pH-sensitive behavior of two-component hydrogels composed of N,O-carboxymethyl chitosan and alginate

A two-component pH-sensitive hydrogel system composed of a water-soluble chitosan derivative (N,O-carboxymethyl chitosan, NOCC) and alginate cross-linked by genipin, glutaraldehyde or Ca2+ was investigated. Preparation and structures of these hydrogels and their swelling characteristics and release profiles of a model protein drug (bovine serum albumin, BSA) in simulated gastrointestinal media are reported. At pH 1.2, the swelling ratios of the hydrogels cross-linked by distinct methods were limited. Of note is that the lowest swelling ratios of test hydrogels were found at pH 4.0. At pH 7.4, the carboxylic acid groups on test hydrogels became progressively ionized and led to a significant swelling. There was barely any BSA released from the glutaraldehyde-cross-linked hydrogel throughout the entire course of the study. The amounts of BSA released at pH 1.2 from the genipin- and Ca(2+)-cross-linked hydrogels were relatively low (approx. 20%). At pH 4.0, there was still significant BSA release from the Ca(2+)-cross-linked hydrogel, while the cumulative BSA released from the genipin-cross-linked hydrogel was limited due to its shrinking behavior. At pH 7.4, the amount of BSA released from the genipin- and Ca(2+)-cross-linked hydrogels increased significantly (approx. 80%) because the swelling of both test hydrogels increased considerably. The aforementioned results indicated that the swelling behaviors and drug-release profiles of these test hydrogels are significantly different due to their distinct cross-linking structures.     

Swelling characteristics and drug delivery properties of nifedipine-loaded pH sensitive alginate-chitosan hydrogel beads

The aim of the present work was to investigate the swelling behavior and in vitro release of nifedipine from alginate-chitosan hydrogel beads. Structure and surface morphology of the hydrogel were characterized by FTIR and SEM, respectively. Alginate-chitosan mixed beads and alginate-chitosan coated beads were prepared by ionic gelation method. The swelling ability of the beads and in vitro release of nifedipine in simulated gastric fluid (pH 1.5) and different phosphate buffer solutions (pH 2.5, 5.0, 6.8, 7.4, and 8.0) were found to be dependent on the presence of the polyelectrolyte complex between chitosan and alginate. The amount of nifedipine released from the mixed beads at pH 1.5 was relatively low (42%), whereas this value approached to 99% at pH 6.8. In comparison with the mixed beads, the released nifedipine from the coated beads was minimal at pH 1.5 (18%), whereas approximately 99% nifedipine was released at pH 6.8. The results suggested that the coated beads can hold drug better at low pH than the mixed beads and show excellent pH sensitivity. Therefore, the alginate-chitosan coated beads could be a suitable polymeric carrier for drug delivery in the intestinal tract.     

Adsorption of bovine serum albumin onto surface-modified polyhydroxyethyl methacrylate beads

The adsorption of bovine serum albumin (BSA) onto poly(2-hydroxyethyl methacrylate) (PHEMA) beads modified by using the pair of hexamethylene diisocyonate-suberic acidbis-N-hydroxy succinimide has been studied as a function of protein concentration and adsorption time. The adsorption studies were carried out in phosphate buffer solution (PBS) at pH = 7.4. The isotherm data have been analysed using the Langmuir model and the adsorption parameters Q0 and b were calculated. It is determined that the adsorbed amount of BSA increases by the increase of the adsorption time and BSA concentration until a certain value. PHEMA beads were characterized by using FTIR spectra and SEM analysis. The adsorption of BSA onto PHEMA beads were clearly observed from SEM micrographs. The swelling tests of the beads were performed at 37 degrees C in PBS.     

Biodegradation of chitosan-tripolyphosphate beads: in vitro and in vivo studies

In this study, chitosan [(1 --> 4) linked 2-amino-2-deoxy-beta-D-glucopyranose] beads were prepared by interacting this polycation (> 90% deacetylated) with the tripolyphosphate (TPP) polyanion. The resulting chitosan-TPP beads (C) were modified either by coating with sodium alginate (CA) or by cross-linking with glutaraldehyde (CGA). The in vitro degradation of C beads was found to be faster than its CA and CGA counterparts. C beads degraded faster at pH 6.5, compared to pH 7.4 conditions. At pH 7.4, about 41%, 37% and 10% of dry mass loss after 12 months was determined for C, CA and CGA, respectively. At pH 6.5, the dry mass loss of CA and CGA after the same period of time was found to be 73% and 37%, respectively. However, C beads completely degraded at pH 6.5 after 8 months of in vitro incubation. The in vivo biodegradation experiments were performed on Wistar rats (n = 24) for a duration of 6 months. No sign of fibrotic capsule formation was observed around any of the implanted beads at 2 and 6 months post-transplantation. At 2 months, the in vivo-degradation was slow-going and the beads in all groups were intact; CGA beads had more tissue reaction than C and CA beads at this time point. While the C beads had almost completely degraded after 6 months, the biodegradation process in CA and CGA beads was progressing. Histomorphometric analysis revealed that the in vivo biodegradation was in the order of C (approximately 85%) > CA (approximately 50%) > CGA (approximately 25%) after 6 months. Neovascularization was observed at the vicinity of the bead implants close to major blood vessels, both at 2 and 6 months time-points.     

Heparin/chitosan nanoparticle carriers prepared by polyelectrolyte complexation

In this study, novel nanoparticles were prepared by polyelectrolyte complexation between heparin and chitosan on simple and mild conditions. The size, polydispersity, zeta potential, and morphology of the nanoparticles were characterized. Entrapment studies of the nanoparticles were conducted using bovine serum albumin (BSA) as a model protein. Specifically, the effects of the pH value of chitosan solution, chitosan molecular weight (MW), chitosan concentration, heparin concentration, and BSA concentration on the nanoparticle size, the nanoparticle yield, and BSA entrapment were studied in detail. We found that, the size and the yield of the nanoparticles were affected by the above factors. The nanoparticle yield played a crucial role in BSA entrapment, namely, more nanoparticles could encapsulate more BSA. At length, suitably high pH value of chitosan solution, moderate chitosan MW, increasing both heparin concentration and chitosan concentration at an optimal concentration ratio favored more nanoparticles formed and consequently a higher BSA entrapment efficiency.     

A pH-sensitive chitosan-tripolyphosphate hydrogel beads for controlled glipizide delivery

A chitosan(CS)-tripolyphosphate (TPP) hydrogel bead was prepared by the ionic gelation method for the controlled delivery of glipizide. The structure and surface morphology of the beads were characterized by FT-IR and SEM, separately. Factors influencing the swelling behavior of the hydrogel beads were also investigated, such as CS concentration (X(1)), TPP concentration (X(2)), the weight ratio of drug to polymer (X(3)), crosslinking time (X(4)), and the volume ratio of CS to TPP (X(5)). In addition, the swelling property and the delivery behavior of the hydrogel bead was studied as well. With decreasing of pH value, the swelling ratio of the bead was increasing. The swelling ratio of hydrogel bead at pH 1.5 was relatively high, while this value was low at pH 6.8. The amount of glipizide released from the hydrogel bead at pH 1.5 was about 90%, while this value approached 36% at pH 6.8. The results clearly suggested that the CS-TPP hydrogel beads were used as a pH-sensitive controlled release system for the delivery of glipizide.     

Quaternized chitosan/alginate nanoparticles for protein delivery

Quaternized chitosan (QCS)/alginate (AL) nanoparticles (QCS/AL) were successfully prepared in neutral condition for the oral delivery of protein. The physicochemical structure of the QCS/AL nanoparticles was characterized by IR spectroscopy and transmission electron microscopy. The diameter of the nanoparticles with a positive surface charge was about 200 nm. The load of bovine serum albumin (BSA) was affected by the concentration and the molecular parameters, i.e. degree of substitution (DS) and weight-average molecular weight (Mw) of QCS, as well as the concentration of BSA. The release of BSA from nanoparticles was pH-dependent. Quick release occurred in 0.1M phosphate buffer solution (PBS, pH=7.4), while the release was slow in 0.1M HCl (pH=1.2). The DS and Mw of QCS play important roles in the release of BSA in vitro. QCS with high Mw accelerated the release of BSA in acid, while high DS retarded the release of BSA in both 0.1M HCl and 0.1M PBS.     

The influence of molecular weight of chitosan on the physical and biological properties of collagen/chitosan scaffolds

Biopolymer blends between collagen and chitosan have the potential to produce cell scaffolds with biocompatible properties. However, the relationship between the molecular weight of chitosan and its effect on physical and biological properties of collagen/chitosan scaffolds has not been elucidated yet. Porous scaffolds were fabricated by freeze-drying the solution of collagen and chitosan, followed by cross-linking by dehydrothermal treatment. Various types of scaffolds were prepared using chitosan with various molecular weights and blending ratios. Fourier transform infrared spectroscopy proved that collagen and chitosan scaffolds at all blending ratios contained mainly electrostatic interactions at the molecular level. The compressive modulus decreased with increasing the concentration of chitosan. Equilibrium swelling ratios of approximately 6-8, determined in phosphate-buffered saline at physiological pH (7.4), were found in case of collagen-dominated scaffolds. The lysozyme biodegradation test demonstrated that the presence of chitosan, especially the high-molecular-weight species, could significantly prolong the biodegradation of collagen/chitosan scaffolds. In vitro culture of L929 mouse connective tissue fibroblast evidenced that low-molecular-weight chitosan was more effective to promote and accelerate cell proliferation, particularly for scaffolds containing 30 wt% chitosan. The results elucidated that the blends of collagen with low-molecular-weight chitosan have a high potential to be applied as new materials for skin-tissue engineering.     

The influence of molecular weight of chitosan on the physical and biological properties of collagen/chitosan scaffolds

Biopolymer blends between collagen and chitosan have the potential to produce cell scaffolds with biocompatible properties. However, the relationship between the molecular weight of chitosan and its effect on physical and biological properties of collagen/chitosan scaffolds has not been elucidated yet. Porous scaffolds were fabricated by freeze-drying the solution of collagen and chitosan, followed by cross-linking by dehydrothermal treatment. Various types of scaffolds were prepared using chitosan with various molecular weights and blending ratios. Fourier transform infrared spectroscopy proved that collagen and chitosan scaffolds at all blending ratios contained mainly electrostatic interactions at the molecular level. The compressive modulus decreased with increasing the concentration of chitosan. Equilibrium swelling ratios of approximately 6–8, determined in phosphate-buffered saline at physiological pH (7.4), were found in case of collagen-dominated scaffolds. The lysozyme biodegradation test demonstrated that the presence of chitosan, especially the high-molecular-weight species, could significantly prolong the biodegradation of collagen/chitosan scaffolds. In vitro culture of L929 mouse connective tissue fibroblast evidenced that low-molecular-weight chitosan was more effective to promote and accelerate cell proliferation, particularly for scaffolds containing 30 wt% chitosan. The results elucidated that the blends of collagen with low-molecular-weight chitosan have a high potential to be applied as new materials for skin-tissue engineering.     

Synthesis and pH sensitivity of carboxymethyl chitosan-based polyampholyte hydrogels for protein carrier matrices

Novel polyampholyte hydrogels based on carboxymethyl chitosans (CMC) of various degree of deacetylation (DD) and substitution (DS) were prepared by crosslinking with glutaraldehyde. The hydrogel showed typical amphoteric character responding to pH of the external medium. At the isoelectric point (IEP), the hydrogel shrunk most, when the pH deviated from IEP, the swelling degree (Ds) increased. With increasing DD or DS value, the hydrogel changed from polyampholyte into polycations or polyanions, respectively. Osmotic forces and intermolecular interactions among CMC chains regulate the swelling behavior of CMC gel. The carboxymethyl chitin hydrogels were loaded with bovine blood proteins (BSA), and their release studies were performed in both the simulated gastric and intestinal pH conditions. The release was much quicker in pH 7.4 buffer than pH 1.2 solution; the release followed Fickian diffusion in the first 4h and then steadily increased with the dissolution of the hydrogels.     

Magnetic/pH-sensitive κ-carrageenan/sodium alginate hydrogel nanocomposite beads: preparation,swelling behavior,and drug delivery

This work describes the preparation of magnetic and pH-sensitive beads based on κ-carrageenan and sodium alginate for use as drug-targeting carriers. Physical cross-linking using K⁺/Ca²⁺ ions was applied to obtain ionic cross-linked magnetic hydrogel beads. The produced magnetite beads were thoroughly characterized by TEM, SEM/EDS, XRD, FTIR, and VSM techniques. While the water absorbency (WA) of magnetic beads was enhanced by increasing the weight ratio of κ-carrageenan, introducing magnetic nanoparticles caused a decrease in WA capacity from 15.4 to 6.3 g/g. Investigation on the swelling of the hydrogel beads in NaCl, KCl, and CaCl₂ solutions revealed the disintegration of beads depending on the composition of hydrogel beads and the type of metal cations in swelling media. The swelling ratio of beads indicated pH-dependent properties with maximum water absorbing at pH 7.4. Also, it was found that the strength of pH-sensitivity of magnetic beads was low for beads with the high content of carrageenan component. The in vitro drug release studies from hydrogels exhibited significant behaviors on the subject of physiological-simulated pH values and external magnetic fields. The maximum cumulative releases obtained were 98 and 43% at pH values 7.4 and 1.2, respectively. The Introducing magnetite nanoparticles influenced the cumulative release of drug.     

Studies on the pH-dependent swelling properties and morphologies of chitosan/calcium-alginate complexed beads

Chitosan/calcium-alginate beads were prepared by a coacervation method in aqueous medium. Their swelling properties and morphologies were studied. Complexed beads with a mean diameter of 500 μm were obtained by dropwise addition of a sodium alginate solution into a chitosan-calcium chloride solution. From scanning electron microscopic studies, we observed that chitosan modifies the morphology of calcium-alginate beads. The swelling properties of chitosan/calcium-alginate beads are different from those of calcium-alginate beads. In the case of the calcium-alginate beads, the swelling volume increases as the pH of the medium increases. However, chitosan/calcium-alginate beads show a maximum swelling volume at pH 9.0.     

Encapsulation of insulin in chitosan-coated alginate beads: oral therapeutic peptide delivery

Insulin was encapsulated in calcium alginate beads coated with chitosan. Its release from alginate-chitosan and alginate-chitosan-glutaraldehyde beads was studied in artificial gastric (pH 1.2) and intestinal (pH 7.5) fluids. By comparing the release amounts, the ionic interaction between alginate-chitosan matrix with the medium pH's, intestinal fluid was found to be the better. The degradation of released insulin was also searched, even after 6 h incubation, the beads remained stable and the undegraded insulin seemed to be sufficient for the physiological conditions. Consequently, it can be said that the system can be offered for oral delivery of the therapeutic peptide drug insulin.     

Novel polyelectrolyte complexes based on poly(methacrylic acid)-bis(2-aminopropyl)poly(ethylene glycol) for oral protein delivery

In the present investigation a simple and effective strategy was employed for the development of pH-sensitive self-assembling microparticles based on poly(methacrylic acid) (PMAA)-bis(2-aminopropyl)poly(ethylene glycol) (APEG), and their efficiency in oral protein delivery was evaluated. An inter-ionic gelation process was employed for the preparation of microparticles and particles were obtained spontaneously during the process without using any surfactants or stabilizers. Particle size analysis was carried out to measure average particle size and surface morphology was evaluated using scanning electron microscopy (SEM). Bovine serum albumin (BSA) was incorporated onto these microparticles to evaluate the loading and release properties of the matrix. PMAA-APEG microparticles displayed pH responsive release profile, as less than 10% of encapsulated BSA was released at pH 1.2 in 2 h and more than 80% of loaded protein was released within 3 h at pH 7.4. Carboxymethyl beta-cyclodextrin (CM beta CD)-insulin non-covalent inclusion complex was prepared to enhance the stability of insulin formulations and complex formation was analyzed by fluorescence spectroscopic studies. CM beta CD-complexed insulin was encapsulated into PMAA-APEG microparticles by a diffusion filling method and biological activity of entrapped insulin was evaluated using an ELISA. Finally mucoadhesive studies of PMAA-APEG microparticles were carried out on freshly excised rat intestinal mucosa at neutral pH to establish the adhesive nature of the material.     

Preparation of floating alginate gel beads for drug delivery to the gastric mucosa

Alginate gel beads containing ethylcellulose (ALECs) were prepared and investigated with regard to buoyancy, in vitro and in vivo drug release profiles, and drug targeting specificity in the gastric mucosa. When the ethylcellulose (EC) content of ALECs containing metronidazole (MZ) was higher than 3%, the beads floated in all test solutions with a specific gravity of approx. 1.01. ALECs containing 5% EC released MZ gradually and floated throughout the experimental period in simulated gastric juice (pH 1.2), and all of the drug had been released after 90 min. When we orally administered ALECs to guinea pigs, about 85% of the incorporated MZ was released at 1 h. The MZ concentration of the gastric mucosa after administration of ALECs was greater than that observed with administration of MZ solution, despite lower serum concentrations. Furthermore, the similar data were obtained for ALECs with 7% EC. These results suggest that ALECs may become a practical vehicle for delivering drugs to the gastric mucosa.     

Chitosan beads and granules for oral sustained delivery of nifedipine: in vitro studies.

Nifedipine was embedded in a chitosan matrix to develop a prolonged-release form. The in vitro release profiles of nifedipine from chitosan beads and microgranules were monitored by UV spectrophotometer. The studies were performed in a rotating shaker (100 rev min-1) in 0.1 M HCl buffer (pH 2.0) or 0.1 M phosphate buffer (pH 7.4). Comparison was made between drug-loaded microbeads and microgranules. The amount and percentage of drug release were much higher in HCl than in phosphate buffer, probably due to the salt formation of the matrix (chitosan hydrochloride) at acid pH. The release rate of nifedipine from chitosan matrix was slower for beads than granules. These findings suggest the possibility of modifying the formulations to obtain the desired controlled release of the drug in an oral sustained-delivery system.     

Poly methacrylic acid-alginate semi-IPN microparticles for oral delivery of insulin: a preliminary investigation

Microparticles of Poly methacrylic acid (P1) and novel semi-interpenetrating network composed of Poly methacrylic acid-alginate (P2) were prepared and their application in oral insulin delivery was evaluated. The microparticles were characterized by scanning electron microscopy (SEM) for morphological studies. Insulin loading onto the microparticles was performed by the diffusion filling method and insulin encapsulated microparticles were subjected to in vitro release study in buffer solution of pH 1.2 and 7.4. The release kinetics at pH 7.4 exhibited sustained release of insulin for more than 5 h in case of PMAA microparticles whereas burst release of insulin (90% of total insulin loaded) within 1 h of study was observed in the case of PMAA-alginate microparticles. At pH 1.2, around 30% of insulin loaded was released from both microparticles within 2 h of study.     

Novel polyelectrolyte complexes based on poly(methacrylic acid)-bis(2-aminopropyl)poly(ethylene glycol) for oral protein delivery

In the present investigation a simple and effective strategy was employed for the development of pH-sensitive self-assembling microparticles based on poly(methacrylic acid) (PMAA)-bis(2-aminopropyl)poly(ethylene glycol) (APEG), and their efficiency in oral protein delivery was evaluated. An inter-ionic gelation process was employed for the preparation of microparticles and particles were obtained spontaneously during the process without using any surfactants or stabilizers. Particle size analysis was carried out to measure average particle size and surface morphology was evaluated using scanning electron microscopy (SEM). Bovine serum albumin (BSA) was incorporated onto these microparticles to evaluate the loading and release properties of the matrix. PMAA-APEG microparticles displayed pH responsive release profile, as less than 10% of encapsulated BSA was released at pH 1.2 in 2 h and more than 80% of loaded protein was released within 3 h at pH 7.4. Carboxymethyl β-cyclodextrin (CMβCD)-insulin non-covalent inclusion complex was prepared to enhance the stability of insulin formulations and complex formation was analyzed by fluorescence spectroscopic studies. CMβCD-complexed insulin was encapsulated into PMAA-APEG microparticles by a diffusion filling method and biological activity of entrapped insulin was evaluated using an ELISA. Finally mucoadhesive studies of PMAA-APEG microparticles were carried out on freshly excised rat intestinal mucosa at neutral pH to establish the adhesive nature of the material.     

Development and evaluation of a novel polymeric hydrogel of sucrose acrylate-co-polymethylacrylic acid for oral curcumin delivery

A monomer of sucrose acrylate (AC-sucrose) was synthesized by conjugating starting compound sucrose with methyl acrylate (MA). The obtained AC-sucrose was characterized by mass spectrometry (MS) and Fourier transform infrared (FTIR) spectroscopy. AC-sucrose was selected as a monomer to fabricate a novel pH sensitive hydrogel via free radical polymerization. The inner morphology of the final hydrogel was observed with an S-4800 scanning electron microscope (SEM). The swelling and de-swelling behaviors of the hydrogel chips were also studied. Curcumin (CUR) was selected as a model drug and loaded into the final hydrogel. The release profiles of CUR were performed via dialysis method in pH 1.2, 6.8 and 7.4 buffers, respectively. Mass and FTIR spectra confirmed the synthesis of AC-sucrose. SEM photographs showed that poly(AC-sucrose-co-MAA) hydrogels had many 3D meshes. In pH 1.2 buffer, the hydrogel chips showed the biggest swelling ratio (SR) of 34.4 ± 1.9%. However, in pH 7.4 buffer, the SRs of the hydrogel chips reached to 368.7 ± 28.0%, which suggested that the hydrogel had an excellent pH sensibility. The releasing profiles showed that only 4.6 ± 0.4% of CUR was released in pH 1.2 buffer but 93.7 ± 4.7% of CUR was diffused into pH 7.4 buffer. These data suggested that the CUR-loaded poly (AC-sucrose-co-MAA) hydrogel could direct CUR to release in basic environments.     

基于琼脂糖/壳聚糖共混凝胶模型的壳聚糖生物相容性的机理研究

目的 以琼脂糖/壳聚糖共混凝胶为模型,研究壳聚糖材料生物相容性的可能机理.方法 通过共混法,制备出一系列不同壳聚糖含量的琼脂糖/壳聚糖共混凝胶.利用傅里叶变换红外光谱(FTIR)分析共混凝胶的化学基团,利用荧光素-4-异硫氰酸酯(FITC)标记法观察琼脂糖和壳聚糖之间的可共混性.通过Zeta电势测量共混凝胶的电荷,利用二喹啉甲酸(BCA)法分别测定胎牛血清(FBS)总蛋白和牛血清白蛋白(RSA)在共混凝胶上的吸附,利用酶联免疫吸附(ELISA)法测定纤黏连蛋白(FN)在共混凝胶上的吸附.细胞实验以人微血管内皮细胞系(HMEC-1)为模型,通过观测细胞的黏附、增殖和形态来评价共混凝胶的细胞相容性.结果 琼脂糖/壳聚糖共混凝胶含有壳聚糖特征性的化学基团.琼脂糖和壳聚糖之间存在着良好的可共混性,壳聚糖的氨基基团在共混凝胶中呈均匀分布.在pH酸性条件下(pH 3.0)共混凝胶带有较强的正电荷,然而在pH中性条件下(pH 7.4)所有共混凝胶的Zeta电势均降低至0 mV附近.各组共混凝胶之间对FBS总蛋白以及BSA的吸附差异无统计学意义,但是共混凝胶对FN的吸附却随着壳聚糖含量的升高而显著升高.细胞实验结果显示:随着壳聚糖含量的提高,共混凝胶的细胞相容性有明显改善,HMECs在壳聚糖含量较高的凝胶上表现出良好的黏附、铺展和增殖.结论 相对于血清中的其他蛋白,壳聚糖组分对FN存在优先吸附,从而能够促进细胞在共混凝胶表面的黏附铺展.与传统观点不同,本研究发现壳聚糖的生物相容性与其所携带的正电荷无关.