Influence of the deacetylation degree on chitosan emulsification properties

The emulsification of sunflower oil by chitosan solutions with deacetylation degrees (DD) between 73 and 95% was studied using different techniques. The droplet size distributions, conductivity, ageing behavior and viscosity of emulsions were studied as functions of the chitosan DD. All DD gave stable polydisperse water-in-oil-in-water emulsions with different viscosities. Two optimum DD values were found, 81 and 88%, giving complete emulsification without residual oil or sedimentation. Chitosans with intermediate DD were less effective emulsifiers. Chitosans with higher DD gave poor emulsification. Received: 11 January 1999 Accepted in revised form: 31 May 1999     

The use of intense femtosecond laser pulses for the fragmentation of chitosan

The use of ultrashort laser pulses for the fragmentation of chitosan was investigated. Femtosecond Ti-saphire laser pulses were focused into a flask containing 1.0% chitosan in 0.1 M acetic acid. The effects of the pulse energy (between 0.1 and 0.82 mJ) and the focal length on the laser-induced fragmentation were followed by viscometry and size exclusion chromatography. The chemical structure and degree of acetylation of chitosan and its fragments were studied using elemental analysis, IR and ¹H NMR spectroscopy. The experimental results showed that (i) Ti-saphire laser irradiation induced chain scission in the chitosan macromolecules, (ii) the chemical structure, including the degree of acetylation, did not change significantly upon laser irradiation, (iii) the number of chain scission dependence on laser energy suggests that fragmentation was a two-photon process, and (iv) at constant pulse energy, the molecular weight dropped to a minimum as a function of the focal length (between 45 and 330 mm), indicating that the efficiency of fragmentation was very sensitive to the geometry of the laser beam.     

Preparation and characteristics of linoleic acid-grafted chitosan oligosaccharide micelles as a carrier for doxorubicin

The linoleic acid (LA)-grafted chitosan oligosaccharide (CSO) (CSO-LA) was synthesized in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), and the effects of molecular weight of CSO and the charged amount of LA on the physicochemical properties of CSO-LA were investigated, such as CMC, graft ratio, size, zeta potential. The results showed that these chitosan derivatives were able to self-assemble and form spherical shape polymeric micelles with the size range of 150.7–213.9 nm and the zeta potential range of 57.9–79.9 mV, depending on molecular weight of CSO and the charged amount of LA. Using doxorubicin (DOX) as a model drug, the DOX-loaded CSO-LA micelles were prepared by dialysis method. The drug encapsulation efficiencies (EE) of DOX-loaded CSO-LA micelles were as high as about 75%. The sizes of DOX-loaded CSO-LA micelles with 20% charged DOX (relating the mass of CSO-LA) were near 200 nm, and the drug loading (DL) capacity could reach up to 15%. The in vitro release studies indicated that the drug release from the DOX-loaded CSO-LA micelles was reduced with increasing the graft ratio of CSO-LA, due to the enhanced hydrophobic interaction between hydrophobic drug and hydrophobic segments of CSO-LA. Moreover, the drug release rate from CSO-LA micelles was faster with the drug loading. These data suggested the possible utilization of the amphiphilic micellar chitosan derivatives as carriers for hydrophobic drugs for improving their delivery and release properties.     

羟丙基三甲基氯化铵壳聚糖制备的可控性研究

用壳聚糖与缩水甘油三甲基氯化铵反应制备羟丙基三甲基氯化铵壳聚糖,所得产物的结构受壳聚糖分子量和脱乙酰度、反应温度、反应时间、壳聚糖与缩水甘油三甲基氯化铵投料比的影响。实验结果表明：随着反应温度升高,羟丙基三甲基氯化铵壳聚糖的取代度增加,在70～80℃达最大;反应时间增加,取代度增加,产物分子量降低。缩水甘油三甲基氯化铵与壳聚糖比例达3：1前取代度随比例升高而增加。脱乙酰度和分子量越大的壳聚糖其季铵盐取代度越高。控制反应温度在30～90℃,反应时间3～10h,投抖比为1：1～4：1,可以得到取代度15％～909／6,分子量1万到100万的羟丙基三甲基氯化铵壳聚糖。     

Effect of temperature,particle size and percentage deacetylation on the adsorption of acid dyes on chitosan

The adsorption of five acidic dyes on chitosan—a by-product from waste crustacean shell—has been studied. The equilibrium data have been studied using Langmuir, Freundlich and Redlich-Peterson equations. The best correlations are obtained using the Langmuir isotherm suggesting the mechanism involves one process step of dyes complexing with the free amino group. The effect of chitosan particle size was investigated and showed an increase in adsorption capacity with decreasing particle size indicating that the available external surface was an important factor. Increasing solution temperature resulted in an increase in adsorption capacity indicating an exothermic process with a negative ΔH. Finally, the effect of varying the percentage degree of deacetylation showed that from 52% to 97% resulted in decrease in the dye adsorption capacity suggesting that more amorphisation may cause changes in the internal structure of chitosan and reduce the capacity.     

The influence of oxidative degradation on the preparation of chitosan nanoparticles

Chitosan nanoparticles were obtained via ionic crosslinking by using the sulfate ion. Chitosan molecular weight was varied by oxidative degradation of the chitosan β-glycoside bond, the molecular weight being indirectly monitored as the chitosan solution reduced viscosity at a fixed polymer concentration. The dependence between some physical properties of the resultant dispersions (turbidity, viscosity, zeta potential, and sedimentation column profile) and reduced viscosity was established. Atomic force microscopy images have shown the resultant particles formed to be clusters of chitosan nanoparticles with a diameter of ca. 70 nm, the interaction between these particles being characterized by FTIR spectroscopy as the result of sulfate bridging. At the end of the paper, the potential of these dispersions for the incorporation of anionic drugs via adsorption was evaluated using a model compound. The resultant dispersions were capable of adsorbing more than 25% of mass of chitosan, being the partition coefficient higher than 3,500.     

Characterization and in vitro release kinetics of chitosan based biocomposites from Scotch Bonnets

The main aim of this study is to formulate the combination of the bioactive composite containing chitosan/β -tricalcium phosphate (CH/β-TCP) as potential drug delivery platforms for the sustained release of antibiotics. Herein the mode of amoxicillin (AMX) maintained in the β-TCP/chitosan composite was characterized using XRD, FT-IR to confirm the phase purity and functional groups. SEM was used to examine the size and shape of particles. The SEM images of the biocomposites after drug release confirmed that they are biodegradable. In vitro drug release experiments in PBS (pH 7.4) revealed a sustained release profile in a neutral medium. Drug release profiles were evaluated according to five different kinetic models including Zero Order, First Order, Higuchi, Hixon Crowel, and Korsmeyer-Peppas. The release profile was best expressed by the Korsmeyer Peppas model because the results showed high linearity. Overall, the positive effect of chitosan coating on the drug elution profile of β-TCP as carriers for the controlled delivery of antibiotics was regarded as biocompatible for the controlled drug delivery system.     

The effect of different storage temperatures on the physical properties of pectin solutions and gels

The stability (in terms of viscosity and gel strength) of pectin solutions and gels potentially plays an important role in their behaviour and functional properties in a wide range of applications and therefore any changes over time must be understood. The gel strength of pectin gels and intrinsic viscosity of pectin solutions at different temperatures (4 °C, 25 °C and 40 °C) have been investigated using a “rolling ball” viscometer and a texture analyser respectively. Both the intrinsic viscosity ([η]) and gel strength decrease with increased storage time, although this more pronounced at elevated temperatures. The changes in intrinsic viscosity with storage time and temperature were used to determine the depolymerisation constant (k). Pectin storage conditions and particularly temperature have an influence on depolymerisation, particularly elevated storage temperatures, but whether or not this will be detrimental to its intended application will depend on the functional significance of the changes that occur. In this case based on the previous diffusion studies on a model drug (paracetamol) we conclude that the decreases in viscosity and gel strength within the range observed have no detrimental effect on the drug release properties.     

Relationship between the structure and physicochemical characteristics of 1,2,3,4-tetrahydroquinoline derivatives

A number of physicochemical characteristics of ten 1,2,3,4-tetrahydroquinoline derivatives synthesized for the first time, along with their third order Wiener and Randi? indices are calculated by quantum chemical methods. Correlations between the topological indices, physicochemical parameters, and retention factors of the mentioned compounds are obtained for conditions of reversed-phase high performance liquid chromatography on porous graphitized carbon.     

Emulsification properties of chitosan

 The chitosans use as an emulsifier in food emulsions was explored. The properties of chitosan (air/solution surface activity, electrical conductivity, HLB) were studied. The obtained emulsions were stable multiple w/o/w emulsions, whose characteristics were explained on the basis of the emulsifier structure and solution properties. The reaction with an anionic surfactant, sodium dodecylsulfate, was also studied, giving a water-insoluble complex at a given surfactant/chitosan ratio. Received: 24 March 1998 Accepted: 13 July 1998     

Effects of surface modifications on the physicochemical properties of iron oxide nanoparticles and their performance as anticancer drug carriers

Surface of iron oxide nanoparticles were modified with citric acid (CA), chitosan (CS) and folic acid conjugated chitosan (FA-g-CS), respectively. Their physicochemical properties, doxorubicin loading capacity, drug release patterns and in vitro cytotoxicity were comparatively studied.     

共价键合修饰壳聚糖pH传感器的研制

以共价键合的方法将壳聚糖修饰到玻碳电极上制成了pH传感器,探讨了该传感器的性能及作用机理.结果表明该传感器在pH 0.7～11.0的范围内电极电势与pH符合Nernst响应,斜率为58.3 mV/pH,可准确测定较高酸度溶液的pH,克服了玻璃pH传感器的"酸误差"的缺点.该传感器内阻小,易微型化,在一定的pH范围内对温度不敏感且具有较好的准确度和重现性,较快的响应速度.可用于雨水和饮料等实际样品溶液的pH的测定.     

Effects of medium oil on electroresponsive characteristics of chitosan suspensions

Biocompatible chitosan particle suspensions in host oils of corn, soybean, and silicone were prepared and their electrorheological (ER) characteristics were examined under the imposition of electric fields. The effects of the weight concentration of particulate chitosan and the strength of the applied electric field on ER response in the various chitosan particle suspensions were investigated via measurements of rheological properties including flow curve, shear viscosity, and yield stress. The yield stresses of the three different chitosan–oil systems showed different values of slope in the electric field, but all data were found to fit well with our previously proposed universal scaling function.     

Preparation and properties of chitosan nanocomposites with nanofillers of different dimensions

In this work, the chitosan ternary nanocomposites with two-dimensional (2D) clay platelets and one-dimensional (1D) CNTs have been successfully prepared by a simple solution-intercalation/mixing method in acid media. It was found that the thermal degradation temperature of chitosan (at 50% weight loss) could be only improved in about 20-30 °C by adding 3 wt% either clay or CNTs, however, almost 80 °C increase of degradation temperature could be achieved by adding 2 wt% clay and 1 wt% CNTs together. Dynamic mechanical measurement demonstrated an obviously improved storage modulus for chitosan/clay-CNTs than that for the corresponding binary chitosan/clay or chitosan/CNT nanocomposites with the same total filler content (3 wt%). For the solvent vapor permeation properties, a largely improved benzene vapor barrier property was observed only in chitosan/clay-CNT ternary nanocomposites and depended on the ratio of clay to CNTs. XRD, SEM and TEM results showed that both clay and CNTs could be well dispersed in the ternary nanocomposites with the nanotubes located around the clay platelets. FTIR showed an improved interaction between the fillers and chitosan by using both clay and CNTs. A much enhanced solid-like behavior was observed in the ternary nanocomposites, compared with the corresponding binary nanocomposites with the same total filler content, as indicated by rheological measurement. The unique synergistic effect of two-dimensional (2D) clay platelets and one-dimensional (1D) CNTs on the property enhancement could be tentatively understood as due to a formation of much jammed filler network with 1D CNTs and 2D clay platelets combined together. Our work demonstrates a good example for the preparation of high performance polymer nanocomposites by using nanofillers with different dimensions together.     

壳聚糖/乙酰半胱氨酸纳米粒子的性质及体外释药性

制备了一种基于壳聚糖/乙酰半胱氨酸偶合物(CS-NAC)的新型巯基纳米粒子并进行了结构表征, 同时对纳米粒子的黏附性、溶胀性和药物释放进行了测试. 结果表明, 纳米粒子具有较小的粒径(140~210 nm)和正的表面电位(19.5~31.7 mV), 胰岛素的载药量达到13%~42%. 这些性质随着巯基含量的变化而变化. 与壳聚糖纳米粒子相比, 巯基壳聚糖纳米粒子表现出了更强更快的黏附性质. 体外释放研究结果表明, 巯基壳聚糖纳米粒子的胰岛素释放具有pH响应性. 在pH=6.8时, 15 min即能释放58.6 %的胰岛素; 而在pH=5.4时, 24 h内仅有不到40%的胰岛素被释放. 因此, CS-NAC纳米粒子用于胰岛素的黏膜给药体系具有很好的应用前景.     

Structural and dynamical properties of aqueous mixtures of pectin and chitosan

In this study phase separation, structure, and dynamics of aqueous pectin-chitosan mixtures of different ratios and a pure aqueous pectin sample have been investigated under various conditions by turbidimetry, SANS and dynamic light scattering (DLS). Only the mixture with r = 0.75 gelled upon decreasing the temperature ((r ≡ m_pectin/(m_pectin + m_chitosan), where m denotes the mass of the considered component). The pure pectin sample (r = 1) did not gel and the decrease in temperature seemed to promote phase separation. The addition of chitosan reduced the tendency of pectin to phase separate in the mixtures of pectin and chitosan. The general trend when cooling the samples was that the turbidity and the growth of the turbidity became more pronounced as the amount of pectin in the mixture was increased. The wavelength dependence of the turbidity indicated a change of the conformation of pectin chains from an extended form to a more compact structure in pectin solutions without chitosan as the temperature decreased. This was not observed for the mixture of pectin and chitosan. SANS measurements revealed excess scattered intensity in the low wave vector area with the strongest upturn for the pure pectin sample (r = 1). DLS experiments showed longer slow relaxation times after a temperature quench for all samples, with the most pronounced effect for the mixture of pectin and chitosan with r = 0.75. The synergism between pectin and chitosan at high pectin contents (r = 0.75) generated large association complexes over time.     

pH and ionic sensitive chitosan/carboxymethyl chitosan IPN complex films for the controlled release of coenzyme A

pH and ionic sensitive interpenetrating polymer network (IPN) complex films based on chitosan (CS) and carboxymethyl chitosan (CM-CS) were prepared by using glutaraldehyde as crosslinking agent. Its structure was characterized by FT-IR, which indicated that the IPN was formed. The films were studied by swelling, weight loss with time, and release of coenzyme A (CoA). It was found that the IPN films were sensitive to pH and ionic strength of the medium. The cumulative release rate of CoA decreased with CoA loading content, ionic strength or crosslinking agent increasing. The composition of the IPN films and pH of release medium also had significant effect on the release of CoA. The differences in the rates and amounts of released CoA may be attributed to the swelling behavior, the degradation of films, and interaction between drug molecule and polymer matrix. These results suggested CS/CM-CS IPN films could be used as drug delivery carrier.     

Influence of electron beam irradiation on physicochemical properties of poly(trimethylene carbonate)

Electron beam (EB) irradiation of poly(trimethylene carbonate) (PTMC), an amorphous, biodegradable polymer used in the field of biomaterials, results in predominant cross-linking and finally in the formation of gel fraction, thus enabling modification of physicochemical properties of this material without significant changes in its chemical structure. PTMC films (M_w: 167-553 kg mol⁻¹) were irradiated with different doses using an electron accelerator. Irradiation with a standard sterilization dose of 25 kGy caused neither significant changes in the chemical composition of the polymer nor significant deterioration of its mechanical properties. Changes in viscosity-, number-, weight-, and z-average molecular weights of PTMC for doses lower than the gelation dose (D_g) as well as gel-sol analysis and swelling tests for doses above D_g indicate domination of cross-linking over degradation. EB irradiation can be considered as an effective tool for increasing the average molecular weight of PTMC and sterilization of PTMC-based biomaterials.     

Self-aggregated nanoparticles of cholesterol-modified chitosan conjugate as a novel carrier of epirubicin

Cholesterol-modified chitosan conjugate with succinyl linkages (CHCS) was synthesized and characterized by fourier transform infrared (FTIR) and proton nuclear magnetic resonance (¹H NMR). The degree of substitution (DS) of cholesterol moiety determined by elemental analysis was 7.3%. The self-aggregation behavior of CHCS was evaluated by the fluorescence probe technique and the critical aggregation concentration (CAC) was 1.16 × 10⁻² mg mL⁻¹ in 0.1 M acetic acid solution. CHCS formed monodisperse self-aggregated nanoparticles with a roughly spherical shape and a mean diameter of 417.2 nm by probe sonication in aqueous media. Epirubicin (EPB), as a model anticancer drug, was physically entrapped inside CHCS self-aggregated nanoparticles by the remote loading method and the characteristics of EPB-loaded CHCS self-aggregated nanoparticles were analyzed using dynamic laser light scattering (DLLS), transmission electron microscopy (TEM) and fluorescence spectroscopy. EPB-loaded CHCS self-aggregated nanoparticles were almost spherical in shape and their size increased from 338.2 to 472.9 nm with the EPB-loading content increasing from 7.97% to 14.0%. The release behavior of EPB from CHCS self-aggregated nanoparticles was studied in vitro by dialysis method. The results showed that EPB release rate decreased with the pH increase of the release media. In phosphate buffered saline (PBS, pH 7.4), the EPB release was very slow and the total release amount was about 24.9% in 48 h.