title: Evaluation of fetal tissue viscoelastic characteristics for robotic fetal surgery.
abstract: OBJECTIVE
  Minimally invasive fetal surgery is expected to improve therapeutic outcomes, and surgical robots are expected to aid the dexterous manipulation of fragile fetal tissues. Although robots are currently used for surgery on soft tissues, practical information concerning the viscoelastic characteristics of fetal tissues is lacking. Hence, the mechanical properties of fetal tissues should be quantified to design robotic devices that facilitate computer-assisted fetal surgery.
  
  
  METHODS
  Shear creep tests were performed on abdominal wall tissues of rat fetuses, aged 16-20 days, and on the brain, lung, and liver tissues of adult rats. Viscoelastic properties of these tissues were evaluated using a rheometer. Histological sections of fetal rat tissues were stained with hematoxylin and eosin.
  
  
  RESULTS
  The viscoelastic properties of fetal tissues were quantified using models. Fetal tissues displayed 2 distinct phases of fragility, i.e., gelatinous characteristics with a markedly lower viscoelasticity before day 18 than after day 19. Concomitantly, skin morphology matured remarkably after day 19. As judged by the morphology, the gestation age of 19 days in rats corresponds to that of 23 weeks in human fetuses. From our data, we prepared artificial phantoms; phantoms made from 1.0% gelatin showed mechanical properties very similar to those of the fetuses before day 18.
  
  
  CONCLUSIONS
  We observed unique mechanical characteristics in fetal tissue, a previously unknown target for surgical robots. From the data obtained, we produced phantoms that have similar viscoelastic properties, aiming at designing surgical robots capable of handling early fetuses.
authors.affiliation: Clinical Research Center, National Center for Child Health and Development, 2-10-1 Okura, Setagaya-ku, Tokyo 157-8535, Japan. kanako@nml.t.u-tokyo.ac.jp
authors.forename: Kanako
authors.initials: K
authors.lastname: Harada
authors.forename: Shin
authors.initials: S
authors.lastname: Enosawa
authors.forename: Bo
authors.initials: B
authors.lastname: Zhang
authors.forename: Wenji
authors.initials: W
authors.lastname: Yuan
authors.forename: Toshio
authors.initials: T
authors.lastname: Chiba
authors.forename: Masakatsu G
authors.initials: MG
authors.lastname: Fujie
mesh_terms: D000818:Animals; D001921:Brain / Q000196:embryology / Q000601:surgery; D062109:Dermatologic Surgical Procedures; D004548:Elasticity; D005260:Female; D005333:Fetus / Q000601:surgery*; D008099:Liver / Q000196:embryology / Q000601:surgery; D008168:Lung / Q000196:embryology / Q000601:surgery; D019060:Minimally Invasive Surgical Procedures / Q000379:methods*; D008954:Models, Biological; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar; D012371:Robotics; D012867:Skin / Q000196:embryology; D014783:Viscosity