Laser-Modified Surface Enhances Osseointegration and Biomechanical Anchorage of Commercially Pure Titanium Implants for Bone-Anchored Hearing Systems

Furqan A Shah; Martin L Johansson; Omar Omar; Hanna Simonsson; Anders Palmquist; Peter Thomsen

doi:10.1371/journal.pone.0157504

Laser-Modified Surface Enhances Osseointegration and Biomechanical Anchorage of Commercially Pure Titanium Implants for Bone-Anchored Hearing Systems

PLoS One. 2016 Jun 14;11(6):e0157504. doi: 10.1371/journal.pone.0157504. eCollection 2016.

Authors

Furqan A Shah^{1

2}, Martin L Johansson^{1

2

3}, Omar Omar^{1

2}, Hanna Simonsson^{2

3}, Anders Palmquist^{1

2}, Peter Thomsen^{1

2}

Affiliations

¹ Department of Biomaterials, Institute of Clinical Sciences, Sahlgrenska Academy at University of Gothenburg, Göteborg, Sweden.
² BIOMATCELL VINN Excellence Center of Biomaterials and Cell Therapy, Gothenburg, Sweden.
³ Oticon Medical AB, Askim, Sweden.

Abstract

Osseointegrated implants inserted in the temporal bone are a vital component of bone-anchored hearing systems (BAHS). Despite low implant failure levels, early loading protocols and simplified procedures necessitate the application of implants which promote bone formation, bone bonding and biomechanical stability. Here, screw-shaped, commercially pure titanium implants were selectively laser ablated within the thread valley using an Nd:YAG laser to produce a microtopography with a superimposed nanotexture and a thickened surface oxide layer. State-of-the-art machined implants served as controls. After eight weeks' implantation in rabbit tibiae, resonance frequency analysis (RFA) values increased from insertion to retrieval for both implant types, while removal torque (RTQ) measurements showed 153% higher biomechanical anchorage of the laser-modified implants. Comparably high bone area (BA) and bone-implant contact (BIC) were recorded for both implant types but with distinctly different failure patterns following biomechanical testing. Fracture lines appeared within the bone ~30-50 μm from the laser-modified surface, while separation occurred at the bone-implant interface for the machined surface. Strong correlations were found between RTQ and BIC and between RFA at retrieval and BA. In the endosteal threads, where all the bone had formed de novo, the extracellular matrix composition, the mineralised bone area and osteocyte densities were comparable for the two types of implant. Using resin cast etching, osteocyte canaliculi were observed directly approaching the laser-modified implant surface. Transmission electron microscopy showed canaliculi in close proximity to the laser-modified surface, in addition to a highly ordered arrangement of collagen fibrils aligned parallel to the implant surface contour. It is concluded that the physico-chemical surface properties of laser-modified surfaces (thicker oxide, micro- and nanoscale texture) promote bone bonding which may be of benefit in situations where large demands are imposed on biomechanically stable interfaces, such as in early loading and in compromised conditions.

MeSH terms

Animals
Biocompatible Materials / chemistry*
Biomechanical Phenomena
Bone-Implant Interface / anatomy & histology
Bone-Implant Interface / growth & development*
Cochlear Implants
Female
Hearing Aids*
Implants, Experimental
Lasers
Osseointegration*
Osteocytes / cytology
Osteocytes / ultrastructure
Rabbits
Surface Properties
Temporal Bone / cytology
Temporal Bone / growth & development*
Temporal Bone / ultrastructure
Titanium / chemistry*

Substances

Biocompatible Materials
Titanium

Grants and funding

This study was supported by grants from Oticon Medical AB, the BIOMATCELL VINN Excellence Center of Biomaterials and Cell Therapy, the Västra Götaland Region, the Swedish Research Council (grant K2015-52X-09495-28-4), the ALF/LUA Research Grant “Optimization of osseointegration for treatment of transfemoral amputees” (ALFGBG-448851), the IngaBritt and Arne Lundberg Foundation, the Hjalmar Svensson Foundation, and the Vilhelm and Martina Lundgren Vetenskapsfond. FAS holds a PhD position financed by the Swedish Government Strategic Funding of Materials Science Area of Advance, provided to Chalmers and Department of Biomaterials, University of Gothenburg. MLJ holds an industrial PhD position financed by Oticon Medical AB. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The funder (Oticon Medical AB) provided support in the form of salaries for MLJ and HS, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.