Liposome Lamellarity Analysis

Liposomes are composed of phospholipid bilayers surrounding an aqueous core, with sizes spanning nanometer to micrometer scales.  They are widely used as nano-carrier for drug delivery and as cellular model systems for studying membrane properties, transmembrane processes, and intracellular biochemistry. Understanding the lamellarity of liposomes is crucial for optimizing their performance in these applications.

Background

The lamellar structure refers to the number of phospholipid bilayers surrounding the internal aqueous core of the liposome vesicles. This characteristic is a key factor defining both the structure and function of these vesicles and their capacity to accommodate and retain drugs. They are classified by lamellarity into small unilamellar vesicles (SUVs) under 100 nm, large unilamellar vesicles (LUVs) from 100 to 1000 nm, and giant unilamellar vesicles (GUVs) over 1000 nm. Multilamellar vesicles (MLVs) exhibit an onion-like structure made of concentric bilayer membranes.

Fig.1 Particle size and lamellarity-based classification of lipid-based drug delivery systems.

Importance of Liposome Lamellarity

Lamellarity is a critical factor that influences encapsulation efficiency, liposome stability, release dynamics, and the subsequent behavior of liposomes in cellular interactions. It also governs the mechanical and dielectric properties essential for both cellular engagement and electrokinetic manipulation. In the context of cellular model systems, meticulous regulation of lamellarity is imperative. Typically, unilamellar vesicles (ULVs) exhibit a more rapid drug release profile than MLVs, which provide a greater volume for drug encapsulation. SUVs are often more stable than their larger counterparts due to their reduced surface area, which minimizes the risk of membrane damage. In contrast, MLVs, with their multilayered structure, offer enhanced protection and are generally more stable under adverse conditions.

Table 1. Classification and Characteristics of Liposomes.

Factors Influencing Liposome Lamellarity

The lamellarity of liposomes is influenced by various factors, including lipid composition and concentration, preparation methods, environmental conditions such as temperature and pH, and microfluidic flow rates. Different lipid compositions and preparation techniques can lead to the formation of distinct types of liposomes, such as SUVs and MLVs. Generally, the use of saturated lipids enhances stability, while unsaturated lipids increase the flexibility of the lipid bilayer but reduce stability.

Detection Techniques for Liposome Lamellarity

Liposome lamellarity is typically determined using techniques that monitor the change in visible or fluorescent signals from lipid markers upon the addition of reagents. The assessment is based on the comparison between the overall signal and the signal derived from the interaction between the lipid markers and the specific reagents.

• Cryo-Transmission Electron Microscopy (Cryo-TEM): This is the most commonly used method that provides high-resolution images of liposomes, yielding information about their lamellarity, such as bilayer thickness and inter-bilayer distances.
• Small-Angle X-ray Scattering (SAXS): This technique determines the size and lamellarity of liposomes by analyzing the intensity of scattered X-rays, offering insights into the internal structure and organization of lipid bilayers. Beyond studying bilayer morphology, SAXS can also characterize liposome sizes ranging from a few nanometers to hundreds of nanometers, depending on the type of liposomes and the instrument used.
• ³¹P-nuclear magnetic resonance (NMR): This method employs external shift reagents such as Mn²⁺, Co²⁺, and Pr³⁺ that interact with phospholipids, causing perturbations in nuclear spin relaxation times. The signal loss induced by these metal ions can be quantified to assess the lamellarity of the sample.
• In-Liquid Scanning Dielectric Microscopy: This technology measures the dielectric properties of individual liposomes, from which lamellarity can be inferred.
• Other Methods: Electron paramagnetic resonance (EPR) is also utilized to investigate the permeability, lamellarity of bilayers, and the impact of particle size on the transport of bioactive molecules within liposomes.

The lamellarity of liposomes is a key determinant of their functionality and performance in various applications. At Creative Biolabs, we are committed to providing the expertise and technology necessary to characterize and optimize liposome lamellarity, ensuring that your lipid-based drug delivery systems and cellular models are as effective as possible. Contact us today to learn more about how our services can support your research and development efforts.

For Research Use Only. Not For Clinical Use