In vitro release of bovine serum albumin from alginate/HPMC hydrogel beads

Interpenetrating polymer networks as innovative drug delivery systems

Polymers have always been valuable excipients in conventional dosage forms, also have shown excellent performance into the parenteral arena, and are now capable of offering advanced and sophisticated functions such as controlled drug release and drug targeting. Advances in polymer science have led to the development of several novel drug delivery systems. Interpenetrating polymer networks (IPNs) have shown superior performances over the conventional individual polymers and, consequently, the ranges of applications have grown rapidly for such class of materials. The advanced properties of IPNs like swelling capacity, stability, biocompatibility, nontoxicity and biodegradability have attracted considerable attention in pharmaceutical field especially in delivering bioactive molecules to the target site. In the past few years various research reports on the IPN based delivery systems showed that these carriers have emerged as a novel carrier in controlled drug delivery. The present review encompasses IPNs, their types, method of synthesis, factors which affects the morphology of IPNs, extensively studied IPN based drug delivery systems, and some natural polymers widely used for IPNs.

Stability and Release Kinetics of an Advanced Gliclazide-Cholic Acid Formulation: The Use of Artificial-Cell Microencapsulation in Slow Release Targeted Oral Delivery of Antidiabetics

Introduction

In previous studies carried out in our laboratory, a bile acid (BA) formulation exerted a hypoglycaemic effect in a rat model of type-1 diabetes (T1D). When the antidiabetic drug gliclazide (G) was added to the bile acid, it augmented the hypoglycaemic effect. In a recent study, we designed a new formulation of gliclazide-cholic acid (G-CA), with good structural properties, excipient compatibility and exhibits pseudoplastic-thixotropic characteristics. The aim of this study is to test the slow release and pH-controlled properties of this new formulation. The aim is also to examine the effect of CA on G release kinetics at various pH values and different temperatures.

Method

Microencapsulation was carried out using our Buchi-based microencapsulating system developed in our laboratory. Using sodium alginate (SA) polymer, both formulations were prepared: G-SA (control) and G-CA-SA (test) at a constant ratio (1:3:30), respectively. Microcapsules were examined for efficiency, size, release kinetics, stability and swelling studies at pH 1.5, pH 3, pH 7.4 and pH 7.8 and temperatures of 20 and 30 °C.

Results

The new formulation is further optimised by the addition of CA. CA reduced microcapsule swelling of the microcapsules at pH 7.8 and pH 3 at 30 °C and pH 3 at 20 °C, and, even though microcapsule size remains similar after CA addition, percent G release was enhanced at high pH values (pH 7.4 and pH 7.8, p < 0.01).

Conclusion

The new formulation exhibits colon-targeted delivery and the addition of CA prolonged G release suggesting its suitability for the sustained and targeted delivery of G and CA to the lower intestine.

Interpenetrating Polymer Networks polysaccharide hydrogels for drug delivery and tissue engineering

The ever increasing improvements of pharmaceutical formulations have been often obtained by means of the use of hydrogels. In particular, environmentally sensitive hydrogels have been investigated as "smart" delivery systems capable to release, at the appropriate time and site of action, entrapped drugs in response to specific physiological triggers. At the same time the progress in the tissue engineering research area was possible because of significant innovations in the field of hydrogels. In recent years multicomponent hydrogels, such as semi-Interpenetrating Polymer Networks (semi-IPNs) and Interpenetrating Polymer Networks (IPNs) have emerged as innovative biomaterials for drug delivery and as scaffolds for tissue engineering. These interpenetrated hydrogel networks, which can be obtained by either chemical or physical crosslinking, in most cases show physico-chemical properties that can remarkably differ from those of the macromolecular constituents. Among the synthetic and natural polymers that have been used for the preparation of semi-IPNs and IPNs, polysaccharides represent a class of macromolecules of particular interest because they are usually abundant, available from renewable sources and have a large variety of composition and properties that may allow appropriately tailored chemical modifications. Sometimes both macromolecular systems are based on polysaccharides but often also synthetic polymers are present together with polysaccharide chains. The description and discussion of (semi)-IPNs reported here, will allow to acquire a better understanding of the potential and wide range of applications of IPN polysaccharide hydrogels. A quite large number of polysaccharides have been investigated for the design of (semi)-IPNs for drug delivery and tissue engineering applications. This review article however mainly focuses on two of the most studied polysaccharide-based (semi)-IPNs, namely those obtained using alginate and hyaluronic acid. An overview of the methods of preparation, the properties, the performances as drug delivery systems and as scaffolds for tissue engineering, of (semi)-IPNs obtained using these two polysaccharides and their derivatives, will be given.

Cation effect on slow release from alginate beads: a fluorescence study

In this study, spherical alginate beads containing pyranine (P y ) as a fluorescence probe were prepared by ionotropic gelation of a sodium alginate solution. The steady state fluorescence technique was used to study pyranine release from the alginate beads crosslinked with calcium, barium and aluminum ions, respectively. The slow release of P y was observed with the time drive mode of the spectrophotometer at 512 nm. Fluorescence emission intensity (I p ) from P y was monitored during the release process, and the encapsulation efficiency (EE) of pyranine from the alginate beads was calculated. The Fickian Diffusion model was used to measure the release coefficients, D sl . It was seen that the slow release coefficients of pyranine from the alginate beads crosslinked with Ca(2+), Ba(2+), and Al(3+) ions increased in the following order: D sl (Al(3+))> D sl (Ca(2+))> D sl (Ba(2+)). In contrast, the initial amount of pyranine and EE into the beads showed the reverse behavior.

Biodegradable IPN hydrogel beads of pectin and grafted alginate for controlled delivery of diclofenac sodium

A novel diclofenac sodium (DS) loaded interpenetrating polymer network (IPN) beads of pectin and hydrolyzed polyacrylamide-graft-sodium alginate (PAAm-g-SA) was developed through ionotropic gelation and covalent cross-linking. The graft copolymer was synthesized by free radical polymerization under the nitrogen atmosphere followed by alkaline hydrolysis. The grafting, alkaline hydrolysis, and characterization of beads were confirmed by Fourier transforms infrared spectroscopy. The crystalline structure of drug after encapsulation into IPN beads were evaluated by differential scanning colorimetry and X-ray diffraction analyses. DS encapsulation was up to 96.45 %. The effect of hydrolyzed graft copolymer/pectin ratios and glutaraldehyde concentration on drug release in acidic and phosphate buffer solutions were investigated. The release of drug was significantly increased with increase of pH. The release of drug depends on the extent of cross-linking. The results indicated that IPN beads of hydrolyzed PAAm-g-SA and pectin could be used for sustained release of DS.

Optimizing microencapsulation of nisin with sodium alginate and guar gum

Nisin is a widely used bacteriocin active against gram positive bacteria and is also reported to be active against some gram negative bacteria. Incorporation of nisin into food systems is another challenge as directly added nisin is prone to inactivation by food constituents. Encapsulation of nisin has been done so far in liposomes which is rather an expensive technology involving multiple processes. Other cost effective alternatives with good encapsulation efficiency and better control release properties are sought. Alginate is useful as a matrix for entrapment of bioactive compounds. Present study was aimed at optimizing conditions for microencapsulation of nisin using calcium alginate as primary wall material and guar gum as filler at different air pressures using response surface methodology. The optimum conditions were: sodium alginate concentration (2 % w/v), guar gum concentration (0.4 % w/v), and air pressure (0.5 bar gauge). The encapsulation efficiency of nisin in microcapsules produced under optimal conditions was 36.65 %.

Biodegradable polymer based encapsulation of neem oil nanoemulsion for controlled release of Aza-A

Azadirachtin a biological compound found in neem have medicinal and pesticidal properties. The present work reports on the encapsulation of neem oil nanoemulsion using sodium alginate (Na-Alg) by cross linking with glutaraldehyde. Starch and polyethylene glycol (PEG) were used as coating agents for smooth surface of beads. The SEM images showed beads exhibited nearly spherical shape. Swelling of the polymeric beads reduced with coating which in turn decreased the rate of release of Aza-A. Starch coated encapsulation of neem oil nanoemulsion was found to be effective when compared to PEG coated encapsulation of neem oil nanoemulsion. The release rate of neem Aza-A from the beads into an aqueous environment was analyzed by UV-visible spectrophotometer (214 nm). The encapsulated neem oil nanoemulsion have the potential for controlled release of Aza-A. Neem oil nanoemulsion encapsulated beads coated with PEG was found to be toxic in lymphocyte cells.

Calcium alginate/dextran methacrylate IPN beads as protecting carriers for protein delivery

In the present study, mechanical and protein delivery properties of a system based on the interpenetration of calcium-alginate (Ca-Alg) and dextran-methacrylate (Dex-MA) networks are shown. Interpenetrated hydrogels beads were prepared by means of the alginate chains crosslinking with calcium ions, followed by the exposure to UV light that allows the Dex-MA network formation. Optical microscope analysis showed an average diameter of the IPN beads (Ca-Alg/Dex-MA) of 2 mm. This dimension was smaller than that of Ca-Alg beads because of the Dex-MA presence. Moreover, the strength of the IPN beads, and of their corresponding hydrogels, was influenced by the Dex-MA concentration and the crosslinking time. Model proteins (BSA and HRP) were successfully entrapped into the beads and released at a controlled rate, modulated by changing the Dex-MA concentration. The enzymatic activity of HRP released from the beads was maintained. These novel IPN beads have great potential as protein delivery system.

Controlled release of lipase from Candida rugosa loaded into hydrogels of N-isopropylacrylamide and itaconic acid

The series of poly(N-isopropylacrylamide-co-itaconic acid) hydrogels, with lipase from Candida rugosa as a model protein, were synthesized by free radical copolymerization. The composition of hydrogels was varied by monomers ratio, crosslinking agent concentration and amounts of lipase, which was loaded by in situ polymerization. All samples were characterized regarding morphology. The investigation of hydrogel swelling properties revealed their pH and temperature sensitive character. Protein loading efficiency, release profiles and the specific activity yield of the released lipase were also investigated as a function of hydrogel composition, protein content and pH, at the physiological temperature of 37 °C. Copolymers of N-isopropylacrylamide and itaconic acid presented high lipase loading efficiency. Another very important feature of these copolymers was that the protein release kinetic strongly depended on the pH value of the medium. The diffusion exponents values around 1 denoted that these hydrogel compositions could be adjusted to follow near zero-order kinetics. Namely, hydrogel formulations released low amounts of lipase at pH 2.20, but much higher released protein quantities were observed at pH 6.80 enabling these copolymers to be attractive candidates as site specific protein oral drug delivery systems.

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.

Hydrogels of N-isopropylacrylamide copolymers with controlled release of a model protein

Temperature- and pH-sensitive hydrogels, based on N-isopropylacrylamide (NiPAAm) and itaconic acid (IA), were synthesized by free radical crosslinking copolymerization in the presence of lipase from Candida rugosa. The samples were characterized for their sensitivity to the changes of external conditions and the ability to control the release of a hydrophilic model protein, lipase. These hydrogels were highly responsive to temperature and pH, at constant ionic strength. Parameters, such as the crosslinking degree and non-ionic/ionic (NiPAAm/IA) ratio, were found to impact the hydrogel structure, mechanical properties, morphology and swelling kinetics at different pH and temperatures. The hydrogels demonstrated protein loading efficiency as high as 95 wt%. Release studies of a hydrophilic model protein at a physiological temperature of 37 degrees C were performed at different pH values. High dependence of lipase release kinetics on hydrogel structure and the environmental pH was found, showing generally low release rates, lower in acidic media (pH 2.20) and higher at higher pHs (6.80). Lipase activity was retained even after treatment conditions that would provoke denaturation of the enzyme if it was not protected in the gel. The obtained hydrogels were found suitable for releasing therapeutic proteins in a controlled manner at specific sites in gastrointestinal tract.