Fluorescence enhanced BA-LIFT for single cell detection and isolation

Towards single-cell bioprinting: micropatterning tools for organ-on-chip development

Organs-on-chips (OoCs) hold promise to engineer progressively more human-relevant in vitro models for pharmaceutical purposes. Recent developments have delivered increasingly sophisticated designs, yet OoCs still lack in reproducing the inner tissue physiology required to fully resemble the native human body. This review emphasizes the need to include microarchitectural and microstructural features, and discusses promising avenues to incorporate well-defined microarchitectures down to the single-cell level. We highlight how their integration will significantly contribute to the advancement of the field towards highly organized structural and hierarchical tissues-on-chip. We discuss the combination of state-of-the-art micropatterning technologies to achieve OoCs resembling human-intrinsic complexity. It is anticipated that these innovations will yield significant advances in realization of the next generation of OoC models.

Precision isolation and cultivation of single cells by vortex and flat-top laser ejection

Single-cell isolation stands as a critical step in single-cell studies, and single-cell ejection technology based on laser induced forward transfer technology (LIFT) is considered one of the most promising methods in this regard for its ability of visible isolating single cell from complex samples. In this study, we improve the LIFT technology and introduce optical vortex laser-induced forward transfer (OV-LIFT) and flat-top laser-induced forward transfer (FT-LIFT) by utilizing spatial light modulator (SLM), aiming to enhance the precision of single-cell sorting and the cell's viability after ejection. Experimental results demonstrate that applying vortex and flat-top beams during the sorting and collection process enables precise retrieval of single cells within diameter ranges of 50 μm and 100 μm, respectively. The recovery rates of Saccharomyces cerevisiae and Escherichia coli DH5α single cell ejected by vortex beam are 89 and 78%, by flat-top beam are 85 and 57%. When employing Gaussian beam sorting, the receiving range extends to 400 μm, with cultivation success rates of S. cerevisiae and E. coli DH5α single cell are 48 and 19%, respectively. This marks the first application of different mode beams in the ejection and cultivation of single cells, providing a novel and effective approach for the precise isolation and improving the viability of single cells.

Isolating and culturing of single microbial cells by laser ejection sorting technology

Single cell isolation and cultivation play an important role in studying physiology, gene expression and functions of microorganisms. A series of single-cell isolation technologies have been developed, among which single-cell ejection technology is one of the most promising. Single cell ejection technology has applied Laser Induced Forward Transfer Technique (LIFT) to isolate bacteria but the viability (or recovery rate) of cells after sorting has not been clarified in the current research progress. In this work, to keep the cells alive as much as possible, we propose a three-layer LIFT system (top layer: 25-nm aluminum film; second layer: 3 μm agar media; third layer: liquid containing bacterial) for the isolation and cultivation of single Gram-negative (E. coli), Gram-positive (Lactobacillus rhamnosus GG, LGG), and eukaryotic microorganisms (Saccharomyces cerevisiae). The experiment results showed that the average survival rates for ejected pure single cells were 63% for Saccharomyces cerevisiae, 22% for E. coli DH5α, and 74% for LGG. In addition, we successfully isolated and cultured the GFP expressing E. coli JM109 from the mixture containing complex communities of soil bacteria by fluorescence signal. The average survival rate of E. coli JM109 was demonstrated to be 25.3%. In this study, the isolated and cultured single colonies were further confirmed by colony PCR and sequencing. Such precise sorting and cultivation technique of live single microbial cells could be coupled with other microscopic approaches to isolate single microorganisms with specific functions, revealing their roles in the natural community. Importance We developed a laser induced forward transfer (LIFT) technology to accurately isolate single live microbial cells. The cultivation recovery rates of the ejected single cells were 63% for Saccharomyces cerevisiae, 22% for E. coli DH5α, and 74% for Lactobacillus rhamnosus GG (LGG). Coupled LIFT with fluorescent microscope, we demonstrated that single cells of GFP expressing E. coli JM109 were sorted according to fluorescence signal from a complex community of soil bacteria, and subsequently cultured with 25% cultivation recovery rate. This single cell live sorting technology could isolate single microbes with specific functions, revealing their roles in the natural community.

Laser induced forward transfer isolating complex-shaped cell by beam shaping

Beam shaping techniques have been widely used in holographic optical tweezers to accurately manipulate tiny particles and hologram optimization algorithms have also been widely reported to improve the optical trapping performance. In this paper, we presented a beam shaping laser induced forward transfer (BS-LIFT) technique to isolate complex-shaped cells. To do this, we built up a BS-LIFT instrument which combined beam shaping methods and laser induced forward transfer using liquid-crystal-on-silicon spatial light modulator. The laser beam was modulated into multiple desired points at the focal plane employing the Gerchberg-Saxton (GS) algorithm. Feasibility was verified through transferring various samples. To our knowledge, this is the first demonstration of BS-LIFT applied to the transfer complex-shaped cells. We successfully transferred cells whose size ranged from 1 µm to 100 µm. Our design will provide a novel approach for the application of this beam shaping technique and the isolation of single cells with variable shapes.

Laser-based bioprinting for multilayer cell patterning in tissue engineering and cancer research

3D printing, or additive manufacturing, is a process for patterning functional materials based on the digital 3D model. A bioink that contains cells, growth factors, and biomaterials are utilized for assisting cells to develop into tissues and organs. As a promising technique in regenerative medicine, many kinds of bioprinting platforms have been utilized, including extrusion-based bioprinting, inkjet bioprinting, and laser-based bioprinting. Laser-based bioprinting, a kind of bioprinting technology using the laser as the energy source, has advantages over other methods. Compared with inkjet bioprinting and extrusion-based bioprinting, laser-based bioprinting is nozzle-free, which makes it a valid tool that can adapt to the viscosity of the bioink; the cell viability is also improved because of elimination of nozzle, which could cause cell damage when the bioinks flow through a nozzle. Accurate tuning of the laser source and bioink may provide a higher resolution for reconstruction of tissue that may be transplanted used as an in vitro disease model. Here, we introduce the mechanism of this technology and the essential factors in the process of laser-based bioprinting. Then, the most potential applications are listed, including tissue engineering and cancer models. Finally, we present the challenges and opportunities faced by laser-based bioprinting.

Methylcellulose – a versatile printing material that enables biofabrication of tissue equivalents with high shape fidelity

This minireview highlights the use of the polysaccharide methylcellulose for biofabrication applications. Its properties are useful for printing of dissolvable support structures as well as the development of novel bioinks.