Microencapsulation by coacervation of poly(lactide-co-glycolide): 1. Physicochemical characteristics of the phase separation process

Polymeric microparticle systems for modified release of glucagon-like-peptide-1 receptor agonists

Type 2 diabetes is a fast-growing worldwide epidemic. Despite the multiple therapies available to treat type 2 diabetes, the disease is not correctly managed in over half of patients, mainly due to non-compliance with prescribed treatment regimes. The development of analogues to the glucagon-like peptide 1 (GLP-1) has resulted in the extension of its half-life and associated benefits. Further benefits in the use of peptide-based GLP-1 receptor agonists have been achieved by the use of controlled-release systems based on polymeric microparticles. In this review, we focus on commercially available formulations and others that remain in development, discussing the preparation methods and the relationship between in vitro and in vivo kinetic release behaviours.

Poly(lactic-co-glycolic acid) devices: Production and applications for sustained protein delivery

Injectable or implantable poly(lactic-co-glycolic acid) (PLGA) devices for the sustained delivery of proteins have been widely studied and utilized to overcome the necessity of repeated administrations for therapeutic proteins due to poor pharmacokinetic profiles of macromolecular therapies. These devices can come in the form of microparticles, implants, or patches depending on the disease state and route of administration. Furthermore, the release rate can be tuned from weeks to months by controlling the polymer composition, geometry of the device, or introducing additives during device fabrication. Slow-release devices have become a very powerful tool for modern medicine. Production of these devices has initially focused on emulsion-based methods, relying on phase separation to encapsulate proteins within polymeric microparticles. Process parameters and the effect of additives have been thoroughly researched to ensure protein stability during device manufacturing and to control the release profile. Continuous fluidic production methods have also been utilized to create protein-laden PLGA devices through spray drying and electrospray production. Thermal processing of PLGA with solid proteins is an emerging production method that allows for continuous, high-throughput manufacturing of PLGA/protein devices. Overall, polymeric materials for protein delivery remain an emerging field of research for the creation of single administration treatments for a wide variety of disease. This review describes, in detail, methods to make PLGA devices, comparing traditional emulsion-based methods to emerging methods to fabricate protein-laden devices. This article is categorized under: Biology-Inspired Nanomaterials > Protein and Virus-Based Structures Implantable Materials and Surgical Technologies > Nanomaterials and Implants Biology-Inspired Nanomaterials > Peptide-Based Structures.

In situ forming biodegradable poly(ε-caprolactone) microsphere systems: a challenge for transarterial embolization therapy. In vitro and preliminary ex vivo studies

BACKGROUND

In situ forming biodegradable poly(ε-caprolactone) (PCL) microspheres (PCL-ISM) system was developed as a novel embolic agent for transarterial embolization (TAE) therapy of hepatocellular carcinoma (HCC). Ibuprofen sodium (Ibu-Na) was loaded on this platform to evaluate its potential for the treatment of post embolization syndrome.

METHODS

The influence of formulation parameters on the size/shape, encapsulation efficiency and drug release was investigated using mixture experimental design. Regression models were derived and used to optimize the formulation for particle size, encapsulation efficiency and drug release profile for TAE therapy. An ex vivo model using isolated rat livers was established to assess the in situ formation of microspheres.

RESULTS

All PCL-ISM components affected the studied properties and fitting indices of the regression models were high (Radj² = 0.810 for size, 0.964 encapsulation efficiency, and 0.993 or 0.971 for drug release at 30 min or 48 h). The optimized composition was: PCL = 4%, NMP = 43.1%, oil = 48.9%, surfactant = 2% and drug = 2%. Ex vivo studies revealed that PCL-ISM was able to form microspheres in the hepatic arterial bed.

CONCLUSIONS

PCL-ISM system provides a novel tool for the treatment of HCC and post-embolization syndrome. It is capable of forming microspheres with desirable size and Ibu-Na release profile after injection into blood vessels.

Polímeros sintéticos biodegradáveis: matérias-primas e métodos de produção de micropartículas para uso em drug delivery e liberação controlada

Micropartículas produzidas a partir de polímeros sintéticos têm sido amplamente utilizadas na área farmacêutica para encapsulação de princípios ativos. Essas micropartículas apresentam as vantagens de proteção do princípio ativo, mucoadesão e gastrorresistência, melhor biodisponibilidade e maior adesão do paciente ao tratamento. Além disso, utiliza menores quantidade de princípio ativo para obtenção do efeito terapêutico proporcionando diminuição dos efeitos adversos locais, sistêmicos e menor toxidade. Os polímeros sintéticos empregados na produção das micropartículas são classificados biodegradáveis ou não biodegradáveis, sendo os biodegradáveis mais utilizados por não necessitam ser removidos cirurgicamente após o término de sua ação. A produção das micropartículas poliméricas sintéticas para encapsulação tanto de ativos hidrofílicos quanto hidrofóbicos pode ser emulsificação por extração e/ou evaporação do solvente; coacervação; métodos mecânicos e estão revisados neste artigo evidenciando as vantagens, desvantagens e viabilidade de cada metodologia. A escolha da metodologia e do polímero sintético a serem empregados na produção desse sistema dependem da aplicação terapêutica requerida, bem como a simplicidade, reprodutibilidade e factibilidade do aumento de escala da produção.

Microcapsules with a pH responsive polymer: influence of the encapsulated oil on the capsule morphology

Microcapsules were prepared by microsieve membrane cross flow emulsification of Eudragit FS 30D/dichloromethane/edible oil mixtures in water, and subsequent phase separation induced by extraction of the dichloromethane through an aqueous phase. For long-chain triglycerides and jojoba oil, core-shell particles were obtained with the oil as core, surrounded by a shell of Eudragit. Medium chain triglyceride (MCT oil) was encapsulated as relatively small droplets in the Eudragit matrix. The morphology of the formed capsules was investigated with optical and SEM microscopy. Extraction of the oil from the core-shell capsules with hexane resulted in hollow Eudragit capsules with porous shells. It was shown that the differences are related to the compatibility of the oils with the shell-forming Eudragit. An oil with poor compatibility yields microcapsules with a dense Eudragit shell on a single oil droplet as the core; oils having better compatibility yield porous Eudragit spheres with several oil droplets trapped inside.

Formation of nanoparticles of a hydrophilic drug using supercritical carbon dioxide and microencapsulation for sustained release

PURPOSE

Our purpose was to produce nanoparticles of a hydrophilic drug with use of supercritical carbon dioxide (CO2), encapsulate the obtained nanoparticles into polymer microparticles with use of an anhydrous method and study their sustained in vitro drug release.

METHODS

The hydrophilic drug, dexamethasone phosphate, is dissolved in methanol and injected in supercritical CO2 with an ultrasonic field for enhanced molecular mixing (supercritical antisolvent technique with enhanced mass transfer [SAS-EM]). Supercritical CO2 rapidly extracts methanol leading to instantaneous precipitation of drug nanoparticles. The nanoparticles are then encapsulated in poly(lactide-co-glycolide) (PLGA) polymer by use of the anhydrous solid-oil-oil-oil technique. This results in a well-dispersed encapsulation of drug nanoparticles in polymer microspheres. In vitro drug release from these microparticles is studied.

RESULTS

With supercritical CO2 used as an antisolvent, nanoparticles of dexamethasone phosphate were obtained in the range of 150 to 200 nm. On encapsulation in polylactide coglycolide, composite microspheres of approximately 70 microm were obtained. The in vitro drug release of these nanoparticles/microparticles composites shows sustained release of dexamethasone phosphate over a period of 700 hours with almost no initial burst release.

CONCLUSIONS

Nanoparticles of dexamethasone phosphate can be produced with the SAS-EM technique. When microencapsulated, these particles can provide sustained drug release without initial burst release. Because the complete process is anhydrous, it can be easily extended to produce sustained release formulations of other hydrophilic drugs.

PLGA-PEG microspheres of teverelix: influence of polymer type on microsphere characteristics and on teverelix in vitro release

Teverelix microspheres were produced by coacervation using a new type of poly(ester-carbonates) made of block copolymers of poly(lactic-glycolic acid) (PLGA) and poly(ethylene glycol) (PEG). Five different PLGA-PEG copolymers and one PLGA were used. The 'stability window' has been determined for all polymers. It varied depending on the molecular weight and the weight percentage of PEG. With increasing core loading (from 9.4 to 34.2%), the microparticle size increased from 10-50 to 5-1000 micrometer. The core loading did not have any influence on encapsulation yield, which remained above 80%. The influence of polymer type on microsphere characteristics was studied at two different core loadings: 9.4 and 28%. At a low core loading, the nature of the polymer had no influence on microsphere characteristics whereas at 28%, only PLGA-PEG copolymers gave acceptable microparticles in term of particle size. At 28%, the glass transition temperature (T(g)) of loaded particles was 1-8 degrees C higher than the T(g) of the corresponding polymer. Increasing the core loading increased teverelix release whereas polymer degradation was decreased. All microparticles made of PLGA-PEG copolymers showed a faster release of teverelix than PLGA-based microspheres, whatever the core loading. One PLGA-PEG was selected on the basis of in vitro release rate for further in vivo investigations.

Modulated release of IdUrd from poly (D,L-lactide-co-glycolide) microspheres by addition of poly (D,L-lactide) oligomers

This paper reports the release characteristics of a radiosensitizer, 5-iodo-2'-deoxyuridine (IdUrd), from poly (D,L-lactide-co-glycolide) 50: 50 (PLGA) microparticles obtained by a phase separation technique. Poly (D,L-lactide) oligomers (D,L-PLA) were incorporated into the PLGA matrix in order to accelerate the overall drug release rate and regulate the triphasic release profile exhibited by the standard PLGA microparticles. For D,L-PLA (800), the burst effect was large and the IdUrd release was complete between 28 and 35 days. These results were attributed to rapid pore formation on the periphery of the microsphere in the early stages of incubation, due to hydrosolubility of the smallest oligomers (D,L-PLA (800)). In the case of D,L-PLA (1,100), drug release occurred over a six week period, the standard time course of conventional radiation therapy. The period during which the radiosensitizer was incorporated in human brain tumor cell nuclei after its entrapment in biodegradable microspheres was determined by using an organotypical tissue culture. The presence of radiosensitizer in the DNA of tumor cell nuclei was detected by immunohistochemical labelling of tumor fragments. IdUrd release from standard microspheres (7+/-0.5 weeks) was longer than from oligomer-containing batches. For D,L-PLA (800)-containing microspheres, the radiosensitizer was entirely released within 4. 5+/-0.5 weeks. The microspheres containing D,L-PLA (1,100) allowed an IdUrd release over a 5 to 6 week period. The ex vivo data were consistent with the in vitro findings in terms of release duration.

The application of microspheres from the copolymers of lactide and epsilon-caprolactone to the controlled release of steroids

The microspheres made of the copolymers of lactide and epsilon-caprolactone were used for the controlled release of progesterone and beta-estradiol. The copolymers contained 83-94% of l or d,l-lactide. The influence of the microstructure of lactidyl blocks in the copolymer chains on the drug release rate was studied. More uniform release rate was observed in the case of the copolymer derived from d,l-lactide as composed to l-lactide. For the copolymer containing 83-94% of d,l-lactide units the progesterone and beta-estradiol release rate in vitro was found to be practically constant within over 40 days. The in vivo studies performed on rats revealed that the period of constant release rate of beta-estradiol can be prolonged to about 70 days. The microspheres made of the applied poly-(d,l-lactide-co-epsilon-caprolactone) are the convenient system for long time release of steroids.

Drug microencapsulation by PLA/PLGA coacervation in the light of thermodynamics. 1. Overview and theoretical considerations

Phase separation of poly(lactide) (PLA) and poly(lactide-co-glycolide) (PLGA), often called "coacervation" in the pharmaceutical field, is one of the classical methods for peptide drug microencapsulation in biodegradable polyesters. Although numerous studies have used this technique, the underlying physicochemical mechanisms of polyester coacervation under conditions of microsphere production have not been well-described yet. Moreover, the quality of microencapsulation in terms of drug loading efficiency and residual organic solvents is often not entirely satisfactory and depends greatly on the specific drug and polymer used. The first part of this contribution reviews briefly the scientific and patent literature on PLA/PLGA coacervation. Then, the underlying physicochemical principles of polyester coacervation are discussed and relevant thermodynamic models presented. More specifically, attempts were made to clarify the necessary characteristics of polymers, solvents, and coacervating and hardening agents for successful phase separation and microsphere formation. These basic considerations may contribute to a better understanding of the boundary conditions crucial for efficient drug microencapsulation by polyester coacervation.