Domain: Engineering — Biomedical Engineering
Target concept: Biomedical Materials

Video generation prompt: In the in vitro degradation experimental setup, equally sized biomedical degradable material samples of polylactic acid (PLA), polyglycolic acid (PGA), and polylactic-co-glycolic acid (PLGA) were placed and immersed in phosphate buffer solution (PBS) with pH = 7.4, maintained at 37°C. A schematic mass-loss progress curve for each sample was displayed over time, with the degradation areas marked in white.

Evaluation guide:
(i) Target concept: Real-time visualization of comparative hydrolytic degradation kinetics of three aliphatic polyesters in physiological buffer.
Minimum mechanism: Immersion in aqueous PBS at 37°C must drive surface-localized, time-dependent ester bond hydrolysis, producing measurable mass loss and visible surface erosion (marked in white), with inherent material-dependent rate hierarchy (PGA > PLGA > PLA) due to differences in hydrophilicity, crystallinity, and chain flexibility.
(ii)Storyline: Frame 1–2: Static wide shot showing three equally sized, labeled, side-by-side polymer samples immersed in clear PBS within temperature-controlled environment (37°C visible). Frame 3–5: Close-up region reveals initial white erosion markings appearing selectively on PGA surface only. Frame 6–8: Markings expand contiguously on PGA, then appear on PLGA; curve updates synchronously with new markings. Frame 9–10: PLA marking appears last; all three trend lines diverge visibly on curve with correct rank order; no sample detaches or distorts. Perspective: Fixed frontal view, no camera motion, full samples and curve always in frame; all labels, markings, and curve elements remain legible and spatially anchored.

Manual:
Experimental Procedure
1. Place equally sized rectangular PLA, PGA, and PLGA samples side-by-side in a transparent PBS-filled container.
2. Maintain at 37°C (e.g., inside labeled incubator).
3. Display real-time mass loss curve with three labeled trend lines.
Observation of Experimental Phenomena
- White degradation markings appear first on PGA, then PLGA, then PLA.
- Markings expand progressively on sample surfaces, never in bulk or liquid.
- Mass loss curve shows PGA steepest, PLGA intermediate, PLA shallowest.
Summary of Experimental Principles
- Degradation is hydrolytic, pH 7.4 PBS accelerates ester bond cleavage.
- Degradation rate depends on crystallinity and glycolide/lactide ratio: PGA (highly hydrophilic) > PLGA (tunable) > PLA (hydrophobic, semi-crystalline).

Prompt Grounding rubric:
level_1: None of the three material samples (PLA, PGA, PLGA) appear; no liquid-filled container representing the PBS bath is shown; there is no 37°C or incubator/heating context anywhere in the shot; no on-screen curve or progress indicator appears; no white markings appear on any sample.
level_2: At least one of the three samples is shown, but not all three; a container is visible but nothing marks it as a PBS bath; there is no visible 37°C label, incubator housing, or other heating context; the on-screen curve or progress indicator is missing or impossible to identify as such; no white degradation marking appears on any sample.
level_3: All three samples (PLA, PGA, PLGA) are visible and appear to be the same size as each other; the container is a clear, liquid-filled vessel with a PBS label or another clear indication that it holds phosphate buffer; a 37°C label, incubator housing, or other heating context is visible; an on-screen curve or progress indicator is displayed; white markings appear on the samples to indicate degraded areas.
level_4: All elements of score 3 are present AND: the three samples sit side by side in the same shot for the whole clip; the on-screen curve or indicator updates while the samples remain visible, rather than as a separate disconnected screen; white markings appear only on the sample surfaces (never on the container or background) and look the same shade of white on all three samples.
level_5: All elements of score 4 are present AND: each of the three samples is clearly labeled by name (PLA, PGA, PLGA) so a viewer can tell which is which without guessing; the curve or indicator shows three separate lines or markers, one per named sample, that do not overlap into a single unreadable line; white markings appear only where erosion is occurring on each sample, spread without flickering on and off, and clearly stay attached to their correct sample throughout.

Scientific and Causal Correctness rubric:
level_1: None of the three samples show any sign of degrading (no white marking ever appears); or a sample dissolves away almost instantly; or a sample changes to an unnatural color unrelated to degradation (e.g., turning blue); or a sample floats free or produces visible gas bubbles.
level_2: At least one sample shows a visible surface change, but all three samples show the same amount of change at the same time, with no visible difference between PLA, PGA, and PLGA; the on-screen curve (or indicator) shows the same trend for all three rather than three different ones; white marking appears on all three samples at the same rate regardless of which material it is.
level_3: PGA shows the earliest and most extensive white marking; PLA shows the least marking, appearing latest; PLGA falls visibly in between, matching the expected order (PGA fastest, PLGA in the middle, PLA slowest); the on-screen curve or indicator shows three different, steadily increasing trends rather than flat or identical lines; white markings appear only on the solid samples, never in the surrounding liquid, and grow over time in this same order.
level_4: All elements of score 3 are present AND: white markings stay on the outer surface or edges of each sample rather than appearing to originate from inside the sample's bulk; none of the three samples appears to swell, melt, or separate into layers; the order in which markings begin (PGA first, then PLGA, then PLA) matches the order in which the curve/indicator for each sample begins to rise.
level_5: All elements of score 4 are present AND: white marking only grows in areas where degradation is actively happening, never appearing ahead of time or fading back after it appears; none of the three samples breaks apart, crumbles, or comes loose from its position; the steepness of each sample's curve/indicator matches the expected order (PGA rising fastest, PLA slowest) without any two lines crossing or reversing order; placement, immersion, time passing, surface erosion, white marking, and curve rising all follow logically from one another.

Spatiotemporal Consistency rubric:
level_1: A sample's position jumps between frames; the container disappears and reappears; the curve or indicator jumps from one value to a very different one with no visible transition; a white marking blinks on and off without growing gradually; the lighting suddenly changes; a sample's apparent size or rotation changes without cause.
level_2: A sample's position visibly drifts more than about 10% of the frame's width between key moments; white markings appear or disappear abruptly instead of growing gradually; the curve line breaks apart or appears to redraw itself partway through the clip; the direction of shadows flips; the liquid level in the container appears to rise or fall in a way that doesn't make physical sense.
level_3: All three samples stay in the same position relative to each other for the whole clip; no sample or object disappears, duplicates, or visibly breaks apart; white markings appear and spread gradually, without blinking on and off or jumping in size; the curve or indicator updates smoothly, without gaps or sudden redraws; the lighting and shadows look the same from start to end; the liquid surface in the container stays level and still.
level_4: All elements of score 3 are present AND: the surface texture on each sample changes gradually rather than jumping between very different-looking states; the curve or indicator appears to draw in smoothly over time rather than jumping in large steps; white markings spread as a connected area rather than as scattered, disconnected specks; labels and markings do not flicker in and out of visibility.
level_5: All elements of score 4 are present AND: no frame appears frozen, duplicated, or skipped; there is no strobing, ghosting, or blur that makes it hard to tell which sample is which or where a marking's edge is; if the container shows any reflection or refraction, it stays visually consistent across frames; the spacing between samples and the position of each curve/label relative to its sample stay visually steady with no noticeable drift.