The Effects of Laser Marking and Symbol Etching on the Fatigue Life of Medical Devices

Abstract

This paper examines the question;“ does permanent laser marking affect the mechanical performance of a metallic medical component?” The literature review revealed the surprising fact that very little has been presented or studied even though intuition suggests that its effect could be detrimental to a component's fatigue life. A brief investigation of laser marking suggests that defects greater than 25 μm are possible. A theoretical investigation further suggests that this is unlikely to cause issues with relation to fast fracture but is highly likely to cause fatigue life issues. An experimental investigation confirmed that laser marking reduced the fatigue life of a component. This combination of lines of evidence suggests, strongly, that positioning of laser marking is highly critical and should not be left to chance. It is further suggested that medical device designers, especially those related to orthopaedic implants, should consider the position of laser marking in the design process. They should ensure that it is in an area of low stress amplitude. They should also ensure that they investigate worst-case scenarios when considering the stress environment; this, however, may not be straightforward.

Laser Marking of Spine Rods Is Strongly Associated With Risk of Clinical Rod Failure

“…Laser marking is something that has been theoretically suggested in a limited study to change the life expectancy of devices in vivo. 12 Rod laser marking in this study clearly changed the surface morphology and thus their fatigue properties (Figures 5 and 6). 14 The titanium rod subsurface microstructure also changed because of surface and subsurface heating (Figure 6) that melted the alloy for marking.…”

“…In addition, laser marking creates microscopic grooves or notches that can act as stress concentrators leading to early initial fracturing during cyclic loading. 12 Continuing with Ti6Al4V as an example, another intrinsic property of the alloy that can result in early fracture is what is called the Bauschinger effect. 11 The crystal structure of titanium is such that when the alloy is bent without proper heat treatment, its strength in bending the opposite direction is markedly diminished.…”

Laser engravings as reason for mechanical failure of titanium-alloyed total hip stems

“…Laser engraving is the most commercially available mean of permanent marking for medical devices [16]. The procedure works by focusing energy from a heat generated beam onto the designated surface to be marked, in the process altering the metal alloy surface [17].…”

“…The high concentration of oxygen under the laser engraving from the EDX analysis presents evidence for the occurrence of oxidation in the TMZF alloy. The associated melting of the titanium alloy through means of laser etching promotes the increased oxygen uptake by the material leading to a reduction in the fatigue strength, and hence making it brittle [14,16]. The local stress and cyclic loading of forces at the brittle region induced fatigue in the component, which resulted in the fracture of the hip stem.…”

FPCB magnetic micromirror for laser marking/engraving systems

“…Hence, they can be focused over a long distance with minimal divergence to a small spot. Owing to the very small spot size, majority of the light energy is converted into heat energy which is responsible for the surface modifications on the target [1]. Based on the type of target material used the same machine can be used for marking, engraving and cutting operations [2].…”