Millimeter-thick 3D tissues constructed by densely cellularized core-shell microfluidic bioprinting

Recently, microfluidic bioprinting methods, which utilize microfluidic devices as printheads to deposit microfilaments, have improved printing resolution. Despite the precise placement of cells, current efforts have not succeeded in forming densely cellularized tissue within the printed constructs, which is highly desired for the biofabrication of solid-organ tissues with firm tissue consistency. In this paper, we presented a microfluidic bioprinting method to fabricate 3D tissue constructs consisting of core-shell microfibers where ECMs and cells can be encapsulated within the core of the fibers. Using the optimized printhead design and printing parameters, we demonstrated the bioprinting of core-shell microfibers into macroscale constructs and checked the viability of cells after printing. After culturing the printed tissues using the proposed dynamic culture methods, we analyzed the morphology and function of the tissues both in vitro and in vivo. The confluent tissue morphology in the fiber cores indicates the establishment of intensive cell-cell contacts in the fiber cores, which also leads to the upregulation of the albumin-secretion function compared to the cells cultured in a 2D format. Analysis on the cell density of the confluent fiber cores indicate the formation of densely cellularized tissues with a similar level of cell density of in-vivo solid organ tissues. In the future, better culture techniques with improved perfusion design are anticipated to enable further the fabrication of thicker tissues, which can be used as thick tissue models or implantation grafts for cell therapy.

Establishment of a resazurin-based aortic valve tissue viability assay for dynamic culture in a microphysiological system

BACKGROUND/AIM

Tissue pathogenesis of aortic valve (AV) stenosis is research focus in cardiac surgery. Model limitations of conventional 2D culture of human or porcine valvular interstitial/endothelial cells (VIC/VECs) isolated from aortic valve tissues but also limited ability of (small) animal models to reflect human (patho)physiological situation in AV position raise the need to establish an in vitro setup using AV tissues. Resulting aim is to approximate (patho)physiological conditions in a dynamic pulsatile Microphysiological System (MPS) to culture human and porcine AV tissue with preservation of tissue viability but also defined ECM composition.

MATERIALS/METHODS

A tissue incubation chamber (TIC) was designed to implement human or porcine tissues (3×5 mm2) in a dynamic pulsatile culture in conventional cell culture ambience in a MPS. Cell viability assays based on lactate dehydrogenase (LDH)-release or resazurin-conversion were tested for applicability in the system and applied for a culture period of 14 days with interval evaluation of tissue viability on every other day. Resazurin-assay setup was compared in static vs. dynamic culture using varying substance saturation settings (50-300μM), incubation times and tissue masses and was consequently adapted.

RESULTS

Sterile dynamic culture of human and porcine AV tissue segments was established at a pulsatile flow rate range of 0.9-13.4μl/s. Implementation of tissues was realized by stitching the material in a thermoplastic polyurethane (TPU)-ring and insertion in the TIC-MPS-system. Culture volume of 2 ml caused LDH dilution not detectable in standard membrane integrity assay setup. Therefore, detection of resazurin-conversion of viable tissue was investigated. Optimal incubation time for viability conversion was determined at two hours at a saturated concentration of 300μM resazurin. Measurement in static conditions was shown to offer comparable results as dynamic condition but allowing optimal handling and TIC sterilization protocols for long term culture. Preliminary results revealed favourable porcine AV tissue viability over a 14 day period confirmed via resazurin-assay comparing statically cultured tissue counterparts.

CONCLUSIONS

Human and porcine AV tissue can be dynamically cultured in a TIC-MPS with monitoring of tissue viability using an adapted resazurin-assay setup. Preliminary results reveal advantageous viability of porcine AV tissues after dynamic TIC-MPS culture compared to static control.