Viscoelastic properties of decellularized and freeze-dried human dermis between i909c and 40cC.

BACKGROUND: Human donor skin is processed to make the acellular dermis matrix (ADM) for tissue repair and regeneration. There is no data on the viscoelastic properties of ADM at room and subzero temperatures. OBJECTIVE: The work evaluated the temperature dependence of viscoelastic properties of freeze-dried ADM. MATERIALS AND METHODS: Donor skin was de-epidermized, de-cellularized and freeze-dried with trehalose as the lyo-protectant. Glass transition of freeze-dried ADM was measured by differential scanning calorimeter (DSC), and viscoelastic properties were examined by dynamic mechanical analyzer (DMA). RESULTS: At the low moisture range (1.4 +/- 0.5%), the glass transition temperature (Tg) of freeze-dried ADM was 90 degree C to 100 degree C. As the moisture content increased, the Tg decreased steadily. At the high moisture range (10.8 +/- 2.9%), the Tg was 40 degree C to 60 degree C. There were large donor-to-donor variations in viscoelastic properties of freeze-dried ADM as demonstrated by the changes in storage modulus (G'), loss modulus (G") and damping factor tan delta (G"/G'). However, the trends of the temperature dependence for G', G" and tan delta were similar among all 8 donors. For each donor, changes in G' and G" were relatively small between -90 degree C and 40 degree C, and G' was at least one order of magnitude greater than G". Two viscoelastic relaxations were observed in freeze-dried ADM, one at -20 degree C and the other at -60 degree C respectively. CONCLUSION: Freeze-dried ADM was protected in the glassy carbohydrate matrix. DMA observed two viscoelastic relaxations (i.e., alpha process at -20 degree C and beta process at -60 degree C). Overall changes in G' and G'' of freeze-dried ADM were relatively small within one order of magnitude between -90 degree C and 40 degree C. https://doi.org/10.54680/fr24110110612.

PERSPECTIVE: Cryopreservation of Human Oocytes and the 'Carryover' Effect on Early Embryo Development.

Worldwide women are increasingly facing the issue of delayed child-bearing and fertility decline. Oocyte cryopreservation provides an option for fertility preservation, especially for women with diseases and other special needs to conceive babies later. In this review we examine the effect of oocyte cryopreservation on early development of human embryos. Databases (Medline, PubMed and Web of Science) were searched for relevant clinical studies published between 1999 and 2020. A total of 27 studies on oocyte cryopreservation and embryo development were identified, and data in those studies are retrieved for meta-analysis on the outcomes of oocyte survival, fertilization and early embryo development. In comparison to the slow freezing technique, vitrification yields significantly better oocyte survival (84.7% ± 0.6% vs 58.0% ± 0.5%), and subsequently higher rates of fertilization (65.5% ± 0.9% vs 40.0% ± 0.6%), cleavage (58.8% ± 0.9% vs 34.6% ± 0.8%), as well as embryo implantation (5.9% ± 0.3% vs 2.9% ± 0.2%). This analysis reveals a negative 'carryover' effect of oocyte cryopreservation on early development of embryos after oocyte fertilization (i.e., cleavage and implantation). This 'carryover' effect is greater for slowly-frozen oocytes than for vitrified oocytes, and may represent subtle functional or molecular alterations that are not severe enough to affect cell survival and fertilization, but sufficient to impair later development. The nature of the 'carryover' effect is unknown. Hypothermia, membrane ion channels, bioenergy metabolism and epigenetic modifications are likely involved. In conclusion, oocyte cryopreservation can negatively affect early development of human embryos. Future studies should go beyond oocyte survival and look further into the effects on epigenetic changes.