The research objective of this award is to investigate the cutting mechanics of biological tissue in needle biopsy procedures by viewing biopsy as a cutting process with tissue as the work-material. This will be accomplished by testing novel needle tip geometries using high speed tissue cutting test machines to characterize the mechanics of tissue cutting and by modeling the mechanics of tissue cutting. Advanced helical needle-tips and micro-grinding methods will be applied to generate novel needle-tip geometries with sharp, burr-free cutting edges. Two test machines, one for high speed orthogonal and oblique tissue cutting and another for high speed needle insertion, will be built to investigate the effects of cutting speed and needle tip geometry. Mechanistic models will be built to predict the tissue cutting force related to the needle geometry and cutting speed. Tissue fracture and tissue-needle tribological phenomena in high-speed tissue cutting will be studied to develop the fundamentals of tissue cutting mechanics.
If successful, the benefits of this research will be improved performance of the most commonly used medical device - the needle. Tissue cutting efficiency will increase thereby reducing pain and trauma in biopsy procedures. New biopsy machines with advanced needles and optimized operating parameters will increase the volume of tissue samples collected in each needle insertion and improve the accuracy of pathology diagnoses in a wide range of biopsy procedures. Results of the proposed research will also extend the traditional field of machining to biomedical and health care applications and promote the emerging research frontiers in biomedical manufacturing.
The objective of this award was to establish the scientific principles for the design and manufacture of the next generation of biopsy needles including the formulation of biopsy needle-tip geometry models and the geometric and kinematic relationships for its manufacture, tissue cutting models that allow the prediction of tissue cutting/insertion forces, and experimental methods for the assessment of needle performance. In regard to the above objectives the major findings of the project can be enumerated as follows: (1) Development of generalized and specific mathematical models for the characteristic angles of the cutting edges for a variety of needles that have led to a number of newly conceived needle tip configurations that can potentially lower the insertion force during percutaneous procedures and also provide better targeting. (2) Formulation of control strategies for a prototype 5-axis computer controlled needle tip grinding machine based on the generalized helical needle tip geometry model. Several types of needle geometries were manufactured. (3) Formulation of both analytical and numerical force models, based on the fracture mechanics approach, to analyze the effects of cutting edge speed in conventional and rotating cannula biopsy on the cutting/insertion forces. Experiments were performed to validate the cutting force predictions. (4) Development of a setup and procedures for laser surface texturing (LST) of medical needles for friction and ultrasound visibility studies. Micro-channels and micro-dimples with various sizes, densities, and orientations were created. Friction tests were carried out to study the effect of surface texture on the friction between the needle and tissue. The results from the project provide the foundation for designing, manufacturing, and evaluating medical needles. The findings will assist medical needle manufacturers in developing ultra-sharp needles with lower penetration force to minimize pain and trauma. Improved biopsy needles will increase the quality of tissue samples and improve diagnosis accuracy. Needles with sharper tips will also lead to reduced needle placement errors in brachytherapy.
