Tissue cutting mechanics of dynamic needle insertion
Open Access
- Author:
- Barnett, Andrew Charles
- Graduate Program:
- Mechanical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 04, 2015
- Committee Members:
- Jason Zachary Moore, Dissertation Advisor/Co-Advisor
Jason Zachary Moore, Committee Chair/Co-Chair
Zoubeida Ounaies, Committee Member
Mary I Frecker, Committee Member
Scarlett Rae Miller, Committee Member
Siyang Zheng, Committee Member - Keywords:
- Tissue Cutting
Vibration Cutting
Cutting Geometry
Compliant Geometry - Abstract:
- Needles are commonly used in many medical procedures to sample blood and tissue, inject drugs and anesthetics, and implant radioactive seeds among other uses. The procedures of brachytherapy cancer treatment and tissue biopsy utilize needles to reach precise locations inside the body. However, due to high insertion forces, high accuracy is difficult to achieve. Previous researchers have demonstrated that vibration can reduce these high needle insertion forces. However, little research has currently focused on how the dynamic motions of vibration and velocity effect needle insertion force. This dissertation directly fills this void in knowledge to help reduce needle insertion force, which increases needle position accuracy. This research creates a further understanding of how velocity and vibration affect needle insertion force. This work also presents experimental results and force modeling of dynamic needle insertions. Based on this research, a novel compliant needle is designed and developed that utilizes vibration to reduce insertion forces. Three major topics are explored in this research: fracture mechanics model development, analysis of vibrational effect on insertion force, and the development of a novel compliant needle geometry to reduce needle insertion force. Firstly, a fracture mechanics model was developed that allowed for the understanding of how fracture force, tissue spreading force, and friction force impact the overall needle insertion force over a range of velocities (1-80 mm/s). The parameters of tissue toughness and tissue shear modulus were experimentally tested on ex vivo porcine skin. Model results showed the total needle insertion force was comprised of 70% tearing force which was dependent on the fracture toughness, 13% spreading force which was dependent on the shear modulus, and the remaining 17% friction force. To analyze the effect of vibration on insertion force, two needle insertion experiments were performed. First, lancet hypodermic needles were inserted into ex vivo porcine skin with applied vibration. The insertion force was reduced up to 35% with the application of vibration compared to insertion without applied vibration. Next, experiments were performed using five conical tipped needles of varying grind angle sharpness between 15° and 75°. These needles were inserted with applied vibration into ex vivo bovine liver and polyurethane sheets. The experiments into bovine liver showed that any vibratory combination of amplitude and frequency reduced the insertion force of the sharpest needle, grind angle of 15°, by an average of 55.1% compared to the insertion of the needle without applied vibration. However, the bluntest geometry needle, grind angle of 75°, had no significant reduction in bovine liver insertion force from applied vibration compared to the insertion without vibration. The experiments into polyurethane reinforced these findings that sharper needles benefit more from vibration in reducing insertion force compared to blunter needles. Lastly, a novel compliant geometry was developed that transforms applied axial vibration into transverse motion at the needle tip. The needle geometry consisted of four grind planes to create the tip and a single axis flexural hinge created with two slits. Finite element modal analysis was performed on this needle tip geometry to determine the motion upon vibration. Experimentally the motion was measured using a stereomicroscope to be 16.0 µm in the transverse direction for the compliant geometry. Experiments showed the compliant needle was able to reduce the puncture and friction forces of insertion (18.8% and 71.0% respectively) compared to a standard non-compliant needle without applied vibration. This was due to the crack length in the skin simulant increasing by 190% with the compliant needle over the non-compliant needle, allowing the compliant needle to pass through the crack with less force. This reduced friction force can improve needle placement accuracy, thereby improving the efficacy of needle based procedures such as biopsy and brachytherapy.