General Session: Innovative Technologies II - Hall F

Presented by: D.J. Hickey

Author(s):

D.J. Hickey(1), T.J. Webster(2), S. Adams(3), I. Fedder(4)

(1) Tyber Medical, Research & Development, Bethlehem, PA, United States
(2) Northeastern University, Chemical Engineering, Boston, MA, United States
(3) Duke University Hospital, Orthopedics, Durham, NC, United States
(4) St. Joseph's Hospital, Spine and Scoliosis Center, Baltimore, MD, United States

Abstract

Objective: To characterize the growth and bone-forming functions of osteoblasts on titanium surface-treated PEEK compared to bare PEEK and plain titanium.

Introduction: Polyether ether ketone (PEEK) provides excellent mechanical properties as an interbody cage material, as it reduces stress shielding between itself and surrounding tissues compared to stiffer materials such as titanium. Its radiolucency under x-ray/fluoroscopy also enables better visualization of bone formation through the cage. However, the biologically inert surface of PEEK does not promote bony union, and forces the body to sequester the implant within a fibrous capsule, thereby limiting nutrient transport and minimizing implant integration, which can lead to bony nonunion, subsequent pain, and potentially revision surgery. To enhance the bioactivity of implants for spinal fusion, a titanium coating has been plasma sprayed onto PEEK to provide a significantly more wettable surface with a structure that mimics healthy bone at the cellular level.

Methods: Surgical grade PEEK pucks were plasma sprayed with titanium in a manner to create roughness at the cellular level. These titanium-modified PEEK (ProTi 360°™* (TYPEEK® **)) samples were then directly compared to bare PEEK and plain Ti6Al4V. The sample surfaces were characterized using high-magnification scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact angle analysis to provide insight into the morphology and wetting properties of each surface. To evaluate bone cell responses to these materials in vitro, primary human osteoblasts (PromoCell, Heidelberg, Germany) were cultured on the samples for up to 3 weeks. The adhesion and proliferation of osteoblasts was measured using an MTS cell viability assay (Promega). The viability of the cells was then verified visually using fluorescent microscopy and by viewing the cells under SEM after cell fixation. The differentiation of osteoblasts into bone tissue-producing cells was also studied. Alkaline phosphatase (ALP) activity, an early indicator of bone growth, was measured using a fluorescent ALP detection kit (Sigma). Collagen production, as well as calcium deposition, was measured using a hydroxyproline assay (Sigma) and a calcium quantification kit (Sigma), respectively. All experiments were run in triplicate and repeated three separate times.

Results: ProTi 360° (TYPEEK) samples exhibited increased roughness at the cellular level and significantly improved hydrophilicity compared to plain PEEK and Ti6Al4V samples. Osteoblasts grown on ProTi 360° (TYPEEK) samples adhered in greater numbers, proliferated at a faster rate, and displayed a considerably more spread out morphology, especially compared to plain PEEK. Most importantly, osteoblasts grown on ProTi 360° (TYPEEK) samples showed increased levels of ALP activity, collagen production, and calcium deposition, indicating in vitro that the surface of the ProTi 360° (TYPEEK) samples are well suited to direct robust bone tissue ongrowth.

Conclusions: The titanium-modified PEEK (ProTi 360° (TYPEEK)) surfaces presented here considerably enhance the attachment, growth, and bone-forming functions of osteoblasts, while preserving the favorable bulk mechanical properties of the underlying PEEK. Thus, although requiring further in vivo investigation, it is predicted that the increased surface bioactivity of ProTi 360° (TYPEEK) interbody cages may significantly improve spinal fusion outcomes by promoting bony union. * ProTi 360°™ is a registered trademark of DePuy-Synthes, Inc. ** TyPEEK® is a registered trademark of Tyber Medical, LLC.