Intervertebral disc degeneration, an inevitable process of aging, is one of the major causes of low back pain. Currently, there are two major surgical interventions for treating conditions related to the degenerative disc: discectomy and fusion. Although discectomy and fusion produce a relatively good short-term clinical results, both these surgical treatment alter the biomechanics of the spine, possibly leading to further degeneration of the surrounding tissues and the discs at adjacent level. Alternatively, the solution to a degenerated disc involves the use of an artificial disc substitute.
Over the past 35 years, a tremendous effort has been made to develop a suitable artificial disc substitutes to replace the degenerated disc. The artificial disc prostheses on the market (or in development) to date, however, have been reported to frequently undergo failure due to wear and degeneration of the materials, to the surgery techniques used for the implantation, or to the mismatch between the mechanical properties of the devices and the natural tissue.
In order to design an alternative intervertebral disc prostheses with appropriate transport, mechanical and biological properties the research has been focused on the basic concept of mimicking the natural structure of the disc tissues.
The natural intervertebral disc consists principally of collagen fibers embedded in a proteoglycan-water gel. The latter component develops a large swelling pressure which enable the disc to resist compressive properties.
The type and orientation of collagen in the disc have an important influence on how load is distributed. In the disc there is a gradation of collagen type and orientation from nucleus to annulus. The collagen fibers orientation decreases from 62 to 45 degrees. Water is the main constituent of the disc, it occupies 65 to 85 per cent of the tissue volume depending on age and region.
The structure of the intervertebral disc as well as its biomechanical and transport properties are unique and very complex.
To satisfy all these requirements Hydrogels has been used not only for nucleus substitution but also for the total disc substitution where high mechanical properties are required. However, the mechanical properties of these materials in the hydrated state are not sufficient for biomedical applications where high mechanical strength is required. An improvement in mechanical properties of polymeric hydrogels could be obtained by using PET fibre reinforcement and by reinforcing with Hydroxyapatite and Calcium Phosphate. The inclusion of hydroxyapatite and/or Calcium Phosphate would be beneficial as these materials are bioactive and can stiffen polymers as required for the end-plate realization.
The preparation of the device has been performed by using the filament winding technology and subsequently by moulding technology where PET fibers impregnated in the hydrophilic polymer solution were wound, by using a winding angle varying from 45 to 65 degree ) on a mandrel having a geometry of the nucleus, until the final size of the disc is obtained. Upon the completion of this phase, the wound structure was transferred in a mould, filled with the hydrophilic polymer solution to allow a complete polymerisation. During this process Hydroxyapatite and/or calcium phosphate reinforcing hydrogels are used for end plate interface. The hydrophilic and composite intervertebral disc prostheses reported in figure, has shown high biocompatibility, appropriate t
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