Hydrogel encapsulation as a handling and vitrification tool for zebrafish ovarian tissue

Hydrogel encapsulation facilitates a low-concentration cryoprotectant for cryopreservation of mouse testicular tissue

Cryopreserved testicular tissue offers a promising method to restore fertility in male infertility patients. Current protocols rely on high concentrations of penetrating cryoprotectants (pCPAs), such as dimethyl sulfoxide (DMSO), which necessitating complex washing procedures and posing risks of toxicity. Hydrogel encapsulation presents a non-toxic alternative for cellular cryopreservation. This study investigates the effects of various types, concentrations, and thicknesses of hydrogel encapsulation on the cryopreservation of mouse testicular tissue. Testicular tissues loaded with varying concentrations of DMSO were encapsulated in alginate or gelatin-methacryloyl (GelMA) hydrogels. We evaluated hydrogels as potential CPAs to reduce pCPA concentrations and determine optimal combinations for cryopreservation. Post-cryopreservation, tissues were cultured using organ culture methods to assess spermatogenesis progression. Cryomicroscopy and differential scanning calorimetry (DSC) were used to examine ice crystal formation, melting enthalpy, and non-freezing water content in different hydrogels during cooling. Results indicate that 3 % alginate or 5 % GelMA hydrogel with thin encapsulation optimally preserves mouse testicular tissue. Using 20 % DMSO in 5 % GelMA thin encapsulation showed comparable apoptosis rates, improved morphology, higher mitochondrial activity, and enhanced antioxidant capacity compared to conventional 30 % DMSO without encapsulation. This suggests that hydrogel encapsulation reduces pCPA concentration by 10 %, thereby mitigating toxic damage. Hydrogel encapsulation can reduce basement membrane shrinkage of testicular tissue during cryopreservation. Moreover, frozen tissues remained viable with preserved germ cells after being cultured for one week on alginate methacryloyl (AlgMA) hydrogel using the gas-liquid interphase method. Cryomicroscopy and DSC studies confirmed the hydrogel's ability to inhibit ice crystal growth. In conclusion, this study introduces novel strategies for male fertility preservation and advances cryopreservation technology for clinical applications in assisted reproduction.

Biodegradable capsules as a sustainable and accessible container for vitrification of gonadal tissue using the zebrafish animal model

Cryopreservation of fish gonadal tissue is an important technique for preserving genetic variability. However, this technique involves the use of cryotubes, plastic containers with low degradability that are expensive and difficult to obtain in certain parts of the world. Therefore, this study aimed to evaluate the efficiency of gelatin and hypromellose hard capsules as a sustainable and accessible alternative container to the cryotube for vitrification of zebrafish (Danio rerio) gonadal tissue. The gonadal tissues (testicular or ovarian) were vitrified in cryotubes, hard-gelatin, and hard-hypromellose capsules. Gelatin capsules exhibited comparable efficacy to cryotubes in preserving spermatogonia viability (33.03 ± 10.03 % and 37.96 ± 8.35 %, respectively), whereas hypromellose capsules showed decreased viability (18.38 ± 2.09 %). Immature oocyte viability remained unaffected by the capsule materials, with no difference compared to cryotubes at all oocyte stages (Primary Growth: p < 0.0001; Cortical Alveolar: p < 0.0001; Vitellogenic: p < 0.0001). Mitochondrial activity and lipid peroxidation demonstrated no difference among cryotubes and capsules for both gonadal tissues. However, antioxidant activity was notably higher in gelatin capsules (Testes: 147.2 ± 32.32 μg; Ovary: 87.98 ± 10.91 μg) than in cryotubes (Testes: 81.04 ± 26.05 μg; Ovary: 54.35 ± 11.23 μg) and hypromellose capsules (Testes: 62.36 ± 17.10 μg; Ovary: 63.96 ± 7.51 μg), likely due to the inherent antioxidant properties of gelatin. The results obtained in this study demonstrate that the cryotube can be replaced by gelatin capsules for vitrification of both gonadal tissues of zebrafish, being a sustainable and accessible alternative as it is a low-cost and environmentally friendly container.

Vitrification of Mammalian Oocytes: Recent Studies on Mitochondrial Dysfunction

Vitrification of reproductive cells is definitely essential and integral in animal breeding, as well as in assisted reproduction. However, issues accompanied with this technology such as decreased oocyte competency and relatively low embryo survival rates appear to be a tough conundrum that has long perplexed us. As significant organelles in cell metabolism, mitochondria play pivotal roles in numerous pathways. Nonetheless, extensive evidence has demonstrated that vitrification can seriously impair mitochondrial function in mammalian oocytes. Thus, in this article, we summarize the current progress in oocyte vitrification and particularly outline the common mitochondrial abnormalities alongside subsequent injury cascades seen in mammalian oocytes following vitrification. Based on existing literature, we tentatively come up with the potential mechanisms related to mitochondrial dysfunction and generalize efficacious ways which have been recommended to restore mitochondrial function.