title: Using eddy currents for noninvasive in vivo pH monitoring for bone tissue engineering.
abstract: OBJECTIVE
  The metabolic processes that regulate bone healing and bone induction in tissue engineering models are not fully understood. Eddy current excitation is widely used in technical approaches and in the food industry. The aim of this study was to establish eddy current excitation for monitoring metabolic processes during heterotopic osteoinduction in vivo.
  
  
  METHODS
  Hydroxyapatite scaffolds were implanted into the musculus latissimus dorsi of six rats. Bone morphogenetic protein 2 (BMP-2) was applied 1 and 2 weeks after implantation. Weekly eddy current excitation measurements were performed. Additionally, invasive pH measurements were obtained from the scaffolds using fiber optic detection devices. Correlations between the eddy current measurements and the metabolic values were calculated.
  
  
  RESULTS
  The eddy current measurements and pH values decreased significantly in the first 2 weeks of the study, followed by a steady increase and stabilization at higher levels towards the end of the study. The measurement curves and statistical evaluations indicated a significant correlation between the resonance frequency values of the eddy current excitation measurements and the observed pH levels (p = 0.0041).
  
  
  CONCLUSIONS
  This innovative technique was capable of noninvasively monitoring metabolic processes in living tissues according to pH values, showing a direct correlation between eddy current excitation and pH in an in vivo tissue engineering model.
authors.affiliation: Department of Oral and Maxillofacial Surgery, Medical University Center Hamburg-Eppendorf, Campus Forschung, Martinistraße 52, 20246, Hamburg, Germany, b.beck-broichsitter@uke.de.
authors.forename: Benedicta E
authors.initials: BE
authors.lastname: Beck-Broichsitter
authors.forename: Frank
authors.initials: F
authors.lastname: Daschner
authors.forename: David W
authors.initials: DW
authors.lastname: Christofzik
authors.forename: Reinhard
authors.initials: R
authors.lastname: Knöchel
authors.forename: Jörg
authors.initials: J
authors.lastname: Wiltfang
authors.forename: Stephan T
authors.initials: ST
authors.lastname: Becker
mesh_terms: D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000502:physiology; D001842:Bone and Bones / Q000502:physiology*; D017886:Durapatite; D004574:Electromagnetic Fields; D006863:Hydrogen-Ion Concentration; D008991:Monitoring, Physiologic; D009999:Ossification, Heterotopic / Q000503:physiopathology*; D051381:Rats; D013223:Statistics as Topic; D023822:Tissue Engineering / Q000379:methods*; D054457:Tissue Scaffolds
chemical_list: D055396:Bone Morphogenetic Protein 2; D017886:Durapatite