Ultrasonic Liposome Preparation -Hielscher Ultrasonics0 pages

Hielscher Ultrasonics – Your Expert for Ultrasonic Processes

Hielscher Ultrasonics: Ultrasonic Liposome Preparation for
Pharmaceuticals and Cosmetics
Kathrin Hielscher, Hielscher Ultrasonics GmbH
Liposomes (liposome-lipid based vesicles), transferosomes (ultradeformable
liposomes), ethosomes (ultradeformable vesicles with high alcohol content), and
niosomes (synthetic vesicles) are microscopic vesicles, which can be artificially
prepared as globular carriers into which active molecules can be encapsulated. These
vesicles with diameters between 25 and 5000 nm are often used as drug carriers for
topical purposes in the pharmaceutical and cosmetic industry, such as drug delivery,
genetherapy, and immunization. Ultrasound is a proven method of liposome
preparation and the encapsulation of active agents into these vesicles.
Liposomes: Liposomes are unilamellar, oligolamellar or multilamellar vesicular systems
and are composed of the same material as a cell membrane (lipid bilayer). Regarding
to their composition and size, one differs between multi-lamellar vesicles (MLV, 0.110μm) and unilamellar vesicles, which are distinguished between small (SUV, <100
nm), large (LUV, 100–500 nm) or giant (GUV, ≥1 μm) vesicles.
The composite structure of liposomes consists of phospholipids. Phospholipids have a
hydrophilic head group and a hydrophobic tail group, which consists of a long
hydrocarbon chain. The liposome membrane has a very similar composition as the skin
barrier, so that they can be easily integrated into the human skin. As the liposomes
fusionate with the skin, they can unload the entrapped agents directly to the
destination, where the actives can fulfill their functions. Thus, the liposomes create an
enhancement of skin penetrability/ permeability for the entrapped pharmaceutical
and cosmetical agents. Also liposomes without encapsulated agents, the vacant
vesicles, are potent actives for the skin, as the phosphatidylcholin incorporates two
essentials, which the human organism cannot produce by itself: linoleic acid and
choline.

Chemical stucture of hydrogenated phosphatidylcholine

Liposomes are used as biocompatible carriers of drugs, peptides, proteins, plasmic
DNA, antisense oligonucleotides or ribozymes, for pharmaceutical, cosmetic, and
biochemical purposes. The enormous versatility in particle size and in physical
parameters of the lipids affords an attractive potential for constructing tailor-made
vehicles for a wide range of applications. (Ulrich 2002)