Functional substitution of zona pellucida with modified sodium hyaluronate gel in human embryos

Zona pellucida-free (ZP-free) embryos often fail to achieve good developmental outcomes and are routinely discarded in assisted reproductive laboratories. Existing attempts to rescue ZP-free embryos are not widely used due to operational complexity and high technical requirements. To handle cases with missing ZP, we applied modified sodium hyaluronate gel (MSHG) to embryo culture to determine if it can function as a substitute for human zona pellucida.

The developmental process and the blastocyst formation rate of embryos were analyzed in both mouse and human. The first clinical application of MSHG was reported, and the pregnancy outcome was continuously followed up.

Human and mouse ZP-free embryos cultured with MSHG showed a blastocyst formation rate similar to ZP-intact embryos. MSHG improves blastocysts formation rate by maintaining blastomere spatial arrangement at early stages. Compared to ZP-free embryos, the proportion of tetrahedrally arranged blastomeres at the 4-cell stage increased significantly in embryos cultured with MSHG in humans. A ZP-free blastocyst cultured in MSHG with the highest score was successfully implanted after day 5 transplantation and developed normally.

These data demonstrate that MSHG can substitute the function of zona pellucida and rescue human ZP-free embryos during assisted reproductive technology.