The individual-cell-based cryo-chip for the cryopreservation, manipulation and observation of spatially identifiable cells. I: methodology

Freezing and thawing of cells on a microfluidic device: a simple and time-saving experimental procedure

Developing cell cryopreservation methods on chips is not only crucial for biomedical science but also represents an innovative approach for preserving traditional cell samples. This study presents a simple method for direct cell freezing and thawing on chip, allowing for long-term storage of cells. During the freezing process, cells were injected into the microchannel along with a conventional cell cryopreservation solution, and the chip was packed using a self-sealing bag containing isopropyl alcohol and then stored in a -80°C refrigerator until needed. During the thawing process, microcolumn arrays with a spacing of 8 µm were strategically incorporated into the microfluidic chip design to effectively inhibit cells from the channel. The breast cancer cell lines MDA-MB-231 and B47D demonstrated successful thawing and growth after cryopreservation for 1 month to 1 year. These findings offer a direct cell freezing and thawing method on a microfluidic chip for subsequent experiments.

Advanced technologies for the preservation of mammalian biospecimens

The three classical core technologies for the preservation of live mammalian biospecimens-slow freezing, vitrification and hypothermic storage-limit the biomedical applications of biospecimens. In this Review, we summarize the principles and procedures of these three technologies, highlight how their limitations are being addressed via the combination of microfabrication and nanofabrication, materials science and thermal-fluid engineering and discuss the remaining challenges.

Bioinspired materials and technology for advanced cryopreservation

Cryopreservation can help to meet the demand for biosamples of high medical value. However, it remains difficult to effectively cryopreserve some sensitive cells, tissues, and reproductive organs. A coordinated effort from the perspective of the whole frozen biological system is necessary to advance cryopreservation technology. Animals that survive in cold temperatures, such as hibernators and cold-tolerant insects, offer excellent natural models. Their anti-cold strategies, such as programmed suppression of metabolism and the synthesis of cryoprotectants (CPAs), warrant systematic study. Furthermore, the discovery and synthesis of metabolism-regulating and cryoprotective biomaterials, combined with biotechnological breakthroughs, can also promote the development of cryopreservation. Further advances in the quality and duration of biosample storage inspired by nature will promote the application of cryopreserved biosamples in clinical therapy.

Two new, near-infrared, fluorescent probes as potential tools for imaging bone repair

A precise imaging technique to evaluate osteogenesis, osteodifferentiation, and osseointegration following peri-implant surgery is in high clinical demand. Herein, we report the generation of two new, near-infrared (NIR) fluorescent probes for use in the molecular imaging of bone repair. The first probe aims to monitor the in vitro differentiation of human mesenchymal stem cells (MSCs) into osteoblasts. A NIR fluorochrome was conjugated to a cyclic peptide that binds to integrin α5β1, a factor that promotes osteogenesis in MSCs and therefore functioned as an osteoblast-specific marker. The second probe aims to monitor osteogenesis, and was generated by conjugating the drug pamidronate to a NIR fluorescent gold nanocluster. Pamidronate specifically binds to hydroxyapatite (HA), a mineral present in bone that is produced by osteoblasts, and therefore provides a functional marker for new bone formation. Our results show that both probes bind to their specific targets in vitro-differentiated osteoblasts, and not to undifferentiated MSCs, and emit NIR fluorescence for functional detection. This in vitro work demonstrates the ability of these probes to bind to active osteoblasts and their mineral deposits and highlight their potential utility as clinical tools for the imaging of the osseointegration process at the molecular level.

IVF-on-a-Chip: Recent Advances in Microfluidics Technology for In Vitro Fertilization

In vitro fertilization (IVF) has been one of the most exciting modern medical technologies. It has transformed the landscape of human infertility treatment. However, current IVF procedures still provide limited accessibility and affordability to most infertile couples because of the multiple cumbersome processes and heavy dependence on technically skilled personnel. Microfluidics technology offers unique opportunities to automate IVF procedures, reduce stress imposed upon gametes and embryos, and minimize the operator-to-operator variability. This article describes the rapidly evolving state of the application of microfluidics technology in the field of IVF, summarizes the diverse angles of how microfluidics has been complementing or transforming current IVF protocols, and discusses the challenges that motivate continued innovation in this field.

Microfluidics for cryopreservation

Cryopreservation has utility in clinical and scientific research but implementation is highly complex and includes labor-intensive cell-specific protocols for the addition/removal of cryoprotective agents and freeze-thaw cycles. Microfluidic platforms can revolutionize cryopreservation by providing new tools to manipulate and screen cells at micro/nano scales, which are presently difficult or impossible with conventional bulk approaches. This review describes applications of microfluidic tools in cell manipulation, cryoprotective agent exposure, programmed freezing/thawing, vitrification, and in situ assessment in cryopreservation, and discusses achievements and challenges, providing perspectives for future development.

Controlled loading of cryoprotectants (CPAs) to oocyte with linear and complex CPA profiles on a microfluidic platform

Oocyte cryopreservation has become an essential tool in the treatment of infertility by preserving oocytes for women undergoing chemotherapy. However, despite recent advances, pregnancy rates from all cryopreserved oocytes remain low. The inevitable use of the cryoprotectants (CPAs) during preservation affects the viability of the preserved oocytes and pregnancy rates either through CPA toxicity or osmotic injury. Current protocols attempt to reduce CPA toxicity by minimizing CPA concentrations, or by minimizing the volume changes via the step-wise addition of CPAs to the cells. Although the step-wise addition decreases osmotic shock to oocytes, it unfortunately increases toxic injuries due to the long exposure times to CPAs. To address limitations of current protocols and to rationally design protocols that minimize the exposure to CPAs, we developed a microfluidic device for the quantitative measurements of oocyte volume during various CPA loading protocols. We spatially secured a single oocyte on the microfluidic device, created precisely controlled continuous CPA profiles (step-wise, linear and complex) for the addition of CPAs to the oocyte and measured the oocyte volumetric response to each profile. With both linear and complex profiles, we were able to load 1.5 M propanediol to oocytes in less than 15 min and with a volumetric change of less than 10%. Thus, we believe this single oocyte analysis technology will eventually help future advances in assisted reproductive technologies and fertility preservation.

The individual-cell-based cryo-chip for the cryopreservation, manipulation and observation of spatially identifiable cells. II: functional activity of cryopreserved cells

Background

The cryopreservation and thawing processes are known to induce many deleterious effects in cells and might be detrimental to several cell types. There is an inherent variability in cellular responses among cell types and within individual cells of a given population with regard to their ability to endure the freezing and thawing process. The aim of this study was to evaluate the fate of cryopreserved cells within an optical cryo apparatus, the individual-cell-based cryo-chip (i3C), by monitoring several basic cellular functional activities at the resolution of individual cells.

Results

In the present study, U937 cells underwent the freezing and thawing cycle in the i3C device. Then a panel of vital tests was performed, including the number of dead cells (PI staining), apoptotic rate (Annexin V staining), mitochondrial membrane potential (TMRM staining), cytoplasm membrane integrity and intracellular metabolism (FDA staining), as well as post-thawing cell proliferation assays. Cells that underwent the freezing - thawing cycle in i3C devices exhibited the same functional activity as control cells. Moreover, the combination of the multi-parametric analysis at a single cell resolution and the optical and biological features of the device enable an accurate determination of the functional status of individual cells and subsequent retrieval and utilization of the most valuable cells.

Conclusions

The means and methodologies described here enable the freezing and thawing of spatially identifiable cells, as well as the efficient detection of viable, specific, highly biologically active cells for future applications.