Chitosan-reinforced alginate microspheres obtained through the emulsification/internal gelation technique

Development of pH-sensitive pectinate/alginate microspheres for colon drug delivery

The purposes of this study were to develop and evaluate calcium pectinate/alginate microspheres (PAMs) and to exploit their pH-sensitive properties for colon-targeted delivery of encapsulated cisplatin. PAMs were prepared using an electrospraying method. The PAMs, as cores, were then coated with Eudragit S100 using a polyelectrolyte multilayer coating technique in aqueous solution. The morphology of the microspheres was observed under scanning electron microscopy. In vitro drug release studies were performed in simulated gastrointestinal fluid, and the results indicated that approximately 5 % of the cisplatin was released from the Eudragit S100-coated PAMs, and 51 % of the cisplatin was released from the uncoated PAMs at 1 h. The release of cisplatin from the Eudragit S100-coated PAMs was more sustained in simulated gastric fluid than in simulated intestinal fluid due to the increased solubility of the coating polymer in media with pH >7.0. Drug release from the Eudragit S100-coated PAMs was best described by the Higuchi's square root model. From these results, it was concluded that Eudragit S100-coated PAMs are a potential carrier for delivery of cisplatin to the colon.

Preparation of controlled nano-MgO and investigation of its bactericidal properties

Nano-MgO is a good bactericide but with strong alkalinity in water due to its rapid hydrolysis. To control its hydrolysis rate and keep its bactericidal properties, we synthesized nano-MgO microspheres using chitosan-alginate system in this study. The synthesized nano-MgO release-controlled microspheres (nMgO-RCM) were with 0.98-1.20mm of particle sizes. Also, their embedding ratio and loading percentage was 63.52% and 12.27%, respectively. Based on the characterization results, nano-MgO was only observed on surface of the nMgO-RCM. Its release rate from the nMgO-RCM could be controlled by the chitosan-alginate system, and the observed rate constant (k(obs)) increased from 0.0289 h(-1) to 0.0358 h(-1) with the increment of the dosage from 10 mg L(-1) to 80 mg L(-1). Furthermore, the nMgO-RCM could maintain pH value lower than 8.5 and colony counts less than 20 CFU mL(-1) for at least 120 h.

Evaluation of mucoadhesive coatings of chitosan and thiolated chitosan for the colonic delivery of microencapsulated probiotic bacteria

Probiotic bacteria were previously encapsulated in sub-100 µm Ca(2+) alginate microcapsules for enhanced survival in human gastrointestinal tract. The aim of this study is to evaluate the altered mucoadhesive property of the probiotic delivery system by coating it with mucoadhesive chitosan or thiolated chitosan, for prolonged retention in human colon. The results confirmed that cross-linking with calcium ions reduced the mucoadhesive property of alginate hydrogel, thus questioning the intrinsic mucoadhesiveness of uncoated systems. In contrast, chitosan and thiolated chitosan were found to be adsorbed on sub-100 µm Ca(2+) alginate microcapsules, and substantially improved the mucoadhesion performance of the system. The adhesion performance was correlated to the amount of mucoadhesive coating polymer adsorbed on the surface of the system. The coated system was demonstrated on HT29-MTX colonic epithelial monolayer to deliver markedly higher amount of probiotic bacteria to the in vitro model of colonic mucosa. Additionally, the coatings were also found to exert significantly stronger mucoadhesion to colonic mucosa tissue at slight acid neutral pH with less ambient water, which conforms to the physiological environment of the colon, thus supporting prolonged retention in this region.

EFFECTS OF PH OF NA5P3O10/NAOH REACTION SOLUTION ON THE PROPERTIES OF CHITOSAN MICROSPHERES

With an attempt to expand the versatilities and applications in chitosan microspheres, chitosan were first converted into micro-droplets by using a high voltage electrostatic field system, and then treated with Na5P3O10/NaOH solution of volume ratio of 17/3, 19/1, 1/0 (pure Na5P3O10) or 0/1 (pure NaOH) to fabricate chitosan microsphere. By varying the pH values of these reacting agents, distinct morphological structures and properties of chitosan microspheres were further be changed. Chitosan microsphere prepared in this study exhibited a good spherical shape and was in a range of 185.8 ± 13.8 μm to 380.9 ± 11.5 μm in diameter. The size of chitosan microspheres varied by treating with various pH values of these reaction reagents. The prepared chitosan microspheres upon treatment with pH 7 of various ratios Na5P3O10/NaOH solution, all exhibited a shrunken surface morphological structure. This densely shrunken structure of microspheres yielded a stronger mechanical strength and a slower release rate of drug (5-FU), no matter what the ratios of Na5P3O10/NaOH solution was used. From the data of FTIR analyses, the protonated amino peak of NH3+ at around 1562 cm−1 has decreased significantly after treated with various pH values of these reaction reagents. It could be attributed to the linkage between phosphoric and ammonium ion of the protonated chitosan molecules. Besides, another boarder absorption at about 3366cm−1 of treated chitosan microspheres (under the employed range of pH values), which represented the hydrogen bonding was enhanced as compare with the pure chitosan material.

Novel preparation techniques for alginate-poloxamer microparticles controlling protein release on mucosal surfaces

The objective of this study was to develop novel preparation techniques for protein-loaded, controlled release alginate-poloxamer microparticles with a size range suitable for pulmonary administration. Bovine serum albumin (BSA)-loaded microparticles were prepared by spray-drying aqueous polymer-drug solutions, followed by cross-linking the particles in aqueous or ethanolic CaCl(2) or aqueous ZnSO(4) solutions. The microparticles were characterized with respect to their morphology (optical and scanning electron microscopy), particle size (laser light diffraction), calcium content (atom absorption spectroscopy), alginate content (complexation with 1,9-dimethyl methylene blue) and in vitro drug release (modified Franz diffusion cell). The spray-dried microparticles were spherical in shape with a size range of 4-6μm. Aqueous cross-linking led to a significant size increase (10-15μm), whereas ethanolic cross-linking did not. The substantial drug loss (∼50%) during aqueous CaCl(2) cross-linking could be avoided by using aqueous ZnSO(4) or ethanolic CaCl(2) solutions. Protein release from microparticles cross-linked with ethanolic CaCl(2) solutions was much faster than in the case of aqueous CaCl(2) solutions, probably due to the lower calcium content. The salt concentration and temperature of the cross-linking solutions also affected the composition of and drug release from the microparticles. Cross-linked alginate-poloxamer microparticles can be produced in a size range appropriate for deep lung delivery and with controlled protein release kinetics (time frame: hours to days) with these novel preparation techniques. The systems offer an interesting potential for the controlled mucosal delivery of protein drugs.

Marine polysaccharides in microencapsulation and application to aquaculture: "from sea to sea"

This review's main objective is to discuss some physico-chemical features of polysaccharides as intrinsic determinants for the supramolecular structures that can efficiently provide encapsulation of drugs and other biological entities. Thus, the general characteristics of some basic polysaccharides are outlined in terms of their conformational, dynamic and thermodynamic properties. The analysis of some polysaccharide gelling properties is also provided, including the peculiarity of the charged polysaccharides. Then, the way the basic physical chemistry of polymer self-assembly is made in practice through the laboratory methods is highlighted. A description of the several literature procedures used to influence molecular interactions into the macroscopic goal of the encapsulation is given with an attempt at classification. Finally, a practical case study of specific interest, the use of marine polysaccharide matrices for encapsulation of vaccines in aquaculture, is reported.

Alginate graft copolymers and alginate-co-excipient physical mixture in oral drug delivery

OBJECTIVES

Use of alginate graft copolymers in oral drug delivery reduces dosage form manufacture complexity with reference to mixing or coating processes. It is deemed to give constant or approximately steady weight ratio of alginate to covalently attached co-excipient in copolymers, thereby leading to controllable matrix processing and drug release. This review describes various grafting approaches and their outcome on oral drug release behaviour of alginate graft copolymeric matrices. It examines drug release modulation mechanism of alginate graft copolymers against that of co-excipients in non-grafted formulations.

KEY FINDINGS

Drug release from alginate matrices can be modulated through using either co-excipients or graft copolymers via changing their swelling, erosion, hydrophobicity/hydrophilicity, porosity and/or drug adsorption capacity. However, it is not known if the drug delivery performance of formulations prepared using alginate graft copolymers is superior to those incorporating graft-equivalent co-excipient physically in a dosage form without grafting but at the corresponding graft weight, owing to limited studies being available.

CONCLUSIONS

The value of alginate graft copolymers as the potential alternative to alginate-co-excipient physical mixture in oral drug delivery cannot be entirely defined by past and present research. Such an issue is complicated by the lack of green chemistry graft copolymer synthesis approach, high grafting process cost, complications and hazards, and the formed graft copolymers having unknown toxicity. Future research will need to address these matters to achieve a widespread commercialization and industrial application of alginate graft copolymers in oral drug delivery.

Immobilization of glucose oxidase in alginate-chitosan microcapsules

In order to improve its stability and catalytic rate in flour, the immobilization of glucose oxidase (GOX) was investigated in this work. The enzyme was encapsulated in calcium alginate-chitosan microspheres (CACM) using an emulsification-internal gelation-GOX adsorption-chitosan coating method. The interaction between alginate and chitosan was confirmed by infrared spectroscopy (IR). The resultant CACM in wet state, whose morphology was investigated by scanning electron microscopy (SEM), was spherical with a mean diameter of about 26 μm. The GOX load, encapsulation efficiency and activity of the CACM-GOX were influenced by concentration of chitosan, encapsulation time and encapsulation pH. The highest total enzymatic activity and encapsulation efficiency was achieved when the pH of the adsorption medium was near the isoelectric point (pI) of GOX, approximately pH 4.0. In addition, the molecular weight of chitosan also evidently influenced the encapsulation efficiency. Storage stabilities of GOX samples were investigated continuously over two months and the retained activity of CACM-GOX was 70.4%, markedly higher than the 7.5% of free enzyme. The results reveal the great potential of CACM-GOX as a flour improver.

Designing bioactive delivery systems for tissue regeneration

The direct infusion of macromolecules into defect sites generally does not impart adequate physiological responses. Without the protection of delivery systems, inductive molecules may likely redistribute away from their desired locale and are vulnerable to degradation. In order to achieve efficacy, large doses supplied at interval time periods are necessary, often at great expense and ensuing detrimental side effects. The selection of a delivery system plays an important role in the rate of re-growth and functionality of regenerating tissue: not only do the release kinetics of inductive molecules and their consequent bioactivities need to be considered, but also how the delivery system interacts and integrates with its surrounding host environment. In the current review, we describe the means of release of macromolecules from hydrogels, polymeric microspheres, and porous scaffolds along with the selection and utilization of bioactive delivery systems in a variety of tissue-engineering strategies.

Bile salt-reinforced alginate-chitosan beads

A polymeric delayed release protein delivery system was investigated with albumin as the model drug. The polysaccharide chitosan was reacted with sodium alginate in the presence of calcium chloride to form beads with a polyelectrolyte. In this study, attempts were made to extend albumin release in the phosphate buffer at pH 6.8 from the alginate-chitosan beads by reinforcing the matrix with bile salts. Sodium taurocholate was able to prevent albumin release at pH 1.2, protecting the protein from the acidic environment and extending the total albumin release at pH 6.8. This effect was explained by an interaction between the permanent negatively charged sulfonic acid of sodium taurocholate with the amino groups of chitosan. Mild formulation conditions, high bovine serum albumin (BSA) entrapment efficiency, and resistance to gastrointestinal release seem to be synergic and promising factors toward the development of an oral protein delivery form.

Defensin carriers for better mucosal immunity in the digestive system

The innate immunity utilizes a battery of broad-spectrum antibacterial cationic polypeptides named defensins. In humans, defensins are the first line of defense against pathogens, and their expression has been implicated in several diseases. In addition to exerting direct antimicrobial effects, defensins facilitate and amplify innate and adaptive immune responses. HD-5 is a polypeptide that plays a pivotal role in combating bacteria in the digestive system. Our results show that HD-5 can be entrapped within alginate carriers and strengthen their structure without changing their brittleness. In addition, carrier-entrapped HD-5 is released when incubated in buffer and/or stomach-simulating solution and still retains its activity after the release. This incubation also led to a decrease in carrier strength as well as an increase in their brittleness. Nevertheless the carriers did not disintegrate and remained intact throughout the diffusion process. The release of the defensin exhibited a bimodal behavior, suggesting that it was found both in a cross-linked and non-cross-linked form within the carrier. These results indicate that defensins encapsulated within alginate carriers could possibly be used for better mucosal immunity in the digestive system.

Alginate-crosslinked chitosan scaffolds as pentoxifylline delivery carriers

To prevent fibrous encapsulation of implants, measures are taken to suppress inflammatory reactions around them. Sustained anti-inflammatory drug release from the scaffolds can potentially be a way to reduce inflammation around these implants. Alginate-crosslinked chitosan is often used to make biocompatible tissue engineered scaffolds. However, there is a lack of quantitative studies on the drug delivery properties of alginate-crosslinked chitosan scaffolds. For this study, chitosan, crosslinked with different concentrations of alginate, was made into porous scaffolds. Infrared and thermal gravimetric analyses showed polyelectrolyte complex formation between chitosan and alginate units. The alginate-crosslinked chitosan scaffolds were more hydrophilic, showed less swelling, had lower pentoxifylline (PTX) release efficacies, were more favorable for initial cell attachment, and were mechanically stronger and more resistant to enzymatic degradation when compared to non-crosslinked chitosan scaffolds. The differences became more significant as the concentrations of chitosan and alginate increased. Furthermore, in vitro tests showed that when PTX was slowly released from the scaffolds, it became more effective in suppressing the production of TNF-alpha and IL-6 by stimulated macrophage cells.

Oral peptide delivery: in-vitro evaluation of thiolated alginate/poly(acrylic acid) microparticles

The purpose of this study was to develop an oral thiomer-based microparticulate delivery system for insulin by ionic gelation. The microparticulate matrix consisted of either poly(acrylic acid)-cysteine (PAA-Cys) and alginate-cysteine (Alg-Cys) or the corresponding unmodified polymers (PAA, Alg). Two different viscosities of alginates were provided for the study, low and medium. Three different types of microparticles were prepared via ionic gelation with calcium (Alg, AlgPAA and AlgPAA-Cys) and their different properties evaluated in-vitro (particle size and shape, drug loading and release profile, swelling and stability). The mean particle size of all formulations ranged from 400 to 600 μm, revealing the lowest for thiolated microparticles. SEM micrographs showed different morphological profiles for the three different types of microparticles. Encapsulation efficiency of insulin increased within the following rank order: Alg (15%) < AlgPAA (40%) < AlgPAA-Cys (65%). Alginate and AlgPAA microparticles displayed a burst release after 30 min, whereas the thiolated particles achieved a controlled release of insulin over 3 h. The swelling ratio was pH dependent: in simulated intestinal fluid microparticles exhibited a much higher water uptake compared with simulated gastric fluid. Due to the formation of intraparticulate disulfide bonds during the preparation process, thiolated particles revealed a higher stability. It was also observed that the viscosity of the two alginates used had no influence on the properties of the particles. According to these results AlgPAA-Cys microparticles obtained by ionic gelation and stabilized via disulfide bonds might be an alternative tool for the oral administration of therapeutic peptides.

Colloidal carrier integrating biomaterials for oral insulin delivery: Influence of component formulation on physicochemical and biological parameters

Strategies to design effective and safe colloidal carriers for biopharmaceuticals have evolved through applying the knowledge gained in nanotechnology to medicine. Designing a colloidal carrier to serve as a protein delivery device requires an understanding of the effect of different materials on the physicochemical, physiological and toxicological parameters for clinical application. The purpose of this study was to evaluate the influence of formulation components on the physicochemical factors and biological function involved in the development and optimization of newly designed nanoparticles for orally dosed insulin. Biodegradable, biocompatible, mucoadhesive and protease-protective biomaterials were combined through ionotropic pre-gelation and polyelectrolyte complexation forming an alginate, dextran sulfate and poloxamer hydrogel containing insulin, stabilized in nanoparticles with chitosan and poly(ethyleneglycol) and coated with albumin. Nanoparticles ranged in size from 200 to 500nm with 70-90% insulin entrapment efficiency, and electrostatic stabilization was suggested by zeta potential values lower than -30mV. This combination of formulation components was selected for insulin protection against harsh gastric pH and proteolytic conditions, and to improve insulin absorption through intestinal mucosa by combining nanoparticle uptake and insulin release at the site of absorption. Insulin was shown to be bioactive after nanoparticle formulation and release in neutral pH conditions. Fourier transform infrared spectroscopy was used to confirm the presence of formulations components in the nanoparticle structure and to identify potential interactions between biomaterials.

Development of budesonide microparticles using spray-drying technology for pulmonary administration: design, characterization, in vitro evaluation, and in vivo efficacy study

The purpose of this research was to generate, characterize, and investigate the in vivo efficacy of budesonide (BUD) microparticles prepared by spray-drying technology with a potential application as carriers for pulmonary administration with sustained-release profile and improved respirable fraction. Microspheres and porous particles of chitosan (drug/chitosan, 1:2) were prepared by spray drying using optimized process parameters and were characterized for different physicochemical parameters. Mass median aerodynamic diameter and geometric standard deviation for conventional, microspheres, and porous particles formulations were 2.75, 4.60, and 4.30 microm and 2.56, 1.75, and 2.54, respectively. Pharmacokinetic study was performed in rats by intratracheal administration of either placebo or developed dry powder inhalation (DPI) formulation. Pharmacokinetic parameters were calculated (Ka, Ke, T(max), C(max), AUC, and Vd) and these results indicated that developed formulations extended half life compared to conventional formulation with onefold to fourfold improved local and systemic bioavailability. Estimates of relative bioavailability suggested that developed formulations have excellent lung deposition characteristics with extended T(1/2) from 9.4 to 14 h compared to conventional formulation. Anti-inflammatory activity of BUD and developed formulations was compared and found to be similar. Cytotoxicity was determined in A549 alveolar epithelial cell line and found to be not toxic. In vivo pulmonary deposition of developed conventional formulation was studied using gamma scintigraphy and results indicated potential in vitro-in vivo correlation in performance of conventional BUD DPI formulation. From the DPI formulation prepared with porous particles, the concentration of BUD increased fourfold in the lungs, indicating pulmonary targeting potential of developed formulations.

Controlled delivery of VEGF via modulation of alginate microparticle ionic crosslinking

Clinical application of therapeutic angiogenesis is hampered by a lack of viable systems that demonstrate controlled, sustained release of vascular endothelial growth factor (VEGF). Alginate has emerged as a popular material for VEGF delivery; however most alginate-based systems offer limited means to control the rate of VEGF release beyond reducing the VEGF:alginate ratio to suboptimal efficiency. This study describes methods to control the release of VEGF from small (<10 microm mean diameter) alginate microparticles via the use of different ionic crosslinkers. Crosslinking with Zn(2+) versus Ca(2+) reduced VEGF diffusional release and the combination of discrete populations of either Zn(2+)- or Ca(2+)-crosslinked particles allowed for control over the sustained release profiles for VEGF. The particle preparations were non-toxic and VEGF was bioactive after release. These results demonstrate that ionic modulation of alginate crosslinking is a viable strategy for controlling release of VEGF while retaining the high protein:polymer ratio that makes alginate an attractive carrier for delivery of protein therapeutics.

Microencapsulation by spray coagulation of diltiazem HCl in calcium alginate-coated chitosan

The aim of this work was to develop a procedure for encapsulation of diltiazem HCl by spray coagulation. Factors affecting the formulations such as the effect of NaCl on the solubility of diltiazem in alginate solution, surface tension, pH, viscosity of the coagulation medium, and the effect of drug load on drug release were studied. The drug load was increased substantially from 10 up to 320 mg/mL by adding 1.2% w/v NaCl in 1% w/v alginate solution. More stable microcapsules were obtained at pH 4.6 (acetate buffer) than at a pH 2.8 (lactic acid), and the microencapsulation process was favored by the type of chitosan that produced low turbidity and viscosity in the coagulation medium. A dose of 50 mg/mL of diltiazem HCl, 1.2% w/v NaCl, and chitosan CS allowed higher amount of drug to be encapsulated. The high water solubility of diltiazem HCl leads to fast release from the microcapsules.

Effect of Chitosan-Coated Alginate Microspheres on the Permeability of Caco-2 Cell Monolayers

Alginate microspheres were prepared by emulsification/internal gelation and coated with chitosan. The ability of chitosan-coated alginate microspheres to increase the paracellular transport across Caco-2 cell monolayers was evaluated in comparison to uncoated microspheres and chitosan solutions. Transport studies were performed by using a permeability marker, Lucifer Yellow (LY), and by measuring the transepithelial electric resistance (TEER) variations. Furthermore, the occurrence of cytotoxic effects was assessed by evaluating neutral red uptake in viable cells and lactate dehydrogenase (LDH) release from damaged cells. A 3-fold increase on LY permeability was obtained for coated microspheres when compared to chitosan solutions. TEER variations were in agreement with permeability results. Chitosan solutions exhibited a dose-dependent toxicity, but coated microspheres did not decrease the viability of cells. Chitosan-coated alginate microspheres have potential to be used as carriers of poorly absorbable hydrophilic drugs to the intestinal epithelia and possibly increase their oral bioavailability.

Chitosan coated alginate beads containing poly(N-isopropylacrylamide) for dual-stimuli-responsive drug release

Chitosan coated alginate beads containing poly(N-isopropylacrylamide) (PNIPAAM), were prepared to be used as a controlled pH/temperature sensitive drug delivery system with improved encapsulation efficiency and delayed release rate. The studied beads were characterized by differential scanning calorimetry, scanning electron microscopy, and Fourier transform infrared spectroscopy. Water uptake and release studies using indomethacin as a model drug were also performed. The drug loading efficiency of the beads with the polyelectrolyte complex coating is significantly higher (84%) than that of the uncoated ones (74%). The equilibrium swelling of the developed materials was found to be pH- and thermo- responsive. For all the conditions it was found that the release profile was slower for the coated beads, indicating that the polyelectrolyte complex coating could slow down the release rate effectively. These results suggest that the studied smart system has potential to be used as an effective pH/temperature sustainable delivery system for biomedical applications.

Preparation of calcium alginate microgel beads in an electrodispersion reactor using an internal source of calcium carbonate nanoparticles

An electrodispersion reactor has been used to prepare calcium alginate (Ca-alginate) microgel beads in this study. In the electrodispersion reactor, pulsed electric fields are utilized to atomize aqueous mixtures of sodium alginate and CaCO3 nanoparticles (dispersed phase) from a nozzle into an immiscible, insulating second liquid (continuous phase) containing a soluble organic acid. This technique combines the features of the electrohydrodynamic force driven emulsion processes and externally triggered gelations in microreactors (the droplets) ultimately to yield soft gel beads. The average particle size of the Ca-alginate gels generated by this method changed from 412 +/- 90 to 10 +/- 3 microm as the applied peak voltage was increased. A diagram depicting structural information for the Ca-alginate was constructed as a function of the concentrations of sodium alginate and CaCO3 nanoparticles. From this diagram, a critical concentration of sodium alginate required for sol-gel transformation was observed. The characteristic highly porous structure of Ca-alginate particles made by this technique appears suitable for microencapsulation applications. Finally, time scale analysis was performed for the electrodispersion processes that include reactions in the microreactor droplets to provide guidelines for the future employment of this technique. This electrodispersion reactor can be used potentially in the formation of many reaction-based microencapsulation systems.