Production of Protein-Loaded Polymeric Microcapsules by Compressed CO2 in a Mixed Solvent

Current advances in sustained-release systems for parenteral drug delivery

Major progresses in the development of parenteral sustained-release systems have been made in recent years as evidenced by the regulatory approval and market launch of several new products. Both the availability of novel carrier materials and the advances in method of fabrication have contributed to these commercial successes. With the formulation challenges associated with biologics, new delivery systems have also been evolved specifically to address the unmet needs in the parenteral sustained release of proteins. In this review paper, different new carriers systems and preparation methods are discussed with special focus on their applications to biologicals.

Nisin-loaded poly-L-lactide nano-particles produced by CO2 anti-solvent precipitation for sustained antimicrobial activity

Nisin-loaded poly-L-lactide (PLA) nano-particles were fabricated by processing protein/polymer organic solutions by semi-continuous compressed CO2 anti-solvent precipitation. Preliminary solubility studies were carried out for an optimised selection of organic solvent mixtures leading to preparation of protein/polymer solutions. The particles were prepared by processing 50:50 dimethylsulfoxide/dichloromethane mixtures containing 1% polymer (w/v) and 5 or 20% nisin (nisin/polymer, w/w). Proper operative conditions (organic solution injection rate, precipitation temperature and gas pressure, CO2 flow rate, washing time, etc.) were set up to yield production reproducibility, high product recovery (over 70%) and high drug loading (over 95% of the recovered protein). Scanning electron microscopy demonstrated that spherical, smooth surfaced particles were produced. Light scattering showed that the particle size was in the range of 200-400 nm and the products were characterised by narrow polydispersity. In vitro release studies showed that the protein is slowly released throughout 1000 h. However, the release was slower as the salt concentration and the pH of the release buffer increased. Solubility investigations suggested that the observed differences in protein release rate out of nano-particles was attributable to the protein interaction with the polymer which was found to increase as the pH or the salt concentration increased in the release buffer. In vitro studies carried out by nano-particle incubation in medium containing Lactobacillus delbrueckeii showed that nisin was released in the active form and the antibacterial activity was maintained up to 45 days incubation.

Plasticization and spraying of poly (DL-lactic acid) using supercritical carbon dioxide: control of particle size

Exposure of poly(DL-lactic acid) (PDLLA), and related polymers, to supercritical CO2 (scCO2) at or below, physiological temperatures leads to very effective plasticization and liquefying of the polymers. The phenomenon arises from the high solubility and interaction of the scCO2 in the polymer. Under these unique conditions, temperature and solvent labile molecules can be mixed efficiently into the liquefied polymer. This liquefied polymer/drug/CO2 mixture can then be sprayed into a collecting chamber, and during this process particles of drug-loaded polymer are formed. This process is very different from rapid expansion and antisolvent based techniques that have been previously reported. In this article, we describe a method of controlling particle size during the spray process by introducing a backpressure of N2 in the collecting chamber. This backpressure dynamically regulates the loss of CO2 from the issuing polymer/CO2 mixture, leading to control over sprayed particle size. In situ observation of the viscosity of the plasticized polymer indicates that a backpressure of 68 bar or greater is necessary to ensure the production of fine particles. The influences of backpressure and saturation temperature on particle size for the sprayed products are discussed in terms of observed PDLLA/CO2 mixture viscosities.

Novel Formulations of Vitamins and Insulin by Nanoengineering of Polyelectrolyte Multilayers around Microcrystals

Microcapsules loaded with vitamin K3 (VK3), biotin, or insulin were prepared by using a novel coating technology based on the layer-by-layer (LbL) deposition of oppositely charged polyelectrolytes onto microcrystal templates. This produced multilayered, polymeric shells of varying thickness around the crystalline cores. Dissolution of the core material (VK3 with ethanol, biotin with basic solution, and insulin with acidic solution), resulted in its release through the shells. Microelectrophoresis was employed to monitor the microcrystal coating process; confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM) were used to verify multilayer coating and the formation of hollow polymer shells following removal of the microcrystal templates. The release rates of both VK3 and insulin decreased as the wall thickness (the number of polyelectrolyte layers deposited onto the microcrystal cores), increased. The release time could be varied by a factor of more than ten, depending on the number of polyelectrolyte layers applied. Following the addition of 70 mass % ethanol, the solubility of VK3 increased by as much as 170-fold, resulting in an increased rate of VK3 release. By selecting appropriate polymer materials for the shells, and by controlling the number of polyelectrolyte layers applied, shells of various thickness, stiffness, aqueous solubility, dispersibility, biocompatibility, and permeability can be constructed.

Effective protein release from PEG/PLA nano-particles produced by compressed gas anti-solvent precipitation techniques

Homogeneous PLA/insulin solutions containing different amounts of 350, 750 or 1900 Da PEG (0-75 wt.% PEG) were processed by semi-continuous compressed CO2 anti-solvent precipitation to fabricate protein-loaded polymeric nano-particles. Proper operative conditions (temperature, pressure, CO2 flow rate and washing time) yielded more than 70% product recovery. Scanning electron microscopy, transmission electron microscopy and light scattering demonstrated that spherical, smooth surfaced particles with size below 1 microm could be obtained. X-ray diffraction analysis showed that the gas anti-solvent process modifies the polylactide crystalline state. PEG concentration and molecular weight were found to affect both optimal operative conditions and morphological and biopharmaceutical properties of the final product. Insulin loading yield dropped from 95% to 65% by increasing the 1900 Da PEG content from 0 to 75 wt.% or the PEG molecular weight from 350 to 1900 Da. The release rate increased significantly as the PEG content in the formulation increases. After 3-month incubation the drug released raised from 10% to 100% by increasing the 1900 Da PEG content from 23 to 7 wt.%. Formulations containing the same 350, 750 or 1900 Da PEG amount (67 wt.% PEG) displayed similar release profiles. Insulin release was found to take place by diffusion mechanism, despite the observation of matrix degradation.

Evaluation of 2-Methacryloyloxyethyl Phosphorylcholine Polymeric Nanoparticle for Immunoassay of C-Reactive Protein Detection

To prepare novel 2-methacryloyloxyethyl phosphorylcholine (MPC)-polymeric nanoparticle (MPC-PNP), water-soluble amphiphilic phospholipid polymer, poly [MPC-co-n-butyl methacrylate (BMA)-co-p-nitrophenyloxycarbonyl poly(ethylene glycol) methacrylate (MEONP) (PMBN)], which has active ester groups for bioconjugation on the side chains, was synthesized. MPC-PNP was prepared by a solvent evaporation technique where the poly(l-lactic acid) was used as core and PMBN was applied as an emulsifier and a surface modifier under systematical design of well-arranged phospholipids polar groups in its surface. Characteristics for MPC-PNP were thoroughly investigated with dynamic light scattering, electrophoresis light scattering, X-ray photoelectron spectroscopy, and field emission scanning electron microscopy measurements. Through a protein adsorption test, the phosphorylcholine group on the surface of MPC-PNPs, which had their active ester groups substituted by glycine, were shown to suppress the nonspecific adsorption of bovine serum albumin. These particles were used for C-reactive protein (CRP) detection, where anti-CRP monoclonal antibodies were immobilized on the MPC-PNP using the active ester group, while the remaining active ester groups were thoroughly reacted with glycine. The detection limit about serum-free CRP in the calibration curve was shown to extend from 0.01 to 10 mg/dL when anti-CRP antibody immobilized MPC-PNP was used for serum-free CRP detection. This compares favorably with measurement using polystyrene nanoparticles that were shown to detect from 0.1 to 10 mg/dL by an immunoagglutination technique. Also, for the detection of CRP in serum, MPC-PNP was shown to give the same calibration curve explained by the efficient suppression of nonspecific binding. Furthermore, denaturation of immobilizing anti-CRP antibody on the MPC-PNP hardly occurred despite increasing the temperature. It is concluded that MPC-PNP is unique due to the design of its interfacial properties, also it will perform well in a diagnostic immunoassay because of its optimized material properties.

Production of insulin-loaded poly(ethylene glycol)/poly(l-lactide) (PEG/PLA) nanoparticles by gas antisolvent techniques

Insulin and insulin/poly(ethylene glycol) (PEG)-loaded poly(l-lactide) (PLA) nanoparticles were produced by gas antisolvent (GAS) CO(2) precipitation starting from homogeneous polymer/protein organic solvent solutions. Different amounts of PEG 6000 (0, 10, 30, 50, 100, and 200% PEG/PLA w/w) or concentration of 30% PEG/PLA with PEGs with different molecular weight (MW; 350, 750, 1900, 6000, 10,000, and 20,000) were used in the preparations. The process resulted in high product yield, extensive organic solvent elimination, and maintenance of > 80% of the insulin hypoglycemic activity. Nanospheres with smooth surface and compact internal structure were observed by scanning electron microscopy. The nanospheres presented a mean particle diameter in the range 400-600 nm and narrow distribution profiles. More than 90% of drug and PEG were trapped in the PLA nanoparticles when low MW PEGs were used in the formulation, whereas the addition of high MW PEGs significantly reduced the loading yield. In all cases, in vitro release studies showed that only a little amount of drug was released from the preparations. However, formulations containing low MW PEGs allowed for a slow but constant drug release throughout 1500 h, whereas a burst was obtained by increasing the PEG MW. In conclusion, the GAS process offers a mean to produce protein-loaded nanoparticles possessing the prerequisites for pharmaceutical applications. The PEG added to the formulation was found to play a key role in the simultaneous solute precipitation phenomena and in determining the release behavior and the chemical-physical properties of the formulation.