The Folding Behavior Of 4D DLP Printed Pnipam Based Hydrogels

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  • Hydrogels have attracted the attention of growing fields such as tissue engineering because of their unique characteristics such as biocompatibility with several cell types and tunable properties. In our study, we selected poly N- Isopropylacrylamide (pNIPAM) based hydrogel as this material has low critical solution temperature close to the human physiological temperature. However, more information is required on how manufacturing processes can affect the mechanical behaviour of the printed structure. In-vat polymerization processes stand out among additive manufacturing processes capable of efficiently producing NIPAM-based hydrogels. Among them, the digital light processing (DLP) process allows for its high resolution, printing speed, dimensional and spatial control of the printing process, isotropy of the layers and reduced process cost when compared to other vat polymerization processes. This work is dedicated to investigating how crosslinking rate and thickness of 4D DLP printed NIPAM based hydrogels affect their folding behaviour. Two different printing approaches were investigated: (i) a constant thickness exposed to constant light intensity over all the sample surfaces, and (ii) a constant thickness but exposed to a gradient light intensity over the sample surface. Results show that printed sample thickness plays a key role in the bending of the samples. Samples smaller than 0.25 mm bend uncontrollably and erratically, samples between 0.25 mm and 0.55 mm bend longitudinally, obtaining the final shape of a cylinder, while samples thicker than 0.55 mm are unable to bend. The variation of light intensity generates variations in the crosslinking rate of the samples, where regions with higher crosslinking rates are more rigid and with less bending capacity.

    Part of the Proceedings of the Canadian Society for Mechanical Engineering International Congress 2022.

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    Attribution-NonCommercial 4.0 International