Sperm-driven microrobots for impaired sperm motility: a scoping review of preclinical evidence

Background Infertility affects a significant proportion of couples worldwide, and asthenozoospermia — impaired sperm motility — is among the leading male factors. Conventional sperm-selection methods such as swim-up, density-gradient centrifugation, and microfluidic sorting depend on intrinsic progressive motility and perform poorly in severe asthenozoospermia. Sperm-driven microrobots (spermbots), hybrid systems that couple a sperm cell to an externally actuated synthetic component, have been proposed as a means of assisting or substituting impaired motility. Methods This scoping review followed JBI methodology and is reported in accordance with PRISMA-ScR. MEDLINE and Google Scholar were searched for English-language experimental studies (2019–2024) of sperm-scale microrobotic systems using mammalian spermatozoa or sperm-mimetic devices. The protocol was registered on PROSPERO (CRD42024529591) when the project was conceived as a systematic review; the review was subsequently reclassified as a scoping review to reflect the nature of the available evidence, and this is reported as a protocol deviation. Consistent with JBI guidance, formal critical appraisal was optional; an exploratory appraisal using RoB 2.0 domains, visualised with the robvis tool, is provided for context only. Results Eight laboratory-based experimental studies met the eligibility criteria. The evidence mapped onto three themes: the influence of environmental factors (fluid viscosity, medium composition) on microrobot performance; optimisation of propulsion and magnetic control; and translational potential, including the capture, transport, and in situ capacitation of immotile sperm. Magnetic actuation conferred controlled propulsion on otherwise non-motile sperm under experimental conditions. No included study evaluated fertilisation, pregnancy, or live-birth outcomes; all evidence is in vitro and proof-of-concept. Conclusions Spermbot technology remains at the preclinical, proof-of-concept stage. The evidence base is small, methodologically heterogeneous, and clinically unvalidated. Research priorities include standardised outcome reporting, biocompatibility assessment, and head-to-head comparison with established sperm-selection methods before any clinical translation. Trial registration (Original protocol, registered as a systematic review; see 2.1): CRD42024529591.