The top scanning electron microscope image (b) shows a cross section of the bioactive hydroxyapatite/YSZ coating without heat treatment. Note how the two layers are distinct. The bottom image (f) shows the coating after heat treatment. Note how the layers are now integrated.
Using plastics in medical implants has certain advantages, but polymers don’t bind well with biological tissues. In orthopedics this leads to instability of implants, damage to surrounding tissue, and corrective procedures that add extra suffering and cost.
Researchers at North Carolina State University were able to apply a bioactive coating to the surface of PEEK (polyether ether ketone) plastic, a commonly used polymer in implants, to make it considerably more compatible with surrounding tissues. The technical challenge was that the coating has to be heated to 500°C (930°F) for it to bond with the polymer, but PEEK melts at around 340°C (660°F). They were able to solve the problem by applying an intermediate layer of yttria-stabilized zirconia (YSZ) that successfully kept the plastic cool enough while the hydroxyapatite (HA) coating was applied.
From the study abstract in Journal of Biomedical Materials Research Part A:
In this study, hydroxyapatite (HA) coatings were deposited onto PEEK substrates using radio-frequency magnetron sputtering for the purpose of improving bioactivity. An intermediate coating layer of yttria-stabilized zirconia (YSZ) was first deposited onto the PEEK substrates to provide heat shielding during subsequent post-deposition heat treatment to prevent degradation of PEEK substrates and coating/substrate interface.
Press release: Researchers Coat Spinal Polymer Implants with Bioactive Film to Improve Bonding with Bone Study abstract in Journal of Biomedical Materials Research Part A: Processing and evaluation of bioactive coatings on polymeric implants
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