Experimental Study On The Thermal Properties Of Cortical Bone Cut By Sodium Chloride Grain Jet

The outermost layer of biological bone is composed of high-strength and hard cortical bone,which bears most of the body’s load.Cutting and correcting bone tissue is the most challenging part of orthopedic surgery.Due to the poor thermal conductivity of the biologic bone material,thermal damage to the bone tissue occurs due to the accumulation of cutting heat,which seriously affects the self-healing ability of the bone tissue.In this paper,the only cold processing tool currently available-abrasive water jet technology-was used to conduct cutting experiments on cortical bone,focusing on issues related to the thermal properties of its cutting process.Biocompatible sodium chloride crystalline particles were used as abrasives,to avoid damage to biological tissue function caused by conventional mineral abrasives.The study results have important implications for the exploration of future applications of abrasive water jet technology in the medical field.From the basic concept of this article,a combination of non-contact thermography and contact thermocouple temperature measurement was used to study the temperature field during the cutting of cortical bone material by abrasive water jet and to analyze the thermal damage in the processing area.Firstly,the cutting mechanism of the abrasive water jet and the source of heat during the cutting process were analyzed to clarify that the primary sources of heat are the heat generated by the removal of material and the convective heat transfer of the high-speed jet beam.Secondly,the experimental system was built,and the test samples were prepared.Since the heat transfer process is affected by the anisotropy of the biological bone material,thermal conductivity measurements were performed in three directions parallel,cross,and perpendicular to the bone unit in this paper.It can be seen that: under the relatively determined conditions of environmental factors such as temperature,humidity,and the properties of the bone material dominated by tissue moisture,the average value of thermal conductivity measurements for cortical bone in the parallel direction was 0.6286 W/（m K）,0.6288 W/（m K）in the cross direction and 0.7257 W/（m K）in the vertical direction;the difference between the thermal conductivity of cortical bone in the cross direction and parallel direction is tiny.The difference between the cutting direction in the parallel and cross direction was negligible in the cutting experiment.Finally,the effect of experimental parameters on the cutting temperature field was studied by keeping the water jet pressure constant and only changing the target distance,nozzle traverse rate,and cutting direction.The following main conclusions were drawn from the analytical study.（1）As the target distance increases,the temperature first decreases and then increases,and the optimal target distance for cutting is 3 mm.when the workpiece length is less than 6 mm,10 mm/min is selected as the nozzle movement rate,the temperature fluctuation is more stable,and the peak temperature does not reach the thermal damage condition threshold;when the workpiece length is greater than 6 mm,20 mm/min is selected as the nozzle movement rate,and the thermal performance of the cutting process is the most excellent.（2）During the water jet cutting of cortical bone with sodium chloride grain abrasive,the thermal conductivity of the cutting direction is better in the vertical direction than in the parallel direction under the same target distance and nozzle’s traverse rate parameters.（3）The temperature trends obtained using contact thermocouple and non-contact thermal imager measurements are similar.While clinical surgery requires monitoring of the cutting process and assessment of the thermal performance of the cutting area,thermocouple measurements do not reflect the temperature change of the entire cutting area,and thermal imager measurements achieve a good monitoring effect.Therefore,in monitoring the thermal performance of water jet cutting biological bone,an infrared thermal imager is best for data acquisition.