Abstract
Cryopreservation of biological materials or systems, including biomarkers, cells, tissues, and organs, has become indispensable in various settings, spanning from fundamental research to biomedical applications. It has been a critical component or even the bottleneck issue for numerous fields, such as fertility preservation, conservation of endangered species, screening and diagnosis of diseases, drug development, cellular or gene therapy, regenerative medicine, tissue or organ transplantation, and others. However, the viability or functionality of biomaterials may be compromised during the cryopreservation process or storage. In addition, damages to the biomaterials caused by the preservation process depend on the sample scale (e.g., cells vs. tissues), cell type, or even species (e.g., sperm of different species).
Therefore, development of optimal biopreservation protocols for each type of biomaterials is essential. For this reason, the journal Cell Preservation Technology was launched in 2002, which was changed to Biopreservation and Biobanking in 2008, and became the official journal for the International Society for Biological and Environmental Repositories (ISBER). Later the journal topic coverage expanded to include best practices for biobanking, governance and sustainability of biobanks, ethical and regulatory issues for biorepositories, and so on.
As Dr. John Baust, the founding editor of the journal, stated in the journal opening editorial, “as more and more of our time is spent providing guidance within the rapidly emerging biomedical technologies, a growing appreciation of the need for improved preservation strategies is apparent” (Cell Preservation Technology, Vol. 1, No. 1, 2002.). 2022 marks the 20th anniversary of the journal and after two decades, we can proudly claim that the necessity of preservation science is fully appreciated, and it has been serving more and more people in various fields. The growth of the journal in the past two decades reflects the expansion of biopreservation technology and its applications.
The cryopreservation process normally consists of a few basic steps, including preprocessing of the samples, addition of cryoprotective agents (CPAs), cooling, storage, rewarming, removal of CPAs, and postprocessing. Each step in a suboptimal protocol may cause severe injuries to the cells or tissues. Optimization of a biopreservation protocol should include the choice of the optimal CPAs with maximum cryoprotective functions and minimum toxicity, protocols of addition/removal of CPAs to ensure sufficient loading/unloading of CPAs and eliminate osmotic injury and possible cytotoxicity during the process, cooling and rewarming procedure to avoid injuries due to intracellular ice formation (IIF), recrystallization, or devitrification, and optimizing the pre- and postpreservation processing of the samples.
It also includes the design or application of effective biopreservation devices complying with Good Manufacturing Practices. It is worth emphasizing that fundamental cryobiology research is always important. It can help us understand the mechanisms of cryoinjuries and provide novel strategies to optimize the cryopreservation protocols and to improve biopreservation technology.
In this special issue, interesting articles were selected to exhibit some recent advancements in diverse topics, including fundamental and applied cryobiology, as well as preservation techniques for various sample types (cells, tissues), different cell types (sperm, stem cells, and endothelial cells), and different species (human, goat, bovine, cat, and mouse), using different approaches (hypothermic preservation, freeze–thaw, vitrification, and ex vivo maintenance), by researchers from all over the world (Asia, Europe, North and South America, etc.).
Cryobiology itself is a unique science, focused on studying the mechanisms of cryoinjuries and cryopreservation to develop novel preservation technology. Therefore, cryobiology study lays the foundation for biopreservation and biobanking. Two articles in the fundamental cryobiology field were included in this issue. In Huang et al.'s article, some critical cryobiological characteristics of human umbilical vein endothelial cells were investigated, including the transmembrane hydraulic conductivity, membrane permeability activation energy, osmotically inactive cell volume, IIF, and cell volume excursion during cooling at different cooling rates.
This study and the results are essential for predicting and determining the optimal cooling protocol for cryopreservation. Ren et al. presented a novel single-mode electromagnetic resonance (SMER) method for the rewarming of cryopreserved cells, tissues, and organs. Compared with the currently used methods of rewarming in air or a water bath, the SMER system successfully achieved ultrafast and uniform rewarming for samples with much larger volumes, which is indispensable for the avoidance of injuries caused by recrystallization, devitrification, and thermal stress-induced fractures in large samples. Therefore, SMER may be a paradigm shift for tissue or organ preservation.
Among the selected articles on biopreservation, one article is about the postpreservation processing of biosamples. Eivazkhani et al. investigated the effects of N-acetyl-
The results showed that refrigeration at 5°C was efficient in maintaining viable tissues for up to 30 days, and fibroblasts isolated from the preserved skin tissues were qualified to be used for cloned embryo production, although significant changes did happen to the cells (e.g., cell attachment, proliferation, and viability) after a long period of hypothermic storage. This study demonstrated a convenient and cost-effective storage method in the settings of genetic obtainment and applications for cloning through somatic cell nuclear transfer.
In the other articles, either freeze–thaw or vitrification was applied as the cryopreservation approach. It is very interesting that fertility preservation by cryopreserving sperm, spermatogonial stem cells, ovarian or testicular tissues is still one major field of research interests, even though this has been extensively studied for more than seven decades, ever since the very beginning of modern cryopreservation in the late 1940s (the first successfully cryopreserved mammalian cell type was sperm). This may be attributed not only to the continuous needs or unsolved challenges in fertility preservation, regenerative medicine, and conservation of endangered species, but also by the discrepancy in the response to cryopreservation for sperm from different species.
The selected articles represented some work about the cryopreservation of sperm or spermatogonial stem cells from different species, including human (Ghantabpour et al.), goat (Gungor et al. and Liang et al.), mouse (Nazeri et al.), and fish (Kabir et al.). Obviously, searching for novel and effective cryoprotectants is still the major research topic, especially antioxidants to mitigate the damages caused by reactive oxygen species. The efficiency of a few cryoprotectants, such as hydrated carbon 60 fullerene (Gungor et al.), cyclohexanediol (Liang et al.), trehalose (Liang et al.), astaxanthin (Ghantabpour et al.), and melatonin (Nazeri et al.) was investigated.
These cryoprotectants were demonstrated to possess cryoprotective, antioxidant, or antiapoptotic effects, and could improve the cell survival rate after cryopreservation. Liang et al. also presented a method to assess the ultrastructural alterations in sperm by transmission electron microscope. Besides sperm preservation, cryopreservation of human aortic endothelial cells with trehalose was investigated by Huang et al. The results showed that trehalose could work as an inducer of autophagy to improve the expression of some autophagy-related genes, reduce apoptosis and cell death during cryopreservation. This may provide a new perspective on the cryoprotection mechanism of trehalose, the “magic molecule” in cryopreservation.
Tissue preservation was also covered in this issue. In Macente et al.'s work, the protocol for vitrification of testicular fragments from adult domestic cats was studied, including the vitrification device, warming methods, and subsequent in vitro culture. Crisol et al. reported some interesting results of their long-term research on the cryopreservation of articular cartilage, which showed the effectiveness of clinical-grade chondroitin sulfate and ascorbic acid in the mitigation of cryoprotectant toxicity in porcine articular cartilage. A special recommendation to the readers is the brief report by Lin et al. about the cryopreservation and biobanking of coral reefs. They investigated the coral tissue cryopreservation from 37 species. This study provides an important exploration on the conservation of corals and marine ecosystems.
Biopreservation has facilitated or even transformed the research and development activities in many fields, from fundamental research to clinical practice. In the past two decades since the birth of the journal of Biopreservation and Biobanking (including the first 6 years with the name of Cell Preservation Technology), ample significant achievements have been made in cryobiology research and biopreservation technology. We believe that in the next two decades, more influential progress in biopreservation and biobanking will emerge and benefit various aspects of life science, biomedicine, and beyond.