Journal of Microencapsulation2009ResearchDrug Delivery

Particle size design of PLGA microspheres for potential pulmonary drug delivery using response surface methodology

Jaber Emami, Hamed Hamishehkar, Abdolhossien Rouholamini Najafabadi, Kambiz Gilani, Mohsen Minaiyan, Hamid Mahdavi, Hamid Mirzadeh, Amir Fakhari, Ali Nokhodchi29 September 2026DOI 10.1080/02652040802041738

Summary

Pulmonary administration offers a route for systemic delivery of therapeutics, especially peptides and proteins, but controlled-release polymer particles are needed. Conventional w/o/w methods for hydrophilic drugs suffer from low encapsulation, protein inactivation, and difficult release control. An oil-in-oil (o/o) solvent evaporation method may overcome these limitations, but the particle size of PLGA microspheres must be optimized to the. Particle size range: VMD 2.7–19.7 µm; GSD 1.49–2.78 across all formulations. - Significant factors for size: Stirring speed had the most important negative effect (higher rpm → smaller particles); PLGA concentration had.

Keywords

PLGADrug deliveryPolymericPeptidesNanocarriersGene deliveryNanoparticles

Purpose: Pulmonary administration offers a route for systemic delivery of therapeutics, especially peptides and proteins, but controlled-release polymer particles are needed. Conventional w/o/w methods for hydrophilic drugs suffer from low encapsulation, protein inactivation, and difficult release control. An oil-in-oil (o/o) solvent evaporation method may overcome these limitations, but the particle size of PLGA microspheres must be optimized to the respirable range (1–5 µm) for pulmonary delivery.

Hypothesis: If PLGA microspheres are prepared by a developed oil-in-oil solvent evaporation method and formulation/process variables are optimized using response surface methodology (Box-Behnken design), then particle size and polydispersity can be controlled to achieve the 1–5 µm range suitable for pulmonary drug delivery, with stirring speed, PLGA concentration, temperature, and surfactant concentration as key determining factors.

Aims: Primary aim: Prepare PLGA microspheres by a developed oil-in-oil (o/o) solvent evaporation method for potential pulmonary drug delivery.

Secondary aim 1: Use a three-level, four-factor Box-Behnken design to evaluate the effects of PLGA concentration, surfactant (Span 80) concentration, stirring speed, and temperature on microsphere particle size and polydispersity (geometric standard deviation, GSD).

Secondary aim 2: Characterize microsphere morphology and size distribution.

Secondary aim 3: Identify optimal preparation conditions yielding respirable-size microspheres (1–5 µm) with narrow size distribution.

Delivery system:

Component: Polymer; Description: PLGA 50:50 (RG 504H), Boehringer Ingelheim

Component: Microsphere Type; Description: PLGA microspheres prepared by oil-in-oil (o/o) solvent evaporation

Component: Payload; Description: Hydrophilic model drug (insulin) mentioned for solubilization in acetonitrile/water; no drug loading/release data reported

Component: Targeting Ligand; Description: None

Component: Solvent System; Description: Acetonitrile/water (5:1 v/v) polymer phase; heavy liquid paraffin as external oil phase

Component: Surfactant; Description: Span 80 (0.5–1.5% v/v)

Component: Preparation Conditions; Description: Temperature 25–75 °C; stirring 1000–3000 rpm; PLGA 2.5–10% w/v

Component: Target Size Range; Description: 1–5 µm for pulmonary deposition

Component: Key Design Feature; Description: Single-phase o/o method intended to avoid aqueous/organic interface, reduce protein inactivation, and improve encapsulation of hydrophilic drugs (not evaluated here)

Approach: In vitro only; no cell or animal studies. - Experimental design: Box-Behnken design with four factors at three levels: PLGA concentration (2.5, 6.25, 10% w/v), Span 80 concentration (0.5, 1.0, 1.5% v/v), stirring speed (1000, 2000, 3000 rpm), temperature (25, 50, 75 °C). 27 runs with three center-point replicates. - Response variables: Volume mean diameter (VMD) and geometric standard deviation (GSD). - Microsphere preparation: Polymer solution added dropwise to heavy liquid paraffin containing Span 80, stirred at set temperature/speed for 1.5 h, centrifuged, washed with n-hexane, dried, stored. - Characterization: SEM for morphology; laser diffraction for particle size and GSD. - No drug loading, release, aerosol performance, or biological evaluation.

Key methods:

Technique: Scanning electron microscopy (SEM); Purpose: Microsphere morphology and surface structure

Technique: Laser diffraction particle size analysis (SALD-1100); Purpose: Volume mean diameter (VMD) and geometric standard deviation (GSD)

Technique: Box-Behnken experimental design; Purpose: Response surface modeling and optimization

Technique: ANOVA / regression analysis; Purpose: Identify significant factors and interactions

Technique: Three-dimensional surface plots and contour plots; Purpose: Visualize factor effects and acceptable size regions

Key results: Particle size range: VMD 2.7–19.7 µm; GSD 1.49–2.78 across all formulations. - Significant factors for size: Stirring speed had the most important negative effect (higher rpm → smaller particles); PLGA concentration had a positive effect (higher concentration → larger particles); temperature had a minor negative effect; surfactant concentration was not significant. - Interactions: Significant interaction between PLGA concentration and stirring speed (p = 0.002); smaller interaction between temperature and stirring speed (p = 0.045). - Respirable size: Desired 1–5 µm microspheres could be obtained at stirring speeds above approximately 1900 rpm; at speeds below 1400 rpm, targeted size was not achieved regardless of PLGA concentration. - Polydispersity (GSD): PLGA concentration had the most significant effect; stirring speed, temperature, and PLGA × stirring speed interaction also significant. Surfactant concentration had no significant effect on GSD. - Morphology: Microspheres were spherical, smooth, without pores or cavities, uniform across formulations. - No encapsulation efficiency, drug release, or aerosol deposition data were reported.

Interpretation: The authors conclude that response surface methodology can be successfully applied to design PLGA microspheres with predictable size properties for pulmonary drug delivery. The o/o solvent evaporation method allows control over particle size, with stirring speed and PLGA concentration as the main determinants. They suggest this approach may be valuable for designing PLGA microsphere carriers for drug delivery and targeting, while noting that lung toxicity of PLGA remains unestablished and requires future investigation.

Limitations: No drug loading or release data despite mention of insulin as a model hydrophilic drug; only empty microspheres were characterized for size. - No aerosol performance testing (e.g., MMAD, fine particle fraction) to confirm actual pulmonary deposition. - No in vitro or in vivo efficacy, toxicity, or biocompatibility studies. - No comparison with conventional w/o/w methods for encapsulation efficiency or protein stability. - Surfactant concentration was not significant in the o/o method, but this may not generalize to other drugs or formulation conditions. - PLGA lung toxicity is unknown; authors explicitly state no literature reports assess PLGA toxicity in the lungs. - Only size and GSD were optimized; other critical quality attributes (encapsulation efficiency, burst release, stability) were not evaluated.

Biochemical Pharmacology*, Volume 173, 2020, Article 113648 DOI/

7-Ketocholesterol and 7β-Hydroxycholesterol — In Vitro and Animal Models, Biological Activities, and Toxicity-Preventing Molecules

Nature Reviews Drug Discovery

Engineering Precision Nanoparticles for Drug Delivery

Materials* (MDPI; inferred from format)

Generation of Well-Defined Micro/Nanoparticles via Advanced Manufacturing Techniques for Therapeutic Delivery

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