Catharina S. J. van Hooy-Corstjens

Preliminary evaluation of new intrinsically radiopaque hydrogels for replacing the nucleus pulposus

Treatment of early degenerative disc disease can, in some cases, be accomplished through implantation of a synthetic prosthesis for the nucleus pulposus. This treatment is attractive, since the annulus fibrosus—as well as the function of the disc—is preserved. This study reports on two new synthetic hydrogels which were specifically designed as fully radiopaque prosthetic nucleus biomaterials. Moreover, the new materials were engineered in such a way that they swell in situ (i.e., after implantation) to such an extent that they will fill the entire nucleus cavity. We describe: (i) assessment of the biocompatibility of the new biomaterials in an in vivo animal model, (ii) implantation of the new prosthesis in an ex vivo animal model (porcine spine), followed by (iii) assessment of the visibility of the entire nucleus prosthesis through both CT and MRI. The results further substantiate the idea that the concept of implantation of a prosthesis for the nucleus pulposus can benefit from contemporary insights and developments of novel synthetic biomaterials with intrinsic radiopacity.

Radiopaque polymeric spinal cages: a prototype study

Back pain, originating from degeneration of intervertebral discs, is often alleviated by the insertion of one or more interbody fusion cages. The function of the cage is to restore the height between two adjacent vertebrae and to mediate osseous fusion. Most commercial cages consist of titanium or a titanium alloy, while polymeric cages, mostly consisting of polyether-etherketone (PEEK), are also in use. Titanium is known for its excellent biocompatibility. Titanium cages can be located easily with imaging techniques based on X-ray absorption (e.g. CT scans). However, they introduce artefacts in magnetic resonance (MR images). PEEK cages, on the other hand, do not show up in CT images. For this reason, small metallic markers are usually incorporated. The markers reveal the position of the cage, albeit indirectly. PEEK cages are clearly and integrally seen on MR images, as they are essential free of water. There are no artefacts or disturbances; this feature, as well as its strength, makes PEEK particularly attractive for the construction of cages. Here, we introduce new all-polymeric cages on the basis of an iodine-containing methacrylic copolymer (I-copolymer). This material has been prepared from methylmethacrylate and 2-[4-iodobenzoyl]-oxo-ethylmethacrylate. Copolymerisation of both monomers results in a high molecular weight material. Cytocompatibility experiments reveal that the material contains no toxic leachables and that cells can well adhere to and proliferate on the I-copolymer. Compression experiments at physiologically relevant strains disclose mechanical characteristics comparable to PEEK. The advantage of cages prepared from this I-copolymer over commercially available cages is that the present cage contains no metallic components, implying that it is compatible with MR imaging, and the presence of the iodine atoms ensures X-ray visibility.