# Development of Dynamic Four-Dimensional Printing Technology for Patterned Structures by Applying Microcellular Foaming Process

## TL;DR

This paper introduces a new 4D printing method using microcellular foaming to create dynamic structures with common materials like PLA.

## Contribution

The study presents a novel 4D printing approach using microcellular foaming instead of smart materials.

## Key findings

- 3D-printed specimens with microcellular foaming showed predictable deformations due to asymmetric expansion.
- The method achieved 4D printing using conventional materials like PLA without requiring shape-memory materials.
- Bending behavior was controlled by adjusting patterning and foaming conditions.

## Abstract

Four-dimensional (4D) printing adds the dimension of time to 3D-printed specimens, causing movement when external stimuli are applied. This movement enables applications across various fields, including the soft robotics, aerospace, apparel, and automotive industries. Traditionally, 4D printing has utilized special materials such as shape-memory polymers (SMPs) or shape-memory alloys (SMAs) to achieve this movement. This study explores a novel approach to 4D printing by applying microcellular foaming processes (MCPs) to 3D printing. This study primarily aims to design and fabricate patterned specimens using common materials, such as PLA, through 3D printing and to analyze their dynamic behavior under various foaming conditions. To demonstrate the potential applications of this technology, the degree of bending was measured by controlling the patterning and foaming conditions. The 3D-printed specimens with microcellular foaming exhibited predictable deformations owing to the asymmetric expansion caused by differential gas saturation. The results confirm that 4D printing can be realized using conventional materials without the need for smart materials and can introduce foaming processes as a new external stimulus. This study highlights the potential of combining 3D printing with microcellular foaming for advanced 4D printing applications.