The importance of polyurethane/carbon nanotubes composites fabrication method to mimic mechanical behavior of different types of soft tissues

Polyurethane/Carbon nanotubes (PU/CNTs) composites are widely used materials in biomedical engineering. PU/CNT composites are commonly fabricated by electrospinning and solvent casting methods. The choice of fabrication method can influence the composites structure, which affects the mechanical properties. This study investigated the influence of the fabrication method and proportion of CNTs on the mechanical behavior of PU/CNTs biomaterials, synthesized by electrospinning and solvent casting. The mechanical properties of the fabricated PU/CNTs samples with different amounts of CNTs were evaluated by uniaxial tensile testing, which involved cyclic loading to different strain levels. The results indicated that under tensile loading, electrospun samples displayed strain-stiffening behavior, while solvent-casted films displayed strain-softening behavior, which is similar to the mechanical properties of collagenous and non-collagenous soft tissues, respectively. Pre-loading to each strain level caused softening in both electrospun and solvent-casted samples and changed the trend of the stress–strain curve. It is proposed that the trend of the stress–strain curve, which is affected by pre-loading and choice of biomaterial fabrication technique, should be considered an essential factor when fabricating biomaterials for tissue engineering and regenerative medicine purposes.