POLYMERIC MICELLES Flashcards
Apply Knowledge from Lecture
What impact (if any) will increase the length of the hydrophilic block on the CAC?
CAC - Critical Aggregation Concentration (CMC)
It will decrease the CAC as the polymers will have a high HLB. Decreasing the time it would take to aggregate and form a micelle.
This will increase the stability of the micelle upon parenteral administration.
What formulation will have the fastest release: Micelles made of a semi-crystalline polymer or micelles made of an amorphous polymer?
Micelles are made with an amorphous polymer.
Semi-crystalline polymers have a highly ordered molecular structure with sharp melting points.
They do not soften with a gradual temperature increase so drug release will be slower.
Explain how polyion complex micelles are formed.
Formed from a complex of drug and ionisable segments. PEG chain forms the outside shell.
The ionisable segment makes the core soluble in water.
DNA is a hydrophilic molecule (-ve)
Interaction between the opposite charges neutralises the charge.
Amphiphilic polymer is made and can therefore assemble into a micelle.
What colloidal property can you use to differentiate between an unimolecular and micellar solution?
Scattering behaviour using dynamic scattering microscopy
Explain the difference between thermodynamic and kinetic stability. Why are they both equally as important?
They determine the CAC (CMC in terms of polymer aggregation)
Thermodynamic stability emphasises the importance of CAC and Drug loading
Factors affecting the CAC = Polymer chain length, hydrophilicity of the core
The lower the CAC - the increase in thermodynamic stability.
Kinetic stability is how fast the polymeric micelle will dissociate and emphasises drug release.
The stronger the chains inside the core of the micelle are - the more kinetic energy needed for the drug to leave the core.
Explain how fluorescence can be used to determine the CAC. What properties must the fluorescent probe have to be used for this application.
Pyrene is used as a fluorescent probe.
Properties: Hydrophobic, Fluorescent and Polarity sensitive.
If a low fluorescent signal is emitted the concentration is lower than the CAC.
An intense fluorescent signal means that the C has exceeded the CAC.
What is the most likely mechanism of uptake of passively targeted micelles in cancer cells
EPR effect
Endocytosis
Explain how proteins can contribute to the premature drug release from micelles
Protein enters the core - destabilising the micelle.
Serum proteins can interact with the core of the micelle and cause extraction of the drug from the core - making it physically unstable
