title: Osteoblasts exhibit a more differentiated phenotype and increased bone morphogenetic protein production on titanium alloy substrates than on poly-ether-ether-ketone.
abstract: BACKGROUND
  Multiple biomaterials are clinically available to spine surgeons for performing interbody fusion. Poly-ether-ether-ketone (PEEK) is used frequently for lumbar spine interbody fusion, but alternative materials are also used, including titanium (Ti) alloys. Previously, we showed that osteoblasts exhibit a more differentiated phenotype when grown on machined or grit-blasted titanium aluminum vanadium (Ti6Al4V) alloys with micron-scale roughened surfaces than when grown on smoother Ti6Al4V surfaces or on tissue culture polystyrene (TCPS). We hypothesized that osteoblasts cultured on rough Ti alloy substrates would present a more mature osteoblast phenotype than cells cultured on PEEK, suggesting that textured Ti6Al4V implants may provide a more osteogenic surface for interbody fusion devices.
  
  
  OBJECTIVE
  The aim of the present study was to compare osteoblast response to smooth Ti6Al4V (sTiAlV) and roughened Ti6Al4V (rTiAlV) with their response to PEEK with respect to differentiation and production of factors associated with osteogenesis.
  
  
  METHODS
  This in vitro study compared the phenotype of human MG63 osteoblast-like cells cultured on PEEK, sTiAlV, or rTiAlV surfaces and their production of bone morphogenetic proteins (BMPs).
  
  
  METHODS
  Surface properties of PEEK, sTiAlV, and rTiAlV discs were determined. Human MG63 cells were grown on TCPS and the discs. Confluent cultures were harvested, and cell number, alkaline phosphatase-specific activity, and osteocalcin were measured as indicators of osteoblast maturation. Expression of messenger RNA (mRNA) for BMP2 and BMP4 was measured by real-time polymerase chain reaction. Levels of BMP2, BMP4, and BMP7 proteins were also measured in the conditioned media of the cell cultures.
  
  
  RESULTS
  Although roughness measurements for sTiAlV (S(a)=0.09±0.01), PEEK (S(a)=0.43±0.07), and rTiAlV (S(a)=1.81±0.51) varied, substrates had similar contact angles, indicating comparable wettability. Cell morphology differed depending on the surface. Cells cultured on Ti6Al4V had lower cell number and increased alkaline phosphatase specific activity, osteocalcin, BMP2, BMP4, and BMP7 levels in comparison to PEEK. In particular, roughness significantly increased the mRNA levels of BMP2 and BMP4 and secreted levels of BMP4.
  
  
  CONCLUSIONS
  These data demonstrate that rTiAlV substrates increase osteoblast maturation and produce an osteogenic environment that contains BMP2, BMP4, and BMP7. The results show that modifying surface structure is sufficient to create an osteogenic environment without addition of exogenous factors, which may induce better and faster bone during interbody fusion.
authors.affiliation: Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University, Georgia Institute of Technology, Atlanta, GA 30332-0363, USA.
authors.forename: Rene
authors.initials: R
authors.lastname: Olivares-Navarrete
authors.forename: Rolando A
authors.initials: RA
authors.lastname: Gittens
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Schneider
authors.forename: Sharon L
authors.initials: SL
authors.lastname: Hyzy
authors.forename: David A
authors.initials: DA
authors.lastname: Haithcock
authors.forename: Peter F
authors.initials: PF
authors.lastname: Ullrich
authors.forename: Zvi
authors.initials: Z
authors.lastname: Schwartz
authors.forename: Barbara D
authors.initials: BD
authors.lastname: Boyan
mesh_terms: D000497:Alloys; D001577:Benzophenones; D001672:Biocompatible Materials / Q000494:pharmacology; D019485:Bone Morphogenetic Proteins / Q000096:biosynthesis*; D018929:Cell Culture Techniques / Q000379:methods; D002454:Cell Differentiation / Q000502:physiology; D002460:Cell Line; D006801:Humans; D007659:Ketones / Q000737:chemistry / Q000494:pharmacology*; D018613:Microscopy, Confocal; D008855:Microscopy, Electron, Scanning; D010006:Osteoblasts / Q000166:cytology* / Q000378:metabolism*; D010641:Phenotype; D011092:Polyethylene Glycols / Q000737:chemistry / Q000494:pharmacology*; D011108:Polymers; D060888:Real-Time Polymerase Chain Reaction; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D000497:Alloys; D001577:Benzophenones; D001672:Biocompatible Materials; D019485:Bone Morphogenetic Proteins; D007659:Ketones; D011108:Polymers; C031462:titanium alloy (TiAl6V4); C063834:polyetheretherketone; D011092:Polyethylene Glycols; D014025:Titanium