Simulating 3D printing on hydrogel inks: A finite element framework for predicting mechanical properties and scaffold deformation

Background

Difficulties during the wound healing process may result in scarring, chronic wounds and sepsis. A common tissue engineering strategy to solve these problems rely on the development of 3D hydrogel scaffolds that mimic the structure, stiffness, and biological proprieties of the target tissue. One of the most effective biofabrication techniques to precisely control spatial deposition, architecture and porosity of hydrogels is 3D printing technology. However, final architectures of 3D printed structures can be compromised if the printing properties are not adequately selected.

Purpose

Our main goal was to create a numerical framework able to predict the deformations that arise due to the 3D printing process of hydrogel scaffolds. Our secondary goal was to analyze if the overall mechanical properties of the 3D printed scaffolds were affected by these deformations.

Methods

We applied finite element analysis using ABAQUS finite element software to develop our numerical framework. The finite elements were added in a time sequence, simulating the material deposition. The bulk material was experimentally characterized and represented numerically by the user-defined subroutine UMAT. We tested the simulation by ‘printing’ a 5.0 × 5.0 × 0.8 alginate ink at 5 and 10 mm/s. Afterwards, both the final 3D printed scaffolds and a theoretical non-deformed configuration were subjected to a uniaxial compression of 10 % of the initial height, and differences between their overall mechanical properties were analyzed.

Results

The numerical framework captured the bending between the scaffold filaments and the compression of the bottom layers. On average, the scaffold printed at 5 mm/s deformed ∼6 % more, compared to the scaffold printed at 10 mm/s. However, in terms of overall mechanical properties, both showed similar behavior. This behavior, however, was highly nonlinear and significantly different from the theoretical, non-deformed scaffold, particularly in a small strains’ regime.

Conclusions

A numerical framework that can be used as a preliminary tool to define the printing velocity, sequence and geometry, minimizing the deformations during the 3D printing process was developed. This framework can help to minimize experimentation and consequently, material waste. We also saw that these deformations should not be neglected when predicting the mechanical behavior using finite element analysis, particularly for small strains application.