Glutaraldehyde cross-linked chitosan microspheres for controlled release of centchroman

Glutaraldehyde cross-linked chitosan microspheres were prepared for controlled release of centchroman, a nonsteroidal contraceptive. The cross-linked microspheres with low-molecular-weight (LMW) chitosan (260 kg mol(-1)) have shown maximum degree of swelling (287 wt%) but were found to be poor in loading and release behavior for centchroman. The microspheres with medium-molecular-weight (MMW) chitosan (1134 kg mol(-1)) have shown 250 wt% degree of swelling and 37.5 wt% loading of centchroman, but microspheres with high-molecular-weight (HMW) chitosan (2224 kg mol(-1)) have shown a low degree of swelling (150 wt%) and centchroman loading (30 wt%). The microspheres with MMW chitosan have released 82 wt% of loaded centchroman in a controlled release manner within a period of 70 h in comparison to low- (260 kg mol(-1)) and high-MW (2224 kg mol(-1)) chitosan microspheres. The chitosan microspheres with 62 wt% degree of deacetylation (DDA) were more efficient in the controlled release of centchroman in comparison to chitosan microspheres with low (48 wt%) and high-DDA (75 wt%). The fractional release of centchroman (M(t)/M(infinity)) from chitosan microspheres was used to predict the mechanism of drug release and to determine the diffusion constant (D) of centchroman.     

Preparation and characterization of sodium hexameta phosphate cross-linked chitosan microspheres for controlled and sustained delivery of centchroman

The cross-linked microspheres using chitosan with different molecular weights and degree of deacetylation have been prepared in presence of sodium hexameta polyphosphate (SHMP) as physical cross-linker. The degree of cross-linking through electrostatic interactions in chitosan microspheres has been evaluated by varying the charge density on chitosan and varying degree of dissociation of sodium hexameta polyphosphate by solution pH. The degree of deacetylation and molecular weight of chitosan has controlled electrostatic interactions between hexameta polyphosphate anions and chitosan, which played significant role in swelling, loading and release characteristics of chitosan microspheres for centchroman. The microspheres prepared by hexameta polyphosphate anions cross-linker were compact and more hydrophobic than covalently cross-linked microspheres, which has been attributed to the participation of all amino groups of chitosan in physical cross-linking with added hexameta polyphosphate anions. The microspheres prepared under different experimental conditions have shown an initial step of burst release, which was followed by a step of controlled release for centchroman. The extent of drug release in these steps has shown dependence on properties of chitosan and degree of cross-linking between chitosan and added polyanions. The degree of swelling and release characteristics of microspheres was also studied in presence of organic and inorganic salts, which shown significant effect on controlled characteristics of microspheres due to variations in ionic strength of the medium. The initial step of drug release has followed first order kinetics and become zero order after attaining an equilibrium degree of swelling in these microspheres. The microspheres prepared using chitosan with 62% (w/w) degree of deacetylation and molecular weight of 1134 kg mol⁻¹ have shown a sustained release for centchroman for 50 h at 4% (w/w) degree of cross-linking with SHMP.     

Solute adsorption and enzyme immobilization on chitosan beads prepared from shrimp shell wastes

The equilibrium and kinetics of adsorption of reactive dye RR222 and Cu²⁺, and the activity of immobilization of acid phosphatase, on highly swollen chitosan beads were examined at 30°C. The chitosan was prepared from shrimp shell wastes and was cross-linked with different dosages of glutaraldehyde or glyoxal (100–80,000 mg/l). It was shown that the amounts of solute adsorption and the immobilization capacity of acid phosphatase on cross-linked chitosan beads were substantially affected by their degree of cross-linking. The cross-linking rate of chitosan with glutaraldehyde could be described by a pseudo-second-order equation and the cross-linking equilibrium by the Freundlich equation. This provided an experimental method to control the degree of cross-linking of chitosan beads. Finally, the activity and lifetime of the immobilized enzyme were measured to evaluate the application potential.     

The study of gelation kinetics and chain-relaxation properties of glutaraldehyde-cross-linked chitosan gel and their effects on microspheres preparation and drug release

The effects of gelation kinetics and chain-relaxation properties of glutaraldehyde-cross-linked chitosan gel on microspheres preparation or drug release were studied. The rate of gelation is zero order corresponding to the chitosan concentration but non-zero order corresponding to the glutaraldehyde concentration. It was suggested that the cross-linking reaction was mainly dominated by the concentration of small molecule reactant, glutaraldehyde. The relaxation of an entangled polymer chain in a gel network as a result of the swelling of cross-linked chitosan hydrogel was investigated by the stress–strain determination. The higher the cross-linking density of chitosan hydrogel, the lower the swelling ability of chitosan hydrogel due to the slower relaxation rate of polymer chain, which then results in the decreased drug-release rate.     

In vitro release of lysozyme from gelatin microspheres: effect of cross-linking agents and thermoreversible gel as suspending medium

This study was aimed to characterize the microstructure and the performance of gelatin microspheres (GMs) cross-linked by two different cross-linkers viz. d-glucose and glutaraldehyde. New formulations were obtained, suspending the GMs in a thermoreversible Pluronic F127 (PF127) liquid-crystalline gel. Lysozyme was used as a model biomacromolecular drug to evaluate release features. Both types of cross-linked GMs were prepared by thermal gelation method. The lysozyme-loaded microspheres were characterized by scanning electron microscopy (SEM) for size distribution, shape, and surface texture. SEM revealed that both types of lysozyme-loaded GMs were spherical in shape and that the surface of glutaraldehyde cross-linked GMs was smoother than that of the glucose cross-linked GMs. The degree of cross-linking of microspheres was investigated using ATR-FTIR technique. The prepared GMs were suspended in 20% w/v aqueous PF127 gel for which the usual sol-gel transition temperature of 22 °C did not change in the presence of GMs, as indicated by rheological measurements. SAXS study of the PF127 gel confirmed the occurrence of a discrete cubic liquid-crystalline phase of the Fm3m type whose lattice parameter slightly decreased as a result of GMs addition. The in vitro release of lysozyme from both types of cross-linked GMs was successfully controlled when they were suspended in PF127 gel, thus suggesting the potential use of this new combined formulation as a drug-depot system.     

壳聚糖装载猪胸腺肽微球给药

目的：以猪胸腺肽为芯材、壳聚糖为壁材,采用乳化交联结合单凝聚法制备猪胸腺肽壳聚糖口服微球。方法：以壁材浓度、交联剂含量、油水比值、芯材壁材比值为四因素设计正交实验,确定微球最佳制备条件,并对其体外释放及稳定性进行研究。结果：制备微球最优化条件为壳聚糖浓度1％、25％戊二醛含量7％、油水比值2：1、壳聚糖与胸腺肽比值1：1;微球在pH1．5的HC1溶液中2h释放30％,在pH6．8及7．4的PBS缓冲液中最终释放度约80％,并在24h达到释放终点;微球30rain突释率约为10％,1h释放率约为20％,其后缓慢而持续地释放;猪胸腺肽壳聚糖微球在0℃保存8个月时微球外观及形态没有差异,药物剩余率约为91．8％。结论：采用乳化交联结合单凝聚法制备的猪胸腺肽壳聚糖口服微球为缓释给药系统的临床应用奠定了理论基础,具有重要的实际应用价值和社会意义。     

One-pot synthesis and characterization of cross-linked quaternized chitosan microspheres as protein adsorbent

The one-pot synthesis and characterization of cross-linked quaternized chitosan microspheres (CQCM) as a protein adsorbent are presented. First of all, chitosan particles were prepared by spray drying method, and then they were quaternized and cross-linked in turn with glycidyltrimethylammonium (GTMAC) chloride and glutaraldehyde in isopropanol containing 10% water in one-pot. The effect of the reaction temperature, reaction time and the amounts of added GTMAC and glutaraldehyde on the protein adsorption ability of CQCM was investigated. The adsorption behavior of the CQCM prepared in the optimum synthetic conditions was well described by the Langmuir isotherm with maximum adsorption capacity equal to 1424 mg BSA/g dry weight. The particle size ranged from 7.6 to 48.9 μm. The mechanism of adsorption-desorption of BSA to the CQCM was ion-exchange. Finally, the extraction of soybean peroxidase from crude soybean peroxidase solution using the CQCM was performed.     

Poly(3-hydroxybutyrate)/chitosan/ketoprofen or piroxicam composite microparticles: Preparation and controlled drug release evaluation

Poly(3-hydroxybutyrate)/chitosan/piroxicam or ketoprofen composite microparticles were prepared by the solid-in-water-in-oil emulsion-solvent evaporation technique with the aim of reducing the burst effect and controlling the drug release. Reservoir-type microparticles, composed of poly(3-hydroxybutyrate) microspheres embedded in a chitosan matrix were prepared. The size and morphological characteristics of the composite microparticles were evaluated in relation to the chitosan concentration and cross-linking with glutaraldehyde. Reservoir-type composite microparticles were obtained using 2.0% and 3.0% w/v chitosan solutions. A significant reduction in the burst effect and prolonged drug release were observed, particularly when higher chitosan and glutaraldehyde concentrations were used.     

尺寸均一的壳聚糖微球的制备及其作为胰岛素控释载体的研究

采用新型微孔膜乳化技术制备了载胰岛素的壳聚糖微球。研究表明,要制备粒径均一的壳聚糖微球,必须将亲水性膜修饰成疏水性;制得的微球粒径和所采用的膜孔径之间存在很好的线性关系,使得微球粒径可控;以胰岛素为模型药物,主要考察了交联剂用量和交联时间对微球表面形态、药物包埋率和微球体外释药特性的影响。结果表明当氨基与醛基的摩尔比为1∶0.7、交联时间为1h时,所得载药微球的包埋率最高,随着戊二醛用量的增加和交联时间的延长,药物体外释放速率减慢。     

Synthesis and characterization of chitosan-based pH-sensitive semi-interpenetrating network microspheres for controlled release of diclofenac sodium

pH-Sensitive semi-interpenetrating networks (IPNs) based on chitosan (Cs) and acrylamide-grafted hydroxyethylcellulose (AAm-g-HEC) were prepared in the form of microspheres (MPs) by emulsion-crosslinking technique using glutaraldehyde (GA) as a crosslinker. Diclofenac sodium (DS) drug was successfully encapsulated into IPN microspheres by varying the ratio of Cs and AAm-g-HEC, % drug loading, and amount of GA. DS encapsulation of up to 83% was obtained as measured by UV spectroscopy. MPs with average particle sizes in the range of 188-310 μm were obtained. MPs were characterized by Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), and Differential scanning calorimetry (DSC). Diffusion coefficients (D) of water transport through the microspheres were determined using an empirical equation. In vitro release of DS from these matrices has been investigated in pH 1.2 and 7.4 media.     

Evaluation of mucoadhesive properties of chitosan microspheres prepared by different methods

The mucoadhesive properties of chitosan microspheres prepared by different method were evaluated by studying the interaction between mucin and microspheres in aqueous solution. The interaction was determined by the measurement of mucin adsorbed on the microspheres. A strong interaction between chitosan microspheres and mucin was detected. The intensity of the interaction was dependent upon the method of preparation of chitosan microspheres and the amount of mucin added. The extent of mucus adsorption was proportional to the absolute values of the positive zeta potential of chitosan microspheres. The zeta potential in turn was found to be dependent upon the method of preparation of microspheres. The adsorption of type III mucin (1% sialic acid content) was interpreted using Freundlich or Langmuir adsorption isotherms. The values ofr ² were greater for Langmuir isotherm as compared with Freundlich isotherm. The adsorption of a suspension of chitosan microspheres in the rat small intestine indicated that chitosan microspheres prepared by tripolyphosphate cross-linking and emulsification ionotropic gelation can be used as an excellent mucoadhesive delivery system. The microspheres prepared by glutaraldehyde and thermal cross-linking showed good stability in HC1 as compared with microspheres prepared by tripolyphosphate and emulsification ionotropic gelation.     

Synthesis and characterization of semi-interpenetrating polymer network microspheres of acrylamide grafted dextran and chitosan for controlled release of acyclovir

Semi-interpenetrating polymer network (IPN) microspheres of acrylamide grafted on dextran (AAm-g-Dex) and chitosan (CS) were prepared by emulsion-crosslinking method using glutaraldehyde (GA) as a crosslinker. The grafting efficiency was found to be 94%. Acyclovir, an antiviral drug with limited water solubility, was successfully encapsulated into IPN microspheres by varying the ratio of AAm-g-Dex and CS, % drug loading and amount of GA. Microspheres were characterized by FT-IR spectroscopy to assess the formation of IPN structure and to confirm the absence of chemical interactions between drug, polymer and crosslinking agent. Particle size was measured using laser light scattering technique. Microspheres with average particle sizes in the range of 265–388 μm were obtained. Differential scanning calorimetry (DSC) and X-ray diffraction (X-RD) studies were performed to understand the crystalline nature of drug after encapsulation into IPN microspheres. Acyclovir encapsulation of up to 79.6% was achieved as measured by UV spectroscopy. Both equilibrium and dynamic swelling studies were performed in 0.1 N HCl. Diffusion coefficients (D) and diffusional exponents (n) for water transport were determined using an empirical equation. In vitro release studies indicated the dependence of drug release rates on both the extent of crosslinking and amount of AAm-g-Dex used in preparing microspheres; the slow release was extended up to 12 h. The release rates were fitted to an empirical equation to compute the diffusional exponent (n), which indicated non-Fickian trend for the release of acyclovir.     

Transport of small anionic and neutral solutes through chitosan membranes: dependence on cross-linking and chelation of divalent cations

Chitosan membranes were prepared by solvent casting and cross-linked with glutaraldehyde at several ratios under homogeneous conditions. The cross-linking degree, varying from 0 to 20%, is defined as the ratio between the total aldehyde groups and the amine groups of chitosan. Permeability experiments were conducted using a side-by-side diffusion cell to determine the flux of small molecules of similar size but with different chemical moieties, either ionized (benzoic acid, salicylic acid, and phthalic acid) or neutral (2-phenylethanol) at physiological pH. The permeability of the different model molecules revealed to be dependent on the affinity of those structurally similar molecules to chitosan. The permeability of the salicylate anion was significantly enhanced by the presence of metal cations commonly present in biological fluids, such as calcium and magnesium, but remained unchanged for the neutral 2-phenylethanol. This effect could be explained by the chelation of metal cations on the amine groups of chitosan, which increased the partition coefficient. The cross-linking degree was also correlated with the permeability and partition coefficient. The change in the permeation properties of chitosan to anionic solutes in the presence of these metallic cations is an important result and should be taken into consideration when trying to make in vitro predictions of the drug release from chitosan-based controlled release systems.     

Chitosan as a Biomaterial: Influence of Degree of Deacetylation on Its Physiochemical,Material and Biological Properties

Chitosan is a biomaterial with a range of current and potential biomedical applications. Manipulation of chitosan degree of deacetylation (DDA) to achieve specific properties appears feasible, but studies investigating its influence on properties are often contradictory. With a view to the potential of chitosan in the regeneration of nerve tissue, the influence of DDA on the growth and health of olfactory ensheathing cells (OECs) was investigated. There was a linear increase in OEC proliferation as the DDA increased from 72 to 85%. This correlated with linear increases in average surface roughness (0.62 to 0.78 μm) and crystallinity (4.3 to 10.1%) of the chitosan films. Mitochondrial activity and membrane integrity of OECs was significantly different for OECs cultivated on chitosan with DDAs below 75%, while those on films with DDAs up to 85% were similar to cells in asynchronous growth. Apoptotic indices and cell cycle analysis also suggested that chitosan films with DDAs below 75% were cytocompatible but induced cellular stress, while OECs grown on films fabricated from chitosan with DDAs above 75% showed no significant differences compared to those in asynchronous growth. Tensile strength and elongation to break varied with DDA from 32.3 to 45.3 MPa and 3.6 to 7.1% respectively. DDA had no significant influence on abiotic and biotic degradation profiles of the chitosan films which showed approximately 8 and 20% weight loss respectively. Finally, perceived patterns in property changes are subject to change based on potential variations in DDA analysis. NMR examination of the chitosan samples here revealed significant differences depending upon which peaks were selected for integration; 6 to 13% in DDA values within individual samples. Furthermore, differences between DDA values determined here and those reported by the commercial suppliers were significant and this may also be a source of concern when selecting commercial chitosans for biomaterial research.     

Adsorption behaviour of Fe(II) and Fe(III) ions in aqueous solution on chitosan and cross-linked chitosan beads

A batch adsorption system was applied to study the adsorption of Fe(II) and Fe(III) ions from aqueous solution by chitosan and cross-linked chitosan beads. The adsorption capacities and rates of Fe(II) and Fe(III) ions onto chitosan and cross-linked chitosan beads were evaluated. Chitosan beads were cross-linked with glutaraldehyde (GLA), epichlorohydrin (ECH) and ethylene glycol diglycidyl ether (EGDE) in order to enhance the chemical resistance and mechanical strength of chitosan beads. Experiments were carried out as function of pH, agitation period, agitation rate and concentration of Fe(II) and Fe(III) ions. Langmuir and Freundlich adsorption models were applied to describe the isotherms and isotherm constants. Equilibrium data agreed very well with the Langmuir model. The kinetic experimental data correlated well with the second-order kinetic model, indicating that the chemical sorption was the rate-limiting step. Results also showed that chitosan and cross-linked chitosan beads were favourable adsorbers.     

In vitro efficacy of glutaraldehyde-crosslinked chitosan microspheres against the fish-pathogenic ciliate Philasterides dicentrarchi

Philasterides dicentrarchi is a protozoan ciliate which causes significant economic losses in fish aquaculture. This study investigated the effects of chitosan microspheres cross linked with glutaraldehyde and containing beta-cyclodextrin (betaCD) on the survival of this parasite in 7 d cultures. When used alone in assays, neither chitosan nor betaCD showed any activity, whereas free glutaraldehyde was strongly toxic to the parasite. Microspheres were likewise strongly toxic, at total glutaraldehyde concentrations much lower than with free glutaraldehyde: near-100% ciliate death was obtained (1) with 50 microg ml(-1) of microspheres prepared with 5% glutaraldehyde and no betaCD, or (2) with 10 microg ml(-1) of microspheres prepared with 0.15% glutaraldehyde and 0.1% betaCD. This suggests that the main active component is glutaraldehyde, but that the presence of small amounts of betaCD enhances efficacy. This high efficacy, together with the low toxicity to fish and rapid biodegradability of the individual components, suggest that these microspheres may be an attractive alternative to the formaldehyde baths traditionally used for the control of this parasite.     

壳聚糖载体的改性及其用于固定化漆酶的研究

利用有机酸改性壳聚糖,并用交联法制备酸化的壳聚糖载体,然后用改性壳聚糖载体固定漆酶。甲酸、乙酸改性壳聚糖的最适条件:壳聚糖与甲酸、乙酸的质量摩尔比(g/mol)分别为100∶1、100∶1.5,戊二醛的质量分数为1%,缓冲溶液的pH分别是4.4、5.0,反应时间为3h;壳聚糖与酒石酸、草酸的质量摩尔比(g/mol)分别为100∶0.5、100∶2,戊二醛的质量分数为2%,缓冲溶液的pH分别是3.6、4.2,反应时间为4.5h。不同有机酸改性的壳聚糖用于漆酶的固定,其酶活都有不同程度的提高,尤其用酒石酸改性的壳聚糖载体效果最好,其酶活提高了57%。     

Delivery of dermatan sulfate from polyelectrolyte complex-containing alginate composite microspheres for tissue regeneration

Dermatan sulfate (DS) is a glycosaminoglycan (GAG) with a great potential as a new therapeutic agent in tissue engineering. The aim of the present study was to investigate the formation of polyelectrolyte complexes (PECs) between chitosan and dermatan sulfate (CS/DS) and delivery of DS from PEC-containing alginate/chitosan/dermatan sulfate (Alg/CS/DS) microspheres for application in tissue regeneration. The CS/DS complexes were initially formed at different conditions including varying CS/DS ratio (positive/negative charge ratio), buffer, and pH. The obtained CS/DS complexes exhibited stronger electrostatic interaction, smaller complex size, and more stable colloidal structure when chitosan was in large excess (CS/DS 3:1) and prepared at pH 3.5 as compared to pH 5 using acetate buffer. The CS/DS complexes were subsequently incorporated into an alginate matrix by spray drying to form Alg/CS/DS composite microspheres with a DS encapsulation efficiency of 90-95%. The excessive CS induced a higher level of sustained DS release into Tris buffer (pH 7.4) from the microspheres formulated at pH 3.5; however, the amount of CS did not have a significant effect on the release from the microspheres formulated at pH 5. Significant cell proliferation was stimulated by the DS released from the microspheres in vitro. The present results provide a promising drug delivery strategy using PECs for sustained release of DS from microspheres intended for site-specific drug delivery and ultimately for use in tissue engineering.     

Gadolinium diethylenetriaminopentaacetic acid-loaded chitosan microspheres for gadolinium neutron-capture therapy

In order to provide a suitable device that would contain water-soluble drugs, highly water-soluble gadolinium diethylenetriaminopentaacetic acid-loaded chitosan microspheres (CMS-Gd-DTPA) were prepared by the emulsion method using glutaraldehyde as a cross-linker and Span 80 as a surfactant for gadolinium neutron-capture therapy of cancer. The gadolinium content and the mass median diameter of CMS-Gd-DTPA were estimated. The size and morphology of the CMS-Gd-DTPA were strongly influenced by the initial applied weight ratio of Gd-DTPA:chitosan. FTIR spectra showed that the electrostatic interaction between chitosan and Gd-DTPA accelerated the formation of gadolinium-enriched chitosan microspheres. Sufficient amounts of glutaraldehyde and Span 80 were necessary for producing discrete CMS-Gd-DTPA. The CMS-Gd-DTPA having a mass median diameter 11.7microm and 11.6% of gadolinium could be used in Gd-NCT following intratumoral injection.     

A protein delivery system: biodegradable alginate-chitosan-poly(lactic-co-glycolic acid) composite microspheres

In the present study we developed alginate-chitosan-poly(lactic-co-glycolic acid) (PLGA) composite microspheres to elevate protein entrapment efficiency and decrease its burst release. Bovine serum albumin (BSA), which used as the model protein, was entrapped into the alginate microcapsules by a modified emulsification method in an isopropyl alcohol-washed way. The rapid drug releases were sustained by chitosan coating. To obtain the desired release properties, the alginate-chitosan microcapsules were further incorporated in the PLGA to form the composite microspheres. The average diameter of the composite microcapsules was 31+/-9microm and the encapsulation efficiency was 81-87%, while that of conventional PLGA microspheres was just 61-65%. Furthermore, the burst releases at 1h of BSA entrapped in composite microspheres which containing PLGA (50:50) and PLGA (70:30) decreased to 24% and 8% in PBS, and further decreased to 5% and 2% in saline. On the contrary, the burst releases of conventional PLGA microspheres were 48% and 52% in PBS, respectively. Moreover, the release profiles could be manipulated by regulating the ratios of poly(lactic acid) to poly(glycolic acid) in the composite microspheres.