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Formation of osseointegrating (bone integrating) surfaces on titanium by laser irradiation
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. Laser Nova AB, Östersund, Sweden.ORCID iD: 0000-0002-7706-6994
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
Department of Biomaterials, University of Gothenburg, Gothenburg, Sweden.
Department of Orthopaedic Surgery, University of California, San Francisco, CA, USA.
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2019 (English)In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 31, no 2, article id 022508Article in journal (Refereed) Published
Abstract [en]

Pulsed lasers can be used to modify the surface of medical implants in order to accelerate bone growth (osseointegration). A surface covered in attached droplets with diameters between 1 and 20 μm is a beneficial surface for rapid osseointegration. This paper presents the results of an experimental program in which a broad range of laser parameters and different atmospheres were used to create different surface textures on titanium substrates, including the desired "attached droplet" topology. The resulting surfaces were analyzed by scanning electron microscopy and micro-computer tomography. The paper explains how different types of surfaces are created by the laser-material interaction under different conditions and focus characteristics. It is shown that optimization of the laser parameters results in a robust process, which produces a surface that is fundamentally different from those created by nonlaser methods.

Place, publisher, year, edition, pages
Laser Institute of America , 2019. Vol. 31, no 2, article id 022508
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-73825DOI: 10.2351/1.5096075Scopus ID: 2-s2.0-85064218607OAI: oai:DiVA.org:ltu-73825DiVA, id: diva2:1313352
Note

Validerad;2019;Nivå 2;2019-05-03 (johcin)

Available from: 2019-05-03 Created: 2019-05-03 Last updated: 2019-06-03Bibliographically approved
In thesis
1. Analysis and Monitoring of Laser Welding and Surface Texturing
Open this publication in new window or tab >>Analysis and Monitoring of Laser Welding and Surface Texturing
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Analys och övervakning av lasersvetsning samt ytstrukturering
Abstract [en]

This thesis can be conveniently divided into three sections as follows;

Part I. Monitoring of laser welding 

In laser materials processing there has always been a need for suitable methods to supervise and monitor the processes on-line, to ensure correct production quality or to trigger alarms when failures are detected. Numerous investigations have been made in this field, including experimental and theoretical work. It is common practice in this field to monitor surface temperature, plasma radiation and back-reflected laser light, coaxially with the laser beam.  Traditionally, the monitoring systems involved carry out no statistical analysis of the signals received – they merely involve thresholds.

The first two papers in this thesis look at the feedback collected during laser welding using a co-axial setup from a Digital Signal Processing point of view and also uses high speed video photography to correlate signal perturbations with process anomalies. Digital signal processing techniques such as Kalman filtering, Principal Component Analysis and Cluster Analysis have been applied to on-line measurement data and have generated new ways to describe laser welding behaviour using parameters such as reflected pulse shape. The limitations of commercially available welding supervision systems have been studied and design suggestions for the next generation of on-line weld monitoring equipment have been formulated.

Having progressed from thin section welding with continuous wave lasers to pulsed laser welding, the thesis then moves on to pulsed laser surface melting.

Part II Analysis of surface texturing of titanium.

The second part of the thesis concentrates on laser structuring of titanium surfaces for medical implants. The two papers in this section present an analysis of the laser-material interactions which create surfaces suitable for osseointegration (bone attachment). The work concentrates on a commercially available surface used for screw implants in dentistry; BioHelix™. This surface is generated by an intense bombardment of laser pulses and the surface is thus disrupted during solidification. The formation of various levels and types of roughness are analysed and it is noted that laser generated rough surfaces are fundamentally different from those with a mechanically produced roughness. One key point is that laser generated rough surfaces can include overhanging features. This finding lead to the research carried out in part III of the thesis.

Part III. Analysis and classification of laser generated surfaces.

The final section of the thesis presents research which uses statistical techniques to identify whether or not a roughened surface includes overhanging features. The presence or otherwise of such features is important because they can affect the wettability of surfaces and thus their suitability for implant surfaces, adhesive bonding and lubrication etc. Micro Computer Tomography was used to generate a typical cross section of the surface under investigation. At equally spaced positions the profile of this cross section is then allocated vectors which are normal to the profile at each point. The angles of the vectors can then be analyzed to reveal the presence or otherwise of overhanging features. The presence of overhangs on the material surface is indicated by the existence of normal vectors with angles that exceed 180°. The papers in this section also investigate possibilities and limitations of using statistical methods in conjunction with Micro Computer Tomography.

The papers have in common processing of data for laser materials processing, by advanced methods to identify and extract essential information from the processes and the resulting material properties.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2019
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords
Laser welding, monitoring, Signal processing, laser texturing, texture analysis
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-74145 (URN)978-91-7790-404-5 (ISBN)978-91-7790-405-2 (ISBN)
Public defence
2019-10-15, E632 - Studion, Luleå tekniska universitet, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2019-06-04 Created: 2019-06-03 Last updated: 2019-09-18Bibliographically approved

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Olsson, RickardPowell, JohnFrostevarg, JanKaplan, Alexander

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