3D printing of hydrogels and thickened fluids for dysphagia managementin situ mixing and gelling

Resum

This thesis focuses on the development of new technologies for 3D food printing. Specifically, for foods with controlled rheological properties for use as dysphagia-oriented products. The first part of this work aims to develop a 3D printing system with gelification. It reports a successful 3D printing based in situ temperature-induced gelification procedure of κ-carrageenan aqueous dispersions. 3D printer was modified to handle low viscosity fluid feeding and more efficiently distribute ambient air at room temperature causing forced convection to accelerate the cooling of the printed layer. Thus obtained gel samples showed self sustaining capability and a rheological response comparable with a reference conventionally prepared gel. Moreover, the effect of main printing variables, such as temperature of the hotend, printing speed and layer height, on the linear viscoelastic response of the gels was analysed by application of the response surface methodology (RSM). In general, gel strength linearly increases by decreasing printing speed and layer height. A rise in the temperature of the hotend also increases the strength of the gel network, but only to a certain extent, above which not noticeable improvement in this regard was achieved. Based on the results obtained from this analysis, an optimisation method is proposed to minimise the temperature and time needed to 3D print a gel with pre-set rheological properties. Overall, this study demonstrates that it is possible to generate in situ 3D printed gel materials with potential uses in food and pharmaco-nutrition, without the aid of reactive additives or initiators, and using a facile protocol. After that, the design, implementation and evaluation of an accessory designed and manufactured to be adapted to a 3D printer to allow the in situ and continuous mixing of solid and liquid feeds is also described. In particular, the capacity of this accessory to correctly mix a dysphagia-oriented commercial powder thickener with several conventional fluids (i.e. water, juice, and milk) was studied. Target thickener concentrations were defined in order to achieve mixtures with viscosities corresponding to the textures established by the National Dysphagia Diet Task Force (NDD) —nectar-like, honey-like, and spoon-thick— for thickened fluids. Both the accuracy of the solid content and the rheological response of the obtained mixtures were evaluated. Although fluctuations were observed in the concentrations of the mixtures obtained by continuous mixing with respect to the target values, the viscosities obtained were within the limits established for each of the desired textures. The thickened fluids processed using the 3D printing mixing accessory showed viscosities very similar to their hand-mixed counterparts and a higher degree of structuration, especially when printed at low mass flow rates, as well as a lower amount of entrapped air. It is therefore intended and expected that these alternative methods of preparation allow the personalised production of gels and thickened fluids with more appealing shapes and colours for the long-term dysphagia management, improving the quality of life of patients with dysphagia, and promoting treatment compliance.