Hydrophilicity of 3-D biomaterials: the Washburn equation

Characterisation and quantification of the surface energy of biomaterials used as tissue engineering scaffolds is important, but many of the techniques available to examine these properties are only applicable to smooth flat samples, not porous materials. This paper describes the application of the Washburn equation to measure the surface energy of a range of porous polyether polyurethane scaffolds with three test liquids; n-Hexane was used to measure a material constant, whilst ethanol and xylene were used to measure contact angles. The results show that the Washburn equation is not applicable in its current form, reasons for this could be that the voids in the materials are too wide for effective capillarity; absorption of the solvents into the polymer matrix may further complicate the measured imbibition profile. Another possible reason is the differences between the sizes of the interconnecting pores in scaffolds with varying void sizes; this could affect the capillary effect of the test liquids through the material. The repeatability of the results and the similar patterns observed with the different liquids suggest that if these issues could be quantified and incorporated into the Washburn equation, it may be possible to generate useful results for similar materials.