Fabrication and Testing of Auxetic Foams for Rehabilitation Applications

Negative Poisson's ratio or auxetic foams were fabricated and studied for use in prosthetic applications. A thermomechanical process was used to convert conventional polyurethane (PU) foam into auxetic PU foam. Two types of auxetic PU foams were made using two different volumetric compression ratios, 3.02 and 3.86. Chemical composition analysis showed that chemical structure of the converted auxetic foam remained the same as the conventional PU foam after the thermomechanical process. Compression tests showed that the auxetic foams had higher stiffness than conventional foams, implying that the auxetic foams could be potentially used in seat cushions, shoe soles, and as liners in prosthetic applications. Compression fatigue tests showed that percentage loss in thickness in auxetic foam fabricated using lower compression ratio had loss in thickness that is comparable to conventional foam, whereas auxetic foam fabricated using higher compression ratio had greater loss in thickness. Our study indicates that the auxetic foams made using lower compression ratio need to be further explored for suitability in various rehabilitation applications.