I am trying to design PLGA nanoparticles coated with Tween- 80 that will be carrying a hydrophilic drug. The PLGA NPs with the drug have been successfully made. But I am trying to figure out if there will be any drug loss while it is coated with Tween- 80 solution (in 1XPBS with mild stirring at RT for 30 min). Can any one help me how to measure the loss of drug from these particles after it is coated with tween- 80 during this 30 min time period. I want to be precise with the drug concentration as I have to inject these particles with the drug intravenously in the mice.
With a hydrophilic drug I would expect there to be some drug loss, at least any surface- or near-surface associated drug. Easiest way to quantify the amount of drug lost would be to take an alliquote (or several at varying time points during the coating process), separate free drug from the NPs via ultracentrifugation and then quantify the amount of drug in the supernatant. From there you can calculate how you lost if you know how much drug you started with (and presumably you do). In previous work I coated PLGA NPs for 30 mins at room temperature, and lost ~2% of the hydrophobic drug.
It was actually not possible to completely pellet down all the PLGA NPs with ultracentrifugation when they are in Tween-80 containing PBS solution. The solution after centrifugation still remained turbid. Can you please tell me at what centrifuge speed did u pellet them down? Will be a great help.
In the past we pelleted the PLGA NPs by centifugation at 14,000 rpms for 1 hour, however, the NPs were no coated with Tween-80 like yours are. A potential alternative means would be through ultra-filteration devices (while these are not ideal, they may be able to provide you with a means of separating free drug, but they are a 1 shot deal since the pores do get clogged): http://www.millipore.com/lab_filtration/flx4/psp_concentration&open?cid=bios-x-goog-1032-1044-sp
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