Keywords Fetal surgery Á Soft tissue Á Modeling Á Viscoelasticity
PurposeMinimally 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.
ResultsThe 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. Figure 1 shows the estimated viscoelastic parameters of the tissues and phantoms measured in the experiment.
ConclusionWe 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.
Towards a rheological model for real-time simulation of endovascular repair of abdominal aortic aneurysmsKeywords Endovascular repair simulation Á Smoothed particle hydrodynamic Á Abdominal aortic aneurysms
PurposeTo develop a novel rheological model based on smoothed particle hydrodynamics (SPH) in order to facilitate the development of interactive simulation system for training and planning of endovascular repair of abdominal aortic aneurysms (AAA). Methods Endovascular aneurysm repair (EVAR) is a preferable option in most cases of AAA treatment, where a stent-graft, called endovascular graft (EVG), in a catheter is passed from the patient's leg artery to the aneurysm site and then released. Once secured in place, the EVG forms a new blood vessel, protecting the weakened AAA wall from the blood pressure and, hence, possible rupture [1]. EVAR is preferred over open surgery due to its advantages of minimal invasion, early recovery, reduced mortality and morbidity, though follow-up is still needed to determine whether these advantages are sustained [2]. However, EVAR is a relatively complicated surgery; extensive training is therefore required for novices to acquire the related skills. In addition, currently, mo...