A number of cell culture approaches have been described for maintenance of primary hepatocytes. Forming hepatocytes into 3D spheroids is one well accepted method for extending epithelial phenotype of these cells. Our lab has previously observed enhanced function of 2D (monolayer) hepatocyte cultures in microfluidic devices due to increased production of several hepato-inductive growth factors, including hepatocyte growth factor (HGF). In the present study we wanted to test a hypothesis that placing hepatocytes spheroids (3D) into microfluidic devices will also result in enhanced phenotype and function. To test this hypothesis, we fabricated devices with small and large volumes. Both types of devices included a microstructured floor containing arrays of pyramidal wells to promote assembly of single hepatocytes into spheroids with individual diameter of ~100 µm. The hepatocyte spheroids were found to be more functional in low volume compared to large volume devices. Importantly, high functionality of spheroid cultures correlated with elevated levels of HGF secretion. While decay of hepatic function (albumin secretion) was observed over the course three weeks, this behavior could be abrogated by inhibiting TGF-β1 signaling. With TGF-β1 inhibitor, microfluidic hepatocyte spheroid cultures maintained high and stable levels of albumin synthesis over the course of four weeks. To further highlight utility of this culture platform for liver disease modeling, we carried out alcohol injury experiments in microfluidic devices and tested protective effects of interleukin (IL)-22 - a potential therapy for alcoholic hepatitis.

Hepatocytes are parenchymal cells of the liver responsible for drug detoxification, urea and bile production, serum protein synthesis, and glucose homeostasis. Hepatocytes are widely used for drug toxicity studies in bioartificial liver devices and for cell-based liver therapies. Because hepatocytes are highly differentiated cells residing in a complex microenvironment in vivo , they tend to lose hepatic phenotype and function in vitro . This paper first reviews traditional culture approaches used to rescue hepatic function in vitro and then discusses the benefits of emerging microfluidic-based culture approaches. We conclude by reviewing integration of hepatocyte cultures with bioanalytical or sensing approaches.

Liver cultures may be used for disease modeling, testing therapies, and predicting drug‐induced injury. The complexity of the liver cultures has evolved from hepatocyte monocultures to co‐cultures with non‐parenchymal cells and finally to precision‐cut liver slices. The latter culture format retains liver's native biomolecular and cellular complexity and therefore holds considerable promise for in vitro testing. However, liver slices remain functional for ≈72 h in vitro and display limited utility for some disease modeling and therapy testing applications that require longer culture times. This paper describes a microfluidic device for longer‐term maintenance of functional organotypic liver cultures. This microfluidic culture system is designed to enable direct injection of liver tissue into a culture chamber through a valve‐enabled side port. Liver tissue is embedded in collagen and remained functional for up to 31 days, highlighted by continued production of albumin and urea. These organotypic cultures also express several enzymes involved in xenobiotic metabolism. Conversely, matched liver tissue embedded in collagen in a 96‐well plate loses its phenotype and function within 3–5 days. The microfluidic organotypic liver cultures described here represent a significant advance in liver cultivation and may be used for future modeling of liver diseases or for individualized liver‐directed therapies.

Abstract. Recently, a supramolecular model was developed for predicting striated skeletal muscle intensity profiles obtained by label-free second harmonic generation (SHG) microscopy. This model allows for a quantitative determination of the length of the thick filament antiparallel range or M-band (M), and results in M ¼ 0.12 μm for single-band intensity profiles when fixing the A-band length (A) to A ¼ 1.6 μm, a value originating from electron microscopy (EM) observations. Using simulations and experimental data sets, we showed that the objective numerical aperture (NA) and the refractive index (RI) mismatch (Δn ¼ n 2ω − n ω ) between the illumination wave (ω) and the second harmonic wave (2ω) severely affect the simulated sarcomere intensity profiles. Therefore, our recovered filament lengths did not match with those observed by EM. For an RI mismatch of Δn ¼ 0.02 and a moderate illumination NA of 0.8, analysis of single-band SHG intensity profiles with freely adjustable A-and M-band sizes yielded A ¼ 1.40 AE 0.04 μm and M ¼ 0.07 AE 0.05 μm for skeletal muscle. These lower than expected values were rationalized in terms of the myosin density distribution along the myosin thick filament axis. Our data provided new and practical insights for the application of the supramolecular model to study SHG intensity profiles in striated muscle.

Precision-cut tissue slices are an important in vitro system to study organ function because they preserve most of the native cellular microenvironments of organs, including complex intercellular connections. However, during sample manipulation or slicing, some of the natural surface topology and structure of these tissues is lost or damaged. Here, we introduce a microfluidic platform to perform multiple assays on the surface of a tissue section, unhindered by surface topography. The device consists of a valve on one side and eight open microchannels located on the opposite side, with the tissue section sandwiched between these two structures. When the valve is actuated, eight independent microfluidic channels are formed over a tissue section. This strategy prevents cross-contamination when performing assays and enables parallelization. Using irregular tissues such as an aorta, we conducted multiple in vitro and ex vivo assays on tissue sections, including short-term culturing, a drug toxicity assay, a fluorescence immunohistochemistry staining assay, and an immune cell assay, in which we observed the interaction of neutrophils with lipopolysaccharide (LPS)-stimulated endothelium. Our microfluidic platform can be employed in other disciplines, such as tissue physiology and pathophysiology, morphogenesis, drug toxicity and efficiency, metabolism studies, and diagnostics, enabling the conduction of several assays with a single biopsy sample.