Greetings everyone!
In many pharmaceutical hydrogel formulation articles the particle size (DLS) is not measured (e.g. Poloxamers at concentrations between 15% - 20% generally do not have this characterization).
DLS analysis make sense in a hydrogel formulation of such polymer concentration? Or should the use of Multiple Dynamic Light Scattering be more appropriate?
Matheus Augusto de Castro,
A hydrogel formulation may consist of particles and dissolved polymers/surfactants, which 'particle' you want to know the size of? Those ingredients that can be considered present as hard sphere particles one can analyse for particle size in their pure form and since they could be nano-sized a DLS seems sensible. However, many hydrogels use particles larger than 500 nm and those are preferably not sized by DLS but better by a particle sizer using Mie scattering (range commonly 0.04 to 2000 micrometer).
Your example of poloxamers is slightly confusing as these are dissolved copolymers (poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) block copolymers) which are added for stability, hence they sit at the surface of particles. They only form 'particle-like structures' called micelles when they are added in excess of the quantity needed to cover the available surface area. It is possible but tricky to get the size of micelles by DLS as they generally scatter little light and are mostly below 50 nm. For sizing micelles either static light scattering or SANS is best used.
Hope this helps, kidn regards, Leo
Hello Matheus Augusto de Castro , do the Polaxemer samples look very opaque? If so then you would have multiple scattering. However, backscattering may still be able to separate mostly single scattering from that signal. The problem is data interpretation.... as quite often the diffusion is "hindered" by the presence of the other particles / network nearby. If the gel itself does not scatter but additional particles in the matrix contribute most of the scattered light then you have to take that into account - then you are possibly measuring primarily the diffusion of these "tracer" particles. You may still be able to do some qualitative comparison to see if something changed relatively - however absolute size measurements could be tricky.
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