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A Bezier Profiled Horn for Reducing Penetration Force with Applications in Surgery

This research focuses on the development of a planar Bezier horn that reduces the penetration force in surgical procedures. The aim is to decrease tissue necrosis, increase precision in tissue cutting, and reduce patient strain and pain. The design utilizes a Bezier curve-based geometry to optimize the horn profile, resulting in higher displacement amplification and lower stress concentration compared to traditional horns.

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A Bezier Profiled Horn for Reducing Penetration Force with Applications in Surgery

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  1. A Bezier Profiled Horn for Reducing Penetration Force with Applications in Surgery Dung-An WANG and Hai-Dang Tam NGUYEN Graduate Institute ofPrecision Engineering, National Chung Hsing University Taiwan, ROC

  2. Motivation • Reduced strain for patient’s pain relief • Increased precision of cutting tissue • Reduce necrosis of patient’s tissue Liao et al., 2012.

  3. Market for hard tissue removal • Millennium Research Group, 2010

  4. Industrial and medical interests • Decrease cutting force (penetration force) • Decrease thermal effects: temperature may depend on • Ultrasonic frequency • Penetration force • Cutting speed • Geometry of cutting blade

  5. Aims • Design of an ultrasonic horn with a new profile • To increase in tool-tip vibration amplitude, allowing a significant amount of material to be removed • To decrease the penetration force, reducing tissue necrosis

  6. Design • Working frequency, 28.0 kHz

  7. Bézier profile • Parametric curve based geometry is flexible enough to give a much better control over the profile of horns for design purpose. • The profile of the horn is based on a cubic Bézier curve. • Four-point Bézier polygon Q0 Q1 Q2 Q3

  8. Parametric cubic Bézier curve

  9. Design Specify W120mm, W2=1.5mm, L=94mm. Thickness 1.2 mm f= 28.0 kHz • The profile of the horn is optimized by allowing points Q1 and Q2 to move in the design space

  10. Design • Finite element analysis to obtain f0 and Mof the horn • Material: SS41

  11. Optimized Bézier horn

  12. Comparison • Catenoidal horn: same back and front end widths and length as those of the proposed horn. • Stepped and linear horn:same back and front end widths of the proposed horn. The length of the stepped/linear horn is calculated to have the same working frequency of 28.0 kHz as the proposed horn.

  13. Comparison • Normalized displacements along the normalized length of the horns based on finite element computations

  14. Comparison • The stepped horn: highest displacement amplification, but high stress concentration at the step discontinuity

  15. Experiments • A Bézier horn and a catenoidal horn are fabricated by a lasercutting process from a stainless steel SS41

  16. Experiments • Investigate the effects of ultrasound and horn types on the penetration force of ultrasonic cutting

  17. Specimens • A tissue stimulant, raw potato, as representative for soft material • A polymethylmethacrylate (PMMA) material as representative for hard material • Specimen: 70 mm x 35 mm x 5 mm

  18. Results • Penetration speed 0.25 mm/s • Five repeated trials • Penetration force by the Bézier horn is 75% of that of the catenoidal horn

  19. Results • Penetration force as a function of penetration speed • Use Bezier horn • Penetration depths: the tissue stimulant 2 mm, PMMA material 3 mm Tissue stimulant PMMA material

  20. Mechanics • Reduced penetration force is an effective measure for increasing the critical cutting depth in ultrasonic cutting, and below the critical cutting depth, material can be removed plastically (Zhou et al., 2002). • When the plastic deformation is the predominant mode of deformation, a very smooth and fine surface can be obtained.

  21. Conclusions • A planar Bézier horn with high displacement amplification and low stress concentration is developed. • The displacement amplification of the Bézier horn is 30% higher than that of the traditional catenoidal horn with the same length and end surface widths • The penetration force by the Bézier horn is 75% of that by the catenoidal horn with a penetration speed of 0.25 mm/s during cutting of the tissue stimulant.

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