title: Calcium phosphate coating formed in infusion fluid mixture to enhance fixation strength of titanium screws.
abstract: A novel technique was developed to coat a calcium phosphate (CaP) layer on titanium screws with a titanium oxide surface layer, using infusion fluids officially approved for clinical use. A calcium-containing solution, a phosphate-containing solution, and a sodium bicarbonate solution prepared from the infusion fluids were mixed at a Ca/P molar ratio of 2.0. Each screw was immersed in 10 mL of the resulting mixture at 37 degrees C for 2 days. A low-crystalline apatite layer (Ca/P molar ratio = 1.681 +/- 0.038) was formed on the screws. The layer consisted of a few 100 nm diameter particles fixed on the screw surface. In animal experiments, the screws were percutaneously implanted in both proximal tibial metaphyses of rabbits. The insertion torque was not significantly different between the CaP-coated screws (0.132 +/- 0.002 Nm, n = 10) and uncoated screws (0.140 +/- 0.002 Nm, n = 10) (p = 0.5785). After the insertion torque test, the apatite layer remained on the surface of the screws, which means that the apatite layer survived the friction of screw insertion. The extraction torque of the screws in the CaP-coated group (0.239 +/- 0.066 Nm, n = 19) was significantly higher (by 29.9%) than that in the uncoated group (0.184 +/- 0.062 Nm, n = 18) 4 weeks after the operations (p = 0.0132). Histologically, a larger amount of new bone formation was observed around the CaP-coated screws than that around the uncoated screws. Even after the removal of the screw, the CaP layer remained on the screw at the site where soft tissues were attached. The coating technique with the use of the infusion fluids is an effective method of improving bone-screw interface strength.
authors.affiliation: Department of Orthopaedic Surgery, Institute of Clinical Medicine, Graduate School of Comprehensive Human Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, Japan. mutsu-hiro@ace.odn.ne.jp
authors.forename: Hirotaka
authors.initials: H
authors.lastname: Mutsuzaki
authors.forename: Atsuo
authors.initials: A
authors.lastname: Ito
authors.forename: Masataka
authors.initials: M
authors.lastname: Sakane
authors.forename: Yu
authors.initials: Y
authors.lastname: Sogo
authors.forename: Ayako
authors.initials: A
authors.lastname: Oyane
authors.forename: Yuko
authors.initials: Y
authors.lastname: Ebihara
authors.forename: Noboru
authors.initials: N
authors.lastname: Ichinose
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Ochiai
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001863:Bone Screws; D002130:Calcium Phosphates; D020099:Coated Materials, Biocompatible; D016267:External Fixators; D008297:Male; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D011817:Rabbits; D012996:Solutions; D013499:Surface Properties; D014025:Titanium
chemical_list: D002130:Calcium Phosphates; D020099:Coated Materials, Biocompatible; D012996:Solutions; C009495:titanium dioxide; C020243:calcium phosphate; D014025:Titanium