Digital Light Processing in a Hybrid Atomic Force Microscope: In situ, Nanoscale Characterization of the Printing Process

TL;DR

This paper introduces a hybrid DLP-AFM instrument enabling in situ, nanoscale characterization of the mechanical and rheological properties of resin voxels during 3D printing, advancing understanding of process heterogeneity.

Contribution

The study presents a novel hybrid instrument combining digital light processing with atomic force microscopy for real-time, high-resolution analysis of printing heterogeneity and resin behavior.

Findings

First in situ cure depth measurement during DLP printing.

Mapping mechanical properties of printed voxels in real-time.

Monitoring resin viscoelastic damping during patterning.

Abstract

Stereolithography (SLA) and digital light processing (DLP) are powerful additive manufacturing techniques that address a wide range of applications including regenerative medicine, prototyping, and manufacturing. Unfortunately, these printing processes introduce micrometer-scale anisotropic inhomogeneities due to the resin absorptivity, diffusivity, reaction kinetics, and swelling during the requisite photoexposure. Previously, it has not been possible to characterize high-resolution mechanical heterogeneity as it develops during the printing process. By combining DLP 3D printing with atomic force microscopy in a hybrid instrument, heterogeneity of a single, in situ printed voxel is characterized. Here, we describe the instrument and demonstrate three modalities for characterizing voxels during and after printing. Sensing Modality I maps the mechanical properties of just-printed, resin-immersed voxels, providing the framework to study the relationships between voxel sizes, print exposure parameters, and voxel-voxel interactions. Modality II captures the nanometric, in situ working curve and is the first demonstration of in situ cure depth measurement. Modality III dynamically senses local rheological changes in the resin by monitoring the viscoelastic damping coefficient of the resin during patterning. Overall, this instrument equips researchers with a tool to develop rich insight into resin development, process optimization, and fundamental printing limits.