Dear Rahila Batul if you get more than what you load, then there is obviuosly a fault in your measurement.

Instead if you meant that by increasing the loaded amount of drug, the relelased amount decreases, then this might happens and it can be due to a number of effect (nucleation/aggregation, etc). I recently worked on such a system:

Preprint Role of surface heterogeneous nucleation on nanoporous drug ...

First of all you need to consider that how are you calculating your loading efficiency. Certainly you can not load more than the starting quantity. So by getting more than 100% loading efficiency, i presume you are considering the weight of your nanoparticles as baseline. In this case, some nanoparticles are able to carry more drug than their own weight. However, this is not a standard way to calculate the drug loading efficiency.

The standard formula is to calculate/measure the loaded drug and divide it by the initial quantity and you can get loading percentage after multiplying the fraction by 100.

Another thing which you need to consider is the saturation point of your nanoparticles. So if they are fully loaded with drug, then they have reached saturation point and beyond that, they cannot load more drug. In this case, loading efficiency will decrease as a lot of drug will remain unloaded.

The second part is related to drug release. Drug release is calculated in accumulated way, means by adding the drug released after each time interval.

Again, this release cannot be more than 100%.

I hope this helps you. You can read this publication related to drug release and cellular uptake if you are interested

Article Anti-Tumor Drug-Loaded Oxygen Nanobubbles for the Degradatio...

Dear Muhammad Saad Khan,

I really like the way you explaned. I want if there is any reference for standard method of calculating the loading efficiency, please share it with me. That would be much helpful.

Thank you very much.

I mentioned one of my research papers in previous answers.

Here is another paper which mentions this formula for encapsulation efficiency and its impact on size of liposome. Various other researches can be found in similar manner.

Article Influence of the Encapsulation Efficiency and Size of Liposo...

Thank you very much for your help Dr. Muhammad. I need a little clarification regarding loading efficiency Vs mass% of the drug loaded particles. When I do my theoretical calculations I am getting higher loading efficiency by increasing the initial loading amount but the mass % is decreasing. Is that Really happens?

What do you mean by mass %? Does it means mass of drug/mass of particles, (w/w) ratio?

There are few general things. if you provide some specifics, then may be I will be able to answer more precisely.

1. Loading efficiency will be less than 100% in all conditions. In most cases its near around 50%, while loading efficiency of 80% or more is considered very good. The efficiency can be calculated as I mentioned above. To perform this experiment, you need to create conditions (Dialysis or centrifugation) to remove the unbound drug. Then either measure the unbound drug, or encapsulated drug, and calculate the loading efficiency.

2. Sometimes, nanoparticles can carry more drug than their own mass. This especially happens if the nanoparticle is hollow inside. For example, 2 mg of drug loaded on 1 mg of nanoparticle. This will give you 200% (w/w) loading. But this is not loading efficiency. You can call it loading capacity or may be mass% as you mentioned.

3. Theoretical calculations are often different from practical results in biological experiments. The reason is that often we do not consider environmental factors such as temperature and pH etc. Therefore, the theoretical modeling will just give you an idea.

I hope it helps

Dear Muhammad,

I appreciate your support. Thank you very much for that.

Yes, mass % means loading capacity.

I am using different ratios of drug and polymeric nano particles (NPs) viz: 2:5, 3:5, 4:5 and 5:5, with variable concentration of drug but carrier concentration is kept constant.

I am confused with my results, I am getting.

By increasing the drug to polymeric NPs ratios, the loading capacity is decreasing. Can it be happened?

The drug loading capacities with respect to various drug to polymer ratios are; 2:5, 3:5, 4:5 and 5:5 93%, 78%, 55% and 36%.

While on the other side of my observations such as particle size and zeta potential as well as drug efficacy etc. are increasing with respect to increase in initial feeding amount of drug.

Can you please tell me the technical reason for that?

Nanoparticles can load drug up to the saturation point. May be you need to find the saturation point to have maximum drug loading. The decrease in drug loading capacity you are mentioning seems to be because your nanoparticles are saturated with the drug beyond 2:5, as the trend is similar in increasing ratios.

I would suggest that reduce the drug polymer ratio to 0.5:5, 1:5, 1.5:5 and then check the results. It will give you an idea about the saturation point.

Drug itself might effect the zeta potential, therefore increase in the amount of drug is increasing the zeta potential. So this is understandable.

More drug will also tend to increase the particle size. sometimes unbound drug is also loosely attached to the particle and contributes towards size measurement. Especially if you are using DLS, then DLS measures the hydrodynamic diameter. Which means it can be measuring the size of unbound drug floating in the solution.

Overall, I believe, try to reduce the ratios of drug vs polymer. Most probably the NPs have reached saturation point at 2:5 or even before that.