Determining the absolute surface hydrophobicity of microparticulates usingthin layer wicking

Surface hydrophobicity is an important factor in the transport of micropart iculates (MPs) across biological barriers. We have previously shown in our laboratory that the surface properties of polystyrene MPs influence the dif fusion and transport through gastrointestinal (GI) mucus and mucin. Unfortu nately, most currently used methods for evaluating the surface hydrophobici ty of MPs involve a relative measurement resulting in a rank order rather t han an absolute hydrophobicity value. Obtaining an absolute assessment of h ydrophobicity is necessary in order to obtain meaningful comparisons and co rrelations across laboratories, polymers, methods of fabrication, and so on . A modified thin layer wicking (TLW) technique was developed and validated to allow for the determination of absolute surface hydrophobicity of intac t MPs. The TLW method was validated by constructing a standard curve and co mparing the rate of solvent rise through MPs dried on microscope slides to the known contact angle of PLGA polymers. MPs with surface contact angles r anging between 67.04 degrees and 90.18 degrees were evaluated using the TLW technique. The modified TLW technique was also successfully Validated usin g surface-modified polystyrene and OVA MPs. Based on the results of the cur rent study, the modified TLW technique appears to be a reliable and quantit ative method for assessing the surface hydrophobicity of intact MPs. (C) 19 99 Elsevier Science B.V. All rights reserved.