My liposome is a non-phospholipid liposome (sterosome) composed of palmitic acid and cholesterol, 20mg of palmitic acid and 70mg of cholesterol. After several months of storage in a refrigerator at 4 degrees Celsius, the particle size increased from about 140 nm to 180 nm.
The formula of the stereosome in other groups is the same, except that I packed PEG with different molecular weights and concentrations into the interior of the stereosome (in the water chamber). The particle size of the group with PEG was a little smaller than that of the control group (about 125-130nm).
Then it became more stable one month later, and the particle size almost did not change. Could you please tell me what the reason might be? Thank you!
Dear I-Hsuan Shih, this is a form of NPs dispersion instability named "ripening", which means smaller NPs associate to form bigger ones. It is a diffusion process. The presence of PEG impede such ease of diffusion by making an outer shell protecting the NPs, thus stability is enhanced. My Regards
These are interesting references that may bring further information:
https://doi.org/10.1021/acsomega.3c10346
https://doi.org/10.1021/acs.langmuir.2c02657
Abdelkader BOUAZIZ Hello expert, thank you for answering my question, but my PEG is not pegylated with a layer on the outside as everyone knows! My PEG is treated as a hydrophilic substance and is packed into the water-soluble cavity. This may be the case. Is it because the viscosity of PEG makes the nanoparticles more stable? Or maybe it is because the PEG rehydration chamber occupies space, making it less likely that water will penetrate into the nanoparticles and rupture?
No thanks. All your queries are subject of characterization. Pegylation may be a physical adsorption. In your case, may be part of PEG is adsorbed on the outer surface. Other important thing to elucidate is the type of mechanism of instability, is it dissolution or fusion for example. By knowing that, one may expect how PEG has contributed to keep the integrity of liposomes. More experimental work is to be carried out to understand what really is happening. Best of luck in your work.
factors that likely contributed to these effects:
A_ PEG (Polyethylene Glycol) Influence:
The addition of PEG to the liposome interior can impact its properties.PEG is hydrophilic and can create a steric barrier, preventing liposome aggregation and fusion. In the PEG group, this steric stabilization likely led to smaller particle sizes (around 125-130 nm).
B_ Initial Equilibration:
Liposomes undergo dynamic processes during preparation and storage. Initially, there might have been some instability due to formulation changes or storage conditions. Over time (around one month), the system likely reached a more stable state, resulting in consistent particle sizes.
C_ PEG Concentration and Molecular Weight:
The specific PEG concentration and molecular weight matter. Higher PEG concentration or larger PEG molecules enhance steric stabilization.This could explain why the PEG group had smaller particles initially.
D_Storage Conditions:
Refrigeration at 4°C is generally suitable for liposome stability.
Avoiding temperature fluctuations and freeze-thaw cycles is crucial.
Stable storage conditions likely contributed to the subsequent size stability.
In summary, the interplay between PEG, initial equilibration, and storage conditions influenced your liposome behavior. The observed stability after one month suggests a balanced state.
Thanks
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