Development of 4D Printed PLA Actuators with an Induced Internal Strain Upon Printing

The field of four-dimensional (4D) printing is still in its prime and lacking in tools to help designers and researchers in creating applicable structures that are 4D printed. In order for these tools to be available for researchers, testing and simulation work must be done on 4D printing and the shape memory effect of printed materials. In this work, testing of 4D printed actuators that have an induced strain upon printing is performed. The strain is induced in the printing process of fused deposition modelling. The induced strain allows a shape change upon stimulation of the materials after printing, removing the need for a programming step at which force, and stimulation are needed to program the temporary shape of the print. Two actuators and an open-sided box reservoir for drug delivery applications are proposed. Printing and shape change of polylactic acid are achieved and measured for the degree of bending of the actuators. The designs are printed at speed values of 10 mm/s and 60 mm/s for the passive and active layers, respectively. The printed samples are heated, and their bending angles are measured for replication by simulation. Finite element analysis (FEA) of the actuators is carried out to replicate the induced strain by using the thermal expansion of materials. The settings of the FEA are used to create a more complex structure and simulate its shape change. Deformation is achieved with values of 7.81 mm, 6.06 mm, and 4.84 mm in the z-axis direction for Design 1, Design 2, and the reservoir, respectively.