Bioinspired 4D printing of nanocellulose hydrogels

Bioinspired 4D printing of nanocellulose hydrogels

• Autor
• Beatriz Arsuffi
• Co-autores
• Gilberto Siqueira , Mathilde Champeau , Silvia Titotto
• Resumo

• 4D printing consists in the design of responsive and dynamic structures. The concept of 4D printing arises from the addition of a 4th dimension to 3D printed parts. This 4th dimension is time combined with the possibility of transformation triggered by external passive stimuli, such as changes in temperature, light, pH, humidity, pressure, ion concentration, and vibration. Thus, unlike conventional 3D printing technologies that fabricate static and inanimate objects, 4D printing allows the creation of active structures that can be programmed to change their shape, function and/or properties over time after fabrication. To print dynamic structures with self-transformation (e.g. self-morphing, self-assembly, self-bending, self-curling), it is necessary to use responsive materials, i.e. materials that exhibit a stimuli-responsive behaviour, also known as smart materials. Most of the materials used in 4D printing are hydrogels, due to the availability of numerous responsive hydrogels and to their high absorption and swelling capacity. The changes of shape of 4D printed hydrogels is driven by a stress mismatch arising from the different swelling degrees in distinct parts of the structure upon application of external stimuli, mainly temperature and pH variations. Among the various smart hydrogels, the thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) is one of the most used in 4D printing, generally through the direct ink writing (DIW) technique. In DIW, a gel-like material, called ink, is dispensed out of small nozzles under controlled flow rates and deposited along digitally defined paths to fabricate 3D structures layer-by-layer. A crucial factor for a good printability of an ink by DIW is its shear behaviour. Naturally, gels exhibit shear-thinning behaviour, as they are composed of polymers, whose chains align during shearing. However, it is possible to enhance this behaviour by adding specific particles such as nanocellulose to its composition, which increases the zero-shear rate viscosity of the material, without increasing as much the viscosity at high shear rates. Moreover, the incorporation of cellulose nanocrystals (CNC) and nanofibers (CNF) in hydrogel inks is especially interesting because these particles can be aligned  during the shear thinning of the extrusion process of printing. And once aligned, nanocellulose can provide oriented swelling behaviour, which can be used to choreograph actuation and shape-morphing of the printed parts, generating anisotropic smart structures. However, unlike hygromorph biocomposites in which the natural fibres provide hygroscopic induced swelling, in bioinspired inks based on nanocellulose it is the hydrogel matrix that swells. In a similar mechanism to that present in certain plants, which have the ability to respond to environmental changes autonomously, by means of passive movements, known as nastism and tropism, due to variable cellular organisation and triggering cell wall swelling or shrinkage, which is achieved by orienting cellulose fibres in a swellable matrix of hemicellulose and lignin. Moreover, the use of nanocellulose, a natural, biodegradable, and biocompatible material, is in line with the growing interest in the materials science field for more environmentally friendly technologies. Therefore, bioinspired nanocellulose inks are potential candidates for several 4D printing applications, including tissue engineering, medicine, drug delivery, sustainable sensors, autonomous actuators, soft robotics, and smart packaging.

• Palavras-chave
• 4D printing, nanocellulose, hydrogels, programmable materials
• Modalidade
• Pôster
• Área Temática
• Nanociências & Nanotecnologia