Reproduction Abstracts

Introduction: The interdisciplinary field of microrobotics recently sparked interest especially in potential applications of mobile microscale devices that can operate remotely-controlled inside the human body. This study presents an approach towards such an application, namely assisted reproduction with the help of tiny sperm carriers, so-called spermbots. Spermbots are synthetic tubes or helices that couple to single sperm cells and assist their movement by providing guidance or propulsion when actuated by external magnetic fields. Sperm cells with insufficient motility or navigation capabilities are thus supported on their journey, in vitro and possibly even in vivo, which signifies a wholly new approach to counter male factor infertility.

Methods: Tubular and helical microdevices were fabricated by nanomembrane-roll-up (Magdanz et al 2016 Adv Mater doi: 10.1002/adma.201505487) and direct laser writing (Medina-Sánchez et al 2016 Nano Lett 16: 555–561). The synthetic devices were actuated in vitro with weak magnetic fields and their coupling to bovine sperm cells was recorded under the microscope. Imposed hypoosmotic swelling of sperm cells facilitated proper sperm selection. Motion performance and biocompatibility studies with coupled spermbots served to evaluate their capability to emulate potent sperm behavior.

Results and Discussion: Single sperm cells were successfully captured by tubular and helical microdevices while remaining viable and intact. External magnetic guidance of tubular carriers and directed propulsion of helical motors was achieved. Tubular spermbots were able to release captured sperm via thermoresponsive shape alteration helical spermbots released sperms by reversion of their magnetically imposed rotation. With helical spermbots, sperm transport and release at the zona pellucida of an oocyte was shown in vitro. Our results illustrate the potential of assisted fertilization with microrobots. This novel approach is meant to deal with severe cases of male factor infertility, with its main strength lying in its potential in vivo applicability. (funded by DFG priority program SPP1726).