Mechanical testing of injectable polyurethanes for nucleus pulposus replacement

L. SACCHETTI; G.A. ABRAHAM; F. BUFFA; P.M. FRONTINI

Milán

Simposio; XIX Convegno Italiano di Scienza e Tecnologia delle Macromolecole.; 2009

Associazione Italiana di Scienza e Tecnologia delle Macromolecole (AIM)

Lower back pain is one of the most common medical problems in the world, mainly cause by degenerative disc disease (DDD). Nucleus arthroplasty has been considered as a treatment of early stage DDD with an intact annulus or status post microdiscectomy procedures where nuclear material has been removed. Currently, the available and developing devices are either implantable or injectable materials that replace the nucleus pulposus. The replacement of the nucleus pulposus with in situ formed nucleus prosthesis constitutes a promising non-fusion technology that involves minimally invasive surgical techniques. In situ curing polymers are liquid-based compounds which harden in minutes after implantation in vivo. This allows the introduction of the implant through a minimally invasive approach (small anulotomy) and minimizes the risk of implant migration following polymer curing. In order to understand the mechanics of the implant, the mechanics of the synthetic material should be known. The material should be able to withstand mechanical loading states experienced under physiological conditions. While the ideal requirements for a nucleus replacement material have been described, test methodologies for determining the device behaviour are yet to be agreed on by the regulatory and scientific communities. Although a number of published works are devoted to nucleus replacement materials and devices, the results of mechanical properties are only limited to uniaxial compression. Nevertheless, the confined compression testing configuration  constrains material deformation which is seems to be more similar to the in vivo loading state of the nucleus. Therefore, it is considered to be more suitable candidate material. The objective of this work is to study the mechanical properties of novel self-curing crosslinked polyurethane foams and assess their mechanical feasibility of the materials as potential replacement materials for the degenerated nucleus of the human lumbar intervertebral disc. The stress-strain behaviour of polyurethane foams prepared by using the same procedure followed in the surgical practice is investigated through uniaxial and confined compression tests.