Oral sustained delivery of theophylline using in-situ gelation of sodium alginate

Alginate biopolymeric structures: Versatile carriers for bioactive compounds in functional foods and nutraceutical formulations: A review

Alginate-based biopolymer products have gained attention for protecting and delivering bioactive components in nutraceuticals and functional foods. These naturally abundant anionic, unbranched, and linear copolymers are also produced commercially by microorganisms. Alone or in combination with other copolymers, they efficiently transport bioactive molecules in food and nutraceutical products. This review aims to provide an in-depth understanding of alginate-based products and structures, emphasizing their role in delivering functional molecules in various formulations and delivery systems. These include edible coatings/films, gels/emulsions, beads/droplets, microspheres/particles, and engineered nanostructures where alginates have been used potentially. By exploring these applications, readers gain insights into the benefits of these products. Because, alginate-based biopolymer products have shown promise in delivering bioactive compounds like vitamin C, vitamin D3, curcumin, β-carotene, resveratrol, folic acid, gliadins, caffeic acid, betanin, limonoids, quercetin, several polyphenols and essential oils, etc., which are chief contributors to treating specific/overall nutritional and chronic metabolic disorders. So, this review summarizes the potential of alginate-based structures/products in various forms for delivering a wide range of functional food ingredients and nutraceutical components that offer promising perspectives for future investigations.

Factorial design of in situ gelling two-compartment systems containing chlorhexidine for the treatment of periodontitis

Periodontitis is one of the most widespread bacterial infectious oral diseases that affects a significant percentage of the population worldwide. Different bacterial strains are responsible for the chronic inflammation and subgingival plaque that could be effectively treated with prolonged exposure to therapeutic levels of antibiotics and antiseptics in the periodontal pockets. Medicated in situ gels of chlorhexidine (CHX), for extended drug release and long-lasting antiseptic effect in the targeted cavities, were prepared in a two-compartment system. One compartment was loaded with sodium alginate solution while other was filled with CHX and calcium solution. The mixing of the solutions during the application resulted in gelation. Two 33 full factorial designs were applied in this study in order to optimize the gel formulation. Initially, the effects of concentration of gelling agent, crosslinker, and pH of the system on the dependent variables such as gel formation and structure characteristics were investigated. Then, the concentration of the crosslinker was optimized. Afterwards, the effect of gelling agent, loading of the drug, and pH of the gel system were correlated with the gel characteristics through another factorial design. Optimized formulations were tested for mucoadhesion, in vitro drug release, and microbiological investigation. Based on the results of the factorial design, mucoadhesiveness, antimicrobial investigation, and drug release, a 4 % alginate composition can be considered optimal. Overall, the optimized in situ periodontal gel was found to be effective with prolonged retention time and desirable outcomes.

Green polymer altered in-situ gel oral liquid sustainable release preparation of vildagliptin suitable for dysphagic diabetic patients: assessment in-vitro & in-vivo

PURPOSE

This work aimed to fabricate alginate based in-situ gelling matrix of vildagliptin improved by calcium and carboxy methyl cellulose (CMC) for appropriate adjustment of the onset and duration of action. This easy-to-swallow thickened liquid preparation aimed to improve compliance for dysphagic or elderly diabetic patients.

METHODS

Vildagliptin dispersions containing alginate were fabricated in the presence or absence of calcium chloride to assess the effect of calcium ion, then a matrix containing 1.5% w/v of sodium alginate with calcium was further examined after the addition of CMC with different concentrations ranging from 0.1% to 0.3%. The viscosity, gelling forming property, Differential scanning calorimetry, and in-vitro drug release were assessed before monitoring the hypoglycemic effect of the selected formulation.

RESULTS

In-situ gel matrixes were fabricated at gastric pH with and without calcium ions. The best formula concerning viscosity and the gel-forming property was achieved with higher CMC concentrations, which in turn decreased the rate of vildagliptin release in stimulated gastric pH. In-vivo results confirmed the extended hypoglycemic effect of the vildagliptin in-situ gelling matrix compared to the vildagliptin aqueous solution.

CONCLUSION

This study represents a green polymeric-based in-situ gel as a liquid oral retarded release preparation intended for reducing dose frequency, easier administration of vildagliptin, and improving compliance in geriatric and dysphagic diabetic patients.

pH-Responsive Hydrogel as a Potential Oral Delivery System of Baicalin for Prolonging Gastroprotective Activity

Gastric ulcer is one of the most common gastrointestinal diseases, and natural products have obvious advantages in the treatment of gastrointestinal diseases. Baicalin (Bai) extracted from scutellaria baicalensis exhibits anti-inflammatory, antioxidant, and anti-apoptotic activities. Herein, a pH-responsive sodium alginate/polyaspartate/CaCO₃ (SA/PASP@CaCO₃) in situ hydrogel was established for the oral delivery of Bai. In this study, we detected the gelling properties, mechanical strength, in vitro erosion, and in vitro release behavior of the hydrogels. Meanwhile, the efficiency of Bai/SA/PASP@CaCO₃ hydrogel on ethanol-induced acute gastric ulcers, acetic acid-induced chronic gastric ulcers, and H₂O₂-stimulated human gastric epithelial GES-1 cells was explored. The pathological examination revealed that Bai-loaded hydrogel alleviated acute and chronic gastric ulcers. In vivo and in vitro results further confirmed that Bai/SA/PASP@CaCO₃ in situ hydrogels significantly relieved oxidative stress injury. Moreover, through Western blot assay, Bai/SA/PASP@CaCO₃ hydrogel was also found to dramatically increase the proteins levels of NRF2, HO-1, and Bcl2, and reduce levels of p-JNK, cleaved-caspase-3 and Bax; through flow cytometry, it was observed to significantly inhibit the H₂O₂-induced apoptosis of GES-1 cells. Importantly, the Bai/SA/PASP@CaCO₃ in situ hydrogel system showed better anti-gastric ulcer efficiency than free drug, and could serve as a potential drug delivery system for the clinical treatment of gastric ulcers.

A Critical Review on the Synthesis of Natural Sodium Alginate Based Composite Materials: An Innovative Biological Polymer for Biomedical Delivery Applications

Sodium alginate (Na-Alg) is water-soluble, neutral, and linear polysaccharide. It is the derivative of alginic acid which comprises 1,4-β-d-mannuronic (M) and α-l-guluronic (G) acids and has the chemical formula (NaC6H7O6). It shows water-soluble, non-toxic, biocompatible, biodegradable, and non-immunogenic properties. It had been used for various biomedical applications, among which the most promising are drug delivery, gene delivery, wound dressing, and wound healing. For different biomedical applications, it is used in different forms with the help of new techniques. That is the reason it had been blended with different polymers. In this review article, we present a comprehensive overview of the combinations of sodium alginate with natural and synthetic polymers and their biomedical applications involving delivery systems. All the scientific/technical issues have been addressed, and we have highlighted the recent advancements.

Cellulose Beads Derived from Waste Textiles for Drug Delivery

Cellulose beads were successfully prepared from waste denim using a dissolution-regeneration approach with ionic liquids as the dissolving solvent. Cellulose beads with different morphologies were achieved by altering the dissolving and coagulating solvents. The morphological differences were quantified by N₂ physisorption. The impact of morphology on the cellulose beads’ potential application was investigated in the context of drug loading and release. The results show that the fibrous morphology showed a better loading capacity than the globular analogue due to its higher surface area and pore volume.

Novel Bilayer Emulsions Costabilized by Zein Colloidal Particles and Propylene Glycol Alginate. 2. Influence of Environmental Stresses on Stability and Rheological Properties

Novel bilayer emulsions co-stabilized by zein colloidal particles (ZCPs) and propylene glycol alginate (PGA) were designed to overcome some limitations of conventional emulsions or Pickering emulsions. The bilayer emulsions of various concentrations of PGA (0.01-1.50%, w/v) and different incorporation sequences of ZCPs and PGA (ZCPs/PGA and PGA/ZCPs) were fabricated using the layer by layer (LBL) electrostatic deposition technique. Influence of environmental stresses (pH 2.5-8.5; temperature 60-80 °C ; ionic strength 0-100 mM NaCl) was focused on the stability and rheological properties of the novel bilayer emulsions. In comparison to the Pickering emulsion stabilized by ZCPs alone, bilayer emulsions exhibited improved stability and unique rheological characteristics under environmental stresses. The microstructure of well-defined spheres existing a branchlike network was observed in bilayer emulsions by TEM. A comprehensive evaluation was made of the physical characteristics and stimuli-responsive behavior of bilayer emulsions. The result provided meaningful information for understanding the changing mechanism of rheology of bilayer emulsions under environmental stresses.

In situ gelling and mucoadhesive polymers: why do they need each other?

INTRODUCTION

Mucosal drug delivery is an attractive route of administration, particularly in overcoming deficits of conventional dosage forms including high first-pass metabolism and poor bioavailability. Fast drainage from the target mucosa, however, represents a major limitation as it prevents sufficient drug absorption. In order to address these problems, mucoadhesive in situ gelling drug delivery systems have been investigated as they facilitate easy application in combination with a longer residence time at the administration site resulting in more desirable therapeutic effects.

AREAS COVERED

The present review evaluates the importance of the combination of mucoadhesive and in situ gelling polymers along with mechanisms of in situ gelation and mucoadhesion. In addition, an overview about recent applications in mucosal drug delivery is provided.

EXPERT OPINION

In situ gelling and mucoadhesive polymers proved to be essential excipients in order to prolong the mucosal residence time of drug delivery systems. Due to this prolonged residence time both local and systemic therapeutic efficacy of numerous drugs can be substantially improved. Depending on the site of administration and the incorporated drug, combinations of different polymers with in situ gelling and mucoadhesive properties are needed to keep the delivery system as long as feasible at the target site.

Aqueous clay suspensions stabilized by alginate fluid gels for coal spontaneous combustion prevention and control

We have developed aqueous clay suspensions stabilized by alginate fluid gels (AFG) for coal spontaneous combustion prevention and control. Specially, this study aimed to characterize the effect of AFG on the microstructure, static and dynamic stability, and coal fire inhibition performances of the prepared AFG-stabilized clay suspensions. Compared with aqueous clay suspensions, the AFG-stabilized clay suspensions manifest high static and dynamic stability, which can be ascribed to the formation of a robust three-dimensional gel network by AFG. The coal acceleration oxidation experimental results show that the prepared AFG-stabilized clay suspensions can improve the coal thermal stability and effectively inhibit the coal spontaneous oxidation process by increasing crossing point temperature (CPT) and reducing CO emission. The prepared low-cost and nontoxic AFG-stabilized clay suspensions, exhibiting excellent coal fire extinguishing performances, indicate great application potentials in coal spontaneous combustion prevention and control.

Development and evaluation of in situ gel of pregabalin

Aim and Background:

Pregabalin (PRG), an analog of gamma-aminobutyric acid, reduces the release of many neurotransmitters, including glutamate, and noradrenaline. It is used for the treatment of epilepsy; simple and complex partial convulsion. The present research work aims to ensure a high drug absorption by retarding the advancement of PRG formulation through the gastrointestinal tract. The work aims to design a controlled release PRG formulation which is administered as liquid and further gels in the stomach and floats in gastric juice.

Materials and Methods:

In situ gelling formulations were prepared using sodium alginate, calcium chloride, sodium citrate, hydroxypropyl methylcellulose (HPMC) K100M, and sodium bicarbonate. The prepared formulations were evaluated for solution viscosity, drug content, in vitro gelling studies, gel strength, and in vitro drug release. The final formulation was optimized using a 3² full factorial design.

Results:

The formulation containing 2.5% w/v sodium alginate and 0.2% w/v calcium chloride were considered optimum since it showed minimum floating lag time (18 s), optimum viscosity (287.3 cps), and gel strength (4087.17 dyne/cm²). The optimized formulation follows Korsmeyer-Peppas kinetic model with n value 0.3767 representing Fickian diffusion mechanism of drug release.

Conclusion:

Floating in situ gelling system of PRG can be formulated using sodium alginate as a gelling polymer and calcium chloride as a complexing agent to control the drug release for about 12 h for the treatment of epilepsy.

Prevention of Polyglycolic Acid-Induced Peritoneal Adhesions Using Alginate in a Rat Model

Postoperative intra-abdominal or intrathoracic adhesions sometimes cause significant morbidity. We have designed three types of alginate-based treatments using strongly cross-linked (SL), weakly cross-linked (WL), and non-cross-linked (NL) alginate with calcium gluconate. In rat experiments, we compared the antiadhesive effects of the three types of alginate-based treatments, fibrin glue treatment (a standard treatment), and no treatment against adhesions caused by polyglycolic acid (PGA) mesh (PGA-induced adhesions). The antiadhesive materials were set on the PGA sheet fixed on the parietal peritoneum of the abdomen. Fifty-six days later, the adhesions were evaluated macroscopically by the adhesion scores and microscopically by hematoxylin-eosin staining and immunostaining. We also tested the fibroblast growth on the surface of the antiadhesive materials in vitro. The antiadhesive effects of WL and NL were superior to the no treatment and fibrin glue treatment. A microscopic evaluation confirmed that the PGA sheet was covered by a peritoneal layer constructed of well-differentiated mesothelial cells, and the inflammation was most improved in the NL and WL. The fibroblast growth was inhibited most on the surfaces of the NL and WL. These results suggest that either the WL or NL treatments are suitable for preventing PGA-induced adhesions compared to SL or the conventional treatment.

Development of floating in situ gelling system as an efficient anti-ulcer formulation: in vitro and in vivo studies

The aim of the present work was to design gellan gum and calcium carbonate based floating in situ gel as an efficient anti-ulcer formulation using andrographolide (AG) as a model drug.

Soya nuggets – a potential carrier: swelling kinetics and release of hydrophobic drugs

Soya nuggets were used as a drug delivery vehicle. The swelling degree of the soya nuggets was responsible for efficient drug loading and release.

Invivo absorption behaviour of theophylline from starch-methyl methacrylate matrix tablets in beagle dogs

This study evaluates in vivo the drug absorption profiles from potato starch-methyl methacrylate matrices(*) using theophylline as a model drug. Healthy beagle dogs under fasting conditions were used for in vivo studies and plasma samples were analyzed by a fluorescence polarization immunoassay analysis (FPIA method). Non-compartmental and compartmental (population approach) analysis was performed to determine the pharmacokinetic parameters. The principle of superposition was applied to predict multiple dose plasma concentrations from experimental single dose data. An in vitro-in vivo correlation (IVIVC) was also assessed. The sustained absorption kinetics of theophylline from these formulations was demonstrated by comparison with two commercially available oral sustained-release theophylline products (Theo-Dur(®) and Theolair(®)). A one-compartment model with first order kinetics without lag-time best describes the absorption/disposition of theophylline from the formulations. Results revealed a theophylline absorption rate in the order FD-HSMMA≥Theo-Dur(®)≥OD-CSMMA>Theolair(®)≥FD-CSMMA. On the basis of simulated plasma theophylline levels, a twice daily dosage (every 12h) with the FD-CSMMA tablets should be recommended. A Level C IVIVC was found between the in vitrot50% and the in vivo AUC/D, although further optimization of the in vitro dissolution test would be needed to adequately correlate with in vivo data.

Utility of gastric-retained alginate gels to modulate pharmacokinetic profiles in rats

A gastric-retentive formulation amenable to dosing in rodents has the potential to enable sustained release in a preclinical setting. This may be useful to provide systemic exposure over a longer duration or to increase duration of exposure for compounds with targets localized in the gastrointestinal tract. Previous work has shown that a mixture of 1% sodium alginate and 0.625% karaya gum in the presence of a calcium chelator can form gels in situ that are gastric retained in rats. The aim of this work was to define the physicochemical boundaries of compounds within this technology and their relation to in vivo release using a series of model compounds with high permeability but varying solubility. In vitro data demonstrated a good correlation between solubility and initial release rates from the gels. In vivo studies were conducted in Sprague-Dawley rats to compare the exposure profile of compounds dosed in gel relative to a standard formulation. In vivo data were consistent with trends from the in vitro studies. These data suggest that, in conjunction with an understanding of compound solubility, sodium alginate/karaya gum gels may be a useful tool to modulate exposure profiles in rodent models in a preclinical setting.

Locust bean gum: a versatile biopolymer

Biopolymers or natural polymers are an attractive class of biodegradable polymers since they are derived from natural sources, easily available, relatively cheap and can be modified by suitable reagent. Locust bean gum is one of them that have a wide potentiality in drug formulations due to its extensive application as food additive and its recognized lack of toxicity. It can be tailored to suit its demands of applicants in both the pharmaceutical and biomedical areas. Locust bean gum has a wide application either in the field of novel drug delivery system as rate controlling excipients or in tissue engineering as scaffold formation. Through keen references of reported literature on locust bean gum, in this review, we have described critical aspects of locust bean gum, its manufacturing process, physicochemical properties and applications in various drug delivery systems.

Advancement in stimuli triggered in situ gelling delivery for local and systemic route

INTRODUCTION

Current research efforts focused on the design and evaluation of drug delivery systems that are easy to administer require decreased administration frequency, and provide sustained drug release in order to increase clinical efficacy and compliance of the patients. The gel forming smart polymeric formulations offer numerous applications resemble sustained and prolonged action in contrast to conventional drug delivery systems.

AREAS COVERED

Article summarizes type of bioactive, sol-gel triggering factors, dose, rationales, and polymers involved in gelation with respect to their route of administration. A lot of work has been done with smart polymeric gelling system taking the advantage of stimuli (temperature and pH) triggered sol-gel phase-transition in the administered area that have great prospective in biomedical and pharmaceutical applications, particularly in target-specific controlled drug delivery systems.

EXPERT OPINION

Although the principle of gelation is so attractive, key issues remain to be solved which include (i) variability of the drug release, (ii) avoidance of burst release in case of depot formulation, and (iii) issues related to toxicity. Unfortunately, till now area concerning the detailed processes of the gelling formation is still not much explored. Despite this proclamation, many efforts are made in industry and institutions to improve concerned approaches. New materials and approaches enter the preclinical and clinical phases and one can be sure that this strategy will gain further clinical importance within the next years. Thus, this review article will assuredly serve as an informative tool for the innovators working in the concern area.

Formulation and evaluation of in situ forming PLA implant containing tinidazole for the treatment of periodontitis

Periodontitis is caused by periodontopathic bacteria and antibacterial agents are placed in a periodontal pocket with the intention of enhancing the local effect. To maximize the therapeutic effects while reducing the adverse effects, tinidazole was delivered by in situ forming system. One approach for reducing burst release rate was to testify in situ forming effect. The effect of 0%-10% (w/w) polyethylene glycol 400 and 3% (w/w) glycerol on the tinidazole release from a poly(DL-lactide) (PLA) injectable implant was evaluated. The results showed that the in vitro initial burst release rate was decreased in the presence of poly(ethyleneglycol) PEG 400 and glycerol. A formulation containing 30% (w/w) PLA (M(w) 7300) dissolved in 62% (w/w) N-methyl-2-pyrrolidone, 5% (w/w) PEG 400, and 3%(w/w) glycerol with 5% (w/w) tinidazole was shown to be optimum. Twelve adult beagle dogs were used in the periodontitis model. The treatment group I, II, and positive control group was administrated with gel containing 5%(w/w) tinidazole, 2.5%(w/w) tinidazole, and periocline, respectively. Dog studies revealed that periocline and the developed formulation could significantly decrease symptoms of periodontitis, and they were better than gel containing 2.5% (w/w) tinidazole. The developed formulation could sustain the release of tinidazole for local delivery over 7 days. These findings suggested that the developed formulation was a viable alternative to conventional drug to cure periodontitis.

Oral sustained delivery of diclofenac sodium using calcium chondroitin sulfate matrix

Chondroitin sulfate (CS) is a potential candidate for colon-specific drug carriers. However, the readily water-soluble nature limits its application as a solid-state drug-delivery vehicle. In this study, the CS formation of a polyelectrolyte complex (PEC) with Ca2+ (CS-Ca) was adapted to retain CS in a solid form for use in a drug-delivery system. Pre-treated CS with poly(ethylene glycol) diglycidyl ether (EX-810) followed by complexation with Ca2+ was also tested (CS-Ca-EX). Diclofenac sodium was used as a drug probe to evaluate the performance of the drug-release behavior of the complexes. The amount of diclofenac sodium released was higher in simulated intestinal fluid (SIF) than in simulated gastric fluid (SGF) due to the anionic groups on CS or the higher solubility of drug itself in PBS. The release profile of diclofenac sodium from CS-Ca-EX was most notably sustained when compared to other groups. Enzymatic degradation by chondroitinase ABC of CS, CS-Ca and CS-Ca-EX exhibited a similar degradation mechanism and GPC revealed the dissolution rate of CS from the three matrix types was, in decreasing order: CS, CS-Ca, CS-Ca-EX. The synergy of the anti-inflammatory activity of diclofenac sodium in CS-based complexes was evaluated using the carrageenan-induced edema rat test. The percentage of swelling was lower for all experimental groups as compared to the control, untreated group. The anti-inflammatory activity of diclofenac in the CS matrix gradually increased up to 9 h but CS-Ca or CS-Ca-EX matrices showed less potency than the CS matrix in reducing inflammation.

HEC-cysteamine conjugates: influence of degree of thiolation on efflux pump inhibitory and permeation enhancing properties

Within the present study hydroxyethyl cellulose-cysteamine conjugates are investigated regarding biocompatibility, in situ gelling, permeation enhancing and efflux pump inhibitory properties. For this purpose, a series of concentrations of sodium periodate was prepared to oxidize HEC leading to ring opening of glucose subunits. The resulting polymers showing varying degrees of oxidation (DO) were then conjugated with cysteamine stabilized via reductive amination. Consequently, HEC-cysteamine conjugates with increasing degree in thiolation were obtained. Since the conjugates are positively charged, potency of cytotoxicity was tested by resazurin assay. In situ gelling properties of the conjugates were studied to investigate change of their viscosity due to inter- and/or intramolecular crosslinking via disulfide bonds. The influence of the presence of the conjugates on transport of rhodamine 123 and fluoresceinisothiocyanate-dextran 4 (FD4) representing model compounds for P-glycoprotein (P-gp) inhibition and permeation enhancing studies, respectively, across Caco-2 cell monolayers was determined. The conjugates showed a degree of thiolation in the range of 316-2158 μmol/g. Within 30 min, dynamic viscosity of the conjugate with the lowest degree of thiolation 0.5% (m/v) increased up to 300-fold. The conjugates showed a degree of thiolation-dependent increase in cytotoxicity but they all were found comparatively low cytotoxic. The addition of the conjugate with thiol group content of 1670 μmol/g resulted in the highest improvement in the transport of both rhodamine 123 and FD4 as compared to buffer control. Accordingly, the degree of thiolation strongly influences the properties of the conjugates and the modulation of the degree of thiolation could be exploited for development of various drug delivery systems.

Phase behavior, rheological and mechanical properties of hydrophilic polymer dispersions

Liquid polymeric systems that can undergo phase change (sol to gel) upon administration into the teat canal of cow's mammary gland can serve as a physical barrier to invading pathogens and can also serve as a reservoir for controlled release of therapeutic agents. The aim of the study was to investigate the phase behavior, rheological and mechanical properties of selected in situ gelling systems. Six in situ gelling polymer formulations were identified using phase behavior studies. Rheological studies revealed pseudoplastic flow with thixotropy. All six formulations showed significantly different viscosity, pseudoplasticity and thixotropy values except for CMC1 and HPMC2 which where statistically similar. The gel strength was dependent on the solvent system used and amount of water in the system. These in situ gelling systems have the potential to serve as a platform for development of intramammary formulations intended for administration into the teat canal of the cow's mammary gland. They can serve as a physical barrier or a matrix for controlled drug release.

Floating drug delivery of a locally acting H2-antagonist: an approach using an in situ gelling liquid formulation

In the present work, a gastroretentive in situ gelling liquid formulation for controlled delivery of ranitidine was formulated using sodium alginate (low, medium and high viscosity grades), calcium carbonate (source of cations) and ranitidine. Prepared formulations were evaluated for viscosity, buoyancy lag time and buoyancy duration, drug content and in vitro drug release. Formulation variables such as concentration of sodium alginate, calcium carbonate and drug significantly affected the formulation viscosity, floating behavior and in vitro drug release. Analysis of the release pattern showed that the drug release from in situ gel followed a diffusion mechanism.

New amphiphilic and pH-sensitive hydrogel for controlled release of a model poorly water-soluble drug

This paper presents the development of new pH-sensitive, amphiphilic and biocompatible hydrogels based on alginate-g-PCL, cross-linked with calcium ions to form beads, prepared for controlled delivery of poorly water-soluble drug. We have focused our study on the effect of the length of PCL chains (530 and 1250 g mol(-1)). Swelling profiles obtained clearly indicated that these hydrogels swell slightly (10-14%) in a simulated gastric fluid (pH 1.2), and strongly (700-1300% before disintegration) in a simulated intestinal fluid (pH 6.8). In both media, rates of swelling were lower for beads based on amphiphilic derivatives than for alginate/Ca2+ ones due to the hydrophobic PCL grafts, and decreased when hydrophobic character increased. A model drug, theophylline, was entrapped into these hydrogels and release studies were carried out. The drug was protected in acidic fluid (only 14-20% of release for alginate-g-PCL hydrogel against 35% of release for alginate hydrogel during 350 min). The drug is released completely in neutral fluid due to ion exchanges and disintegration of the hydrogel. PCL leads to decrease in the release kinetics in SIF (2h for alginate-g-PCL/Ca2+ beads against 1h for alginate/Ca2+ beads). It was demonstrated that the establishment of clusters inside beads by intramolecular interactions between PCL grafts of 530 g mol(-1) in salt media allowed to retain the drug and to slow down its release considerably.

Marine derived polysaccharides for biomedical applications: chemical modification approaches

Polysaccharide-based biomaterials are an emerging class in several biomedical fields such as tissue regeneration, particularly for cartilage, drug delivery devices and gelentrapment systems for the immobilization of cells. Important properties of the polysaccharides include controllable biological activity, biodegradability, and their ability to form hydrogels. Most of the polysaccharides used derive from natural sources; particularly, alginate and chitin, two polysaccharides which have an extensive history of use in medicine, pharmacy and basic sciences, and can be easily extracted from marine plants (algae kelp) and crab shells, respectively. The recent rediscovery of poly-saccharidebased materials is also attributable to new synthetic routes for their chemical modification, with the aim of promoting new biological activities and/or to modify the final properties of the biomaterials for specific purposes. These synthetic strategies also involve the combination of polysaccharides with other polymers. A review of the more recent research in the field of chemical modification of alginate, chitin and its derivative chitosan is presented. Moreover, we report as case studies the results of our recent work concerning various different approaches and applications of polysaccharide-based biomaterials, such as the realization of novel composites based on calcium sulphate blended with alginate and with a chemically modified chitosan, the synthesis of novel alginate-poly(ethylene glycol) copolymers and the development of a family of materials based on alginate and acrylic polymers of potential interest as drug delivery systems.