Influence of water layer thickness on hard tissue ablation with pulsed CO[sub 2] laser

Abstract

The theory of hard tissue ablation reported for IR lasers is based on a process of thermomechanical interaction, which is explained by the absorption of the radiation in the water component of the tissue. The microexplosion of the water is the cause of tissue fragments being blasted from hard tissue. The aim of this study is to evaluate the influence of the interdependence of water layer thickness and incident radiant exposure on ablation performance. A total of 282 specimens of bovine shank bone were irradiated with a pulse CO(2) laser. Irradiation was carried out in groups: without a water layer and with a static water layer of thickness ranging from 0.2 to 1.2 mm. Each group was subdivided into five subgroups for different radiant exposures ranging from 18 to 84 J/cm(2), respectively. The incision geometry, surface morphology, and microstructure of the cut walls as well as thermal injury were examined as a function of the water layer thickness at different radiant exposures. Our results demonstrate that the additional water layer is actually a mediator of laser-tissue interaction. There exists a critical thickness of water layer for a given radiant exposure, at which the additional water layer plays multiple roles, not only acting as a cleaner to produce a clean cut but also as a coolant to prevent bone heating and reduce thermal injury, but also helping to improve the regularity of the cut shape, smooth the cut surface, and enhance ablation rate and efficiency. The results suggest that desired ablation results depend on optimal selection of both water layer thickness and radiant exposure.

Influence of environmental conditions in bovine bone ablation by ultrafast laser

“…This can be explained by the fact that the amount of ablated tissue per pulse (μm/pulse) is small, it increases two or three times (from ~1 to 2 or 3 μm/pulse) when the fluence increases from ablation threshold (F th ) to high fluence for femtosecond lasers . However, it is reported that at high ablation rates (eg, 300, 80 and 14 um/pulse for Er lasers, Ho:YSGG and Nd:YAG, respectively), the crater edges become irregular and rough . Compared with the cavity edges produced by only air or both water conditions (Figure A,C,D), cavities created by the air flow process showed smoother surfaces (Figure B).…”

“…Advantages of using laser ablation over mechanical cutting include more precise cuts, minimal mechanical stress and thermal collateral damage, the ability to work without physical contact and integration with real‐time optical feedback . Many studies have been carried out to characterize bone ablation using infrared (IR) lasers with long pulse duration (nanoseconds to microseconds), for example, CO 2 ( λ = 9.6 μm), Er:YAG ( λ = 2.94 μm), Ho:YAG ( λ = 2.1 μm) and Nd:YAG ( λ = 1.06 μm) . It was shown that long‐pulse IR laser ablation may cause melting, carbonizing, cracking and fissuring of hard tissue .…”

Influence of static pressure on dynamic characteristics of laser-induced cavitation and hard-tissue ablation under liquid environment

“…The non-contact mode of laser beam offers arbitrary intricate and more precise cut geometry; aseptic effects can be expected by some special laser systems [2][3][4] .As we know that during laser ablation on the surface of hard tissue leads to thermal damage to surrounding tissue 5 . A number of studies presented that the additional water Hight -speed camera applied to target tissue surface not only makes it possible to reduce the thermal stress and prevent damage [6][7][8][9] ,but also serves to increase the ablation rate and efficiency, improve surface morphology [10][11] . Different investigators have performed several methods to find out the influence of additional water on the hard tissue ablation process, the primary mechanism reported for laser-water interaction is cavitation effect which included vapor channel and cavitation bubble 12 .…”

Influence of liquid medium with different absorption and its layer thickness on bovine bone tibia ablation induced by CO2laser

“…Compared to non-spray case, the spray application exhibited no thermal injury by cooling the tissue with water, during the laser irradiation the lager craters due to strong pressure emission of water vaporization 11 . By applying water layer on tissue, the desired ablation result depends on both water layer thickness and incident radiant exposure; the geometry of the crater presented a more regular and clean shapes 12 The application of a perfluorocarbon layer removed lager ablation volume than water layer and dry 13 .…”