Liposome Preparation Method 2 - CD Bioparticles Blog

Liposomes have attracted researchers’ attention because of their unique properties. Its successful application as a drug delivery carrier makes it a key research object in the field of drug delivery. There are already many methods for the preparation of liposomes, the above has introduced thin film method, reverse evaporation method, re-emulsion method and centrifugation method. Immediately above, this article focuses on the injection method, calcium fusion method, ammonium sulfate gradient method, and high-pressure homogenization.

Figure 1. A schematic representation of different liposome preparation methods, characterization aspects, and drug delivery applications.

Injection Method

Dissolve lipids in water-miscible or immiscible organic solvents, inject into the aqueous phase with a micro syringe at an appropriate rate, and remove organic solvents by ultrafiltration, dialysis, reverse osmosis, reduced-pressure evaporation, etc. as needed. The formed liposome particle size and drug encapsulation rate are affected by various factors such as the ratio of organic solvent to water, stirring rate, solution temperature, aqueous solution pH, solution ionic strength, physical and chemical properties of the drug, types and formulations of phospholipids, and so on. According to different solvents used, the injection method is mainly divided into ether injection method and ethanol injection method. Generally speaking, under the same conditions, the size of liposome formed by ether injection method is larger than that of ethanol injection method.

Calcium Fusion

Calcium ions are added to the single-chamber liposomes composed of phosphatidylserine (PS), the phospholipids are fused into a snail shell-shaped cylinder, and ethylenediaminetetraacetic acid (EDTA) is added to remove the calcium ions to produce large single-chamber liposome with a diameter between 100 and 1000m. This method is limited to acidic phospholipids such as phosphatidic acid (PA), phosphatidylglycerol (PG), and phosphatidylserine (PS). The characteristic is that the formed single-chamber liposome has large particle size and mild conditions, and can encapsulate DNA, RNA and other biopolymers.

Ammonium Sulfate Gradient Method

Doxorubicin liposome (Doxil) is a preparation with high encapsulation efficiency prepared by ammonium sulfate gradient method. The ammonium sulfate gradient method to encapsulate doxorubicin is designed according to the principle of chemical equilibrium movement. When the concentration gradient is formed inside and outside the liposome membrane, the drug in the aqueous phase of the liposome will spontaneously move to the liposome, and gathered inside. The specific steps of the ammonium sulfate gradient method are as follows: ① The liposome membrane component is dissolved in an organic solvent, and vacuum reduced pressure rotary evaporation; ② The lipid membrane is hydrated with a high concentration ammonium sulfate solution (Hydration ), the system forms a crude liposome suspension after hydration, and the liposomes of smaller particle size are prepared by extrusion to obtain blank liposomes; ③The blank liposome vesicles have equal concentration of ammonium sulfate inside and outside. After the solution is filtered through dialysis or gel chromatography column, the ammonium sulfate outside the liposome vesicles is removed, so that the concentration gradient of the ammonium sulfate inside and outside the liposome vesicles forms a difference in concentration. When the difference reaches a certain level (such as 1000 times), add the doxorubicin hydrochloride solution to the blank liposome suspension. After a certain period of time, a higher encapsulation rate of doxorubicin liposomes is obtained.

High Pressure Homogenization Technology

The molten lipid is added to the surfactant-dissolved water phase, and after vortexing to form colostrum, the high-pressure flow is used to pass precisely regulated micro-channels to accelerate the fluid and generate strong shear in the specially-made reaction chamber. Under the effect of impact and cavitation, fine and dense liposomes are formed. The advantage of the high-pressure homogenization method is to avoid the use of additives and organic solvents that are harmful to the body. The method has good repeatability, can be mass-produced, and the prepared liposome particles are uniform and have good stability.

Precursor Liposome

Adsorption of lipids on very fine water-soluble carriers such as sodium chloride, and polysaccharide alcohol excipients such as sorbitol and mannitol to increase the area of lipid dispersion to make precursor liposomes; lipids swell when exposed to water The carrier dissolves to form a multi-chamber liposome, where the size of the carrier directly affects the size and uniformity of the liposome. Proliposomes can prevent liposomes from agglomerating with each other, and are more suitable for encapsulating fat-soluble drugs.