Researchers from theUniversidad Politécnica de Madridand theIMDEA Materials Institute, in collaboration with German medical technology companyMeotec, have developed a degradation-triggered 4D printing method that allows gradual, time-controlled shape changes using standard fused filament fabrication (FFF). Published inAdditive Manufacturing, the study shows that hydrolytic degradation of polyvinyl alcohol (PVA) can be used as a programmed trigger to release elastic energy stored in polyethylene terephthalate glycol-modified (PETG), creating a new option for biomedical implants and adaptive structures.
Using degradation as an actuation mechanism
Four-dimensional (4D) printing refers to 3D printed structures that change shape over time in response to internal or external stimuli. Most existing systems rely on heat, light, electrical fields, or humidity to trigger transformation. In contrast, this research explores degradation itself as the trigger.
“This strategy introduces degradation as a powerful, yet underexplored, mechanism for triggering actuation in 4D-printed systems,” said Dr. William Solórzano, one of the authors behind the publication.
The approach combines PVA, a water‑soluble polymer traditionally used as a sacrificial support material in FFF, with PETG, a structural polymer capable of storing elastic energy and exhibiting shape recovery behavior.
In the printed multi-material system, PVA functions as a temporary mechanical constraint. When immersed in water, it gradually degrades, reducing its stiffness. As this constraint weakens, PETG releases stored elastic energy, producing a controlled and progressive shape transformation. Unlike rapid stimulus-driven systems, this mechanism enables slow, time-dependent actuation, which is particularly relevant for biomedical applications where gradual adaptation is required.
Mechanical degradation and exponential stiffness decay
The team conducted tensile and flexural testing to measure how PVA’s mechanical properties evolve during hydrolytic degradation. Initial tensile tests showed that dry PVA is stiff (elastic modulus around 5 GPa) and brittle. After immersion in water, samples exhibited an approximately 36% reduction in elastic modulus within 80 minutes, along with lower yield and tensile strength. The material also shifted from brittle to more ductile behavior. The degradation followed an exponential curve, consistent with molecular weight reduction during hydrolysis.
The study further found that, in solid samples, infill pattern did not significantly affect degradation rate. Instead, erosion speed depended on the surface area-to-volume ratio. This means designers can tune degradation timing by adjusting geometry.
PETG remained mechanically stable under immersion, though stress relaxation accelerated due to plasticization effects. The researchers modeled this behavior using a Prony-series viscoelastic model to predict long-term mechanical response.
Source: 3D Printing Industry
