title: 3D printed Ti6Al4V implant surface promotes bone maturation and retains a higher density of less aged osteocytes at the bone-implant interface.
abstract: For load-bearing orthopaedic applications, metal implants having an interconnected pore structure exhibit the potential to facilitate bone ingrowth and the possibility for reducing the stiffness mismatch between the implant and bone, thus eliminating stress-shielding effects. 3D printed solid and macro-porous Ti6Al4V implants were evaluated after six-months healing in adult sheep femora. The ultrastructural composition of the bone-implant interface was investigated using Raman spectroscopy and electron microscopy, in a correlative manner. The mineral crystallinity and the mineral-to-matrix ratios of the interfacial tissue and the native bone were found to be similar. However, lower Ca/P ratios, lower carbonate content, but higher proline, phenylalanine and tyrosine levels indicated that the interfacial tissue remained less mature. Bone healing was more advanced at the porous implant surface (vs. the solid implant surface) based on the interfacial tissue ν1 CO3(2-)/ν2 PO4(3-) ratio, phenylalanine and tyrosine levels approaching those of the native bone. The mechanosensing infrastructure in bone, the osteocyte lacuno-canalicular network, retained ∼40% more canaliculi per osteocyte lacuna, i.e., a 'less aged' morphology at the interface. The osteocyte density per mineralised surface area was ∼36-71% higher at the interface after extended healing periods.
  
  
  CONCLUSIONS
  In osseointegration research, the success of an implant surface or design is commonly determined by quantifying the amount of new bone, rather than its maturation, composition and structure. This work describes a novel correlative methodology to investigate the ultrastructure and composition of bone formed around and within 3D printed Ti6Al4V implants having an interconnected open-pore structure. Raman spectroscopy demonstrates that the molecular composition of the interfacial tissue at different implant surfaces may vary, suggesting differences in the extent to which bone maturation occurs even after long-term healing. Bone maturation corresponded well with the structural parameters associated with remodelling kinetics, for example, the osteocyte density and the average number of canaliculi per osteocyte lacuna.
authors.affiliation: Department of Biomaterials, Institute of Clinical Sciences, Sahlgrenska Academy at University of Gothenburg, Göteborg, Sweden; BIOMATCELL VINN Excellence Center of Biomaterials and Cell Therapy, Göteborg, Sweden. Electronic address: furqan.ali.shah@biomaterials.gu.se.
authors.forename: Furqan A
authors.initials: FA
authors.lastname: Shah
authors.affiliation: Arcam AB, Mölndal, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Snis
authors.affiliation: Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
authors.forename: Aleksandar
authors.initials: A
authors.lastname: Matic
authors.affiliation: Department of Biomaterials, Institute of Clinical Sciences, Sahlgrenska Academy at University of Gothenburg, Göteborg, Sweden; BIOMATCELL VINN Excellence Center of Biomaterials and Cell Therapy, Göteborg, Sweden.
authors.forename: Peter
authors.initials: P
authors.lastname: Thomsen
authors.affiliation: Department of Biomaterials, Institute of Clinical Sciences, Sahlgrenska Academy at University of Gothenburg, Göteborg, Sweden; BIOMATCELL VINN Excellence Center of Biomaterials and Cell Therapy, Göteborg, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Palmquist
mesh_terms: D000497:Alloys; D000818:Animals; D001861:Bone Regeneration; D018786:Bone Substitutes / Q000737:chemistry / Q000494:pharmacology; D000069343:Bone-Implant Interface; D016922:Cellular Senescence; D020007:Implants, Experimental; D010011:Osteocytes / Q000378:metabolism* / Q000473:pathology; D066330:Printing, Three-Dimensional; D012756:Sheep; D014025:Titanium / Q000737:chemistry / Q000494:pharmacology
chemical_list: D000497:Alloys; D018786:Bone Substitutes; C031462:titanium alloy (TiAl6V4); D014025:Titanium
keywords: 3D printing; Electron microscopy; Osseointegration; Osteocyte; Raman spectroscopy; Ti6Al4V