Abstract
The unique properties of supercritical fluids, in particular supercritical carbon dioxide (CO2), provide numerous opportunities for the development of processes for pharmaceutical applications. One of the potential applications for pharmaceuticals includes microencapsulation and nanoencapsulation for drug delivery purposes. Supercritical CO2 processes allow the design and control of particle size, as well as drug loading by utilizing the tunable properties of supercritical CO2 at different operating conditions (flow ratio, temperature, pressures, etc.). This review aims to provide a comprehensive overview of the processes and techniques using supercritical fluid processing based on the supercritical properties, the role of supercritical carbon dioxide during the process, and the mechanism of formulation production for each process discussed. The considerations for equipment configurations to achieve the various processes described and the mechanisms behind the representative processes such as RESS (rapid expansion of supercritical solutions), SAS (supercritical antisolvent), SFEE (supercritical fluid extraction of emulsions), PGSS (particles from gas-saturated solutions), drying, and polymer foaming will be explained via schematic representation. More recent developments such as fluidized bed coating using supercritical CO2 as the fluidizing and drying medium, the supercritical CO2 spray drying of aqueous solutions, as well as the production of microporous drug releasing devices via foaming, will be highlighted in this review. Development and strategies to control and optimize the particle morphology, drug loading, and yield from the major processes will also be discussed.
Highlights
Well-established processes using supercritical CO2 in pharmaceutical applications include micronization by Rapid Expansion of Supercritical Solutions (RESS), SAS, or supercritical melt micronization (ScMM), microencapsulation via co-precipitation, active ingredient coating, sterilization, biopolymeric microporous foam/sponges
This paper aims to provide the reader with a comprehensive review of the currently available options to design and produce microencapsulated and nanoencapsulated formulations ranging from microparticles to nanoparticles, and including recent developments such as fluidized bed coating using supercritical CO2 and the production of drug-releasing three-dimensional microporous foam for pharmaceutical applications
Depending on the active ingredient or drug compound of interest, the type of formulation required, and the morphology of the final encapsulated product, it is possible to modify the configuration of the supercritical fluid system to perform different processes, as shown in our earlier studies where experiments for SAS [10,11,20], SAS with enhanced mass transfer (SAS-EM) [10], supercritical foaming [12,13,14,21], and supercritical drying [22] were performed with a custom-built supercritical fluid system
Summary
Well-established processes using supercritical CO2 in pharmaceutical applications include micronization by RESS (rapid expansion of supercritical solutions), SAS (supercritical antisolvent), or ScMM (supercritical melt micronization), microencapsulation via co-precipitation (in RESS, SAS, supercritical spray drying, etc.), active ingredient coating (spray coating, supercritical CO2 fluid bed coating, etc.), sterilization (due to microbial inactivation properties of pressurized CO2), biopolymeric microporous foam/sponges (supercritical foaming, supercritical impregnation, etc.). Polylactide-co-glycolide (PLGA) has a low glass transition temperature (Tg), and the further depression of its Tg in the presence of supercritical CO2 makes it difficult to produce discrete free-flowing powders via the SAS process This property of PLGA makes it suitable for the production of microporous polymeric foams with very low residual organic solvent content, allowing the production of microporous drug-releasing polymeric foams that can be used as implant and scaffold material [12,13,14]. This paper aims to provide the reader with a comprehensive review of the currently available options to design and produce microencapsulated and nanoencapsulated formulations ranging from microparticles to nanoparticles, and including recent developments such as fluidized bed coating using supercritical CO2 and the production of drug-releasing three-dimensional microporous foam for pharmaceutical applications. The discussion will introduce readers to different supercritical fluid processing techniques that utilize the favorable and versatile properties displayed by supercritical CO2, with an understanding of the underlying mechanism behind each method, and the modifications applied to improve the particle size, morphology, and process efficiency
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