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Polymer implants coated with bioactive film improve success rate of such implants

Polymer implants coated with bioactive film improve success rate of such implants

28-Feb-13

PEEK polymer implants have been successfully coated with a bioactive film for the first time by researchers from North Carolina State University. The discovery should improve the success rate of such implants which are often used in spinal surgeries. PEEK does not bond well with bone or other tissues in the body. This can result in the implant rubbing against surrounding tissues, which can lead to medical complications and the need for additional surgeries. The team wanted to apply a bioactive coating that would allow the polymer implants to bond with surrounding tissues. Since the polymer melts at 300 degree Celcius, a challenge was posed by these coatings that need to be heated to 500 degrees Celsius. A solution to this has been found:
The first step in the new technique coats the implant with a thin film of yttria-stabilized zirconia (YSZ). The second step applies a coating of hydroxyapatite, which is a calcium phosphate that bonds well with bone. The researchers then heat the hydroxyapatite layer. The YSZ layer acts as a heat shield, preventing the PEEK from melting. Meanwhile, the heat gives the hydroxyapatite a crystalline structure that makes it more stable in the body, meaning that the calcium phosphate will dissolve more slowly - promoting bonding with surrounding bone.

Polyetheretherketone (PEEK) is a high performance polymer with advantages over metallic biomaterials for application in spinal implants. 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 in order to provide heat shielding during subsequent post deposition heat treatment to prevent degradation of PEEK substrates and coating/substrate interface. Plasma activation of the PEEK substrate surfaces before deposition resulted in a significant increase in coating adhesion strength. Post deposition heat treatments of microwave and hydrothermal annealing were studied with the goal of forming crystalline HA without the use of high temperatures required in conventional annealing. Microstructural and compositional analysis by scanning electron microscopy and X-ray diffraction revealed that the YSZ layer exhibited a crystalline structure as-deposited, with columnar shaped grains oriented along the growth direction, while the HA layer was shown to be amorphous as deposited. After microwave annealing, the HA coating exhibited a columnar crystalline microstructure, similar to that of the underlying YSZ crystalline layer; XRD analysis confirmed a crystalline HA phase in the coating. It is suggested that the existence of the crystalline YSZ layer aids in the formation of the HA layer upon heating, possibly lowering the activation energy for crystallization by providing nucleation sites for HA grain formation. Cell culture tests showed a significant increase in initial cell attachment and growth on the microwave-annealed coatings, compared with uncoated PEEK and amorphous HA surfaces.

 
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