Approach For Microencapsulation Research Articles

A Novel Approach for Microencapsulation of Nanoemulsions to Overcome the Oxidation of Bioactives in Aqueous Phase

Microencapsulation is a promising technique to retain the physical attributes of nanoemulsions and to overcome the oxidation of bioactives that become more available to aqueous phase during emulsification. Purity Gum Ultra (PGU) and Hi-CAP 100 (HiCap) emulsified nanoemulsions of Clove Oil (CO) co-encapsulated with Canola oil (CA) and Medium Chain Triglyceride (MCT) (5:5% v/v CO:CA and CO:MCT) were prepared through high pressure homogenization. Microencapsulation of nanoemulsions was performed using Whey Protein Isolates (WPI) under vacuum using freeze drying, which is considered as appropriate method for heat sensitive compounds. The reconstituted emulsions of microencapsulated powder had similar particle sizes as that of fresh nanoemulsions while uncoated showed a big increase (<400 nm). Oxidation of bioactives with and without CO, before and after freeze drying was investigated at different intervals during 60 days of storage at 4 and 25°C by Thiobarbituric Acid Reactive Substances (TBARS) assay. Microencapsulated PGU-CO:CA showed minimum TBARS values compared to other emulsions. Gas chromatography analysis of microcapsules also showed higher retention of CO and lower content on the interphase for aqueous interaction. Conclusively, this study proposes a novel strategy using a freeze drying process to microencapsulate nanoemulsion.

Device design and materials optimization of conformal coating for islets of Langerhans

Encapsulation of islets of Langerhans may represent a way to transplant islets in the absence of immunosuppression. Traditional methods for encapsulation lead to diffusional limitations imposed by the size of the capsules (600-1,000 μm in diameter), which results in core hypoxia and delayed insulin secretion in response to glucose. Moreover, the large volume of encapsulated cells does not allow implantation in sites that might be more favorable to islet cell engraftment. To address these issues, we have developed an encapsulation method that allows conformal coating of islets through microfluidics and minimizes capsule size and graft volume. In this method, capsule thickness, rather than capsule diameter, is constant and tightly defined by the microdevice geometry and the rheological properties of the immiscible fluids used for encapsulation within the microfluidic system. We have optimized the method both computationally and experimentally, and found that conformal coating allows for complete encapsulation of islets with a thin (a few tens of micrometers) continuous layer of hydrogel. Both in vitro and in vivo in syngeneic murine models of islet transplantation, the function of conformally coated islets was not compromised by encapsulation and was comparable to that of unencapsulated islets. We have further demonstrated that the structural support conferred by the coating materials protected islets from the loss of function experienced by uncoated islets during ex vivo culture.

Optimization of the formulation for preparing Lactobacillus casei loaded whey protein-Ca-alginate microparticles using full-factorial design

Context: This article presents specific approach for microencapsulation of Lactobacillus casei using emulsion method followed by additional coating with whey protein.Methods: Experimental design was employed using polynomial regression model at 2nd level with three independent variables, concentrations of alginate, whey protein and CaCl2. Physicochemical, biopharmaceutical and biological properties were investigated.Results: In 11 series generated, negatively charged microparticles were obtained, with size 6.99–9.88 µm, Ca-content 0.29–0.47 mg per 10 mg microparticles, and viability of the probiotic 9.30–10.87 log10CFU/g. The viability after 24 hours in simulated gastrointestinal conditions was between 3.60 and 8.32 log10CFU/g.Discussion: Optimal formulation of the microparticles that ensures survival of the probiotic and achieves controlled delivery was determined: 2.5% (w/w) alginate, 3% (w/w) CaCl2 and 3% (w/w) whey protein.Conclusion: The advantageous properties of the L. casei-loaded microparticles make them suitable for incorporation in functional food and/or pharmaceutical products.

Microfluidic-Based Synthesis of Hydrogel Particles for Cell Microencapsulation and Cell-Based Drug Delivery

Encapsulation of cells in hydrogel particles has been demonstrated as an effective approach to deliver therapeutic agents. The properties of hydrogel particles, such as the chemical composition, size, porosity, and number of cells per particle, affect cellular functions and consequently play important roles for the cell-based drug delivery. Microfluidics has shown unparalleled advantages for the synthesis of polymer particles and been utilized to produce hydrogel particles with a well-defined size, shape and morphology. Most importantly, during the encapsulation process, microfluidics can control the number of cells per particle and the overall encapsulation efficiency. Therefore, microfluidics is becoming the powerful approach for cell microencapsulation and construction of cell-based drug delivery systems. In this article, I summarize and discuss microfluidic approaches that have been developed recently for the synthesis of hydrogel particles and encapsulation of cells. I will start by classifying different types of hydrogel material, including natural biopolymers and synthetic polymers that are used for cell encapsulation, and then focus on the current status and challenges of microfluidic-based approaches. Finally, applications of cell-containing hydrogel particles for cell-based drug delivery, particularly for cancer therapy, are discussed.

Microencapsulation approach for orally extended delivery of glipizide: In vitro and in vivo evaluation

Glipizide is an effective antidiabetic agent, however, it suffers from relatively short biological half-life. To solve this encumbrance, it is a prospective candidate for fabricating glipizide extended release microcapsules. Microencapsulation of glipizde with a coat of alginate alone or in combination with chitosan or carbomer 934P was prepared employing ionotropic gelation process. The prepared microcapsules were evaluated in vitro by microscopical examination, determination of the particle size, yield and microencapsulation efficiency. The filled capsules were assessed for content uniformity and drug release characteristics. Stability study of the optimised formulas was carried out at three different temperatures over 12 weeks. In vivo bioavailability study and hypoglycemic activity of C9 microcapsules were done on albino rabbits. All formulas achieved high yield, microencapsulation efficiency and extended t1/2. C9 and C19 microcapsules attained the most optimised results in all tests and complied with the dissolution requirements for extended release dosage forms. These two formulas were selected for stability studies. C9 exhibited longer shelf-life and hence was chosen for in vivo studies. C9 microcapsules showed an improvement in the drug bioavailability and significant hypoglycemic activity compared to immediate release tablets (Minidiab® 5 mg). The optimised microcapsule formulation developed was found to produce extended antidiabetic activity.

Towards xenotransplantation of pig islets in the clinic

Porcine islet xenotransplantation into humans faces two major hurdles - safety issues related to xenosis and xenorejection of the transplants. The former has been overcome mainly by selection of a suitable disease-free source herd. Four strategies have been employed to date to overcome the rejection, all of which have shown some efficacy in animal models. Immune suppression, Sertoli cell co-transplantation and microencapsulation have been tried in type 1 diabetic humans with some clinical benefit derived reported from the latter two. Unaware hypoglycemia in particular seems amenable to the microencapsulation approach.

Control of hepatic differentiation via cellular aggregation in an alginate microenvironment

Integral to the development of embryonic stem cell therapeutic strategies for hepatic disorders is the identification and establishment of a controllable hepatic differentiation strategy. In order to address this issue we have established an alginate microencapsulation approach which provides a means to modulate the differentiation process through changes in key encapsulation parameters. We report that a wide array of hepatocyte specific markers is expressed by cells differentiated during a 23-day period within an alginate bead microenvironment. These include urea and albumin secretion, glycogen storage, and cytochrome P450 transcription factor activity. In addition, we demonstrate that cellular aggregation is integral to the control of differentiation within the bead environment and this process is mediated by the E-cadherin protein. The temporal expression of surface E-cadherin and hepatocyte functional expression occur concomitantly and both cellular aggregation and albumin synthesis are blocked in the presence of anti E-cadherin immunoglobulin. Furthermore, by establishing a compartmental model of differentiation, which incorporates this aggregation phenomenon, we can optimize key encapsulation parameters.

The Bioartificial Pancreas: Progress and Challenges

Diabetes remains a devastating disease, with tremendous cost in terms of human suffering and healthcare expenditures. A bioartificial pancreas has the potential as a promising approach to preventing or reversing complications associated with this disease. Bioartificial pancreatic constructs are based on encapsulation of islet cells with a semipermeable membrane so that cells can be protected from the host's immune system. Encapsulation of islet cells eliminates the requirement of immunosuppressive drugs, and offers a possible solution to the shortage of donors as it may allow the use of animal islets or insulin-producing cells engineered from stem cells. During the past 2 decades, several major approaches for immunoprotection of islets have been studied. The microencapsulation approach is quite promising because of its improved diffusion capacity, and technical ease of transplantation. It has the potential for providing an effective long-term treatment or cure of Type 1 diabetes.

Reacetylated chitosan microspheres for controlled delivery of anti-microbial agents to the gastric mucosa

The high aqueous solubility of chitosan restricts the utility of chitosan microspheres for gastric drug delivery. This paper describes the preparation of reacetylated chitosan microspheres with suitable properties for the controlled release of active anti-microbial agents, such as amoxycillin and metronidazole, in the gastric cavity. Two different microencapsulation approaches were developed and optimized in order to encapsulate hydrophilic (amoxycillin) and hydrophobic (metronidazole) compounds efficiently. The reacetylated chitosan microspheres exhibited a controlled water swelling capacity and gelified at acidic pH, resulting in prolonged release of the encapsulated antibiotics. The reacetylation time was found to be a key factor that affects not only drug release, but also encapsulation efficiency and anti-microbial activity of the encapsulated compound. The last two parameters were also dependent on drug solubility in the reacetylating agent. Using short reacetylation time periods, it was possible to efficiently control the release of both hydrophilic and lipophilic antibiotics while maintaining their activity against different bacteria. Consequently, reacetylated chitosan microspheres are promising vehicles for the controlled delivery of anti-microbial agents to the gastric cavity and, hence, for the eradication of Helicobacter pylori, a pathogen strongly associated with gastric ulcers and possibly gastric carcinoma.

A novel system based on a poloxamer/PLGA blend as a tetanus toxoid delivery vehicle.

Previous work on the encapsulation of proteins and antigens in poly(lactic-co-glycolic acid) (PLGA) microspheres has led to the conclusion that microencapsulated antigens are frequently inactivated due to their interaction with the polymer. To improve the compatibility of the antigen with the polymer, we have devised a novel microencapsulated system consisting of a blend of PLGA 50:50 and poloxamer 188 (Pluronic F68) and applied it to the delivery of tetanus antigen. Tetanus toxoid was encapsulated in microspheres containing different amounts of poloxamer using an anhydrous procedure based on an oil-in-oil solvent extraction process. The compatibility of the polymers was studied by Fourier transform infrared (FT-IR) spectroscopy. Microspheres were assayed in vitro and in vivo for their ability to deliver active antigen for extended periods of time. Analysis by FT-IR spectroscopy evidenced the miscibility of both polymers by a hydrogen bonding mechanism. In vitro release studies revealed that microspheres containing poloxamer released antigenically active TT, in a pulsatile manner, for up to 50 days. In addition, it was observed that the intensity and duration of the pulses were dependent on both poloxamer content and TT loading in the microspheres. The in vivo evaluation of this new system showed that the neutralizing antibodies elicited by the TT encapsulated in poloxamer-PLGA microspheres were considerably higher and more prolonged than those obtained after administration of the aluminum phosphate-adsorbed toxoid. These results indicate the importance of devising new microencapsulation approaches specially adapted for preserving the activity of protein antigens incorporated within PLGA microspheres.

Comparative testing between conventional and microencapsulation approaches in controlling pyrite oxidation

Oxidation of pyrite in mining waste or overburden is the main source of acid mine drainage (AMD) production, which causes major environmental pollution. Presently, the most common method of controlling AMD is through the mixing of alkaline substances, such as limestone, with the AMD producing materials. However, the effectiveness of this method is still questionable due to the potential for iron armoring. Pyrite microencapsulation, utilizing either phosphate or silica coatings, is a novel approach for controlling AMD that is under development in our laboratory. Although under laboratory conditions these approaches have been shown to be very effective in controlling pyrite oxidation, testing under natural conditions for possible field application is necessary. We are monitoring an outdoor leaching column experiment to evaluate the performance of both conventional and microencapsulation approaches for controlling AMD. The experiment consists of control, limestone, phosphate, and silica treatments on mine spoil and tailing samples contained in leaching columns and set up in the field. Preliminary results indicate that, after a period of nineteen months in the field, application of microencapsulation and conventional approaches significantly reduced pyrite oxidation. Among the microencapsulation approaches used with the mine spoil, the silica coatings seemed to be superior. The average leachate sample pH was 1.9 from the control, 2.1 from the limestone, 4.6 from the phosphate and 5.9 from the silica coatings. The results of these outdoor leaching experiments have shown that the application of silica coatings could offer an improved solution for the abatement of AMD. However, long-term monitoring and evaluation are still needed.

New strategies for the microencapsulation of tetanus vaccine

The progress toward the development of a single dose tetanus vaccine has been limited by the poor stability of the protein antigen, tetanus toxoid (TT), during its encapsulation in, and release from, biodegradable polymer microspheres. To investigatc alternative microencapsulation approaches that may improve the stability of TT under these conditions, a two-step microencapsulation method has been devised to form microcapsules which consist of (a) forming micro-cores of TT in a hydrophilic support matrix by spray-congealing, followed by (b) coating the microcores with poly(lactide-co-glycolide) (PLGA) by an oil-in-oil solvent extraction method. Several protein stabilizers including gelatin (with or without poloxamer 188), dextran, sodium glutamate, and polyethylene glycol were examined as potential core-materials. Among them, gelatin was superior in its ability to impart stability to TT against heat and moisture-induced inactivation. Microcores of this latter stabilizer and TT were encapsulated in PLGA using the foregoing technique, which exposed the dry antigen to minimal water in order to prevent its irreversible inactivation during exposure to the organic solvent. The microencapsulation method resulted in minimal loss of antigenically active TT (∼10–20%). Microscopic analysis of the micro-capsules following preparation showed the microcores to be fully encapsulated. However, microcapsules containing TT and gelatin released the active antigen nearly completely within one day. Fluorescence confocal microscopy revealed that the swelling of the hydrophilic core-material was responsible for the burst-release behaviour. Manipulation of the polymer coating could not slow down this 'explosion' of the microcapsules. TT-containing PLGA microcapsules have been prepared using a novel microencapsulation method, which retains an extremely high fraction of antigenically active TT. Hence, these mechanistic approaches may be useful in the development of effective single-dose vaccines.

A parametric study of microencapsulation approach to the preparation of polystyrene shells

Spherical polystyrene shells for laser fusion experiments were made in a density-matched microencapsulation approach. The yield, diameter, wall thickness, vacuole content, and surface finish were determined for different polystyrene concentrations varied from 5 to 13 wt% in an equivolume mixture of toluene and 1,2-dichloroethane, and an internal water phase containing surfactants, Tween 40 and Brij 30, at concentrations of 0.05 and 0.1 wt%, respectively. The main observations are: (1) The yield of shells is improved with added surfactants, and the effect is more pronounced at a higher polymer concentration; (2) The outer shell diameter increased with added surfactants at a constant polymer concentration. This is attributed to larger droplets being more stable in the first stage of the fabrication process; (3) Thicker shell walls are achieved with higher polymer concentrations; (4) The outer shell diameter increased with increasing polymer concentration regardless of added surfactants. This is attributed to a thicker wall providing greater mechanical stability; (5) The number of vacuoles over the cross-sectional area of the wall increases with increasing polymer concentration and with the addition of surfactants; and (6) The shells possess a smooth surface with a root-mean-square surface roughness less than 25 nm over a 30 μm × 30 μm area, and a sphericity greater than 99.6%.

The development of oyster diets

Although oyster larvae and spat have been reared successfully on algal diets for many decades, these are expensive to produce and do not always synchronize with hatchery requirements; considerable research has been conducted to determine which and why certain algal species are most appropriate and to investigate substitutes to algal feeds. Algal concentrates, commonly used in the United States, have overcome some problems associated with fresh algal feeds. However, work continues to develop cheaper non-algal alternatives. Recent promising advances have been in the formulation and preparation of experimental microencapsulated diets. However, further work upon capsules is required before the process can be commercialized. The possibility of rearing and substituting marine yeasts and bacteria for algae is an exciting and cost competitive alternative even to the microencapsulation approach.