Liposome preparations consist of artificial spherical vesicles whose main chemical components are phospholipids and cholesterol organised in two layers. The process of forming this bilayer is known as sonication. Based on the structure, the vesicles may be classified as either multilammellar or unilamellar. The former have several bilayers while the latter has just a single bilayer. Most vesicles measure less than 400nm in diameter.
One of the methods used in forming the vesicles is known as sonication. Here, the lipid suspension containing cholesterol and phospholipids is hydrated and made to swell so as to separate the various bilayers. As the bilayers separate, they form large lipid vesicles. These are later broken down into smaller units by use of an instrument known as a sonicator. The sonicator delivers high levels of energy to the large molecules and breaks them down within 5 to 10 minutes.
Another popularly used technique is known as extrusion. In this technique, the suspension is subjected to a cyclical process of freezing and thawing that eventually results in the breakdown of the large vesicles. Homogenous of size is achieved after a few cycles. Another variant of the same is the passage of the vesicles through progressively decreasing pores until very fine particles are obtained.
A number of factors are known to cause a variation in the size of vesicles. These include among others, the duration for which the vesicles are processed, the amount of energy applied, composition and proportion of the lipids and the the tuning of the sonicator. The vesicles have a lot of similarities with cell membranes due to the presence of phospholipids and cholesterol. Both have a hydrophobic and hydrophilic ends.
There are numerous uses of lipid vesicles currently. Perhaps the most important of them is the delivery of pharmacological agents to various sites. They are increasingly being preferred over viral vectors due to a number of reasons. One of them is the fact that they are rarely immunogenic and do not lead to allergic reactions unlike the viral vectors. They are also much easier to synthesize than the vectors.
Many drugs that utilize lipid vesicles are in use today. These include, among others, liposomal amphotericin B, a potent antifungal agent, liposomal cytarabine (a drug used for treatment of malignant meningitis and other cancers), liposomal IRIV vaccine (used for hepatitis A and influenza), doxorubicin and morphine. There are many more others that are the subject of research.
Another common application of the vesicles is in the delivery of various nutrients. Many of these nutrients are either deficient in the diet or are difficult to absorb because of a low bioavailability. Vitamin C is frequently administered through lipid encapsulation. Pesticides are applied to plants using the same principle. Other areas of liposome encapsulation application include delivery of enzymes and the fixing of dyes to textiles.