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.

中文翻译：

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模拟水凝胶墨水 3D 打印：用于预测机械性能和支架变形的有限元框架

背景

伤口愈合过程中的困难可能会导致疤痕、慢性伤口和败血症。解决这些问题的常见组织工程策略依赖于开发模拟目标组织的结构、刚度和生物特性的 3D 水凝胶支架。精确控制水凝胶的空间沉积、结构和孔隙率的最有效的生物制造技术之一是3D打印技术。然而，如果没有充分选择打印属性，3D 打印结构的最终架构可能会受到影响。

目的

我们的主要目标是创建一个能够预测水凝胶支架 3D 打印过程中产生的变形的数值框架。我们的第二个目标是分析 3D 打印支架的整体机械性能是否受到这些变形的影响。

方法

我们使用 ABAQUS 有限元软件进行有限元分析来开发我们的数值框架。按时间顺序添加有限元，模拟材料沉积。通过用户定义的子程序 UMAT 对散装材料进行实验表征和数值表示。我们通过以 5 和 10 毫米/秒的速度“打印”5.0 × 5.0 × 0.8 海藻酸盐墨水来测试模拟。随后，最终的 3D 打印支架和理论未变形结构均受到初始高度 10% 的单轴压缩，并分析了它们整体机械性能之间的差异。

结果

数值框架捕获了支架丝之间的弯曲和底层的压缩。平均而言，与以 10 毫米/秒打印的支架相比，以 5 毫米/秒打印的支架变形量增加约 6%。然而，就整体机械性能而言，两者表现出相似的行为。然而，这种行为是高度非线性的，并且与理论的、未变形的支架显着不同，特别是在小应变的情况下。

结论

开发了一种数值框架，可用作定义打印速度、顺序和几何形状的初步工具，从而最大限度地减少 3D 打印过程中的变形。该框架有助于最大限度地减少实验，从而减少材料浪费。我们还发现，在使用有限元分析预测机械行为时，尤其是对于小应变应用，不应忽略这些变形。