An electrical analog permeability model assessing fluid flow in a decellularized organ.

BACKGROUND AND OBJECTIVE: In recellularization, cell-seeding efficiency refers to the uniform distribution of cells across the decellularized organ, which should be enhanced to ensure effective functioning. During cell seeding, flow dynamics influence the distribution of cells because the driving force of cell movement is the fluid force. However, after decellularization, because of flow permeability through the vessel wall, the fluid pressure and velocity in the vessels of vascular trees are significantly reduced compared with those in the native organ, which might affect cell seeding efficiency. Therefore, it is necessary to assess the flow characteristics in the vessels of decellularized organs to select appropriate seeding conditions. Although electrical analog models have been widely used to investigate the flow distribution in organs, current models do not reflect the permeable conditions. This study proposes a model to extend the conventional electrical analog model to simulate the flow characteristics in decellularized organs. METHODS: A resistor reflecting permeable flow was added to the original electrical analog model to describe the permeable conditions in the decellularized organs. Decellularization and pressure drop measurements of the kidney were also conducted for model development, calibration, and validation. The developed model was then applied to a decellularized kidney to reveal changes in flow characteristics. RESULTS: The resistance calculation of permeable flow was determined for each generation of vascular trees. The coefficient of permeability can be indicated by the measured flow exiting through the outlet or the pressure drop across the decellularized organ. The developed permeability model had a qualitative and quantitative agreement with the experimental data without calibration. The results of the permeability model for the decellularized kidney indicated significant reductions of up to 70% in the flow rate and pressure of the organ compared to the native kidney. CONCLUSIONS: The developed model can simulate the flow characteristics in each individual vessel of decellularized organs. The results from the model can be used to assess the optimal flow rate condition for the cell seeding process.

Individual identification of goldfish from eye morphology: the eye mark method.

We developed an individual identification method for goldfish based on morphological variation of the iris. Each goldfish has a few dark lines (eye marks) in the rostral and caudal portion of the iris, which are blood vessels underneath the silvery reflective layer. Through the blood vessels and the locally thin reflective layer, the pigment cell layer is partially visible as a dark line. The pattern of the blood vessels was found to be temporally stable and unique to each individual. Using this feature, we successfully identified 10 individual goldfish, each sampled three times within a 4-month time period. The eye mark identification method was confirmed for a further 20 goldfish by comparison with identification based on screening at polymorphic microsatellite loci. The eye mark method is 100% accurate and can be used for studies in which multiple observations of individually identified goldfish are needed over long time periods, to avoid invasive tagging or individual housing that may affect the behavior of the fish.