Fig 1.
Challenges and solution for multi-organ-systems.
a) General requirements for multi-organ-chips: i) initial separate loading of the respective cells; ii) individual culture for differentiation, formation, equilibration, and maturation of the tissues; and, iii) combined culture for drug screening purposes. b) Underlying concept of the μOrgano system: Schematics depicting the basic μOrgano components: the master-organ-chip and exemplary plug & play connectors. Conceptual idea of the usage principle of the μOrgano system for the connection of two MPSs in series via a simple linear channel connector with a close-up of the connected system highlighting the resulting media flow.
Fig 2.
Fabrication of μOrgano building blocks.
Schematic protocol for the fabrication of connectors (and MPSs) with precise in- and outlet positions via multi step UV-lithography: i) microscopic channel structures are patterned in photoresist using UV lithography; ii) macroscopic in- and outlets are patterned as pillars on top of the microscopic channel structures using a second UV lithography step; iii) microfluidic PDMS devices are fabricated with predefined in- and outlets via exclusion molding; iv) PDMS connectors are cut and bonded to pre-cut microscope slides; and, v) glass capillaries are inserted and bonded into the in- and outlets of the connectors.
Table 1.
Hydraulic resistance and back pressure occurring at a typical feeding rate of 20 μL / h for individual MPSs, linear connectors, and connected systems.
Fig 3.
Characterization of μOrgano building blocks.
a) Transition time of the interface of a liquid advancing through a system of two MPSs and a linear connector. The time necessary to advance from the cell chamber in MPS 1 to the cell chamber in MPS 2 is plotted versus the inner diameters of the glass capillaries in the respective systems. Insets show pictures of the respective glass capillaries (scale bars = 2 mm). b) Scatter plot of the transition times for ten independent systems connected by the same type of connectors featuring 50 μm ID capillaries. c) Time series of microscopy images from a channel section in the proximity of the inlet of the second MPS initially filled with clear water. The continuous transition occurring after connection to a MPS filled with coloured water using a food dye reveals the bubble less connection ability of the system (scale bar = 100 μm). d) Time series of pictures showing two MPSs connected by a linear connector whereby MPS 1 is prefilled with red dyed water, and MPS 2 and the connector with blue dyed water. Pumping red dyed water into MPS 1 leads to the replacement of the blue dyed water in both the connector and MPS 2 without the occurrence of leakage. e) Volume flown through MPS 2 (left; in flow direction) and MPS 3 (right) plotted as percentage of the total volume after connection to MPS 1 via a bifurcation connector.
Fig 4.
Proof of concept of the μOrgano system.
a) General procedure for biological experiments with the μOrgano system. b) Combined culture of two devices with 3T3 fibroblasts: Live (green) /dead (red) staining in both devices after 1 day of individual and 2 days of combined culture show that viability can be maintained. c) In-series culture of two heart-on-a-chip devices: tracings of the beating motion of cardiac tissue formed by hiPSC-cardiomyocytes—i) optical microscopy image—in two connected MPSs (ii) MPS 1; iii) MPS 2). The analysis using computational motion tracking reveals that a physiological phenotype is retained and individual cardiac devices beat with distinct frequencies. (scale bars = 200 μm).