Multilayer 3D bioprinting and complex mechanical properties of alginate-gelatin mesostructures

Abstract

In the biomedical field, extrusion-based 3D bioprinting has emerged as a promising technique to fabricate tissue replacements. However, a main challenge is to find suitable bioinks and reproducible procedures that ensure good printability and generate final printed constructs with high shape fidelity, similarity to the designed model, and controllable mechanical properties. In this study, our main goal is to 3D print multilayered structures from alginate-gelatin (AG) hydrogels and to quantify their complex mechanical properties with particular focus on the effects of the extrusion process and geometrical parameters, i.e. different mesostructures and macroporosities. We first introduce a procedure including a pre-cooling step and optimized printing parameters to control and improve the printability of AG hydrogels based on rheological tests and printability studies. Through this procedure, we significantly improve the printability and flow stability of AG hydrogels and successfully fabricate well-defined constructs similar to our design models. Our subsequent complex mechanical analyses highlight that the extrusion process and the mesostructure, characterized by pore size, layer height and filament diameter, significantly change the complex mechanical response of printed constructs. The presented approach and the corresponding results have important implications for future 3D bioprinting applications when aiming to produce replacements with good structural integrity and defined mechanical properties similar to the native tissue, especially in soft tissue engineering. The approach is also applicable to the printing of gelatin-based hydrogels with different accompanying materials, concentrations, or cells.

Block Polyelectrolyte Additives That Modulate the Viscoelasticity and Enhance the Printability of Gelatin Inks at Physiological Temperatures

“…The diameter D of the deposited filaments was measured by imaging the filaments. At a constant translational speed of V = 1 mm·s –1 , the printability characteristics (estimated using the spreading ratio or the ratio of the deposited filament to the inner nozzle diameter 71 ) were found to be strongly dependent on the extrusion rate Q ( Figure 8 D). The lowest Q = 0.01 μL·s –1 resulted in the highest resolution of printing (or the lowest spreading ratio), emerging from the least accumulation of ink on the substrate.…”

Predicting the hyperelastic properties of alginate-gelatin hydrogels and 3D bioprinted mesostructures

“…We used the experimental data of our previous study on multilayer bioprinting of AG hydrogel 21 . Briefly, alginate (type PH163) was purchased from Vivapharm, JRS PHARMA GmbH & Co. KG, and gelatin (type A, 300 bloom derived from porcine skin) was purchased from Sigma Aldrich (Germany).…”

“…For mechanical testing, we performed cyclic compression-tension tests using a Discovery HR-3 rheometer (TA instruments, New Castle, Delaware, USA) equipped with an 8 mm diameter parallel geometry, as described in detail in Ref. 21 . Briefly, we glued an 8 mm circular piece of fine sandpaper to the top (upper loading surface) geometry and attached the samples to it using an instant adhesive (super glue gel, Pattex).…”

“…2 ), as we limited ourselves to a time-independent Ogden hyperelastic model to characterize the hydrogel material.

Figure 2 Extracting the mean curve from the cyclic compression-tension testing data from 21 for use in hyperelastic FE simulation and validation. The curves are exemplary shown for the third cycle of testing the D6P6H75 sample.

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“…Alginate-gelatin (AG) hydrogels have proven expedient as they are easy to prepare and use and provide a cell-friendly environment 18 – 20 . Moreover, using an appropriate fabrication method makes it possible to bioprint multilayer mesostructures with AG hydrogels 21 .…”