Impact of different mating and surgical protocols on the establishment of a mouse model for fetal scarless skin healing.

Background: The mouse fetal intrauterine wound healing model is crucial and commonly used for investigating mechanisms and evaluating potential therapies for scarless skin regeneration compared to fibrotic healing. However, traditional intrauterine surgery remains technically challenging and understudied, which is associated with high maternal mortality and pregnancy loss, prompting us to refine the surgical protocol. Here, we report how the choice of surgical and mating procedure impact outcomes obtained.

Methods: Pregnant mice underwent fetal surgery at embryonic days 15.5, 16.5 (E15.5, E16.5, scarless) and 18.5 (e18.5, fibrotic). Two surgical protocols were used: traditional method involved purse-string sutures, microsurgical scissors, amniotic fluid supplementation, and suture closure (Traditional); and our modified method omitting purse-string sutures, replacing scissors with needle puncture for uterine and fetal incisions, eliminating amniotic fluid supplementation, and employing skin staples for abdominal closure (Modified).

Results: The modified protocol significantly increased the likelihood of successful pregnancy, reduced operative time, decreased abortion rates, and enabled earlier modeling compared to the traditional method. At 48 h, 7 days, and 9 days post-surgery, E15.5 wounds healed scarlessly, displaying regenerated hair follicles and organized collagen. Conversely, E18.5 wounds formed typical fibrotic scars, characterized by dense, disorganized collagen without hair follicles.

Conclusion: The optimized surgical protocol presented here provides a simplified, reliable fetal mouse model with improved pregnancy success, reduced fetal loss, earlier implementation, and consistent phenotypic outcomes. This refined model enhances experimental efficiency, reproducibility, and animal welfare, having a major impact on mechanistic studies and therapeutic exploration for scarless skin regeneration.