CONICET | Buscador de Institutos y Recursos Humanos

Lower back pain is one of the most common medical problems in the world, mainly produced as a result of degenerative disc disease. Currently, the replacement of the nucleus pulposus with an in situ formed biomaterial is a promising non-fusion technology that involves minimally invasive surgical techniques. This work focuses on the mechanical properties of self-curing crosslinked polyurethane foams. The stress-strain performance of cell-closed foam samples prepared by using the same procedure followed in the surgical practice was investigated through unconfined uniaxial and confined compression tests. The compressive elastic moduli were in the range of 1.7-4.7 MPa, being in the interval proposed for a solid implant to prevent inward bulging of the annulus fibrous. The Poissons ratio was determined by videoextensometry. The values were not significantly different from those obtained for the native nucleus. A very small hysteresis (2%) was observed even after 100 cyclic loadings to 25% strain. Stress softening and residual strain were not found. Stress relaxation experiments displayed the good elastic recovery. The mechanical behavior under confined compression tests showed interesting features. Samples exhibited two regions of behaviour at strains less that 0.25, an approximate linear region followed by a densification region starting at strains about 0.2. Stress softening and residual strain after 100 cycles were not found either. However, samples exhibited considerable hysteresis (20 %) under rigid confinement without undergoing any macroscopic failure. The initial dimensions were completely recovered after unloading. These preliminary results suggest that this novel implant may prove to be a suitable nucleus pulposus substitute.