Shengli Mi

Bioprinting three-dimensional cell-laden tissue constructs with controllable degradation.

Alginate hydrogel is a popular biologically inert material that is widely used in 3D bioprinting, especially in extrusion-based printing. However, the printed cells in this hydrogel could not degrade the surrounding alginate gel matrix, causing them to remain in a poorly proliferating and non-differentiating state. Here, we report a novel study of the 3D printing of human corneal epithelial cells (HCECs)/collagen/gelatin/alginate hydrogel incubated with a medium containing sodium citrate to obtain degradation-controllable cell-laden tissue constructs. The 3D-printed hydrogel network with interconnected channels and a macroporous structure was stable and achieved high cell viability (over 90%). By altering the mole ratio of sodium citrate/sodium alginate, the degradation time of the bioprinting constructs can be controlled. Cell proliferation and specific marker protein expression results also revealed that with the help of sodium citrate degradation, the printed HCECs showed a higher proliferation rate and greater cytokeratin 3(CK3) expression, indicating that this newly developed method may help to improve the alginate bioink system for the application of 3D bioprinting in tissue engineering.

The Boom in 3D-Printed Sensor Technology

Future sensing applications will include high-performance features, such as toxin detection, real-time monitoring of physiological events, advanced diagnostics, and connected feedback. However, such multi-functional sensors require advancements in sensitivity, specificity, and throughput with the simultaneous delivery of multiple detection in a short time. Recent advances in 3D printing and electronics have brought us closer to sensors with multiplex advantages, and additive manufacturing approaches offer a new scope for sensor fabrication. To this end, we review the recent advances in 3D-printed cutting-edge sensors. These achievements demonstrate the successful application of 3D-printing technology in sensor fabrication, and the selected studies deeply explore the potential for creating sensors with higher performance. Further development of multi-process 3D printing is expected to expand future sensor utility and availability.

Microfluidic co-culture system for cancer migratory analysis and anti-metastatic drugs screening

Tumour metastasis is an important reason for cancer death, and cancer cell migration is an important step in the process of tumour metastasis. Studying cancer cell migration is of great significance. Here, we present a novel microfluidic co-culture system and establish mild, moderate and severe cancer models by using HMEpiC and MDA-MB–231 cells to study cancer cell migration and anti-cancer drug screening. Using this device, we achieved high cell viability (over 90%) and a stable analysis of the migration ability of cancer cells. We observed that the density of the cancer cells determined the probability of the occurrence of metastatic cells and that the induction of normal cells affected the metastatic velocity of each cancer cell. We verified that the increase in the migration ability of MDA-MB-231 cells co-cultured with HMEpiC cells was relative to the increased secretion of IL-6 and that this was verified by an IL-6 inhibitor assay. This co-culture also led to decreased CK-14 secretion and morphological changes in HMEpiC cells. Finally, significant inhibition of paclitaxel and tamoxifen on cancer migration was observed. Taken together, our microfluidic device could be a useful tool for the quantitation of the migratory capability and anti-metastatic drug screening.

Tissue-engineered cornea constructed with compressed collagen and laser-perforated electrospun mat

While Plastic Compressed (PC) collagen technique is often used to fabricate bioengineered constructs, PC collagen gels are too weak to be sutured or conveniently handled for clinical applications. To overcome this limitation, electrospun poly (lactic-co-glycolide) (PLGA) mats, which have excellent biocompatibility and mechanical properties, were combined with PC collagen to fabricate sandwich-like hybrid constructs. By laser-perforating holes with different sizes and spacings in the electrospun mats to regulate the mechanical properties and light transmittance of the hybrid constructs, we produced hybrid constructs with properties very suitable to apply in corneal tissue engineering. The maximum tensile stress of the optimal hybrid construct was 3.42 ± 0.22 MPa. The light transmittance of the hybrid construct after perforation was approximately 15-fold higher than before, and light transmittance increased gradually with increasing time. After immersing into PBS for 7 days, the transmittance of the optimal construct changed from 63 ± 2.17% to 72 ± 1.8% under 500 nm wavelength. The live/dead staining, cell proliferation assay and immunohistochemistry study of human corneal epithelial cells (HCECs) and human keratocytes (HKs) cultured on the optimal hybrid construct both demonstrated that the cells adhered, proliferated, and maintained their phenotype well on the material. In addition, after culturing for 2 weeks, the HCECs could form stratified layers. Thus, our designed construct is suitable for the construction of engineered corneal tissue.

Construction of a liver sinusoid based on the laminar flow on chip and self-assembly of endothelial cells

The liver is one of the main metabolic organs, and nearly all ingested drugs will be metabolized by the liver. Only a small fraction of drugs are able to come onto the market during drug development, and hepatic toxicity is a major cause for drug failure. Since drug development is costly in both time and materials, an in vitro liver model that can accelerate bioreactions in the liver and reduce drug consumption is imperative in the pharmaceutical industry. The liver on a chip is an ideal alternative for its controllable environment and tiny size, which means constructing a more biomimetic model, reducing material consumption as well as promoting drug diffusion and reaction. In this study, taking advantage of the laminar flow on chips and using natural degradable gel rat tail Collagen-I, we constructed a liver sinusoid on a chip. By synchronously injecting two kinds of cell-laden collagen, HepG2-laden collagen and HUVEC-laden collagen, we formed two collagen layers with a clear borderline. By controlling the HUVEC density and injection of growth factors, HUVECs in collagen formed a monolayer through self-assembly. Thus, a liver sinusoid on a chip was achieved in a more biomimetic environment with a more controllable and uniform distribution of discrete HUVECs. Viability, album secretion and urea synthesis of the live sinusoid on a chip were analysed on days 3, 5 and 7 after collagen injection with acetaminophen treatment at 0 (control), 10 and 20 mM. The results indicated that our liver sinusoid on a chip was able to maintain bioactivity and function for at least 7 d and was beneficial for hepatotoxic drug screening.

Engineering of Corneal Tissue through an Aligned PVA/Collagen Composite Nanofibrous Electrospun Scaffold

Corneal diseases are the main reason of vision loss globally. Constructing a corneal equivalent which has a similar strength and transparency with the native cornea, seems to be a feasible way to solve the shortage of donated cornea. Electrospun collagen scaffolds are often fabricated and used as a tissue-engineered cornea, but the main drawback of poor mechanical properties make it unable to meet the requirement for surgery suture, which limits its clinical applications to a large extent. Aligned polyvinyl acetate (PVA)/collagen (PVA-COL) scaffolds were electrospun by mixing collagen and PVA to reinforce the mechanical strength of the collagen electrospun scaffold. Human keratocytes (HKs) and human corneal epithelial cells (HCECs) inoculated on aligned and random PVA-COL electrospun scaffolds adhered and proliferated well, and the aligned nanofibers induced orderly HK growth, indicating that the designed PVA-COL composite nanofibrous electrospun scaffold is suitable for application in tissue-engineered cornea.

Generation of Size-controlled Poly (ethylene Glycol) Diacrylate Droplets via Semi-3-Dimensional Flow Focusing Microfluidic Devices

Uniform and size-controllable poly (ethylene glycol) diacrylate (PEGDA) droplets could be produced via the flow focusing process in a microfluidic device. This paper proposes a semi-three-dimensional (semi-3D) flow-focusing microfluidic chip for droplet formation. The polydimethylsiloxane (PDMS) chip was fabricated using the multi-layer soft lithography method. Hexadecane containing surfactant was used as the continuous phase, and PEGDA with the ultraviolet (UV) photo-initiator was the dispersed phase. Surfactants allowed the local surface tension to drop and formed a more cusped tip which promoted breaking into tiny micro-droplets. As the pressure of dispersed phase was constant, the size of droplets became smaller with increasing continuous phase pressure before dispersed phase flow was broken off. As a result, droplets with size variation from 1 µm to 80 µm in diameter could be selectively achieved by changing the pressure ratio in two inlet channels, and the average coefficient of variation was estimated to be below 7%. Furthermore, droplets could turn into micro-beads by UV exposure for photo-polymerization. Conjugating biomolecules on such micro-beads surface have many potential applications in the fields of biology and chemistry.

Microfluidic system for modelling 3D tumour invasion into surrounding stroma and drug screening

Tumour invasion into the surrounding stroma is a critical step in metastasis, and it is necessary to clarify the role of microenvironmental factors in tumour invasion. We present a microfluidic system that simulated and controlled multi-factors of the tumour microenvironment for three-dimensional (3D) assessment of tumour invasion into the stroma. The simultaneous, precise and continuous arrangement of two 3D matrices was visualised to observe the migration of cancer cell populations or single cells by transfecting cells with a fluorescent protein. A vascular endothelial layer was formed to simulate transendothelial transport of nutrients, and its endothelial barrier function was verified by the diffusion of 70 kDa fluorescein isothiocyanate (FITC)-Dextran in 3D matrices. Through high-throughput cell migration tracking observation and statistic evaluation, we clarified that cell density of the tumour directly determined its invasiveness. The results suggested that increased secretion of IL-6 among both cancer cells (MDA-MB-231) and noncancerous cells (MCF-10A or HDF-n) after co-culture contributes to cancer cell invasiveness, and this was verified by an IL-6 inhibitor assay. Finally, the drug efficacy of paclitaxel was reflected as changes in cancer cell migration ability, viability, and morphology. Together, our microfluidic devices could be a useful tool to study the mechanism of tumour invasion into the stroma and to screen anti-metastatic drugs.