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Research Papers

Fabrication and Characterization of Surface Texture for Bone Ingrowth by Sequential Laser Peening Biodegradable Orthopedic Magnesium-Calcium Implants

[+] Author and Article Information
M. P. Sealy

Department of Mechanical Engineering, The University of Alabama, Tuscaloosa, AL 35487

Y. B. Guo1

Department of Mechanical Engineering, The University of Alabama, Tuscaloosa, AL 35487yguo@eng.ua.edu

1

Corresponding author.

J. Med. Devices 5(1), 011003 (Feb 03, 2011) (9 pages) doi:10.1115/1.4003117 History: Received August 05, 2010; Revised November 03, 2010; Published February 03, 2011; Online February 03, 2011

Biodegradable magnesium-calcium (Mg–Ca) implants have the ability to gradually dissolve and absorb into the human body after implantation. The similar mechanical properties to bone indicate that Mg–Ca is an ideal implant material to minimize the negative effects of stress shielding. Furthermore, using a biodegradable Mg–Ca implant prevents the need for a secondary removal surgery that commonly occurs with permanent metallic implants. The critical issue that hinders the application of Mg–Ca implants is the poor corrosion resistance to human body fluids. The corrosion process adversely affects bone ingrowth that is critical for recovery. Therefore, sequential laser shock peening (LSP) of a biodegradable Mg–Ca alloy was initiated to create a superior surface topography for improving implant performance. LSP is an innovative treatment to fabricate functional patterns on the surface of an implant. A patterned surface promotes bone ingrowth by providing a rough surface texture. Also, LSP imparts deep compressive residual stresses below the surface, which could potentially slow corrosion rates. Unique surface topographies were fabricated by changing the laser power and peening overlap ratio. The resultant effects on surface topography were investigated. Sequential peening at higher overlap ratios (75%) was found to reduce the tensile pileup region by over 40% as well as compress the overall surface by as much as 35μm.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic of stress shielding in an orthopedic implant

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Figure 2

Schematic of microdent fabrication using LSP

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Figure 3

Polished surface of Mg–Ca sample

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Figure 4

Experimental setup for vertical LSP

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Figure 5

Diameter and depth of a single dent produced by LSP on Mg–Ca at various powers

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Figure 6

Schematic depicting feed and overlap for an array of dents

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Figure 7

Peening pattern at three overlap ratios

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Figure 8

Geometry of the sample holder used to lock and orient the sample

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Figure 9

Surface topography patterned at 3 W and 8 W with 25%, 50%, and 75% overlap ratios

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Figure 10

Comparison of experimental peening pattern predicted by the theoretical model at a laser power of 3 W

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Figure 11

Comparison of experimental peening pattern to the predicted theoretical model at a laser power of 8 W

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Figure 12

Aspect ratio for a dent produced by LSP at (a) 3 W and (b) 8 W

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Figure 13

Surface topography of polished Mg–Ca sample before peening

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Figure 14

Surface topography of Mg–Ca peened at 3 W and 8 W with 25% overlap

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Figure 15

Surface topography of Mg–Ca peened at 3 W and 8 W with 50% overlap

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Figure 16

Surface topography of Mg–Ca peened at 3 W and 8 W with 75% overlap

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Figure 17

Surface roughness (Ra) for Mg–Ca peened at 3 W and 8 W with 25%, 50%, and 75% overlaps

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Figure 18

Average peak height (Rp) for Mg–Ca peened at 3 W and 8 W with 25%, 50%, and 75% overlaps

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Figure 19

Average valley depth (Rp) for Mg–Ca peened at 3 W and 8 W with 25%, 50%, and 75% overlaps

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Figure 20

Mean amplitude (Rc) for Mg–Ca peened at 3 W and 8 W with 25%, 50%, and 75% overlaps

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