There is growing commercial and scientific interest in spinal implant surface technologies, with the emergence of nanoscale surface characteristics as the most promising. These are biologically inspired surface features that can be “sensed” by individual cells to stimulate osteoblastic differentiation, ultimately leading to rapid bone formation and osseous integration.
In order to interact with a cell membrane, a device must have a submicron scale. Nanotechnology (10–9) directly interacts with cells on a molecular level, generating specific cellular responses to drive fusion bone production that porous or micron scale (10–6) that implant surfaces cannot.
Implants are commonly produced using one of two methods. The first is additive (coating/3D printing), in which titanium layers are sprayed onto another surface. This method requires complex material surface bonding, making it more susceptible to impaction debris and delamination.1 Additive methods cannot achieve nanoscale characteristics without postproduction processing. In the second method, subtractive, titanium is treated to remove some of the surface, leaving behind unique micron (10–6) and nano (10–9) surface textures. This does not weaken the material and allows its surface to remain stable against mechanical insertion forces.
Biomechanical data demonstrate significant wear debris due delamination in polyetheretherketone (PEEK) implants coated with plasma-sprayed titanium (additive) while the nanotechnology (subtractive) surfaces did not.1 These particles may lead to late failure due to chronic inflammatory reactions and osteolysis.
Titanium nanotextured surfaces upregulate physiological bone morphogenetic protein production, without the addition of biological stimulants or additives. They also upregulate factors associated with vascular ingrowth and osteoclastic stability, promoting natural physiological bone formation pathways.2–6
Published scientific literature demonstrates that small surface modifications can significantly improve the osteogenic properties of the nanosurface titanium implants while those made of PEEK generate factors associated with inflammation, fibrosis, and cell necrosis.6
Recent data on porous PEEK report better mineral deposition, compared with smooth PEEK, but only when osteogenic stimulants are added to the media.7 Of note, no biological supplements were used to stimulate cellular responses in the nanotextured titanium studies cited.2–6 This better supports their conclusions that the combination of the material and the nanotexture stimulates ostegenic factor production, rather than exogenous additives.
To date, there is only one FDA-cleared spinal implant with a Centers for Medicare & Medicaid Services new technology category designation, for a nanotechnology surface.8
Nanotechnology surfaces on spinal implants are a disruptive technological advancement with the potential to improve clinical outcomes. Based on peer-reviewed publications, titanium with a nanotextured surface has emerged as the best option for direct interaction with cells on a molecular level.
1. Kienle A, Graf N, Wilke HJ. Does impaction of titanium-coated interbody fusion
cages into the disc space cause wear debris and/or delamination? Spine J
2. Olivares-Navarrete R, Gittens RA, Schneider JM, et al. Osteoblasts exhibit a more differentiated phenotype and increased bone morphogenetic protein production on titanium alloy substrates than on poly-ether-ether-ketone. Spine J
3. Olivares-Navarrete R, Hyzy SL, Gittens RA1st, et al. Rough titanium alloys regulate osteoblast production of angiogenic factors. Spine J
4. Gittens RA, Olivares-Navarrete R, Schwartz Z, et al. Implant osseointegration and the role of microroughness and nanostructures: lessons for spine implants. Acta Biomater
5. Olivares-Navarrete R, Hyzy SL, Berg ME, et al. Osteoblast lineage cells can discriminate microscale topographic features on titanium-aluminum-vanadium surfaces. Ann Biomed Eng
6. Olivares-Navarrete R, Hyzy SL, Slosar PJ, et al. Implant materials generate different peri-implant inflammatory factors: poly-ether-ether-ketone promotes fibrosis and microtextured titanium promotes osteogenic factors. Spine (Phila Pa 1976)
7. Torstrick FB, Evans NT, Stevens HY, et al. Do surface porosity and pore size influence mechanical properties and cellular response to PEEK? Clin Orthop Relat Res
8. 510(K) summaries or 510(K) statements for final decisions rendered during the period October 2014. US Food & Drug Association/FDA.