title: Evaluation of the friction coefficient, the radial stress, and the damage work during needle insertions into agarose gels.
abstract: Agarose hydrogels have been extensively used as a phantom material to mimic the mechanical behavior of soft biological tissues, e.g. in studies aimed to analyze needle insertions into the organs producing tissue damage. To better predict the radial stress and damage during needle insertions, this study was aimed to determine the friction coefficient between the material of commercial catheters and hydrogels. The friction coefficient, the tissue damage and the radial stress were evaluated at 0.2, 1.8, and 10mm/s velocities for 28, 30, and 32 gauge needles of outer diameters equal to 0.36, 0.31, and 0.23mm, respectively. Force measurements during needle insertions and retractions on agarose gel samples were used to analyze damage and radial stress. The static friction coefficient (0.295±0.056) was significantly higher than the dynamic (0.255±0.086). The static and dynamic friction coefficients were significantly smaller for the 0.2mm/s velocity compared to those for the other two velocities, and there was no significant difference between the friction coefficients for 1.8 and 10mm/s. Radial stress averages were 131.2±54.1, 248.3±64.2, and 804.9±164.3Pa for the insertion velocity of 0.2, 1.8, and 10mm/s, respectively. The radial stress presented a tendency to increase at higher insertion velocities and needle size, which is consistent with other studies. However, the damage work did not show to be a good predictor of tissue damage, which appears to be due to simplifications in the analytical model. Differently to other approaches, the method proposed here based on radial stress may be extended in future studies to quantity tissue damage in vivo along the entire needle track.
authors.affiliation: Escuela de Ingeniería Mecánica Universidad del Valle, Calle 13 # 100-00, Cali, Colombia. Electronic address: fabian.urrea@correounivalle.edu.co.
authors.forename: Fabián A
authors.initials: FA
authors.lastname: Urrea
authors.affiliation: Escuela de Ingeniería Mecánica Universidad del Valle, Calle 13 # 100-00, Cali, Colombia. Electronic address: gonzalo.casanova@correounivalle.edu.co.
authors.forename: Fernando
authors.initials: F
authors.lastname: Casanova
authors.affiliation: Escuela de Ingeniería Mecánica Universidad del Valle, Calle 13 # 100-00, Cali, Colombia. Electronic address: gustavo.orozco@correounivalle.edu.co.
authors.forename: Gustavo A
authors.initials: GA
authors.lastname: Orozco
authors.affiliation: Escuela de Ingeniería Civil y Geomática Universidad del Valle, Calle 13 # 100-00, Cali, Colombia. Electronic address: josejgar@gmail.com.
authors.forename: José J
authors.initials: JJ
authors.lastname: García
mesh_terms: D017276:Friction; D020100:Hydrogels; D008422:Materials Testing; D009339:Needles; D012685:Sepharose / Q000737:chemistry*; D013314:Stress, Mechanical
chemical_list: D020100:Hydrogels; D012685:Sepharose
keywords: Agarose hydrogels; Friction coefficient; Insertion velocity; Needle insertion; Pre-stress; Radial stress