Double-layer perfusable collagen microtube device for heterogeneous cell culture

A self-assembly and cellular migration based fabrication of high-density 3D tubular constructs of barrier forming membranes

Three-dimensional (3D) in vitro models, superior in simulating physiological conditions compared to 2D models, offer intricate cell-cell and cell-ECM interactions with diverse signaling cues like fluid shear stress and growth factor gradients. Yet, developing 3D tissue barrier models, specifically perfusable luminal structures with dense, multicellular constructs maintained for extended durations with oxygen and nutrients, remains a technical challenge. Here, we describe a molding-based approach for the fabrication of free-standing, perfusable, high cellular density tissue constructs using a self-assembly and migration process to form functional barriers. This technique utilizes a polytetrafluoroethylene (PTFE)-coated stainless-steel wire, held by stainless steel needles, as a template for a perfusable channel within an elongated PDMS well. Upon adding a bio-ink mix of cells and collagen, it self-assembles into a high cell density layer conformally around the wire. Removing the wire reveals a hollow construct, connectable to an inlet and outlet for perfusion. This scalable method allows creating varied dimensions and multicellular configurations. Notably, post-assembly, cells such as human umbilical vein endothelial cells (HUVECs) migrate to the surface and form functional barriers with adherens junctions. Permeability tests and fluorescence imaging confirm that these constructs closely mimic in vivo endothelial barrier permeability, exhibiting the lowest permeability among all in vitro models in the literature. Unlike traditional methods involving uneven post-seeding of endothelial cells leading to subpar barriers, our approach is a straightforward alternative for fabricating complex perfusable 3D tissue constructs and effective tissue barriers for use in various applications, including tissue engineering, drug screening, and disease modeling.

Schwann cell-encapsulated chitosan-collagen hydrogel nerve conduit promotes peripheral nerve regeneration in rodent sciatic nerve defect models

Chitosan has various tissue regeneration effects. This study was designed to investigate the nerve regeneration effect of Schwann cell (SC)-encapsulated chitosan-collagen hydrogel nerve conduit (CCN) transplanted into a rat model of sciatic nerve defect. We prepared a CCN consisting of an outer layer of chitosan hydrogel and an inner layer of collagen hydrogel to encapsulate the intended cells. Rats with a 10-mm sciatic nerve defect were treated with SCs encapsulated in CCN (CCN+), CCN without SCs (CCN-), SC-encapsulated silicone tube (silicone+), and autologous nerve transplanting (auto). Behavioral and histological analyses indicated that motor functional recovery, axonal regrowth, and myelination of the CCN+ group were superior to those of the CCN- and silicone+ groups. Meanwhile, the CCN- and silicone+ groups showed no significant differences in the recovery of motor function and nerve histological restoration. In conclusion, SC-encapsulated CCN has a synergistic effect on peripheral nerve regeneration, especially axonal regrowth and remyelination of host SCs. In the early phase after transplantation, SC-encapsulated CCNs have a positive effect on recovery. Therefore, using SC-encapsulated CCNs may be a promising approach for massive peripheral nerve defects.

Human endothelial cells form an endothelium in freestanding collagen hollow filaments fabricated by direct extrusion printing

Fiber-shaped materials have great potential for tissue engineering applications as they provide structural support and spatial patterns within a three-dimensional construct. Here we demonstrate the fabrication of mechanically stable, meter-long collagen hollow filaments by a direct extrusion printing process. The fibres are permeable for oxygen and proteins and allow cultivation of primary human endothelial cells (ECs) at the inner surface under perfused conditions. The cells show typical characteristics of a well-organized EC lining including VE-cadherin expression, cellular response to flow and ECM production. The results demonstrate that the collagen tubes are capable of creating robust soft tissue filaments. The mechanical properties and the biofunctionality of these collagen hollow filaments facilitate the engineering of prevascularised tissue engineering constructs.

Flexibly Deformable Collagen Hydrogel Tube Reproducing Immunological Tissue Deformation of Blood Vessels as a Pharmacokinetic Testing Model

Since the biochemical reaction of blood vessels plays an essential role in immune response or various diseases, in vitro vascular models have high demand from medical fields. However, vascular models often tend to be difficult to mimic the biomedical reaction faithfully because of the lack of implementation of the tissue deformation. Here, an inflammatory mediator-induced deformation reaction of a blood vessel on a flexibly deformable collagen hydrogel tube device is reproduced. A self-standing collagen tube enables the tissue to deform flexibly in biochemical reaction and achieves contraction both at tissue and cell level. The contraction of tissue relieves the stress between cells under reaction to maintain cellular junctions even tight junctions are broken. Also, the drug perfusion test with antihistamine chemical is easily performed due to the connector part and properly inhibits the inflammatory reaction. Moreover, the traction force on endothelial cells is analyzed as about 0.9 µN on two types of scaffolds with different stiffness. It is believed that the potential of the flexible tissue model to reproduce biochemical reactions can contribute to the fabrication of vascular tissue models mimicking in vivo in high similarity as a platform for biomedical researches and pharmacokinetic testing.

Travelling ultrasound promotes vasculogenesis of three-dimensional-monocultured human umbilical vein endothelial cells

To generate three‐dimensional tissue in vitro, promoting vasculogenesis in cell aggregates is an important factor. Here, we found that ultrasound promoted vasculogenesis of human umbilical vein endothelial cells (HUVECs). Promotion of HUVEC network formation and lumen formation were observed using our method. In addition to morphological evaluations, protein expression was quantified by western blot assays. As a result, expression of proteins related to vasculogenesis and the response to mechanical stress on cells was enhanced by exposure to ultrasound. Although several previous studies have shown that ultrasound may promote vasculogenesis, the effect of ultrasound was unclear because of unregulated ultrasound, the complex culture environment, or two‐dimensional‐cultured HUVECs that cannot form a lumen structure. In this study, regulated ultrasound was propagated on three‐dimensional‐monocultured HUVECs, which clarified the effect of ultrasound on vasculogenesis. We believe this finding may be an innovation in the tissue engineering field.

Cell-encapsulated chitosan-collagen hydrogel hybrid nerve guidance conduit for peripheral nerve regeneration

Nerve guidance conduits (NGCs) composed of biocompatible polymers have been attracting attention as an alternative for autograft surgery in peripheral nerve regeneration. However, the nerve tissues repaired by NGCs often tend to be inadequate and lead to functional failure because of the lack of cellular supports. This paper presents a chitosan-collagen hydrogel conduit containing cells to induce peripheral nerve regeneration with cellular support. The conduit composed of two coaxial hydrogel layers of chitosan and collagen is simply made by molding and mechanical anchoring attachment with holes made on the hydrogel tube. A chitosan layer strengthens the conduit mechanically, and a collagen layer provides a scaffold for cells supporting the axonal extension. The conduits of different diameters (outer diameter approximately 2-4 mm) are fabricated. The conduit is bioabsorbable with lysozyme, and biocompatible even under bio absorption. In the neuron culture demonstration, the conduit containing Schwann cells induced the extension of the axon of neurons directed to the conduit. Our easily fabricated conduit could help the high-quality regeneration of peripheral nerves and contribute to the nerve repair surgery.

ECM-based microchannel for culturing in vitro vascular tissues with simultaneous perfusion and stretch

We present an extracellular matrix (ECM)-based stretchable microfluidic system for culturing in vitro three-dimensional (3D) vascular tissues, which mimics in vivo blood vessels. Human umbilical vein endothelial cells (HUVECs) can be cultured under perfusion and stretch simultaneously with real-time imaging by our proposed system. Our ECM (transglutaminase (TG) cross-linked gelatin)-based microchannel was fabricated by dissolving water-soluble sacrificial polyvinyl alcohol (PVA) molds printed with a 3D printer. Flows in the microchannel were analyzed under perfusion and stretch. We demonstrated simultaneous perfusion and stretch of TG gelatin-based microchannels culturing HUVECs. We suggest that our TG gelatin-based stretchable microfluidic system proves to be a useful tool for understanding the mechanisms of vascular tissue formation and mechanotransduction.

Engineered Liver-on-a-Chip Platform to Mimic Liver Functions and Its Biomedical Applications: A Review

Hepatology and drug development for liver diseases require in vitro liver models. Typical models include 2D planar primary hepatocytes, hepatocyte spheroids, hepatocyte organoids, and liver-on-a-chip. Liver-on-a-chip has emerged as the mainstream model for drug development because it recapitulates the liver microenvironment and has good assay robustness such as reproducibility. Liver-on-a-chip with human primary cells can potentially correlate clinical testing. Liver-on-a-chip can not only predict drug hepatotoxicity and drug metabolism, but also connect other artificial organs on the chip for a human-on-a-chip, which can reflect the overall effect of a drug. Engineering an effective liver-on-a-chip device requires knowledge of multiple disciplines including chemistry, fluidic mechanics, cell biology, electrics, and optics. This review first introduces the physiological microenvironments in the liver, especially the cell composition and its specialized roles, and then summarizes the strategies to build a liver-on-a-chip via microfluidic technologies and its biomedical applications. In addition, the latest advancements of liver-on-a-chip technologies are discussed, which serve as a basis for further liver-on-a-chip research.