of sorbitol-rich phase, and the higher one was related to chitosan-rich phase. These results implied that the microstructure as well as properties of the plasticized chitosan films can be controlled by adding sorbitol, which is important for their usage as packaging materials.

Effect of salt on the coil-helix transition of gelatin at early stages: Optical rotation, rheology and DSC studies.

The influence of the concentration and type of salt on the physical gelation of gelatin at early stages was explored by polarimeter, rheometer and differential scanning calorimetry (DSC). With the increase of salt concentration, both the triple helix content and the storage modulus of gelatin increased slightly and then decreased in CaCl2 solutions, whereas they decreased monotonically in NaCl and CrCl3 solutions. The addition of CaCl2 at low concentrations facilitated the coil-helix transition of gelatin, which could be significantly inhibited by high salt concentrations. The melting temperature of gels was nearly unchanged with varying salt concentration, but the melting enthalpy decreased monotonically with salt addition. This result indicates that salt additions mainly affect the nucleation of triple helices, but had minor effect on its growth. In addition, the coil-helix transition of gelatin in salt solutions at early stages could be treated successfully by an equation of first order kinetics.

Molecular interactions in gelatin/chitosan composite films.

Gelatin and chitosan were mixed at different mass ratios in solution forms, and the rheological properties of these film-forming solutions, upon cooling, were studied. The results indicate that the significant interactions between gelatin and chitosan promote the formation of multiple complexes, reflected by an increase in the storage modulus of gelatin solution. Furthermore, these molecular interactions hinder the formation of gelatin networks, consequently decreasing the storage modulus of polymer gels. Both hydrogen bonds and electrostatic interactions are formed between gelatin and chitosan, as evidenced by the shift of the amide-II bands of polymers. X-ray patterns of composite films indicate that the contents of triple helices decrease with increasing chitosan content. Only one glass transition temperature (Tg) was observed in composite films with different composition ratios, and it decreases gradually with an increase in chitosan proportion, indicating that gelatin and chitosan have good miscibility and form a wide range of blends.

Solid and hollow pedicle screws affect the electrical resistance: A potential source of error with stimulus-evoked electromyography.

BACKGROUND: Although stimulus evoked electromyography (EMG) is commonly used to confirm the accuracy of pedicle screw placement. There are no studies to differentiate between solid screws and hollow screws to the electrical resistance of pedicle screws. We speculate that the electrical resistance of the solid and hollow pedicle screws may be different and then a potential source of error with stimulus-evoked EMG may happen. MATERIALS AND METHODS: Resistance measurements were obtained from 12 pedicle screw varieties (6 screws of each manufacturer) across the screw shank based on known constant current and measured voltage. The voltage was measured 5 times at each site. RESULTS: Resistance of all solid screws ranged from 0.084 Ω to 0.151 Ω (mean =0.118 ± 0.024 Ω) and hollow screws ranged from 0.148 Ω to 0.402 Ω (mean = 0.285 ± 0.081 Ω). There was a significant difference of resistance between the solid screws and hollow screws (P < 0.05). The screw with the largest diameter no matter solid screws or hollow screws had lower resistance than screws with other diameters. No matter in solid screws group or hollow screws group, there were significant differences (P < 0.05) between the 5.0 mm screws and 6.0 mm screws, 6.0 mm screws and 7.0 mm screws, 5.0 mm screws and 7.0 mm screws, 4.5 mm screws and 5.5 mm screws, 5.5 mm screws and 6.5 mm screws, 4.5 mm screws and 6.5 mm screws. The resistance of hollow screws was much larger than the solid screws in the same diameter group (P < 0.05). CONCLUSIONS: Hollow pedicle screws have the potential for high electrical resistance compared to the solid pedicle screws and therefore may affect the EMG response during stimulus-evoked EMG testing in pedicle screw fixation especially in minimally invasive percutaneous pedical screw fixation surgery.

[Development of a new noninvasive blood sugar detector].

The level of blood sugar is an improtant indicator used in the diagnosis and management of diabetes mellitus. In this respect, polarimeter and blood sugar detector were conventionally and generally used in hospitals; However, the former one is already obsolete; the latter one is invasive. In this paper, the development of a novel noninvasive blood-sugar detector is described. The experiment indicate that this detector is nonivasive, safe, fast, and easy to operate, and it can be of wide application.