Domain: Engineering — Biomedical Engineering
Target concept: Biomechanics

Video generation prompt: The porcine knee cartilage samples were placed on an indentation tester, and a spherical indenter was used to apply a vertical load at a constant rate onto the cartilage surface. The load was maintained for 3 seconds before being removed, and the cartilage surface's subsequent response continued to be recorded, with the indentation depth curve displayed synchronously.

Evaluation guide:
(i) Target concept: Viscoelastic indentation response of hydrated biological tissue under controlled compressive loading.
Minimum mechanism: Cartilage must behave as a porous, permeable, fluid-saturated solid matrix, enabling reversible, time-dependent deformation with recoverable strain and load-dependent fluid redistribution.
(ii)Storyline: Frame 1–2: Static setup, cartilage on platform, indenter suspended above. Frame 3–5: Loading, indenter descends vertically, contacts cartilage, surface deforms downward. Frame 6–7: Hold, indenter motionless, cartilage surface remains stably indented (no creep/sag). Frame 8–9: Unloading, indenter ascends vertically, cartilage surface rises continuously. Frame 10: Recovery complete, surface returns to original contour; curve ends at baseline. Perspective: Fixed frontal/slightly oblique view showing full indenter-cartilage-platform relationship; no occlusion; curve overlay positioned adjacent to setup, always visible.

Manual:
Experimental Procedure
1. Porcine knee cartilage sample placed centrally on indentation tester platform.
2. Spherical indenter lowered vertically until contacting cartilage surface.
3. Indenter applies continuous downward motion at constant rate, indenting cartilage.
4. Motion pauses for observable duration (hold phase).
5. Indenter retracts vertically at constant rate while cartilage recovers.
Observation of Experimental Phenomena
- Cartilage deforms vertically only at contact point during loading.
- Surface remains stable and intact during hold phase.
- Cartilage recovers fully and continuously to original contour after retraction.
- Synchronized indentation depth curve shows loading rise, flat hold segment, unloading descent ending at baseline.
Summary of Experimental Principles
Biomechanical response of articular cartilage to compressive load reflects its viscoelastic and biphasic nature: solid matrix resistance + interstitial fluid pressurization govern instantaneous deformation and time-dependent recovery.

Prompt Grounding rubric:
level_1: No porcine cartilage sample is visible; no spherical indenter is shown; no indentation-tester platform appears; there is no vertical loading action; no indentation depth curve is displayed on screen.
level_2: Only some of the required elements appear: the cartilage sample, the indenter, or the platform is shown alone, without the others; or a curve display appears but no loading action is shown; the cartilage, indenter, and platform never appear together in the same shot.
level_3: The cartilage sample rests on the indentation-tester platform, the spherical indenter is in contact with the cartilage surface, downward motion of the indenter is visible, and an indentation-depth curve is displayed on screen, but the curve's shape does not clearly show three separate segments for loading, hold, and unloading.
level_4: Everything in score 3 holds, and additionally the cartilage sample, indenter, and platform all remain visible together in the same shot throughout loading, the 3-second hold, and unloading; contact between indenter and cartilage is sustained with no sudden separation mid-hold; the on-screen curve clearly shows three distinct segments corresponding to loading, hold, and unloading.
level_5: Everything in score 4 holds, and additionally the indenter, cartilage sample, platform, and curve display all stay fully visible and unobstructed by any extraneous object for the entire sequence; the camera keeps the same framing throughout with no cut, zoom, or pan; the indenter shows no visible drift or wobble while it is held stationary during the 3-second hold.

Scientific and Causal Correctness rubric:
level_1: The cartilage behaves as if perfectly rigid, like bone or metal: the indenter produces no visible deformation at all; or the cartilage shows no return toward its original shape after the indenter lifts away; the depth curve shows no flat hold segment; deformation happens sideways or diagonally instead of straight down.
level_2: The cartilage deforms, but in a way inconsistent with viscoelastic cartilage behavior: it fractures, tears, or collapses irreversibly; the indenter punches all the way through it; the depth curve rises the whole time with no hold plateau and no unloading segment; or the recovery phase is missing, or the surface overshoots past its original contour instead of settling back to it.
level_3: The cartilage deforms straight down under the indenter, holds roughly the same shape during the 3-second hold with no obvious sagging or bulging, and partially rises back toward its original contour once the indenter lifts away; the depth curve shows a rising loading segment, a roughly flat hold segment, and a falling unloading segment, but the surface does not fully return to its starting level, or the curve shows an abrupt discontinuous jump instead of a smooth change.
level_4: Everything in score 3 holds, and additionally the cartilage surface deforms smoothly during loading, holds a steady depth without visible sagging or bulging through the 3-second hold, and rises continuously and essentially all the way back to its original contour after the indenter lifts away; the curve shows a smooth loading rise, a flat hold segment, and a smooth unloading fall that ends back at or very close to the starting baseline, with no jagged jumps.
level_5: Everything in score 4 holds, and additionally the deformation stays localized directly under the indenter tip without spreading out sideways across the whole cartilage surface; the surface shows no visible cracking or splitting; the upward recovery motion mirrors the downward loading motion in speed and smoothness; the curve sits flat at the same baseline level both before loading starts and after recovery finishes.

Spatiotemporal Consistency rubric:
level_1: The cartilage sample or the indenter jumps to a different position between frames; the frame suddenly goes from normally lit to a completely different lighting with no cause; the platform disappears and reappears; the indenter changes size or tilt abruptly mid-motion; the cartilage surface appears indented before the indenter has touched it, or stays indented after the indenter has fully lifted away.
level_2: Multiple spatial breaks occur: the indenter is shown above the cartilage in one frame and at full indentation depth in the very next frame with no motion shown in between; the cartilage surface's height jumps between frames instead of changing smoothly; the depth curve resets or glitches partway through; the background shifts abruptly.
level_3: The cartilage sample and platform stay in the same place relative to each other and to the frame; the indenter moves continuously downward, then holds still, then moves continuously upward, with no jumps; the cartilage surface deforms smoothly with no sudden jumps in height; the on-screen curve updates smoothly in step with the motion; no object flickers, warps, or breaks apart.
level_4: Everything in score 3 holds, and additionally the indenter's path is strictly vertical with no side-to-side wobble; the cartilage's deformation spreads outward from the contact point without distorting into an odd shape; the curve's slope visibly changes at essentially the same moment as each corresponding change in the indenter's motion (loading start, hold start, unloading start), not noticeably before or after; the light on the cartilage and indenter stays the same brightness and direction for the whole sequence, so no shadow suddenly swings to a new angle.
level_5: Everything in score 4 holds, and additionally there is no stretching, shearing, or perspective warping of the cartilage or indenter between frames; the motion never strobes or skips; there is no unexplained shift in relative position between the foreground (indenter, cartilage) and the background; the indenter is never shown passing behind the cartilage edge when it should visibly be in front of it.