动态聚焦条件对脉冲CO2激光骨硬组织消融的影响

激光辐照生物组织消融过程中由于工作距离的变化引起的离焦现象对消融效果具有重要影响。以新鲜离体牛胫骨组织为实验样品,置于一维电动平移台上,移动速度为5.5mm/s;脉冲CO2激光(10.64μm)平行光束经一可移动聚焦透镜后垂直辐照样品表面,光斑直径为200μm。实验时通过移动聚焦透镜位置改变焦点位置,实现消融过程动态聚焦。激光辐照功率为6W,脉冲频率为420Hz,水喷雾协同工作,喷水速度为5.5mL/min。辐照后,利用扫描电镜观察消融凹槽微结构,用光学相干层析成像(OCT)技术测量消融凹槽深度。结果表明,动态聚焦条件可显著提高消融速率,消融深度随等效脉冲数增加而增加,消融速率呈减小趋势;在动态聚焦条件下获得的消融凹槽的表面形貌和微结构较离焦条件下更不规则。

Influence of Dynamic Focusing Conditions on Bone Hard Tissue Ablation with Pulsed CO2 Laser

Defocusing phenomenon induced by the change of the work distance in the irradiating process of biological tissue has an important influence on the effect of hard tissue ablation with pulsed lasers.Fresh bovine shank bone in vitro used in the experiment is put on a computer-controlled motorized linear drive stage and is moved repeatedly with the speed of 5.5 mm/s.A parallel beam of pulsed CO2 laser passes through a mobile focus lens and irradiates the sample surface vertically.Through changing the position of focusing lens,the focus position is altered and dynamic focusing is realized.The laser wavelength is 10.64 μm,the power is 6 W,the pulse repetition rate is 420 Hz,the spot size is about 200 μm,and the water spraying with a speed of 5.5 mL/min is used.The surface morphology and microstructure of ablation grooves are examined by scanning electron microscope(SEM).The crater depth is measured with optical coherence tomography(OCT).The results show that compared with defocusing condition,dynamic focusing condition can enhance the ablation rate and produce more irregular surface morphology and microstructure.The ablation depth increases with the increase of equivalent pulse number and the ablation rate decreases.