脉冲CO_(2)激光诱导液体微射流动力学特性及应用研究

Dynamic Characteristics and Application of Pulsed CO_(2)Laser Induced Liquid Micro⁃Jet

近年来,激光诱导液体微射流技术以其热损伤小、精度高、微创等优点,在无针注射、神经外科等医学领域得到了广泛应用。本团队设计了以10.6μm CO_(2)激光器为激光光源的微射流装置,并探究了CO_(2)激光诱导液体微射流特性与激光强度、激光焦点位置与硒化锌镜片距离D的关系。采用不同弹性模量的琼脂糖凝胶模型作为人体模拟组织,评估了10.6μm CO_(2)激光诱导液体微射流在组织选择性切割方面的可行性。结果显示,射流流速与激光强度、D成正相关,且微射流对不同弹性模量的生物组织具有高度选择性,表明其在精准去除肿瘤且保留高弹性模量组织的应用方面具有一定的潜在价值。

Objective Currently,liquid micro-jet systems induced by pulsed lasers have been applied in surgery,which not only has the anatomical function of the traditional scalpel,but also has the characteristics of intact preservation of blood vessels.It has been used in the treatment of various organs and has rapidly developed.The laser sources of laser-induced micro‑jet devices are mainly Er∶YAG,Nd∶YAG,Ho∶YAG and near-infrared(NIR)semiconductor lasers.Most jet emitters use rubber cortices for the energy transfer.However,the efficiency of the jet generated by these devices is low.According to the latest research on a 10.6μm CO_(2)laser,the wavelength of the laser is close to the absorption wavelength of water,and the laser can be coupled with a zinc selenide lens,which has better performance for generating micro-jets and greatly improves the probability of jet generation.However,there are no reports on the liquid micro‑jet device induced by this wavelength laser,and the influencing factors of the micro‑jet generated by this wavelength laser have rarely been studied.Therefore,we designed a 10.6μm CO_(2)laser-induced liquid micro-jet device,elaborated the mechanism of laser-induced micro‑jet generation,explored the influence of liquid parameters and light dose parameters on laserinduced micro‑jet generation,and evaluated the feasibility of the device technology for tissue-selective cutting and other aspects.Methods In this experiment,a 10.6μm CO_(2)laser was used as the induction device for the laser-induced jet(laser power P was set to 18‒25 W).Quartz glass with a length of 2 cm,cross-section diameter of 1 cm,and conical angle of 14°at the lower end was used as the jet generation chamber,and the laser beam was focused to a point in the generation chamber through a ZnSe focusing lens.In addition,in this experiment,the distance D between the laser focus and zinc selenide lens and the distance S between the nozzle and model were varied from 3 mm to 12 mm.A high-speed camera was combined with a prime lens and a digital microscope to carry out systematic research on the generation of laser-induced jets,interaction with biomimetic biological tissue,penetration depth and other three-dimensional spatial changes,and corresponding ultrafast process.Results and Discussions In the experiment,we observed four different jet shapes:column(CL),mushroom(MS),needle(AC),and turbulent(TS)[Fig.3(a)‒(d)].The turbulent and needle jet velocities can reach 44.17 and 53.31 m/s,respectively[Fig.4(a)].The experimental results show that the diameter of the jet tip is typically in the range of 40‒100μm,and the diameter of the thicker part is usually 600‒750μm[Fig.4(b)].When D is fixed at 3 mm and the incident laser power P(18‒25 W)is changed,the jet velocity increases monotonically with increasing laser power.The jet velocity can be fine-tuned from 10 to 50 m/s by adjusting only the incident laser power[Fig.5(a)].However,when the laser power is fixed(P=20 W)and D=3‒7 mm,the jet velocity increases monotonically in a nonlinear form with an increase in the distance D[Fig.5(b)],and when S is 4 mm,the depth of the hole formed is the largest[Fig.6(c)].In addition,under the same conditions,compared with direct laser irradiation,the micro‑jet cutting accuracy is as high as 50μm.The effect of the jet on the myocardial tissue model is more evident than that on the skin tissue model,and the radius and depth of the generated holes are smaller than those of the skin tissue model[Fig.6(e)].Conclusions In this study,a new laser-induced micro-jet device that uses a 10.6μm CO_(2)laser is designed for the first time.We have studied the generation of a 10.6μm CO_(2)laser-induced liquid micro‑jet and the influence of laser power,the distance D between the laser focus and zinc selenide lens,and the distance S between the nozzle and model on the jet.The experimental results show that the jet shape is related to the cavitation bubble pulsation process,and the increase in laser power or distance D can increase the velocity of the micro-jet,and the jet velocity can be effectively adjusted by laser power,distance D,and so on.In addition,the study compares the acting effect of micro-jet on agarose gel models with different elastic moduli,it is confirmed that laser-induced liquid micro‑jet can cut biological tissue models with different elastic moduli to different degrees,which can achieve the selective cutting of biological tissues with high cutting accuracy and does not damage surrounding tissues.The results provide a basis for promoting the clinical application of this technology.Finally,this research found that the 10.6μm CO_(2)laser-induced liquid micro‑jet(especially turbulent and needle-shaped jets)is obviously unstable,and further optimization of the jet velocity control mechanism is needed.