The Interrelationship Between Friction and Fracture in Needle Insertion

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This award will advance understanding of the fundamental mechanics of needle insertion. Despite the ubiquity of needle-based medical procedures and a wealth of needle insertion studies, there are critical gaps in understanding. Quantification of the sliding friction and material fracture during post-puncture needle insertion is needed to evaluate new needle designs and the soft materials into which they may be inserted. The current shortcomings in computational prediction stem in part from a missing description of the effect of friction and fracture on one another. A more detailed understanding is critical to the successful expansion of minimally invasive methods to areas beyond the body’s surface. Successful description of the fundamental mechanics of these effects will both facilitate control schemes and enable rapid evaluation of novel needle designs. This research is expected to ultimately result in reduced patient discomfort, healing time, and procedure costs. This research will be implemented with a team of graduate researchers who will receive management training to coordinate the effort of undergraduate trainees. The researchers will share their experiences and findings via social media with the aim of illuminating the challenges, rewards, and process of mechanics of materials research for the public.This research will quantify the simultaneous and reciprocal effects of sliding friction and material rupture during post-puncture needle insertion. Initial goals will guide the work toward first understanding the influence of fracture on surface morphology and the latter’s influence on friction. Once gained, these separate effects will be unified in the primary goal of simultaneously describing interfacial mechanics along the needle shaft and fracture at the needle tip. Tests will be performed at quasi-static to surgically-relevant rates. First, surface damage morphology will be systematically varied by controlling both the energy available to fracture (via tip radius and boundary conditions in planar and needle geometries) and material constitutive response using two well-characterized materials systems typical of needle insertion studies, but having different failure behaviors: oil-diluted silicone (tougher) and hydrogel (more brittle). Second, the effect of surface damage morphology on frictional resistance to sliding will be measured to establish correlations and critical regimes as a function of rate and normal force. Finally, using these correlations, planar cutting geometry conditions will be mapped to the cylindrical needle-insertion geometry to quantify frictional effects which will be further tuned via surface modification. This mapping will be initiated via local failure criteria obtained from full field strain measurement during in situ needle insertion and cutting. The resulting fundamental understanding of the interrelationship between friction and fracture will inform the development of more robust computational models of needle insertion and lead to more refined and improved models for robotic needle insertion. Both advances will enhance the development of minimally-invasive, tissue-specific needle designs.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.