Let's start with the definition, in a very simple way.

DIRECT METHOD: you measure the actual mass of a compound in a certain mass of microsphere/matrix/whatever it easy.

INDIRECT METHOD: given the total mass of compound you have used to prepare the sample, you measure what it is not encapsulated and you subtract this value from the total amount used.

If possible, always use the direct method, for obvious reasons... first of all it is, well, a direct measurement of the mass of the compound you used.

If not possible, you can go for the indirect method, which however is a derived result and it may some extra experimental steps. Each experimental step will introduce an experimental error and may cause a loss of product (adsorption/absorption on the vial wall or pipette tips, for example, or incomplete recovery after separation).

The calculations are pretty straight forward and I think you can figure it out yourself based on the information I have just provided you with.

In terms of methodology, it is really down to the compound you want to measure. I can give you some ideas about the general procedure, though. Both methods heavily rely on the separation of the free compound and the "encapsulated" compound. In most cases, this is achieved by centrifugation, but you can also use size exclusion chromatography (if the particles are compatible with the column) or even dialysis. The advantage of centrifugation is that you can keep both fractions without having a further dilution. The disadvantage is that the separation may not be ideal. Once the fraction have been separated, you can decide what to do. If you want to go for a direct measurement, then the idea is to break down the particles/sphere/matrix with a suitable solvent and from there extract the compound  if the compound is not soluble in the same solvent. This step may follow a freeze-dry step, which I always recommend when working with polymeric substances/matrices. After that, you can determine the concentration, and therefore the amount, of compound encapsulated in a given mass of matrix/spheres/particles. For the indirect method, you simply focus on the other fraction and you measure the concentration, and therefore the amount, of the compound in the separated fraction.

I hope it helps.

Hi Marco,

1) what is the freeze-dry step after centrifugation?I don't think I seen it in papers.

2) For direct method:

If my sample (microspheres) wall is soluble in water and core is soluble in methanol.

Is it a good idea to stir it in a 1:1 (water: methanol) solvent? 

and then centrifuge it. 

the Filtrate measure concentration using spectrophotometer (blank: 1:1 water: methanol)

*Does this steps seems ok?Or should I use higher ratio of methanol to water?

3) Is there a difference between encapsulation and entrapment efficiency? I am really confused in this. 

Thanks for replying

Hello, 

look at this paper:

http://www.ncbi.nlm.nih.gov/pubmed/14585722 

Hi Olivia,

1) Freeze drying may be required so you can weigh your sample and you can remove any solvent or dispersant which can interfere with the solubilisation of the matrix. 

2) That's a good question, but knowing little to nothing about your system I would proceed in two steps: first dissolve the shell, then dissolve the core. So, first add water to disrupt the wall, then centrifuge to pellet the core, and finally dissolve the core. The question is: where is the drug suppose to be? I would measure the absorption of each fraction (water and methanol) separately, so you may also try and understand the partition between the shell and the core. It is an extra piece of information that comes for free :)

3) There are never-ending debates about it, and everyone has their own idea. To me they are almost equivalent, with the only difference being that encapsulation means that the compound is inside a core, whereas entrapment indicates that the compound is "intimately connected" to the shell/bilayer. This means that the compound can be adsorbed on the surface or fit in the mesh/matrix. But then we still have to find a definition for a compound that partitions between core and shell... Just technicality.

nice answer

Hi,

Lets focus on your question where you asked:

"What are direct and indirect ways of determining encapsulation efficiency (simple explanation)?"

Because you said: "I am not pharmacy etc based background. "

I give you very simple definition: when you want to send a fragile gift (e.g. an iphone or a glass vessel) by post to a friend, you cannot just put the gift in the post box, can you? You must first "encapsulate" it insider proper packaging (Capsule or "drug delivery system" or "carrier system"). In other words: "the action of enclosing something in a capsule is known as encapsulation".  Here your encapsulation efficiency is 100% because all of your material (the gift) are encapsulated within the package (located precisely inside the package and not glued to the exterior surface of the package).

If you use material at mico or nano size level, it is practically impossible to make sure each single molecule is encapsulated within one single capsule. Therefore, encapsulation at microscopic level is a random event. Thats why we need to have a parameter showing how successful was our encapsulation (Encapsulation efficiency)

Now lets look at Encapsulation vs. entrapment: if your material is exclusively inside (within the core of) the capsule, the term we use is ENCAPSULATION.

In some cases because of chemical interactions between the drug and the capsule the drug will prefer not to be encapsulated but stays on the surface of the capsule,  attached to it like a magnet and iron. In this case we CAN NOT use the term encapsulation, and "encapsulation efficiency", rather we use the word "entrapment". 

I hope these explanations help you, otherwise let me know. Please note we do not receive notification of posts under QUESTIONS in researchgate, thats why I may not know if you or others put anything below my post here. Hence, pls contact me via message or email.

---

Prof. M. R. Mozafari,

AUSTRALASIAN NANOSCIENCE AND NANOTECHNOLOGY INITIATIVE (ANNI),

Unit 12, 353 Springvale Road, Glen Waverley, 3150 Victoria, Australia.

http://anni.com.au/

Emails: [email protected] & [email protected]

Tel: +61 424339961

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