Tissue Mechanics -- Trichoplax adhaerens

12. Vivek N. Prakash, M. S. Bull and M. Prakash
Motility induced fracture reveals a ductile to brittle crossover in the epithelial tissues of a simple animal

(Accepted, in press, Nature Physics) (2020) 

[bioRxiv preprint link]

(Supplementary Video Gallery Below)

Video Gallery 

Video 1: Asexual reproduction by fission in Trichoplax adhaerens.

Time-lapse quasi-dark field imaging of animals in lab culture conditions using a DSLR camera. A single animal ‘splits into two’  by a binary fission process in about one hour. Video playback is sped up, and time stamp represents hours and minutes. Scale bar: 3 mm.

Video 2: Physiological tissue fractures in the ventral epithelium

of Trichoplax adhaerens.

Time-lapse quasi-dark field imaging of animals in lab culture conditions using a DSLR camera. The ventral epithelium sustains fracture holes which heal completely in about one hour. Video playback is sped up, and time stamp represents hours and minutes. Scale bar: 1 mm.

Video 3: Physiological tissue fractures in the dorsal epithelium

of Trichoplax adhaerens.

Time-lapse quasi-dark field imaging of animals in lab culture conditions using a DSLR camera. The dorsal epithelium sustains fracture holes which grow in size and do not heal. These animals eventually become long string-like animals over about 7 hours. Video playback is sped up, and time stamp represents hours and minutes. Scale bar: 3 mm.

Video 4: Ventral tissue fractures at a cellular resolution.

Time-lapse confocal imaging of animals in an open dish configuration matching native culture conditions. The ventral epithelium is tagged with a fluorescent cell membrane dye (green), and a lysotracker dye (red) that labels acidic granules in lipophil cells.  Videos are looped over ~5 secs, and the time stamps on images represent minutes and seconds. Scale bar: 50 um.

Video 5: Ventral tissue fracture healing.

Time-lapse confocal imaging of animals in an open dish configuration matching native culture conditions. This video is a continuation of the previous Video 4, and illustrates the tissue fracture healing process in the same animal. Videos are looped over 10 secs, and the time stamps on images represent minutes and seconds. Scale bar of images: 50 um.

Video 6: Thread rupture at a cellular resolution.

Time-lapse confocal imaging of animals in an open dish configuration matching native culture conditions. This video illustrates the final stages of the thread rupture process going all the way down to the breaking of a single cell-cell junction. The video corresponds to the same image sequence presented in Fig. S4C. The fluorescence and brightfield channels are overlayed for clarity. Video playback is real time, and time stamp represents minutes and seconds.  

Video 7: Model results with steady pulling.

We display the phase diagram from our heuristic tissue model, which explores a parameter sweep of steady force gradient versus the threshold strain for breaking cell-cell bonds. Next, we sequentially show simulations that demonstrate cases of elastic, ductile and brittle tissue properties — and their corresponding parameters on the phase diagram. The time stamps represent simulation units.  

Video 8: Model results with unsteady pulling.

We show simulations with unsteady pulling of the model tissue, and demonstrate how this captures both fractures and healing. The time stamps represent simulation units.

Video 9: Tension force-induced brittle fracture in Trichoplax adhaerens.

Time-lapse fluorescence microscopy imaging reveals a tensile force-induced fracture. The ventral epithelium is tagged using a lysotracker dye, which labels acidic granules in lipophil cells. Video playback is real time, and time stamp represents minutes and seconds. Scale bar: 0.5 mm.

Video 10: Shear force-induced brittle fracture in Trichoplax adhaerens.

Time-lapse fluorescence and bright field microscopy imaging reveals a shear force-induced fracture in the ventral epithelium. The dorsal epithelium is tagged using 0.5 um sticky, fluorescent micro-beads. A Particle Image Velocimetry (PIV) analysis is carried out to quantify the internal tissue velocity fields (highlighted by green arrows).  Video playback is sped up, and time stamp represents minutes and seconds. Scale bar: 1 mm.

Video 11: Non-affine motion analysis on experimental data.

Time-lapse fluorescence and bright field microscopy imaging reveals a shear force-induced fracture in the ventral epithelium. The dorsal epithelium is tagged using 0.5 um sticky, fluorescent micro-beads. A Particle Tracking analysis is carried out to quantify the non-affine motion of the micro-beads (with magnitude highlighted by colors).  Video playback is sped up, and time stamp represents minutes and seconds. Scale bar: 1 mm.

Video 12: Correlation between non-affine motion and internal strain rate,

in experimental data.

Time-lapse fluorescence and bright field microscopy imaging reveals a shear force-induced fracture in the ventral epithelium. The dorsal epithelium is tagged using 0.5 um sticky, fluorescent micro-beads. Larger values of non-affine motion are thresholded and overlayed (white dots) on contours (jet colorbar) of the internal strain rate calculated from the PIV analysis. Video playback is sped up, and time stamp represents minutes and seconds. Scale bar: 1 mm.

© 2020 Prakash Lab, Department of Physics, University of Miami, Coral Gables, FL

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