An in-depth investigation on novel electro-activated shape memory polymer composites (SMPCs) for digital light processing 3D-Printing, consisting of a poly(ethylene glycol) diacrylate/poly(hydroxyethyl methacrylate) matrix embedding multi-walled carbon nanotubes (CNTs), is reported here. The composition of the photocurable (meth)acrylate system is finely tuned to tailor the thermomechanical properties of the matrix, whereas the effect of CNTs on the photoreactivity and rheological properties of the formulations is investigated to assess the printability. Electrical measurements confirmed that the incorporation of CNT into the polymeric matrix enables the electrical conductivity and thus the possibility to remotely heat the nanocomposite using the Joule effect. The feasibility to drive a shape memory cycle via Joule heating is proved, given that the high shape fixity (R f ) and shape recovery (R r ) ratios achieved (R f ≈ 100%, R r > 95%) confirmed the significant electrically-triggered responsiveness of such CNT/SMPCs. Finally, it is shown how to activate a modular and selective electro-activated shape recovery, which may ultimately envisage the 4D-Printing of remotely and selectively controllable smart devices.

Cyclodextrin with up to 10 bis(acyl)phosphanoxide functions serves as an initiator for highly cross-linked swellable hydrogels from mono-acrylates.

A novel cyclodextrin‐derived multiacrylated macromer (Ac‐γ‐CD) is successfully prepared and tested for the generation of highly crosslinked materials by means of UV‐curing. The high photoreactivity of the macromer under UV‐light irradiation is confirmed by means of real‐time photorheology. Moreover, dynamic mechanical thermal analyses proved that the properties of the thermosetting networks can be easily tailored by varying the concentration of the macromer in the precursor formulation. Finally, different Ac‐γ‐CD‐based formulations are successfully used as innovative inks to reproduce several computer‐aided design files by digital light processing 3D printing.

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In the present study, a different approach for the preparation of poly(ethylene glycol) diacrylate-gelatin (PEGDA-gelatin) hydrogels was investigated. Gelatin type A from porcine skin was used as the co-initiator of a radical photo-initiating system instead of the traditional aliphatic or aromatic amines. This became possible because, upon visible-light irradiation, the amine sequences within gelatin generate initiating free-radicals through the intermolecular proton transfer in a Norrish type II reaction with camphorquinone (CQ). PEGDA-gelatin hydrogels were prepared by visible-light-induced photopolymerization. The gelatin content in the precursor formulations was varied. The influence of gelatin on the kinetics of the photocuring reaction was investigated, and it was found that gelatin fastened the rate of polymerization at all concentrations. The covalent attachment of gelatin segments within the cross-linked hydrogels was evaluated by means of attenuated total reflectance-infrared spectroscopy (ATR-FTIR) spectroscopy after solvent extraction. The thermo-mechanical properties, as well as the swelling behavior and gel content, were also investigated.

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The shape memory (SM) capabilities of nanocomposites based on two photocurable acrylated/methacrylated resins, doped with carbon nanotubes (CNTs), and manufactured by digital light processing 3D printing were investigated. The mechanical properties and glass transition temperature (T g ) can be tailored in a broad range by varying the weight ratio of the two resins (T g ranging from 15 to 190 °C; Young's modulus from 1.5 to 2500 MPa). Shape fixity (S F ) and recovery (S R ) ratios are strongly influenced by the temperature being significantly higher at temperatures close to the T g . The results confirm that the S F strongly depends on the stiffness of chain segments between cross-linking points, whereas the S R mainly depends on the cross-link density of the network. CNT addition barely affects the S F and S R in the conventional oven, whereas the recovery speed using IR heating is significantly increased for the doped nanocomposites due to their higher IR absorbance.