3D Printing of Food to Study Oral Processing
Creators: name: RANDO, PIETRO
Publisher: name: University of Surrey
Year: 2021

description: "Food 3D Printing (F3DP) is a novel additive manufacturing process which allows to fabricate three dimensional objects with customized shapes, structure and composition, using edible materials. F3DP is currently being investigated to produce personalised food, such as food with textures adapted for people with swallowing disorders and healthier food with lower amount of fats and sugars, localizing these ingredients between printed layers (Godoi et al., 2019).
description: Often 3DP foods are built with an extrusion process: objects are deposited layer by layer on a build plate, sintering together after deposition. The overall process can be complex and many phenomena occurs at the same time: flow of non-Newtonian material in the nozzle, cooling and solidification after deposition and sintering between adjacent layers. The complexity of the overall printing process was simplified by identifying simple “unit operations”. This approach allowed investigating systemically and quantitatively the relationship between material rheological and heat transfer properties, printing conditions and the characteristics of the final products. Chocolate and starch suspensions were used as printing materials.
description: The rheological behaviour of different chocolate formulations was characterized to investigate the flow behaviour of molten material in the nozzle. Chocolate with 38\% cocoa butter content showed good extrudability at nozzle temperatures higher than 26°C and printing velocities lower than 16 mm/s. A model based on chocolate rheological properties was proposed to to predict the pressure drop and maximum shear rate at printer nozzle wall. During extrusion, the pressure drops decreases at lower printing velocity and higher nozzle temperature; whereas the maximum shear rate was mainly affected by the printing velocity.
description: IR thermography has been used to measure in-situ, during printing, the cooling dynamics of printed structures and interpreted using a heat transfer model; while printing conditions such as nozzle and environmental temperature, printing velocity and printing strategy were varied systematically. 3D structures were successfully manufactured below a critical printing velocity (Vp), depending on the environmental temperature (Te). At Te = 18°C Vp should be lower than 16 mm/s while at 20 °C lower than 8 mm/s, ensuring a sufficient cooling time and solidification of the cocoa butter, which is needed for print stability. The printing strategy can drastically change the local heat transfer dynamics and therefore the printing conditions leading to stability or collapse of the 3D structures. Finally, a stability criterion based on the local yield stress is proposed to explain the stability or collapse of the prints.
description: A computational model has been proposed to simulate the sintering of 3D printed filaments. Navier-Stokes equation were solved using an Arbitrary Eulerian-Lagrangian (ALE) formulation to investigate the coupling between layer sintering and material cooling after deposition. Increasing the filament diameter led to slower sintering and cooling; whereas a nozzle temperature of 32°C enhanced the sintering dynamics due to the lower viscosity of the extruded material. Finally, higher heat transfer coefficients due to convective conditions can improve the cooling of chocolate after deposition resulting on slower sintering dynamics.
description: F3DP is also proposed as a tool to manufacture solid and semi-solid starch products having controlled internal structures, geometrical properties and porosity, to investigate the dispersion kinetics and mechanical behaviour during food destructuration, in conditions inspired by food oral processing.
description: An in-vitro apparatus was developed in order to study the combined effect of hydration, compression and dispersion of starch structures in conditions inspired by oral processing. Results show that, hydration lowered the yielding properties of the starch structures. Most prints yield and collapse under a normal stress of 10 kPa, applied to mimic the palate-tongue compression. After breakage of the food structure, starch disperses rapidly due to the higher solid surface area in contact with the liquid.
description: The results obtained in this work can help optimising F3DP printing conditions, based on the physical properties of the food product to be printed. 3D printed food can in turn be used to study the destructuration of semi-solid food, to better understand oral processing."