A popular method for depot delivery is injection of a thermogel. This includes polyvivo products such as AK12, AK24, AK36 and others. In this method the polymer is dissolved in cold water and then injected into a warm body (37C). The transtion from cold to hot causes the polymer to form into a gel or precipitate so that a solid is formed from the injection which can then control the delivery of drugs (check out some publications on this at: http://informahealthcare.com/doi/abs/10.3109/03639045.2013.789054 and http://pubs.acs.org/doi/abs/10.1021/nn203430m) However some additives can modify or alter how this process works. Notably the addition of low molecular weight PEG can slightly adjust the gelation temperature down. Conversely the addition of hydrotropic agents (materials which prevent water from forming into structures such as sodium salicylate, diethylnicotinamide, urea, and others) can raise the gelation point drastically and at high concentrations may prevent gelation from occuring at all. As you plan your studies make sure to keep this in mind.
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NOTE: mPEG-PCL (AK036) thermogelation properties vary depending on storage time and also conditions such as warming, etc. which lead to self-crystallization of the PCL chains. This material may work as a thermogel but its performance is unreliable. If the batch you have is not thermogelling dissolve in organic solvent (DCM) and dry off quickly to reset polymer chain configuration.
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