I think,this depends on the nature of the drug used ,there are drugs affected by increasing the ratio of the drug to lipid and precipitate after the accumulation insid liposomes and reduce the encapsulation efficiency of this drug in liposomes, because of the change in the internal form of the drug when it starts to deposition and increase its size, for example doxorubicin , in other hand ,there are drugs does not precipitate After accumulation in liposomes therefore not affected by the increase in the ratio of drug/lipid

You have to optimise based on your experiment conditions

There will be a different E.E. If you change drug concentration, the particle will be different. Of course, E.E will not remain the same.

Hi,

Depending on the solubility of the drug (as well as its size and other physicochemical properties) and type of the lipid vesicle you are manufacturing, E.E. will change.

As you know, Large Unilamellar Vesicles (LUV) have more capacity to encapsulate water-soluble molecules, compared to SUV liposomes, while Multilamellar Vesicles (MLV) can take up more lipid-soluble molecules.

Have a look at following papers:

Akbarzadeh, A., Rezaei-Sadabady, R., Davaran, S., Joo, S. W., Zarghami, N., Hanifehpour, Y., ... & Nejati-Koshki, K. (2013). Liposome: classification, preparation, and applications.Nanoscale research letters, 8(1), 102.

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Mayer, L. D., Bally, M. B., Hope, M. J., & Cullis, P. R. (1986). Techniques for encapsulating bioactive agents into liposomes.Chemistry and physics of lipids, 40(2-4), 333-345.

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Gubernator, J. (2011). Active methods of drug loading into liposomes: recent strategies for stable drug entrapment and increased in vivo activity. Expert opinion on drug delivery, 8(5), 565-580.

It depends on the kind of drug. I agree with @Hanan Azzam

If your drug is hydrophilic and does not partition in significant quantities into lipid bilayers (and thus does not much affect their phase behaviour or even make liposomes impossible) then essentially there are two scenarios:

1) You are not using active transport e.g. by pH gradient. In this case the encapsulation efficiency will not be affected much because it is mainly determined by the fraction of the total volume that resides inside your liposomes. E.g. if you have 100 nm LUVs with 1 mM phospholipid you have approx. 100,000 lipids/LUV and about 0.5 attolitre volume/LUV, so about 0.3% of the total volume will be inside your LUVs and this will also be your encapsulation efficiency. It is not really affected by drug/lipid ratio until the drug begins to bind to bilayers in significant quantities and changes bilayer properties.

2) If you are using active transport system, e.g. a pH gradient of 4 pH units, and you have drug that e.g. becomes protonated and possibly precipitates as a salt inside the liposomes. Here the final concentration of the drug inside liposomes will be mainly determined by the gradient. Although the encapsulation efficiency likely decreases with increasing drug concentration, it is good to notice that the driving gradient, whether a pH gradient or ion gradient, will dissipate over time even in the absence of the drug, and using higher drug concentration may enable you to reach higher drug concentration inside the liposomes because the pH gradient has less time to dissipate so you will "use" the gradient more competely, although the encapsulation efficiency will be lower. If the drug remains fairly stably inside the liposomes, then it is very easy to remove the drug outside the liposomes and you need to think about it how important it is to you relatively that little drug is wasted (encapsulation efficiency) or that the liposomes will contain a lot of drug.

If your drug strongly partitions into bilayers so that it mainly resides in lipid phase and not the inner aqueous phase, then your encapsulation efficiency will mostly likely decrease with increasing drug concentration, and since most drugs are not bilayer forming, at some point you will no longer have liposomes at all. Then the key to knowing what will happen is to know the drug/lipid system phase diagram.

hope it will be useful