Investigating key factors in the phase separation step of microspheres fabrication via coacervation

Coacervation, a common method for microspheres preparation, has not been given sufficient attention and study. This study aims to clarify the key factors in the phase separation step. Firstly, based on the thermodynamics of polymer solutions, the phase equilibrium time, binodal line, and the relationship between the concentration of lactic-glycolic acid copolymer (PLGA) in the coacervate phase (CPLGA) and the concentration of polydimethylsiloxane (PDMS) in the PLGA-lean phase (CPDMS) were determined. It was found that the lactic:glycolic ratio (L:G) significantly influences phase separation, and we introduced a method to calculate the compositions and masses of both the coacervate and PLGA-lean phases after phase separation of a system composed of PLGA, PDMS, and dichloromethane (DCM). Furthermore, some impellers aimed at producing narrow size distribution microspheres were designed, and the stirring states were analyzed visually using Computational Fluid Dynamics (CFD), explaining the impact of impeller types and clearance between impeller and vessel on particle size distribution. Measurements of the viscosities of the coacervate and continuous phases, coupled with emulsion theories, clarified the behavior of emulsion during the phase separation step, while also highlighting that the key to preparing narrow size distribution microspheres lies in weakening the coalescence of coacervate droplets. Finally, in vitro release demonstrated that CPLGA and the particle size distribution of coacervate droplets are key factors in the phase separation step.

Formulation composition, manufacturing process, and characterization of poly(lactide-co-glycolide) microparticles

Injectable long-acting formulations, specifically poly(lactide-co-glycolide) (PLGA) based systems, have been used to deliver drugs systemically for up to 6 months. Despite the benefits of using this type of long-acting formulations, the development of clinical products and the generic versions of existing formulations has been slow. Only about two dozen formulations have been approved by the U.S. Food and Drug Administration during the last 30 years. Furthermore, less than a dozen small molecules have been incorporated and approved for clinical use in PLGA-based formulations. The limited number of clinically used products is mainly due to the incomplete understanding of PLGA polymers and the various variables involved in the composition and manufacturing process. Numerous process parameters affect the formulation properties, and their intricate interactions have been difficult to decipher. Thus, it is necessary to identify all the factors affecting the final formulation properties and determine the main contributors to enable control of each factor independently. The composition of the formulation and the manufacturing processes determine the essential property of each formulation, i.e., in vivo drug release kinetics leading to their respective pharmacokinetic profiles. Since the pharmacokinetic profiles can be correlated with in vitro release kinetics, proper in vitro characterization is critical for both batch-to-batch quality control and scale-up production. In addition to in vitro release kinetics, other in vitro characterization is essential for ensuring that the desired formulation is produced, resulting in an expected pharmacokinetic profile. This article reviews the effects of a selected number of parameters in the formulation composition, manufacturing process, and characterization of microparticle systems. In particular, the emphasis is focused on the characterization of surface morphology of PLGA microparticles, as it is a manifestation of the formulation composition and the manufacturing process. Also, the implication of the surface morphology on the drug release kinetics is examined. The information described here can also be applied to in situ forming implants and solid implants.

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.

Stabilization challenges and formulation strategies associated with oral biologic drug delivery systems

Delivery of proteins to mucosal tissues of GI tract typically utilize formulations which protect against proteolysis and target the mucosal tissues. Using case studies from literature and the authors' own work, the in-process stability and solid state storage stability of biopharmaceuticals formulated in delivery systems designed for oral delivery to the GI tract will be reviewed. Among the range of delivery systems, biodegradable polymer systems for protection and controlled release of proteins have been the most studied; hence these systems will be covered in greater depth. These delivery systems include polymeric biodegradable microspheres or nanospheres that contain proteins or vaccines, which are designed to reduce the number of administrations/inoculations and the total protein dose required to achieve the desired biological effect. Specifically, this review will include a landscape survey of the systems that have been studied, the manufacturing processes involved, stability through the manufacturing process, key pharmaceutical formulation parameters that impact stability of the encased proteins, and storage stability of the encapsulated proteins in these delivery systems.

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.

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.

Sustained release system for highly water-soluble radiosensitizer drug etanidazole: irradiation and degradation studies

Etanidazole (one nitro-imidazole hypoxic radiosensitizer) is formulated as polymer matrix type controlled release devices in this study. A novel double polymer drug carrier, unlike the double wall microparticles, is fabricated for the purpose of drug delivery, with the following objectives in mind: (1) to have a high encapsulation efficiency, (2) to achieve a pusatile release profile suitable for the radiation schedule of radiotherapy, (3) to elucidate the degradation profile of these microparticles. Irradiation of the microparticles were also studied to investigate effects on release and degradation. At a dosage of 50 Gy (total dosage during a radiotherapy treatment period) showed no apparent effects on the tri-phase release profile. It consists of an initial burst in the first 72 h, followed by a slow and steady drug release phase, and finally a faster degradation controlled phase corresponding to the degradation state of the different microparticles. At 25 kGy (sterilization dosage), the release profiles of the drug carrier were drastically modified. The faster erosion of the polymer with high dosage irradiation hastened the drug release and shortened the release time span, accompanied by decreases in the polymer molecular weight and glass transition temperatures, which was not apparent from SEM imaging. Degradation studies suggested a heterogeneous degradation process, with the outer layer and inner matrix degrading at different rates. The modifiable tri-phase release profile using microparticles of different polymer blends implies that the release properties of the drug carriers can be modified for different treatment regimes.

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.

Controlled drug delivery by biodegradable poly(ester) devices: different preparative approaches

There has been extensive research on drug delivery by biodegradable polymeric devices since bioresorbable surgical sutures entered the market two decades ago. Among the different classes of biodegradable polymers, the thermoplastic aliphatic poly(esters) such as poly(lactide) (PLA), poly(glycolide) (PGA), and especially the copolymer of lactide and glycolide referred to as poly(lactide-co-glycolide) (PLGA) have generated tremendous interest because of their excellent biocompatibility, biodegradability, and mechanical strength. They are easy to formulate into various devices for carrying a variety of drug classes such as vaccines, peptides, proteins, and micromolecules. Most importantly, they have been approved by the United States Food and Drug Administration (FDA) for drug delivery. This review presents different preparation techniques of various drug-loaded PLGA devices, with special emphasis on preparing microparticles. Certain issues about other related biodegradable polyesters are discussed.

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.