Liposomes and drug delivery systems

    Liposome characterization

    In recent years, liposomes, which are self-assembled and spherical bilayer structures, have been considered as one of the most outstanding drug delivery systems. Due to the amphiphilic characteristics of phospholipids (forming bilayer), liposomes have showed many advantages, such as easy to be modified, high capacity of carrying drugs, low toxicity, and target oriented.

    CryoTEM has been used as one of the most important analytical tools to better characterize the properties of liposomes, in terms of size distribution, circularity, lamellarity, packaging, stability studies, and bilayer thickness.

    Packaging

    Encapsulant percentage (packaging) affects the efficiency of drug release. CryoTEM enables visualization of the encapsulant (e.g., Doxorubicin) inside the liposome (see Figure 1). Our proprietary VAS software is used in combination with cryoTEM images to accurately provide a statistical data on the distinction between full and empty liposomes, see Figure 2. 

    Two images showing an empty liposome and a drug crystal which have been found with our software

    Figure 1. Morphology of empty liposome and liposome with drug crystal inside. 

     

    Graphical representation of packaging of liposomes

    Figure 2. The histogram representing packaging of liposomes obtained from semi-automated detection, see detected image with the detected particles overlayered with blue/green/red circles).  

    The ratios of encapsulation are provided in the analytical report which can be correlated to the efficiency of the drug release. Download example reports here.

    Lamellarity assessment

    Lamellarity is a key factor of drug release efficiency and plays an important role in the mechanism of drug release kinetics. This is a vital feature that must be monitored during the manufacturing process. By using cryoTEM the distinction of liposomes based on their lamellarity is possible. Liposomes consisting of one lipid bilayer is considered as unilamellar liposome, whereas liposomes composed of several lipid bilayers are defined as multilamellar. Liposomes encapsulating several smaller liposomes within a larger one, are called as multiparticle (see Figure 3).

    Several images of liposome particles

    Figure 3. Morphology of liposomes portraying different lamellarities.

    Graphical representation of lamellarities

    Figure 4. The histogram representing lamellarities obtained from semi-automated detection, see detected image with the detected particles overlayered with red/yellow/green circles).

    Size distribution and internal volume 

    The conformation of the native particle is conserved by using cryoTEM, hence cryoTEM is one of the few techniques that can reliably measure the size and the internal volume of the liposomes.

    Graphical representation of an analysis of liposome particles

    Figure 5. The histograms representing size distribution (left) and internal volume (right) obtained from semi-automated detection (about 1500 particles were detected for the analysis).

    Circularity distribution

    The circularity of the liposomes affects the efficiency of drug release in the final product. As the conformation of the native particles is conserved in cryoTEM, the circularity can be measured precisely using proprietary VAS software.

    To the left a histogram showin circularity on the x-axis and number of particles on the y-axis. To the right an image of liposomes.

    Figure 6. CryoTEM image (right) of liposomes containing Doxorubicin and their circularity histogram (left).

    Bilayer thickness measurement

    The thickness of the lipid bilayer is a monitored parameter in the liposomes vesicles design. It will influence the design of the drug carrier, as well as will lead to a better understanding of the efficiency and efficacy of the liposomal products. Using cryoTEM and our proprietary VAS software those measurements are enabled.

    To the left, a histogram showing membrane thickness in nanometres and number of particles on the y-axis. To the right, images of liposomes.

    Figure 7. Histogram representing the distribution of liposomal bilayer thickness (left) and cryoTEM images of liposomes at low magnification (middle) and high magnification (right).

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