Introduction: Polyetheretherketone (PEEK) is shown to be promising for spinal fusion where a cage like device is placed between vertebrae to facilitate fusion[1].
Hydroxyapatite (HA) has been added to PEEK to improve hard tissue integration. Addition of HA particulates into a polymer matrices provides osteoconductive properties.
The dis-similarity between PEEK and HA results in a poor interface. It has been shown that at 10vol% HA in PEEK, HA particulates become debonded from the polymeric matrix[2].
Shortfalls in mechanical properties originate from the poor interfacial interactions. We have addressed this by modifying HA and PEEK to enable covalent linking to allow for more HA incorporation without loss of load bearing properties required for orthopedic application (Figure 1).
Materials and Methods: Thiol groups were introduced to HA surface via silanisation to produce HAthiol. The reduction of PEEK to hydroxylated PEEKOH was achieved via sodium borohydride (NaBH4) reaction. p-Maleimidophenyl isocyanate (PMPI) was used to link the resulting HAthiol and PEEKOH. Material was then thermally processed into sheets to produce PEEK, PEEK/HA and PEEKOH/HAthiol specimens (2wt% HA content). Materials were assessed during formulation using a combination of Raman spectroscopy, thiol assay, SEM, XRD, DSC and TGA. Mechanical testing and cellular seeding studies were carried out on processed composites.
Results: Silinisation of HA was confirmed by Raman spectroscopy and thiol content quantified using a thiol assay. XRD, DSC and TGA confirmed the hydroxylation of PEEK to PEEKOH. SEM demonstrated a more unified composite resulted from the processing of PEEKOH and HAthiol compared to PEEK/HA (Figure 2). Initial mechanical testing of composites showed PEEKOH/HAthiol to be weaker compared to PEEK but properties improved from better dispersion of particulates. Osteoblast like cells cultured on the PEEKOH/HAthiol attached and were able to proliferate.
Conclusions: We have shown PEEK and HA can be covalently linked utilising modifying chemistries. Attaining a covalent linkage such as that described can produce a more unified composite that overcomes the trade-off in strength at higher levels of HA loading.
EPSRC
References:
[1] KURTZ, S. M. & DEVINE, J. N. 2007. PEEK Biomaterials In Trauma, Orthopedic, And Spinal Implants. Biomaterials, 28, 4845-4869.
[2] WANG, L., WENG, L., SONG, S. & SUN, Q. 2010. Mechanical properties and microstructure of polyetheretherketone–hydroxyapatite nanocomposite materials. Materials Letters, 64, 2201-2204.