Cavitation Effect Induced By Pulsed Ho:YAG Laser Under Water And Its Impact On Bone Hard-tissue Ablation

Now laser induce hard tissue ablation facing two major problems, reduce thermal damage and improve ablation efficiency. Different studies have presented that laser-induced ablation effects of hard tissue can be augmented by adding water; cavitation effect plays an important role in mediating ablation. However, the related mechanism has not yet been explained clearly. In this paper, the influence of water depth and ink solution on dynamic characteristics of bubble and its effect on bovine femur ablation with pulsed HO:YAG laser (λ=2.08 μm) were studied by high speed camera.Firstly, the composition, structure and related properties of bone hard tissue were introduced, mechanism of the laser directly ablation and join liquid hard tissue ablation were summarized. The formation, pulsation and collapse of the laser bubble and the influence factors of bubble pulsation characteristics are expound.Secondly, the dynamic process of laser-water interaction, including formation, expansion and subsequent collapse of bubble, was recorded by high-speed camera. Period, maximum longitudinal length and transverse width versus volume of the bubble as a function of water depth under different radiant energy were obtained.Thirdly, the dynamic process of bubble generated with pulsed Ho:YAG laser in different ink solution was monitored by high-speed camera. The maximum longitudinal length and transverse width, volume of bubble are all extend with radiant energy increasing; In contrast to this, cavitation bubble decrease monotonically with absorption coefficient increasing.Lastly, different irradiation conditions (in the air, different water depth and ink solution) on bovine femur ablation with Ho:YAG laser were investigated by high speed camera. Morphological changes of bovine femur ablated crater assessed with stereomicroscope and OCT system. There is a critical water depth for a given radiant exposure at which the ablation rate and efficiency can be maximized and finest cut appeared including regular shape, smooth surface and thermal injury disappeared.