Controlling the internal morphology of aqueous core-PLGA shell microcapsules: promoting the internal phase separation via alcohol addition

Development and In Vivo Evaluation of Sustained Release Microparticles Loaded with Levothyroxine for Hypothyroidism Treatment

Hypothyroidism is a chronic condition combated by a daily oral supplementation of levothyroxine. In addition to the need for frequent dosing, oral administration may result in variable absorption of the drug leading to a failure in achieving normal thyroid function. Therefore, the development of a long-acting injectable system capable of delivering the drug is necessary. This work was aimed at developing sustained release microparticles loaded with levothyroxine. The microparticles were produced through the emulsification-solvent evaporation method using 2 grades of biocompatible and biodegradable polyesters: poly(ᴅ,ʟ-lactide-co-glycolide) (PLGA) and poly(ᴅ,ʟ-lactide) (PLA). Both polymers produced microparticles with very similar sizes (1.9 µm) and zeta potential values (around -22.0 mV). However, PLA microparticles had a significantly higher drug loading (6.1% vs. 4.4%, respectively) and encapsulation efficiency (36.8%, vs. 26.1%, respectively) when compared to PLGA counterparts. While both types of microparticles displayed a biphasic release pattern in vitro, a slower rate of release was observed with PLA microparticles. Moreover, a similar biphasic release pattern was found in vivo, with an initial phase of rapid release followed by a slower phase in the subsequent 10 days. These results indicate the possibility of developing levothyroxine loaded polyester microparticles as a potential long-acting thyroid hormone replacement therapy.

Aqueous core microcapsules as potential long-acting release systems for hydrophilic drugs

We have previously optimized the internal phase separation process to give rise to aqueous core microcapsules with polymeric shells composed of poly(lactide-co-glycolide) (PLGA) or poly(lactide) (PLA). In this study, the ability of these microcapsules to act as controlled release platforms of the model hydrophilic drug phenobarbital sodium was tested. Furthermore, the effect of the initial amounts of drug and water added to the system during microcapsule synthesis was investigated. Finally, the effect of varying polymer properties such as end functionalities, molecular weights, and lactide to glycolide ratios, on the characteristics of the produced microcapsules was studied. This was done by utilizing seven different grades of the polyester polymers. It was demonstrated that, within certain limits, drug loading is nearly proportional to the initial amounts of drug and water. Furthermore, drug encapsulation studies demonstrated that ester termination and increases in polymeric molecular weight result in lower drug loading and encapsulation efficiency. Moreover, drug release studies demonstrated that ester termination, increases in molecular weight, and increases in the lactide to glycolide ratio all result in slower drug release; this grants the ability to tailor the drug release duration from a few days to several weeks. In conclusion, such minor variations in polymer characteristics and formulation composition can result in dramatic changes in the properties of the produced microcapsules. These changes can be fine-tuned to obtain desirable long-acting microcapsules capable of encapsulating a variety of hydrophilic drugs which can be used in a wide range of applications.

Interfacial tension effects on the properties of PLGA microparticles

Many types of long-acting injectables, including in situ forming implants, preformed implants, and polymeric microparticles, have been developed and ultimately benefited numerous patients. The advantages of using long-acting injectables include greater patient compliance and more steady state drug plasma levels for weeks and months. However, the development of long-acting polymeric microparticles has been hampered by the lack of understanding of the microparticle formation process, and thus, control of the process. Of the many parameters critical to the reproducible preparation of microparticles, the interfacial tension (IFT) effect is an important factor throughout the process. It may influence the droplet formation, solvent extraction, and drug distribution in the polymer matrix, and ultimately drug release kinetics from the microparticles. This mini-review is focused on the IFT effects on drug-loaded poly(lactic-co-glycolic acid) (PLGA) microparticles.

A Novel Shell Material-Highland Barley Starch for Microencapsulation of Cinnamon Essential Oil with Different Preparation Methods

Highland barley starch (HBS), as a carbohydrate shell material with excellent performance in microcapsule applications, has rarely been reported. In the present study, three different microcapsules (CEO-SWSM, CEO-PM, and CEO-UM) were synthesized successfully via saturated aqueous solution method, molecular inclusion method and ultrasonic method, respectively, using HBS as shell material coupled with cinnamon essential oil (CEO) as the core material. The potential of HBS as a new shell material and the influence of synthetic methods on the performance of microcapsules, encapsulation efficiency (EE), yield, and release rate of CEO-SWSM, CEO-PM, and CEO-UM were determined, respectively. The results confirmed that CEO-PM had the most excellent EE (88.2%), yield (79.1%), as well as lowest release rate (11.5%, after 25 days of storage). Moreover, different kinetic models were applied to fit the release process of these three kinds of microcapsules: CEO-SWSM, CEO-PM, and CEO-UM had the uppermost R-squared value in the Higuchi model, the zero-order model, and the first-level model, respectively. Over all, this work put forward a novel perspective for the improved encapsulation effect of perishable core materials (e.g., essential oil) for the food industry.

Tunable sustained release drug delivery system based on mononuclear aqueous core-polymer shell microcapsules

Poly(d,l-lactide-co-glycolide) (PLGA) and poly(d,l-lactide) (PLA) polymers were used successfully in the preparation of polymer shell microcapsules with mononuclear aqueous cores by the internal phase separation method. These microcapsules were prepared with varying amounts of polymer and water and loaded with fluorescein sodium as a model water soluble drug. Evaluation of drug loading and encapsulation efficiency reveals an optimum polymer to water ratio of around 1:3. Prepared PLGA and PLA microcapsules exhibit sustained drug release over 7 and 49 days, respectively. Drug release from both microcapsule types follow zero order kinetics over the first 90% release. Further tuning of release rate is found possible by preparing microcapsules with mixtures of PLGA and PLA polymers at varying ratios. These results suggest that aqueous core-PLGA and PLA microcapsules would be promising platforms for a wide range of sustained drug delivery systems for many hydrophilic drugs.