Stomach-specific anti-H. pylori therapy

Reviewing particulate delivery systems loaded with repurposed tetracyclines - From micro to nanoparticles

Tetracyclines (TCs) are a class of broad-spectrum antibacterial agents recognized for their multifaceted properties, including anti-inflammatory, angiogenic and osteogenic effects. This versatility positions them as suitable candidates for drug repurposing, benefitting from well-characterized safety and pharmacological profiles. In the attempt to explore both their antibacterial and pleiotropic effects locally, innovative therapeutic strategies were set on engineering tetracycline-loaded micro and nanoparticles to tackle a vast number of clinical applications. Moreover, the conjoined drug carrier can function as an active component of the therapeutic approach, reducing off-target effects and accumulation, synergizing to an improvement of the therapeutic efficacy. In this comprehensive review we will critically evaluate recent advances involving the use of tetracyclines loaded onto micro- or nanoparticles, intended for biomedical applications, and discuss emerging approaches and current limitations associated with these drug carriers. Owing to their distinctive physical, chemical, and biological properties, these novel carriers have the potential to become a platform technology in personalized regenerative medicine and other therapeutic applications.

Assessment of Melatonin-Cultured Collagen/Chitosan Scaffolds Cross-Linked by a Glyoxal Solution as Biomaterials for Wound Healing

Chitosan (CTS) and collagen (Coll) are natural biomaterials that have been extensively used in tissue engineering or wound healing applications, either separately or as composite materials. Most methods to fabricate CTS/Coll matrices employ chemical crosslinking to obtain solid and stable scaffolds with the necessary porosity and mechanical properties to facilitate regeneration. In this study, we comparatively assessed the physicochemical properties of 3D scaffolds loaded with a cross-linker, glyoxal. Using a scanning electron microscope, we evaluated the microstructure of resultant matrices and their mechanistic testing by the determination of the compressive modulus (E_mod), the maximum force (F_max), thermogravimetric analysis (TG), Fourier Transform Infrared Spectroscopy–Attenuated Total Reflectance (FTIR-ATR), and proliferation rate in vitro using human epidermal keratinocytes and dermal fibroblasts cultured in presence of melatonin solution (10⁻⁵ M). We observed that enhanced content of collagen (50CTS/50Coll or 20CTS/80Coll compared to 80CTS/20Coll) significantly elevated the physicochemical capacities of resultant materials. Besides, presence of 5% glyoxal increased porosity, E_mod and F_max, compared to scaffolds without glyoxal. Finally, keratinocytes and dermal fibroblasts cultured on subjected matrices in presence of melatonin revealed a prominently enhanced growth rate. This indicates that the combination of glyoxal and melatonin make it imperative to consider these materials as a promising approach for targeting skin tissue engineering or regenerative dermatology.

Preparation and properties of chitosan-based microspheres by spray drying

In this study, the chitosan-based release microspheres were prepared by spray drying method. Chitosan was used as the carrier material, and Panax notoginseng extract, Codonopsis extract, and Atractylodes extract (the mass ratio was 2:7:5) were active substance. The spray drying preparation process of microsphere was optimized by single factor experiment and L9 (34) orthogonal design. Drug loading (DL), particle size, and sustained release performance of microspheres were investigated. The mass fraction of chitosan was 1.5%, the mass ratio of drug to chitosan was 1:3, the inlet air temperature was 130°C, and the injection rate was 400 ml/hr. The chitosan-based microspheres prepared under the above conditions had a smooth surface, and the DL was 23.87 ± 0.93%; the average particle diameter was 10.27 ± 1.05 μm, and the encapsulation efficiency (EE) of the microspheres was 91.28 ± 1.04%. The preparation process of chitosan-based drug microsphere prepared by spray drying method was simple and stable. The prepared microspheres in this paper showed a sustained release effect in vitro.

Recent advances in the treatment of pathogenic infections using antibiotics and nano-drug delivery vehicles

The worldwide misuse of antibiotics and the subsequent rise of multidrug-resistant pathogenic bacteria have prompted a paradigm shift in the established view of antibiotic and bacterial-human relations. The clinical failures of conventional antibiotic therapies are associated with lengthy detection methods, poor penetration at infection sites, disruption of indigenous microflora and high potential for mutational resistance. One of the most promising strategies to improve the efficacy of antibiotics is to complex them with micro or nano delivery materials. Such materials/vehicles can shield antibiotics from enzyme deactivation, increasing the therapeutic effectiveness of the drug. Alternatively, drug-free nanomaterials that do not kill the pathogen but target virulent factors such as adhesins, toxins, or secretory systems can be used to minimize resistance and infection severity. The main objective of this review is to examine the potential of the aforementioned materials in the detection and treatment of antibiotic-resistant pathogenic organisms.

Bacteria-targeted biomaterials: Glycan-coated microspheres to bind Helicobacter pylori

Gastric cancer is the third leading cause of cancer related deaths worldwide and Helicobacter pylori (H. pylori) persistent infection has been pointed as a causative agent of this disease. Current antibiotic based treatments to eradicate this bacterium fail in 20% of the patients, potentially leaving 140 million people in the world without alternative therapy. It is herein proposed the use of azide-alkyne coupling ("click chemistry") to produce glycan-coated mucoadhesive microspheres that bind and remove the H. pylori adherent to the gastric mucosa through specific bacterial adhesin-glycan interactions. Glycan immobilization is performed via chitosan's primary alcohol group, rather than the more reactive primary amines in order to preserve the amine groups that confer chitosan its mucoadhesiveness. It is shown that chitosan microspheres decorated with Lewis b glycans (Leb-Mic) bind specifically to H. pylori strains expressing the BabA adhesin (strains recognized as highly pathogenic) (∼230 bacteria/microsphere), are non-cytotoxic, are retained in the stomach of C57BL/6 mice for around 1.5h. Also, these Leb-Mic are able to prevent and remove H. pylori adhesion to gastric mucosa expressing the same glycan, in tissue sections from mice and human gastric mucosa (in vitro) and in fresh mice stomachs (ex vivo). These results provide proof-of-concept on the potential of glycan-decorated microspheres as an innovative therapeutic strategy against H. pylori and highlight the prospective of using targeted biomaterials to fight gastrointestinal infection.

STATEMENT OF SIGNIFICANCE

Gastric cancer has been associated with persistent infection by Helicobacter pylori, a bacterium that colonizes half of world population and whose available antibiotic treatment fails in 20% of cases. H. pylori adhesion to gastric epithelium is mediated between bacterial adhesins and glycans expressed in gastric mucosa. We demonstrate that these glycans can be immobilized in a controlled orientation into mucoadhesive chitosan microspheres, making them selective for different H. pylori strains. Efficacy studies (in vitro and ex vivo) with mice and human gastric mucosa that express the same glycan, revealed microspheres capacity to remove/prevent specific H. pylori adhesion, envisaging their future application as bacteria scavenging from stomach. This bacteria-binding strategy can be extrapolated to target other cells/bacteria using suitable ligands.

Delivery of antibiotics with polymeric particles

Despite the wide use of antibiotics, bacterial infection is still one of the leading causes of hospitalization and mortality. The clinical failure of antibiotic therapy is linked with low bioavailability, poor penetration to bacterial infection sites, and the side effects of antibiotics, as well as the antibiotic resistance properties of bacteria. Antibiotics encapsulated in nanoparticles or microparticles made up of a biodegradable polymer have shown great potential in replacing the administration of antibiotics in their "free" form. Polymeric particles provide protection to antibiotics against environmental deactivation and alter antibiotic pharmacokinetics and biodistribution. Polymeric particles can overcome tissue and cellular barriers and deliver antibiotics into very dense tissues and inaccessible target cells. Polymeric particles can be modified to target or respond to particular tissues, cells, and even bacteria, and thereby facilitate the selective concentration or release of the antibiotic at infection sites, respectively. Thus, the delivery of antibiotics with polymeric particles augments the level of the bioactive drug at the site of infection while reducing the dosage and the dosing frequency. The end results are improved therapeutic effects as well as decreased "pill burden" and drug side effects in patients. The main objective of this review is to analyze recent advances and current perspectives in the use of polymeric antibiotic delivery systems in the treatment of bacterial infection.

Eradication of Helicobacter pylori: Past, present and future

Helicobacter pylori is the major cause of chronic gastritis and peptic ulcers. Since the classification as a group 1 carcinogenic by International Agency for Research on Cancer, the importance of the complete H. pylori eradication has obtained a novel meaning. Hence, several studies have been made in order to deepen the knowledge in therapy strategies. However, the current therapy presents unsatisfactory eradication rates due to the lack of therapeutic compliance, antibiotic resistance, the degradation of antibiotics at gastric pH and their insufficient residence time in the stomach. Novel approaches have been made in order to overcome these limitations. The purpose of this review is to provide an overview about the current therapy and its limitations, while highlighting the possibility of using micro- and nanotechnology to develop gastric drug delivery systems, overcoming these difficulties in the future.

Helicobacter pylori infection: A brief overview on alternative natural treatments to conventional therapy

Helicobacter pylori is a human gastric pathogen considered as the etiologic agent of several gastric disorders, that may range from chronic gastritis to more severe outcomes, including gastric cancer. The current therapeutic scheme relies on the combination of several pharmacological substances, namely antibiotics and proton pump inhibitors. However, the cure rates obtained have been declining over the years, mostly due to bacterial resistance to antibiotics. In this context, the use of non-antibiotic substances is of the utmost importance regarding H. pylori eradication. In this review, we present different classes of compounds obtained from natural sources that have shown to present anti-H. pylori potential; we briefly highlight their possible use in the context of developing new therapeutic approaches.

Bacterial-binding chitosan microspheres for gastric infection treatment and prevention

Helicobacter pylori (H. pylori) colonizes the gastric mucosa of over 50% of the world population, causing several pathologies, such as gastric ulcers and gastric cancer. Since current antibiotic treatments are inefficient in 20% of cases alternative therapies are needed. This work reports the ability of chitosan microspheres to adhere to H. pylori and prevent/remove H. pylori colonization. Adhesion of H. pylori strains with different functional adhesins (BabA and/or SabA) to chitosan microspheres (diameter 167 ± 27 μm) occurs at both pH 2.6 and 6.0, but is higher at pH 6.0. Bacterial adhesion to a gastric cell line expressing sialylated carbohydrates (SabA receptors) was performed at the same pH values using H. pylori strains with and without SabA. At both pH values addition of microspheres to gastric cells before and after pre-incubation with H. pylori decreased bacterial adhesion to cells. Furthermore, the chitosan microspheres were non-cytotoxic. These findings reveal the potential of chitosan microspheres as an alternative or complementary treatment for H. pylori gastric eradication or prevention of H. pylori colonization.

Multiphase flow microfluidics for the production of single or multiple emulsions for drug delivery

Considerable effort has been directed towards developing novel drug delivery systems. Microfluidics, capable of generating monodisperse single and multiple emulsion droplets, executing precise control and operations on these droplets, is a powerful tool for fabricating complex systems (microparticles, microcapsules, microgels) with uniform size, narrow size distribution and desired properties, which have great potential in drug delivery applications. This review presents an overview of the state-of-the-art multiphase flow microfluidics for the production of single emulsions or multiple emulsions for drug delivery. The review starts with a brief introduction of the approaches for making single and multiple emulsions, followed by presentation of some potential drug delivery systems (microparticles, microcapsules and microgels) fabricated in microfluidic devices using single or multiple emulsions as templates. The design principles, manufacturing processes and properties of these drug delivery systems are also discussed and compared. Furthermore, drug encapsulation and drug release (including passive and active controlled release) are provided and compared highlighting some key findings and insights. Finally, site-targeting delivery using multiphase flow microfluidics is also briefly introduced.

Mucoadhesive 4-carboxybenzenesulfonamide-chitosan with antibacterial properties

The mucoadhesive property of chitosan, especially in an acidic (<pH 6.0) environment, was increased by conjugating an aromatic sulfonamide group at the C2-N position of chitosan. Four different feeding ratios of 4-carboxybenzensulfonamide (4-CBS) to chitosan in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride as a coupling agent were investigated. The 0.2:1 (w/w) ratio 4-CBS:chitosan revealed a 20-fold stronger mucoadhesion to mucin type II than the native chitosan in the simulated gastric fluid (SGF; pH 1.2), and a swelling ratio after 1 h in water, SGF and simulated intestinal fluid (pH 7.4) of about 2.9-, 3.0- and 3.4-fold higher than that of chitosan, respectively. In tissue culture, the 4-CBS-chitosan, like chitosan, were found to be non-cytotoxic to the Vero, KB, MCF-7 and NCI-H187 cell lines but showed potential antibacterial activity against Escherichia coli and Staphlyococcus aureus as model gram-negative and gram-positive bacteria, respectively.

Chitosan-alginate microcapsules of amoxicillin for gastric stability and mucoadhesion

Amoxicillin-loaded microcapsules were prepared by ionotropic gelation of sodium alginate (ALG) with chitosan (CS) in presence of calcium chloride as gastroretentive delivery system. The effect of pH, concentration of ALG, CS and calcium chloride, and drug : ALG ratio were optimized in this study for minimizing the degradation of drug in acidic environment and increasing the loading efficacy and mucoadhesive efficiency of microcapsules. The optimum condition for prepared CS-ALG microcapsules was 2%w/v ALG, 0.75%w/v CS (pH5.0), and 1.0% w/v calcium chloride. The resulting microcapsules had drug entrapment efficiency of 84% and average size of 840 mm. CS concentration significantly influenced particle size and encapsulation efficiency of CS–ALG microcapsules (P<0.05). Decrease in the drug: ALG ratio resulted in an increased release of amoxicillin in acidic media. The relative decomposition of drug after encapsulation in CS-ALG microcapsules was decreased to 20.7%, 41.9%, and 83.3% in 2, 4, and 8 hours, respectively.

Preparation and characterization of novel multi-core chitosan microspheres for stomach-specific delivery of hydrophilic antibiotics

Insufficient gastric mucosa drug concentration and short contact time were the main reason for the lack of eradication efficacy of Helicobacter pylori for peptic ulcer patients. Novel multi-core chitosan microspheres were prepared for stomach-specific delivery of hydrophilic antibiotics for the treatment of peptic ulcer. Chitosan microspheres with multiple Eudragit L100 cores were easily prepared by a new emulsification/coagulation encapsulating method. Swelling behaviors, surface amino groups and mucin absorption ability were investigated and the formulation that showed best mucoadhesive potential was adopted. The multi-core chitosan microspheres exhibited good mucoadhesiveness as well as controlled release manner for incorporated antibiotics in acidic environment. The release rate could be easily modulated with accumulative release ranging from 47.3 to 79.3% in 6 h. Accordingly, the multi-core chitosan microspheres could serve as a satisfactory vehicle for stomach-specific delivery of hydrophilic antibiotics.

Characterization of muco- and bioadhesive properties of chitosan, PVP, and chitosan/PVP blends and release of amoxicillin from alginate beads coated with chitosan/PVP

PURPOSE

To investigate the muco/bioadhesive properties of chitosan, polyvinylpyrrolidone (PVP), and chitosan/PVP blends and the release of amoxicillin (AMX) contained in AMX-alginate beads coated with these materials.

METHOD

Chitosan, PVP, and chitosan/PVP blends at various volume ratios were coated onto calcium alginate beads containing AMX. The muco/bioadhesive properties of all materials and the AMX-alginate beads coated with these materials were characterized.

RESULTS

Measurements of their viscosity, texture, and adhesion to HT29 cells demonstrated that chitosan/PVP at a volume ratio of 5/5 had the best muco/bioadhesive properties when compared with chitosan, PVP, and blends of other ratios. Wash-off tests indicated that the mucoadhesive property of the coated AMX-alginate beads was significantly higher than that of the uncoated beads. Diffuse reflectance infrared Fourier transform spectroscopy showed that there were interactions between chitosan-PVP, chitosan-mucin, PVP-mucin, and chitosan/PVP blend-mucin. Scanning electron microscopy revealed that the surfaces of the coated beads were smoother than those of the uncoated beads. All coated AMX-alginate beads were able to provide a controlled release of AMX with Super Case II transport properties, at a pH of 4. This was probably a result of the rapid and extensive swelling of the alginate beads. The more rapid release of AMX at pH 1 was probably because of the rapid dissolution of the drug at this pH.

CONCLUSIONS

From the controlled drug release and muco/bioadhesive properties of these coated AMX-alginate beads, we suggest that the alginate-coated beads might be a promising drug delivery system to assist with the eradication of Helicobacter pylori infections.

Polyelectrolyte coated multilayered liposomes (nanocapsules) for the treatment of Helicobacter pylori infection

Helicobacter pylori infection is one of the major causes of gastric cancers. A number of systems have already been reported, but 100% eradication has never been achieved. The present invention designs a gastro-retentive drug delivery system incorporated with amoxicillin and metronidazole, specifically suited for the eradication of Helicobacter pylori infections due to its mucoadhesiveness in the presence of polyelectrolyte polymers. The system possesses the advantages of both vesicular and particulate carriers, and it was prepared by alternative coating of polyanion (poly(acrylic acid), PAA) and polycation (poly(allylamine hydrochloride), PAH) using liposomes as the core. Compared with the conventional liposomes, the polyelectrolyte based multilayered system (nanocapsules) gave prolonged drug release in simulated gastric fluid, which is well suited for drug delivery against H. pylori infection in the stomach. In vitro growth inhibition study, agglutination assay, and in situ adherence assay in cultured H. pylori suggested the successful in vitro activity and binding propensity of the system. In vivo bacterial clearance study carried out in a H. pylori infected mouse model finally confirmed the success of the developed novel nanocapsule system. Thus, the newly developed composite nanocapsules along with the use of combination therapy proved to have commendable potential in Helicobacter pylori eradication as compared to already existing conventional and novel drug delivery systems.

Enhancing drug incorporation into tetracycline-loaded chitosan microspheres for periodontal therapy

PURPOSE

To identify optimal formulation parameters for enhancing the incorporation of tetracycline hydrochloride into chitosan microspheres for periodontal therapy.

METHODS

Tetracycline-loaded chitosan microspheres were prepared by ionotropic gelation. Various formulation parameters (salt form of drug, aqueous phase pH, anion structure, inorganic salts and electrolytes, preparation method) were investigated for their influence on drug incorporation efficiency. Microspheres were assessed in terms of drug entrapment and content, microsphere recovery, particle size and morphology.

RESULTS

Although drug incorporation efficiency was increased marginally, the use of a dihydrate form of the drug was not considered feasible due to the lowered microsphere recovery and higher costs. A decrease in the aqueous pH from 9 to 6 enhanced drug incorporation efficiency without an adverse effect on microsphere morphology. The use of inorganic salts/electrolytes and other approaches of microsphere preparation did not significantly enhance drug incorporation efficiency and these approaches also adversely affected microsphere morphology. The ionotropic preparation method in terms of the drug loading technique significantly affected drug incorporation efficiencies.

CONCLUSIONS

This study has shown that formulation variables can be exploited in order to enhance the incorporation of a water soluble drug into chitosan microspheres using the ionotropic gelation technique. Based on a comparison of all results obtained with the different approaches, the modification of the aqueous phase to pH 6 was identified as the most feasible approach.

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.

The promise of chitosan microspheres in drug delivery systems

Chitosan is a partially deacetylated polymer obtained from the alkaline deacetylation of chitin, which is a glucose-based, unbranched polysaccharide that occurs widely in nature as the principal component of exoskeletons of crustaceans and insects, as well as of the cell walls of some bacteria and fungi. Chitosan exhibits a variety of physicochemical and biological properties resulting in numerous applications in fields such as waste water treatment, agriculture, fabric and textiles, cosmetics, nutritional enhancement and food processing. In addition to its lack of toxicity and allergenicity, its biocompatibility, biodegradability and bioactivity make it a very attractive substance for diverse applications as a biomaterial in the pharmaceutical and medical fields. This review takes a closer look at the biomedical applications of chitosan microspheres. Based on recent research and existing products, some new and potential future approaches in this fascinating area are discussed.

Uniform Biodegradable Hydrogel Microspheres Fabricated by a Surfactant-Free Electric-Field-Assisted Method

Uniform biodegradable hydrogel microspheres (HMS) with precisely controlled size have been fabricated using an electric-field-assisted precision particle fabrication technique. Particle agglomeration was prevented by charging the hydrogel drops and allowing Coulomb repulsion to separate them. As a result, surfactant-free and non-toxic particle fabrication was possible and the resulting microspheres were most suitable for biomedical and food-related applications. Due to the size uniformity, the present HMS may serve as a convenient yet most accurate vehicle for controlled delivery of therapeutic agents and other active ingredients.

Gastroretentive drug delivery systems

A controlled drug delivery system with prolonged residence time in the stomach is of particular interest for drugs that i) are locally active in the stomach, ii) have an absorption window in the stomach or in the upper small intestine, iii) are unstable in the intestinal or colonic environment, or iv) exhibit low solubility at high pH values. This article gives an overview of the parameters affecting gastric emptying in humans as well as on the main concepts used to design pharmaceutical dosage forms with prolonged gastric residence times. In particular, bioadhesive, size-increasing and floating drug delivery systems are presented and their major advantages and shortcomings are discussed. Both single- and multiple-unit dosage forms are reviewed and, if available, results from in vivo trials are reported.

Gastroretentive dosage forms: Overview and special case of Helicobacter pylori

The challenge to develop efficient gastroretentive dosage forms began about 20 years ago, following the discovery of Helicobacter pylori by Warren and Marshall. In order to understand the real difficulty of increasing the gastric residence time of a dosage form, we have first summarized the important physiologic parameters, which act upon the gastric residence time. Afterwards, we have reviewed the different drug delivery systems designed until now, i.e. high-density, intragastric floating, expandable, superporous hydrogel, mucoadhesive and magnetic systems. Finally, we have focused on gastroretentive dosage forms especially designed against H. pylori, including specific targeting systems against this bacterium.

Are chitosan formulations mucoadhesive in the human small intestine?

Rapid passage through the proximal intestine can result in the low bioavailability of a drug substance with site-specific absorption characteristics in the upper gastrointestinal tract. To overcome this, there is increasing interest in developing gastro-retentive formulations and/or formulations that linger in the proximal parts of the small intestine, e.g. by using mucoadhesive polymers as excipients in formulations. In our recent study, we used neutron activation-based gamma scintigraphy to evaluate the gastro-retentive properties of formulations containing chitosan (Mw 150 kDa) in man. At the same time, we had an opportunity to monitor the transit of the formulations (40 or 95% of chitosan) in the small intestine. Gamma scintigraphic investigations revealed that although the chitosan studied had exhibited marked mucoadhesive capacities in vitro, retention of the chitosan formulations in the upper gastrointestinal tract was not sufficiently reproducible and the duration of retention was relatively short. In 3 volunteers out of 10, the formulation adhered to the gastric mucosa (retention times varied from 1.25 to 2.5 h) and in two volunteers to the upper small intestine (approximate retention time 45 min). In one case, the formulation adhered to the oesophagus. The system failed to increase the bioavailability of furosemide, a drug site-specifically absorbed in the upper gastrointestinal tract. As far as the kind of formulation studied is concerned, preparation of a system that is site-specific to the stomach and/or the upper small intestine seems difficult if the proposed mechanism of action is mucoadhesion. The results suggest that other mechanisms of action should also be studied.

Optimisation and characterisation of bioadhesive controlled release tetracycline microspheres

A Box-Behnken experimental design was employed to statistically optimise the formulation parameters of a tetracycline microsphere preparation for maximum bioadhesivity and controlled drug release. The quantitative effect of the formulation parameters at different levels on bioadhesion and drug release could be predicted using polynomial equations. A formulation comprising of 3% (w/w) chitosan, 10% (w/w) tetracycline HCl and 9% (w/v) tripolyphosphate was identified for maximising bioadhesivity and obtaining controlled drug release. The optimal microsphere preparation was subsequently characterised in terms of hydration dynamics, release kinetics, antimicrobial activity, thermal properties, morphology and surface pH. Kinetic models revealed that drug release followed Fickian diffusion while textural analysis showed minimal hydration over the test period. Antimicrobial studies showed that the drug concentrations in the in vitro release samples were above the minimum concentration of drug required for inhibition of Staphylococcus aureus growth. Thermal analyses showed a possible interaction between the drug and polymer. Scanning electron microscopy confirmed the integrity of the microspheres and identified the morphological changes following drug release. Surface pH of the microspheres was similar to salivary pH and did not show extremes in changes over the test period.

Preparation of chitosan beads by simultaneous cross-linking/insolubilisation in basic pH

A one-step procedure to prepare chitosan beads by simultaneous cross-linking with glutaraldehyde and insolubilisation in 1.5 M NaOH solution has been developed. The optimisation of the procedure was carried out by monitoring the evolution of the loss and storage moduli of chitosan solutions (1.5% (w/v), in acetic acid 0.2 M) in the presence of different proportions of glutaraldehyde. Increasing the chitosan molecular weight, glutaraldehyde concentration and/or process temperature from 20 to 37 degrees C, a reduction of time to reach the gel point was observed. The diameter of freshly prepared swollen beads was 3.2+/-0.4 mm and, after drying 0.48+/-0.18 mm. Swollen or previously dried beads were loaded with metronidazole by immersion in 0.1% (w/v), drug solution in a phosphate buffer pH 7.5, purified water, 0.2 M acetic acid or 0.1 M HCl. Beads synthesised at 37 degrees C experimented faster swelling than the ones prepared at 20 degrees C and even disintegrated in acetic acid. The amounts of metronidazole loaded (ranging from 1 to 286 mg/g dried beads) increased with swelling capacity of beads. The release studies carried out in 0.1 M HCl indicated that, regardless of the medium used to load the beads, all of them released the dose in less than 30 min. In summary, applying this one-step procedure and choosing the adequate glutaraldehyde proportion, it is possible to obtain particles of chitosan cross-linked with itself, which exhibit pH-sensitive swelling and which are able to release all the drug quickly into an acidic environment such as the stomach. The results obtained also highlight the importance of the pH of the medium for modulating the amount of drug loaded (it is remarkably greater at lower pHs) and the influence of temperature at which the beads are prepared on their tendency to disintegrate.