The mechanism of surface-indented protein-loaded PLGA microparticle formation: the effects of salt (NaCl) on the solidification process

Abstract

The purpose of this study was to evaluate ovalbumin (OVA) leakage pathways and to explore the mechanism of the surface-indented microparticle formation in the preparation of OVA-loaded microparticles. OVA-loaded poly (D,L-lacticco-glycolic acid) (PLGA) microparticles were prepared by a water-in oil-in water (w/o/w) solvent evaporation method associated with varied NaCl (NaCl) concentrations and adjusted with urea at 1240 mOsm kg À1 in the external aqueous phase. To evaluate dichloromethane (DCM)-related OVA leakage, three stirring rates, 600, 800, 1000 rpm at 25 C were carried out during the solvent evaporation stage. Both DCM and OVA levels in the external phase medium and total dispersion were sampled and measured. The time course of particle characteristics was evaluated by microscopy or SEM photography. The surface adsorptive capacities of the prepared microparticles were measured by using bovine serum albumin conjugated with fluorescein isothiocyanate (FITC-BSA). The findings were that the DCM-related OVA leakage accounted for $34% of the total leakage. By combining NaCl in the external phase, a faster solidifying crust-like structure was formed as a barrier to remarkably reduce OVA loss and improve OVA content from 40.1 to 72.8 mg mg À1 . The yield and OVA content for formulations containing NaCl were much improved by the ionic effect, in addition to the osmotic effect. The total entrapment efficiency was also highly increased from 43 to 72%. The formations of the crust-like surface structure of the microparticle were affected by entrapped drugs, salt content in the external phase and aqueous volume in the inner phase. A scheme was proposed to interpret the formation mechanism of the surfaceindented microparticles. In comparison to the surface-smooth microparticles, the surface adsorptive capacities of the surface-indented microparticles were highly improved from 26.6 to 87.0%, determined by the adsorption of FITC-BSA.

Evaluation of protective efficacy using a nonstructural protein NS1 in DNA vaccine–loaded microspheres against dengue 2 virus

“…The tortuous polymeric diffusion pathways are varied in smaller particles. 21 This ultimately leads to a sustained diffusion of protein from the particles. Our NS1 protein-loaded microspheres, formulations prepared with a PLGA:PEG ratio of 2:1, with smaller average diameter, showed the most suitable release pattern among the formulations studied.…”

Critical attributes of formulation and of elaboration process of PLGA-protein microparticles

“…In fact, when Chen et al (2004), evaluated the role played by the presence of NaCl to encapsulate proteins into PLA microparticles, the conclusion to be drawn was that the higher the amount of sodium chloride in the continuous phase, the higher both drug loading and encapsulation efficiency, the longer protein biological activity was kept unchanged and the less noticeable the initial burst effect, thanks to the higher osmotic pressure generating denser microparticle internal structures. This means that PVA with sodium chloride in the continuous phase not only increased protein loading and yield, but also retained protein deeper inside a layer of microparticles.…”

“…The stage of formation of the primary W/O emulsion is considered the main cause of protein denaturalization and formation of aggregates, due to both the contact of the proteins with the organic solvent, favored by the dispersion of the small droplets of the aqueous phase into the organic phase, as well as to the mechanical agitation (Checa-Casalengua et al, 2012;Chen et al, 2004;Dorati et al, 2008;Jiskoot et al, 2012;Van de Weert et al, 2000). Other problems of protein microencapsulation are the low loading and the initial burst release effect.…”

rhEGF-loaded PLGA-Alginate microspheres enhance the healing of full-thickness excisional wounds in diabetised Wistar rats

“…Interestingly, the encapsulation efficiency was increased after the incorporation of NaCl into the surfactant solution and the solvent removal phase. This increment may be explained by the osmotic pressure increase in surfactant solution and solvent removal phase caused by NaCl, which prevents rhEGF diffusion from the microsphere and becomes MS homogeneous, smooth and regular (Bilati, et al 2005;Chen, et al 2004;Perugini, et al 2001). Moreover, the addition of alginate increased EE to 88.11 ± 1.51% due to an increment of the viscosity in the internal aqueous phase (w 1 ) which limits the diffusion of rhEGF from the MS and improves the protein-polymer affinity.…”