7 - Composite materials for spinal implants

Abstract

Spinal disorders due to trauma, pathology, or normal aging can compromise the quality of life. The structure and function of the spine are unique and very complex. The intervertebral disc (IVD) plays an important role in the biomechanics of the spine since its mechanical function results in absorbing shock and distributing axial loads whilst providing flexibility. For this reason, the IVD degeneration may be considered one of the most common causes of low back pain. Indeed, the progressive degeneration usually provides a loss of water and a consequent loss of disc height. Thus the annulus fibrosus and ligaments result pretensioned, creating a mechanically unstable environment which may lead to a spinal degenerative cascade. Even though good short-term clinical results have been obtained through spinal fusion for traumatic and degenerative spinal disorders, long-term studies have shown an alteration in the spine stability. In order to overcome these problems, an artificial IVD has been proposed as an alternative to spinal fusion. Consequently, several models of IVD prosthesis have been developed to restore the normal kinematics and load-sharing properties of the natural IVD. Over the past years, metals, ceramics, and polymers have been widely involved in designing interbody fusion devices and IVD prostheses. Because of their ability to mimic the structure and the mechanical properties of natural tissues, polymer-based composite biomaterials have been developed to overcome the drawbacks related to the use of conventional materials. Firstly, the present chapter describes the state of the art of spinal implants such as interbody spacers and IVD prostheses made of conventional materials, then it highlights the role of composite biomaterials for spine applications. In particular, this chapter underlines the possibility to design multifunctional devices with tailored mechanical properties. In this scenario, a biomimetic approach and a pilot-scale production of customised total artificial IVDs with adequate transport, biological and mechanical properties, are also reported. Finally, in the field of advanced biomaterials for spinal applications, future trends and strategies are discussed.