Dynamic Solvent Responsiveness through Polarity-Driven Shape Transformation of 4D-Printed Responsive Cellulosic...

Four-dimensional (4D) printing represents a paradigm shift in additive manufacturing, enabling the creation of dynamic, stimuli-responsive structures that can change shape or function over time. This study introduces a significant advancement in this field by developing 4D-printed responsive cellulosic composite (RCC) strips consisting of varying ratios of AFFINISOL (AFF, a hydroxypropyl methylcellulose derivative) and thermoplastic starch (TPS) using fused filament fabrication (FFF) technology. Further, 4D-printed RCC strips were characterized for thermal properties, which revealed glass transition temperature (T_g) between 97 and 104 °C as well as fluid uptake of approximately 70% in 4 h. Subsequent investigation, focused on evaluating the solvent-responsive shape-memory behavior of RCC strips using water as a solvent, highlighted the maximum shape recovery index (SRI), i.e., 0.98 within 105 min. Next, to demonstrate the responsive nature of the RCC strips, the shape-memory behavior was evaluated in solvents with varying polarities. The results revealed a clear interplay between solvent polarity and the rate of shape recovery of RCC strips. The strips demonstrated exceptional recovery in water; however, their recovery was severely hindered in ethanol (EtOH) with an SRI of 0.14 within 105 min and was completely absent in n-hexane. We attribute this polarity-driven response to RCC matrix-solvent interactions and the differential diffusion rate of solvents within the RCC matrix, validated using various hydroalcoholic solutions. These findings establish an avenue for innovative solvent-responsive shape-memory behavior of RCC and underscore the future potential of FFF-mediated 4D-printed RCC strips for biomedical, tissue engineering, soft robotics, and reconfigurable systems applications.