Progesterone-loaded chitosan microspheres: a long acting biodegradable controlled delivery system

Recent advances on chitosan-based micro- and nanoparticles in drug delivery

Considerable research efforts have been directed towards developing safe and efficient chitosan-based particulate drug delivery systems. The present review outlines the major new findings on the pharmaceutical applications of chitosan-based micro/nanoparticulate drug delivery systems published over the past decade. Methods of their preparation, drug loading, release characteristics, and applications are covered. Chemically modified chitosan or its derivatives used in drug delivery research are discussed critically to evaluate the usefulness of these systems in delivering the bioactive molecules. From a literature survey, it is realized that research activities on chitosan micro/nanoparticulate systems containing various drugs for different therapeutic applications have increased at the rapid rate. Hence, the present review is timely.

Biodegradable polymers for microencapsulation of drugs

Drug delivery has become increasingly important mainly due to the awareness of the difficulties associated with a variety of old and new drugs. Of the many polymeric drug delivery systems, biodegradable polymers have been used widely as drug delivery systems because of their biocompatibility and biodegradability. The majority of biodegradable polymers have been used in the form of microparticles, from which the incorporated drug is released to the environment in a controlled manner. The factors responsible for controlling the drug release rate are physicochemical properties of drugs, degradation rate of polymers, and the morphology and size of microparticles. This review discusses the conventional and recent technologies for microencapsulation of the drugs using biodegradable polymers. In addition, this review presents characteristics and degradation behaviors of biodegradable polymers which are currently used in drug delivery.

Chitosan microspheres as a potential carrier for drugs

Chitosan is a biodegradable natural polymer with great potential for pharmaceutical applications due to its biocompatibility, high charge density, non-toxicity and mucoadhesion. It has been shown that it not only improves the dissolution of poorly soluble drugs but also exerts a significant effect on fat metabolism in the body. Gel formation can be obtained by interactions of chitosans with low molecular counterions such as polyphosphates, sulphates and crosslinking with glutaraldehyde. This gelling property of chitosan allows a wide range of applications such as coating of pharmaceuticals and food products, gel entrapment of biochemicals, plant embryo, whole cells, microorganism and algae. This review is an insight into the exploitation of the various properties of chitosan to microencapsulate drugs. Various techniques used for preparing chitosan microspheres and evaluation of these microspheres have also been reviewed. This review also includes the factors that affect the entrapment efficiency and release kinetics of drugs from chitosan microspheres.

Partition-controlled progesterone release from waterborne, in situ-gelling materials

The primary goal of this work was to evaluate the long-term constant zero-order release of progesterone from a waterborne, in situ-gelling, injectable material. The motivation for this is to develop an intrafallopian tube embolization system for contraception. Poly(ethylene glycol) diacrylate (PEGDA, 575 g/mol) or poly(propylene glycol) diacrylate (PPODA, 540 g/mol) as a Michael-type addition acceptor was combined with pentaerythritol-tetrakis (3-mercaptopropionate; a Michael-type addition donor) to create a 75 wt.% emulsion solution in 0.1M PBS (pH 7.4 for PEGDA and pH 12 for PPODA) that gels in minutes by the Michael-type reaction to form a hydrophobic solid. Samples, with approximately 5.5 or 25 wt.% progesterone, were formed in Tygon tubing. Samples (1.6 mm x 1.0 cm cylinders) showed constant, partition-controlled release of progesterone for a prolonged period (time dependent on the mass of progesterone). Cylinders with approximately 25 wt.% load of progesterone exhibited constant release (approximately 40 microg per day) for more than 50 days in both the PEGDA and PPODA systems. This type of release is normally associated with preformed hydrophobic matrix systems. In contrast, these in situ-gelling materials reported here can be used to provide zero-order, partition-controlled release of progesterone and enhance the efficiency of an intrafallopian tube embolization system through progesterone release in an injectable, in situ-forming system.

Influence of Manufacturing Parameters on Development of Contraceptive Steroid Loaded Injectable Microspheres

The main objective of this work was to develop a system consisting of polymeric microspheres loaded with steroid drugs. The drugs were encapsulated using biodegradable poly(lactide-co-glycolide) (PLG) and poly(epsilon-caprolactone) (PCL) by double emulsion solvent evaporation method. The lipophilic drugs, levonorgestrel and ethinylestradiol were made soluble by adding ethanol/water mixture. The effects of parameters like polymer concentration and stabilizer concentration were studied on the size, size distribution, surface properties and loading efficiencies of microspheres. The formulated microspheres were smooth, spherical and uniform in shape and size. Fourier transformed infrared spectroscopy and differential scanning calorimetry studies seemed to confirm the absence of chemical interaction between the drugs and the polymers, while the drugs were dispersed in the polymer. The increase in polymer concentrations increased the size as well as the loading efficiency of microspheres. Data obtained in this study demonstrated that the PLG/PCL microspheres may be a suitable polymeric carrier for long acting injectable drug delivery.

Facial nerve regeneration through progesterone-loaded chitosan prosthesis. A preliminary report

Biodegradable nerve guides have represented new treatment alternatives for nerve repairing. They are gradually biodegradable, exert biological effects directly to the injured nerve, and act as drug- or cell-delivery devices. Furthermore, progesterone (PROG) has been demonstrated to promote injured peripheral nerve regeneration. In this study, it was hypothesized that PROG delivered from chitosan prostheses provides better facial nerve regenerative response than chitosan prostheses with no PROG. As there are no reports on the use of the former as nerve-guide material in the regeneration of injured nerves, this is the main objective of the present work. Chitosan prostheses containing PROG were used to bridge 10-mm gaps in rabbit facial nerves. The regenerated nerves were evaluated 45 days after implantation in animals with the use of light microscopy and morphometric analysis. Gas chromatography was used in order to quantify PROG content in prosthesis prior to and after implantation in subcutaneous tissue at different periods of up to 60 days. In addition, the prosthesis walls were evaluated with histological techniques in order to assess their integrity and the surrounding tissue reaction. Chitosan prostheses allowed PROG release during the time needed for nerve regeneration. At 45 days myelinated nerve fibers were observed in both the proximal and distal stumps. This parameter and the N ratio were higher in the progesterone-treated group when compared to that of the vehicle control. Findings indicate that chitosan prostheses were useful in nerve regeneration, acting as a long-lasting PROG delivery device a faster nerve regeneration.

Immunological study of a chitosan prosthesis in the sciatic nerve regeneration of the axotomized dog

This study demonstrated that when the regeneration of the axotomized sciatic nerve is induced through tubulization with chitosan, this biomaterial does not induce immunostimulation or immunodepression in the dog. Canine females were distributed among three groups: an intact control group which was only isolated, an axotomized control group, and an axotomized group which was tubulized with 3% chitosan prostheses. In vitro culture and phagocytosis tests, as well as IgG and IgM serum concentrations, were determined in peripheral blood on days 0, 15, 30 and 60. The results showed that chitosan implants did not importantly affect the immune response.

In vitro evaluation of a chitosan membrane cross-linked with genipin

The study was to evaluate the characteristics of a chitosan membrane cross-linked with a naturally-occurring cross-linking reagent, genipin. This newly-developed genipin-cross-linked chitosan membrane may be used as an implantable drug-delivery system. The chitosan membrane without cross-linking (fresh) and the glutaraldehyde-cross-linked chitosan membrane were used as controls. The characteristics of test chitosan membranes evaluated were their cross-linking degree, swelling ratio, mechanical properties. antimicrobial activity, cytotoxicity, and degradability. It was found that cross-linking of chitosan membrane using genipin increased its ultimate tensile strength but significantly reduced its strain-at-fracture and swelling ratio. There was no significant difference in antimicrobial activity between the genipin-cross-linked chitosan membrane and its fresh counterpart. Additionally, the results showed that the genipin-cross-linked chitosan membrane had a significantly less cytotoxicity and a slower degradation rate compared to the glutaraldehyde-cross-linked membrane. These results suggested that the genipin-cross-linked chitosan membrane may be a promising carrier for fabricating an implantable drug-delivery system. The drug-release characteristics of the genipin-cross-linked chitosan membrane are currently under investigation.

Effect of experimental parameters on the in vitro release kinetics of transforming growth factor beta1 from coral particles

Coral bone graft substitutes have been supplemented in the past with growth factors to further enhance bone regeneration in defects. Little is known, however, on the dynamics of protein release from coral. Coral particles were studied for their ability to release transforming growth factor beta 1 (TGF-beta1) in vitro, under different adsorption conditions. Adsorption of TGF-beta1 (0.05 microg/mL) on coral particles (<80 microm or 300-450 microm) after 24 h of incubation was high, regardless of conditions. TGF-beta1 release kinetics in an artificial bone fluid followed a specific profile: an initial 1-h protein burst, followed by a decreasing release during the next 24 h at which time the release increased again to reach a constant rate until the end of the 2-week study. The protein release rate appeared mainly to depend upon the diffusion of TGF-beta1. TGF-beta1 release from coral particles was enhanced in the presence of bovine serum albumin (BSA) compared to the release in the presence of gelatin, and was dependent on the pH of adsorption. The highest total TGF-beta1 release was obtained when adsorption occurred with BSA at pH 7.4 (82 +/- 3%), while the lowest release was observed when adsorption was done in the presence of gelatin at pH 11 (38 +/- 1%). TGF-beta1 release was also found to vary with particle size, higher release being obtained with the smaller particles. These results suggest that coral particles could be used as a delivery system for growth factors, and that the release rate may be modulated through modification of the adsorption conditions and coral particle size.

In vivo biocompatibility and degradability of a novel injectable-chitosan-based implant

A novel injectable-chitosan-based delivery system with low cytotoxicity was fabricated in the study. The chitosan microspheres with small particle size, low crystallinity and good sphericity were prepared by a spray-drying method followed by treating with a crosslinker. In the study, a naturally occurring crosslinking reagent (genipin), which has been used in herbal medicine and in the production of food dyes, was used to crosslink the chitosan microspheres. The glutaraldehyde-crosslinked counterparts were used as a control. Histological study of the genipin-crosslinked chitosan microspheres injected intramuscularly into the skeletal muscle of a rat model showed a less inflammatory reaction than its glutaraldehyde-crosslinked counterparts. The results of the scanning electron microscopic examination indicated that the glutaraldehyde-crosslinked chitosan microspheres retrieved at 12-week postoperatively were already degraded into a loose and porous structure. However, the degradation of the genipin-crosslinked chitosan microspheres was not significant after 20 weeks of implantation. The results of the study demonstrated that the genipin-crosslinked chitosan microspheres have a superior biocompatibility and a slower degradation rate than the glutaraldehyde-crosslinked chitosan microspheres. Accordingly, the genipin-crosslinked chitosan microspheres may be a suitable polymeric carrier for long-acting injectable drug delivery.

Effects of the characteristics of chitosan on controlling drug release of chitosan coated PLLA microspheres

Chitosan has been shown to be a biomaterial with good biocompatibility, and is highly biodegradable. This study investigated the effect of post-coating PLLA microspheres with different chitosans on the initial burst and controlling the drug release of the microspheres. Without chitosan, 19.2% of encapsulated lidocaine would release from PLLA microspheres within the first hour (R1), and the time of 50% release (T50) was 25 h. After the microspheres were coated with chitosan of viscosity (eta) 384 +/- 10cp, R1 and T50 could be reduced and prolonged to 14.6% and 90 h, respectively, for all tested molecular weights (Mw) of chitosan. In the case of the same Mw of chitosan being applied, the efficacy of reducing the initial burst of drug release was higher for a lower degree of deacetylation (D.D.). With chitosan in acetic acid solution, coating the microspheres with high Mw and high viscosity could most effectively reduce the initial burst and control drug release of PLLA microspheres. For example, the microspheres coated with chitosan solution of Mw 800 kDa and eta of 1479 cp, R1 and T50 could be reduced and prolonged to 7.4% and 245 h, respectively. The study indicated that manipulating the viscosity of the chitosan solution was the most important factor in contributing to controlling the drug release of chitosan post-coated PLLA microspheres.

Collagen-chitosan polymeric scaffolds for the in vitro culture of human epidermoid carcinoma cells

A biodegradable polymer scaffold was developed using collagen and chitosan, in the form of interpenetrating polymeric network (IPN), for in vitro culture of human epidermoid carcinoma cells (HEp-2, Cincinnati). Glutaraldehyde was used as cross-linking agent for the development of scaffold. Various types of scaffolds were prepared using different proportionate mixtures of collagen and chitosan solutions in the ratio of 3:7, 4:6, 5:5, 6:4 and 7:3 (collagen:chitosan). These scaffolds were fully characterized by Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and Thermogravimetric analysis (TGA). Equilibrium swelling studies were carried out in phosphate buffer of physiological pH (7.4) to study its swelling characteristics at slightly alkaline pH. The scaffold that showed optimum swelling property was selected as the best scaffold for performing in vitro culture studies. In vitro culture studies were carried out using HEp-2 cells, over the selected scaffold and its growth morphology was determined through optical photographs taken at different magnifications at various days of culture. The results of the above studies suggest that the scaffolds prepared from collagen and chitosan can be utilized as a substrate to culture HEp-2 cells and can also be used as an in vitro model to test anticancerous drugs.

Chitosan microparticles for oral vaccination: preparation, characterization and preliminary in vivo uptake studies in murine Peyer's patches

Although oral vaccination has numerous advantages over parenteral injection, degradation of the vaccine in the gut and low uptake in the lymphoid tissue of the gastrointestinal tract still complicate the development of oral vaccines. In this study chitosan microparticles were prepared and characterized with respect to size, zeta potential, morphology and ovalbumin-loading and -release. Furthermore, the in vivo uptake of chitosan microparticles by murine Peyer's patches was studied using confocal laser scanning microscopy (CLSM). Chitosan microparticles were made according to a precipitation/coacervation method, which was found to be reproducible for different batches of chitosan. The chitosan microparticles were 4.3+/-0.7 microm in size and positively charged (20+/-1 mV). Since only microparticles smaller than 10 microm can be taken up by M-cells of Peyer's patches, these microparticles are suitable to serve as vaccination systems. CLSM visualization studies showed that the model antigen ovalbumin was entrapped within the chitosan microparticles and not only associated to their outer surface. These results were verified using field emission scanning electron microscopy, which demonstrated the porous structure of the chitosan microparticles, thus facilitating the entrapment of ovalbumin in the microparticles. Loading studies of the chitosan microparticles with the model compound ovalbumin resulted in loading capacities of about 40%. Subsequent release studies showed only a very low release of ovalbumin within 4 h and most of the ovalbumin (about 90%) remained entrapped in the microparticles. Because the prepared chitosan microparticles are biodegradable, this entrapped ovalbumin will be released after intracellular digestion in the Peyer's patches. Initial in vivo studies demonstrated that fluorescently labeled chitosan microparticles can be taken up by the epithelium of the murine Peyer's patches. Since uptake by Peyer's patches is an essential step in oral vaccination, these results show that the presently developed porous chitosan microparticles are a very promising vaccine delivery system.

Progesterone release from glutaraldehyde cross-linked casein microspheres: in vitro studies and in vivo response in rabbits

Microspheres of bovine milk protein casein loaded with progesterone were fabricated by glutaraldehyde cross-linking of an aqueous alkaline solution of the protein dispersed in a hexane and dichloromethane non-aqueous dispersion medium with an aliphatic polyurethane as the stabilizer. Microspheres were characterized for their surface morphology and internal structure using scanning electron microscopy. In vitro release studies in phosphate buffer at 37 degrees C demonstrated that the rate of release of the steroid from the microsphere matrix was a function of cross-linking density, particle size, and drug payload. Microsphere formulations released 50% to 60% of the incorporated steroid in about 30 days and, thereafter, attained a steady state. In the presence of a protein-digesting enzyme such as protease, complete release of the steroid was observed in about 4 days in vitro into phosphate buffer. Intramuscular injection of progesterone-loaded microspheres into rabbits showed a plasma concentration of 1 to 2 ng/mL up to 5 months without any significant burst effect, whereas the powdered steroid administered in saline demonstrated a large burst effect peaking over 20 ng/mL, and the plasma concentration was not sustained beyond 4 days. Data obtained suggest that casein microspheres would be promising as a biodegradable drug carrier for sustained delivery of steroids.

Influence of the acid type on the physical and drug liberation properties of chitosan-gelatin sponges

The influence of acid type used to dissolve chitosan on the resulting sponge physical properties, and their consequent effect on the drug liberation were investigated. Chitosan was dissolved in different acid solutions and chitosan-gelatin sponges were produced by frothing up the polymer solution and then freeze-drying the foam. Prednisolone was used as a model drug. Using tartaric or citric acid resulted in instable, soft, elastic and disintegrating sponges with fast drug release. Elastic but harder sponges from stable foams were obtained when hydrochloric or lactic acid were used. The use of acetic or formic acid enabled the production of stable foams, soft and elastic sponges and a slow drug release. The rate of drug release was decreased by crosslinking the polymers with glutaraldehyde, but only if acetic, formic or acetic acid were used. Therefore, it is possible to manipulate the mechanical properties and the drug liberation rate by using different acids to dissolve chitosan.