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).

Figure 1: Filled and empty

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

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. 

Figure 2: Packaging

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).

Figure 3. Lamellarity and morphology.

Figure 3. Morphology of liposomes portraying different lamellarities. 

Figure 4: Lamellarity

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.

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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.

Figure 6: Circularity

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.

Figure 7: Membrane thickness

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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We have various example reports of different types of analyses available for you to download. The reports give you a deeper insight in what to expect from hiring our electron microscopy services.

The example reports are free and easily accessed by submitting a form. Just click the button below to get to the submission page.

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