In the realm of nanomedicine, the size of lipid nanoparticles (LNPs) is a critical attribute that profoundly influences their performance as drug delivery carriers. From stability and encapsulation efficiency to drug release profiles, bio-distribution, and cellular uptake, nanoparticle size is a determining factor.

Impact on Biodistribution

Smaller lipid nanoparticles (20-150 nm) exhibit prolonged circulation times and an enhanced ability to accumulate in target tissues. This is primarily due to the enhanced permeability and retention (EPR) effect, where small nanoparticles can leak through blood vessels and evade immune surveillance, accumulating around tumors. This size range also helps reduce liver clearance and kidney filtration, enhancing therapeutic efficacy.

Importance for Cellular Uptake

The diameter of lipid nanoparticles is crucial for determining their cellular uptake and internalization. Endocytosis, the primary mechanism for cellular uptake of small molecules, varies with nanoparticle size. RNA-LNP complexes around 100 nm are primarily taken up through receptor-mediated endocytosis, a process also utilized by viruses such as influenza and reoviruses. This mechanism ensures efficient delivery of the therapeutic payload into the cells.

Species-Specific Considerations

Optimal nanoparticle characteristics, including size, vary across species. For example, non-human primates benefit from smaller RNA-LNP sizes (50-60 nm) compared to rodents (70-80 nm). Such variations underscore the need for tailored nanoparticle designs to achieve optimal therapeutic outcomes in different biological systems.

Controlling Lipid Nanoparticle Size

The critical characteristics of LNPs are influenced by several factors during formulation and processing:

• Composition: The ratio of different lipids, especially PEG-lipid content, plays a significant role in determining nanoparticle size. A higher mol% of PEG-lipid leads to smaller, more stable nanoparticles.
• Manufacturing Process: Traditional methods like solvent evaporation and high-pressure homogenization often result in broad nanoparticle distributions and low reproducibility. In contrast, microfluidics offers fine control over mixing conditions, yielding more uniform nanoparticle populations with precise sizes.

Integration of Orthogonal and Complementary Techniques

The integration of orthogonal techniques (different physical principles and laws) and complementary techniques (same physical principles and laws) is essential for accurate nanoparticle characterization. This combined approach provides a comprehensive understanding of each technique's limitations and offers a more objective assessment of the Critical Quality Attributes (CQAs).

• Dynamic Light Scattering (DLS): Provides non-invasive size distribution by measuring fluctuating light intensity caused by Brownian motion. However, it is sensitive to polydisperse samples wher30e large objects hide smaller ones. Utilizing a backscattering angle (173°) rather than the traditional 90° reduces sensitivity to large particles, ensuring better detection of smaller ones.
• Multi-Angle Light Scattering (MALS): Used alongside Asymmetric Flow Field-Flow Fractionation (AF4), MALS measures the geometric diameter, offering high-resolution particle size distribution (PSD) in complex samples.
• Nanoparticle Tracking Analysis (NTA): Tracks real-time particle motion using the principles of Brownian motion. While it requires higher sample dilutions, it provides valuable size information, particularly for small particles.

Comparing Measurement Techniques

• Microscopy and NTA: Both are number-based techniques, directly visualizing and counting particles. They provide detailed insights into particle size and shape but may require complex sample preparation.
• DLS: An intensity-based technique that requires conversion to number-based measurements. Accurate interpretation necessitates assumptions such as spherical particle shape, homogeneous density, and known optical properties.

Light Scattering Techniques: DLS vs. MALS

• Dynamic Light Scattering (DLS): Measures the hydrodynamic radius (Rh), which is defined as the radius of an equivalent hard sphere diffusing at the same rate as the molecule under observation. Rh reflects the apparent size adopted by the solvated, tumbling molecule. DLS size is usually measured by correlation spectroscopy (PCS).
• Multi-Angle Light Scattering (MALS): Measures the radius of gyration (Rg), which is the mass-weighted average distance from the core of a molecule to each mass element in the molecule. Rg is related to the molecule's structure and can be determined for macromolecules with radii greater than 10 nm using a Guinier or Zimm plot.

In polymer physics, Rg is the root mean square (RMS) end-to-end distance of an ideal polymer chain. The ratio Rg/Rh provides shape information about a protein or molecule. For globular proteins, the characteristic Rg/Rh value is approximately 0.775, with Rg being smaller than Rh. However, for non-spherical or elongated structures, Rg/Rh tends to be greater than 0.775, as Rg becomes larger than Rh.

Conclusion

Selecting the right nanoparticle size is pivotal for optimizing drug delivery systems. Nanoparticles between 60 and 100 nm strike a balance, being easily endocytosed while minimizing toxicity. As our understanding and technology advance, the ability to finely tune nanoparticle size will continue to enhance the efficacy and safety of nanomedicine.

Nawah Scientific

Nawah Scientific is at the forefront of leveraging nanotechnology for biomedical applications. Their research focuses on synthesizing and characterizing various types of nanoparticles to enhance drug delivery systems. By pushing the boundaries of nanotechnology, Nawah Scientific aims to revolutionize medical treatments and diagnostics.

Nawah Scientific can help you with custom synthesis of the most appropriate nano drug delivery system that can host your drug of choice and matches the needed use and route of administration. Their nanotechnology team can provide tailored tools for solubility enhancement of insoluble drugs, targeted drug delivery purposes, improved pharmacokinetic profiles, stabilization of labile drugs, and enhancement of local or systemic bioavailability.

Range of characterization expertise at Nawah Scientific includes:

• Measurement of particle size, zeta potential and isoelectric point

• Measurement of entrapment efficiency

• Measurement of in vitro release profiles
Check Nawah Scientific website here: https://nawah-scientific.com/