Characterization of microphase separated structure, interaction with blood components, such as
lipids, and
fatigue behavior after immersion in blood components were carried out for segmented poly(urethaneureas). The materials studied were
Biomer and segmented poly(urethaneurea) (TU-Mn) composed of hard segment with
4,4'-diphenylmethane diisocyanate (MDI)-
ethylenediamine (EDA) or
4,4'-diaminodiphenylmethane (DAM) and soft segment with MDI-
polytetramethylene glycol (PTMG) [Mn of 856, 1350, and 2000]. Small-angle x-ray scattering, wide-angle x-ray diffraction, and dynamic viscoelastic measurements revealed that these materials showed the state of microphase separation. TU-Mn with PtMG of Mn = 856 shows the partial phase mixing between hard and soft segments, and phase separation was improved with an increase of Mn of PTMG.
Biomer has the characteristics of stronger aggregation of hard segment than that of TU-Mn. All the specimen showed
lipid absorption, but the amount of absorption decreased remarkably after precoating on the specimen surface with
serum albumin.
Lipid absorption of the specimen was confirmed by dynamic viscoelastic and IR measurements. In the case of segmented poly(urethaneurea) which did not immersed in
lipids solution, their
fatigue strength are sufficient for application to
artificial heart systems. However,
fatigue strength of the TU-Mn series was decreased drastically after absorption of
lipids. On the other hand,
Biomer did not show a decrease of
fatigue strength after
lipid absorption. The reduction of
fatigue strength in the TU-Mn series after
lipid absorption will be attributed to the weak aggregation of hard segment domain. This reduction of
fatigue strength in the TU-Mn series is characterized by formation of microcrack and mirror zone in
fatigue fractured specimen. As the precoating of the specimen surface with
serum albumin inhibits the absorption of
lipids, the reduction of
fatigue strength was not observed for the specimen precoated with
serum albumin even after immersing the TU-Mn series in
lipids solution for 96 days.