The effect of coencapsulation of bovine insulin with cyclodextrins in ethylcellulose microcapsules

Development and Application of a Modified Method to Determine the Encapsulation Efficiency of Proteins in Polymer Matrices

A modified method to determine protein encapsulation efficiency in polymer matrices has been developed and applied to two proteins and two polymers to demonstrate its wide range of applicability. This study was pursued due to the wide variation in reported protein encapsulation efficiency of polymer-based microcapsules, even when the protein, the polymer, and the microcapsule manufacturing method were consistent. Hemoglobin (Hb) and bovine serum albumin (BSA) were chosen as model proteins and ethylcellulose and poly(lactic-co-glycolic acid) (PLGA) as model polymers. The polymer of the microcapsule was dissolved in dichloromethane/ethanol or dichloromethane/ethyl acetate for ethylcellulose or PLGA microcapsules, respectively. Liberated proteins were simultaneously precipitated, pelleted by centrifugation, isolated by decanting the polymer solution, redissolved in 10% w/v sodium dodecyl sulfate in 0.8 N sodium hydroxide, and quantified using a modified Lowry assay. Blank microcapsules and exogenously added proteins demonstrated ≥ 93.8% recovery of proteins. The mean encapsulation efficiency of ethylcellulose or PLGA microcapsules was 52.4 or 76.9% for Hb and 86.4 or 74.7% for BSA, respectively. This demonstrates the effective use of centrifugation and the importance of an appropriate cosolvent system in the measure of encapsulation efficiency where one solvent dissolves the polymer while the other solvent quantitatively precipitates the liberated protein. It is evident that an alkaline solution of sodium dodecyl sulfate is efficient at quantitatively dissolving precipitated proteins. Remediation of problems observed with current methods and high reproducibility suggest that this modified method is generally applicable to the measure of protein encapsulation efficiency of polymer microcapsules.

Affinity of Serum Albumin and Fibrinogen to Cellulose, Its Hydrophobic Derivatives and Blends

This work describes the preparation of spin-coated thin polymer films composed of cellulose (CE), ethyl cellulose (EC), and cellulose acetate (CA) in the form of bi- or mono-component coatings on sensors of a quartz crystal microbalance with dissipation monitoring (QCM-D). Depending on the composition and derivative, hydrophilicity can be varied resulting in materials with different surface properties. The surfaces of mono- and bi-component films were also analyzed by atomic force microscopy (AFM) and large differences in the morphologies were found comprising nano- to micrometer sized pores. Extended protein adsorption studies were performed by a QCM-D with 0.1 and 10 mg mL⁻¹ bovine serum albumin (BSA) and 0.1 and 1 mg mL⁻¹ fibrinogen from bovine plasma in phosphate buffered saline. Analysis of the mass of bound proteins was conducted by applying the Voigt model and a comparison was made with the Sauerbrey wet mass of the proteins for all films. The amount of deposited proteins could be influenced by the composition of the films. It is proposed that the observed effects can be exploited in biomaterial science and that they can be used to extent the applicability of bio-based polymer thin films composed of commercial cellulose derivatives.

Kinetics of solvent extraction/evaporation process for PLGA microparticle fabrication

Organic solvent extraction/evaporation from an o/w-dispersion has been widely used for the fabrication of PLGA microparticles. The purpose of this work was to elucidate the kinetics of the solvent extraction/evaporation process. A mathematical diffusion model was developed and applied to predict the duration of the solvent extraction. As the diffusion coefficient, D(p), plays a major role in the modeled process, a new and experimentally simple method for estimating D(p) was developed. Both the experimental method and the mathematical model were validated through PLGA microparticle fabrication experiments. For microparticles of mode diameters of 2 and 20 microm, the solvent was extracted in approximately 10 s. Sufficient hardening of the microparticles required, however, the evaporation of solvent from the extraction phase. Residual solvent in extraction phase exerted a strong effect on the morphology of the final product as demonstrated by scanning electron microscopy. Only if most solvent was removed from the aqueous extraction phase, a powdery product of individual microparticles was obtained. At residual organic solvent concentration of above 0.2% in the extraction phase, the microparticles strongly aggregated during collection on a membrane filter and final drying. The presented methods may be useful for better controlling microparticle fabrication processes by solvent extraction/evaporation.