Degradation of a Biomedical Polyurethane: Surface Integrity and Fatigue Effects
Polyurethanes degrade under a variety of conditions. In cardiovascular applications of polymeric materials emphasis is placed on elastomers that have extended fatigue lives. The effect of surface integrity on the performance properties of Biomer®, a segmented poly(etherurethaneurea) used on many blood contacting surfaces, has been investigated using tensile tests at room temperature, and biaxial fatigue tests at body temperature. No significant differences other than ultimate tensile strength (UTS) were noted in the stress-strain curves of the specimens with varying surfaces, however preliminary results from fatigue tests indicate a decreasing fatigue life with increasing surface roughness.
This study reports on specimen analysis prior to and following fatigue testing in an attempt to describe mechanisms for mechanical degradation related to differences in surface integrity and fatigue loading. Analysis methods used include Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). FTIR indicated degradation of the polymer occurred related to cyclic stresses applied to the material. All fatigued specimens showed signs of degradation regardless of their surface roughness. Surface evaluation using SEM indicated the presence of micropores prior to and following cyclic loading of the specimens. Micropores seen following cyclic loading were larger and in some instances more numerous. Microcracks were observed propagating between micropores in a typical fatigue failure mechanism.
KeywordsFatigue Life Cyclic Loading Ultimate Tensile Strength Fatigue Test Surface Finish
Unable to display preview. Download preview PDF.
- 1.ASTM Committee on Terminology: Compilation of ASTM Standard Definitions, (sixth edition). Philadelphia, American Society for Testing and Materials, 1986.Google Scholar
- 4.Ethicon, Inc., Somerville, N.J., Technical Product Information.Google Scholar
- 6.Lelah, M.D., Cooper, S.L., Polyurethanes in Medicine, CRC Press Inc, Boca Raton, Florida, 1986, 100.Google Scholar
- 7.Lemm, W., “Biodegradation of Polyurethanes”, in Polyurethanes in Biomedical Engineering, edited by H. Planck, G. Egbers, and I. Syré, Elsevier Science Publishers B.V., Amsterdam, 1984, 103–108.Google Scholar
- 8.Hennig, E., Bucherl, E.S., “Mineralization of Circulatory Devices Made of Polymers”, in Polyurethanes in Biomedical Engineering, edited by H. Planck, G. Egbers, and I. Syré, Elsevier Science Publishers B.V., Amsterdam, 1984,109–134.Google Scholar