| Abstract
| - Pluronic-PAA, a thermogelling copolymer composed of side chains of poly(acrylic acid) (PAA) graftedonto a backbone of Pluronic copolymer, is of interest as a vehicle for the controlled release of compounds.An important feature of such a vehicle is its bioadhesive/mucoadhesive properties, which in the case ofPluronic-PAA are significant due to the presence of the PAA side chains. An atomic force microscopy (AFM)method has been developed and utilized to investigate the interactions between a Pluronic-PAA-modifiedmicrosphere and mucous substrates. The bioadhesive force was successfully measured, and trends wereobserved under conditions of varying pH and ionic strength. Pluronic-PAA exhibits significant mucoadhesionover a range of pH values, with mucoadhesion being optimal at pH 4−5 (adhesive force ∼80 mN/cm2) anddropping sharply at higher pH, to a value of ∼20 mN/cm2 at pH 8. The mucoadhesive force decreased withincreasing ionic strength, from a value of ∼80 mN/cm2 in 0.025 M NaCl to ∼25 mN/cm2 in 1.0 M NaCl.These results have been interpreted in terms of the effect of changing pH and ionic strength on electrostaticinteractions and swelling of the polymer and mucin layers. Tensiometric force measurements indicatedthat hydrophobic interactions, as well as hydrogen bonding and electrostatic interactions, were significantin the mucoadhesion of Pluronic-PAA copolymers. Experiments with a range of Pluronic-PAA copolymerswith varying PPO contents in the Pluronic segments showed that increasing the overall PPO contentincreased the hydrophobicity of the polymer solutions. This was reflected in the increases in the advancingcontact angles with the mucin layer, indicating that hydrophobic interactions play a role in the adhesionof Pluronic-PAA to mucin.
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