Linking Processing Parameters and Rheology to Optimize Additive Manufacturing of k-Carrageenan Gel Systems

Abstract

Additive manufacturing—in particular, three-dimensional (3D) printing—has been introduced since the late 1980s, offering a novel paradigm for engineering design and manufacturing, as it allows the fabrication of very complex structures. Additive manufacturing of hydrogels is a very popular method to produce scaffolds to be used in tissue engineering and other biomedical applications, as well as in other advanced technological areas. When printing a thermoreversible physical hydrogel, a subtle balance between thermal and rheological parameters exists. The characteristic times of the sol–gel transition, regulated by a well-defined thermal history, must be optimized with respect to the characteristic processing times. In this work, we use this thermo-rheological approach to the additive manufacturing of a physical hydrogel. A low-cost desktop 3D printer for thermoplastic polymers was suitably modified to print a 1.5 wt% solution of k-carrageenan. The thermal behavior of the printer was determined by performing experimental measurements of the temperature–time evolution during the different processing steps, from solution loading, to the extrusion of the incoming gel, to the final solidification stage. In parallel, linear viscoelastic oscillatory shear measurements were performed in a rotational rheometer under thermal histories as close as possible to those previously measured in the printing process. The comparison between the rheological results and the quality of printing under different thermal histories is presented and discussed, highlighting the main relations between rheological and processing behavior, which are helpful in the assessment and optimization of the printing conditions.

3D-Printed Chitosan-Based Hydrogels Loaded with Levofloxacin for Tissue Engineering Applications

“…Furthermore, all scaffolds that were printed at 37 °C had a perfect reproducibility, independently of the nozzle size used, and all scaffolds printed at this temperature that were wet were significantly different from those that were dry, with their mean Pr values being nearly the optimum value of 1 ( p < 0.001, Figure b) . Hence, it was concluded that a temperature of 37 °C is the best temperature for printing scaffolds as it promotes good gelation conditions in order for a continuous, smooth, and uniform filament extrusion to manufacture grid constructs with well-formed squared pores . This was also applicable for scaffolds with other infill densities, namely, 60, 80, and 100%, using the G25 extrusion nozzle (Figure ).…”

“…51 Hence, it was concluded that a temperature of 37 °C is the best temperature for printing scaffolds as it promotes good gelation conditions in order for a continuous, smooth, and uniform filament extrusion to manufacture grid constructs with well-formed squared pores. 53 This was also applicable for scaffolds with other infill densities, namely, 60, 80, and 100%, using the G25 extrusion nozzle (Figure 6). CS has been reported to contribute to the formation of compact hydrogels used for 3D printing, though by itself, CS is not sufficient to print scaffolds that have stable structures.…”

“…In addition, the increased pressure also led to higher stress and more visible shear thinning of the hydrogel, which has been reported to result in a higher extrusion swelling rate of the printed filaments. 44,53 Apart from pressure influencing the filament width, temperature also had an effect, as filament width and consecutively U increased when the temperature was increased from 25 to 37 °C (Figure 4a,b). These observations were expected since the increased temperature decreased the viscosity of the hydrogel, facilitating the deposition process and thus resulting in a more uniform flow of the hydrogel through the nozzle with only a few restrictions.…”

Effects of Rheological Properties on 3D Printing of Poly(lactic acid) (PLA) and Poly(hydroxy alkenoate) (PHA) Hybrid Materials

“…There is a minimum adhesion strength at the print speed of 80 mm/s for the virgin PLA. Russo Spena et al 44 investigated the characteristic time, defined as the duration required for the deposition of two consecutive filament layers, as a function of print speed. Their findings indicate that longer depositing times or slower printing speeds result in enhanced adhesion to the previous layer, thus contributing to improved quality of the printed parts.…”

On the gelation of humins: from transient to covalent networks

“…Deformation forces or temperature can provide sufficient energy to break these bonds, eventually reaching a flowing state lacking any interconnected microstructure. 70 Humins, as a physical gel, are prone to undergo this transition, not exclusively under flow (developing a yield stress) but also when exposed to elevated temperatures. For this purpose, humins that were previously reacted at 80 °C for 300 min were then submitted to a temperature ramp of 2 °C min −1 and the corresponding viscoelastic response was measured.…”