Polyurethane formulations for nucleus pulposus replacement: Compression response and modeling

M. MACHADO; L. SACHETTI; GUSTAVO A. ABRAHAM; P. FRONTINI

JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2012

1751-6161

Lower back pain is one of the most common medical problems in the world, mainly produced as a result of degenerative disc disease. Nucleus pulposus replacement appears as a good alternative to current surgical procedures since it involves minimally invasive surgical techniques to restore normal biomechanics by using a non-fusion technology. Although many synthetic materials have been proposed as substitutes for the nucleus pulposus, the use of in situ cured biomaterials is gaining more acceptation than the use of preformed implants. In the present work, in situ polymerizable nucleus pulposus replacements were prepared from a two component self-curing injectable polyurethane formulation. The compressive mechanical behavior of this polyurethane elastomeric foam was studied under uniaxial and confined compression, in order to simulate the mechanical response of the replacement. According to the behavior displayed by materials, a simple constitutive model, Ogden-Storakers, capable of describing highly compressible elastomer mechanics was adopted. To calibrate model parameters taking into account the two loading modes simultaneously a suitable numerical model calibration routine was developed. By successive finite element modeling (FEM) simulations, the program adjusts the model parameters using a trust-region algorithm. Finally, a simple FEM model of an intervertebral disc was constructed to simulate disc biomechanics in intact, denucleated and implanted conditions. Comparison between different cases reveals that the use of the proposed material would be reliable.