For in vitro, the only PK study you can do is the drug release study. Two main methods for liposomes are dialysis and centrifugation. Dialysis requires a large volume, so unless your payload is highly concentrated, you may not be able to measure the released payload concentration effectively. Centrifugation is simpler in that you can spin down the particles and isolate the released payloads by using filters (30K-100K amicon filters depending on your liposome size). But if you spin too fast, you may damage and break your liposomes, and get false positive results. You can choose the method based on what your formulation is like.

If the payload must be active upon release, you should also isolate the released payload and do an activity assay. If you are using just fluorescent dyes as model payload, then no need for this. Just use the dye to quantify release concentration.

For all other PK tests (circulation, biodistribution, etc.) your best bet is to test in vivo.

The most commonly followed method to study drug release kinetics is dialysis. This usually involves the drug loaded nanoparticle of a particular concentration dissolved in a suitable release medium and added in a dialysis bag. Buffer systems of different pH are used as reservoir solutions. Mechanical agitation for an extended period of time along with different reaction temperature are provided.

I would suggest you to refer articles specifically using your desired kind of nanoparticles and application for ideas on the reaction conditions such as pH and temperature.

Thank you @Kim and @Sumithra, your answers were a lot of help .. as we are working with liposomes may be dialysis will be better.

Also regarding this, is there any mathematical models available for drug release kinetic study?