I prepared a solid lipid-NP but after ultracentrifugation the SLN precipitate was on the surface and the entrapped drug was on the bottom. It is very difficult to separate the SLN and the untrapped drug (water is the solvent).
If SNP are on the top because lighter than water and 'entrapped' drug at the bottom it means it was not entrapped, i.e. drug loading onto/into SNP largely or to some extent failed. Why not using simple washing on a filter to remove drug not 'entrapped'?
If they are truly LNP (nanoparticles) then filtration can be challenging. However, the drug is entrapped in the micelles then what the LNP for? What is the drug content in the LNP and loading efficiency? Also, have you done the control by solubilising the drug in Tween 80 and spine them down suing the ultracentrifugation?
Would be useful if you can provide more details e.g. LNP composition, manufacture process, particle size of the NPS and physicochemical properties of the drug.
The aim of my study is encapsulation of curcumin (lipophilic drug, polyphenol) in SLN stabilized by tween 80 (hydrophilic surfactant) and span 80 (lipophilic surfactant). The lipid is melted at 40°C and mixed with span 80 and curcumin (solubility in lipid 0.33 mg/g of lipids). Tween 80 is solubilized in water at the same temperature under stirring (500 rpm) until the solution become transparent. The lipid phase is then added dropwise to the micellar solution of tween 80 under stirring at 500 rpm. The obtained pre-emulsion is homogenized usinf ultra-thurrax during 5 min at 10000 rpm and then sonicated for 5 min using probe sonicator. The obtained nanoemulsion is then cooled down slowly to 20°C for the crystallisation process. The nanoparticles size is 100 nm± 1.895 (using DLS)
I have experienced similar challenge with Solid Lipid Nanoparticles purification and as Titus suggested, washing by ultracentrifugation in a centrifuge tube fitted with an ultrafilter membrane helps to purify and concentrate the SLNs. Alternatively, dialysis against a large volume of deionized water for several days (3-5 days) in a dialysis membrane bag of appropriate molecular weight cut-off could do.
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