PDMS Curing Inhibition on 3D-Printed Molds: Why? Also, How to Avoid It?

Area of Science:

• Materials Science
• Analytical Chemistry
• Microfabrication

Background:

• Three-dimensional (3D) printing, particularly stereolithography (SLA), is increasingly used for microfabricating analytical devices and soft lithography molds.
• Commercial SLA resins often contain components that inhibit the curing of polydimethylsiloxane (PDMS), a common elastomeric material for microfluidics.
• This inhibition prevents reliable replication of 3D-printed structures in PDMS, limiting its application in microdevice fabrication.

Purpose of the Study:

• To investigate the cause of PDMS curing inhibition by commercial SLA resins.
• To identify effective post-curing treatments for 3D-printed structures to enable successful PDMS replication.
• To support the accurate fabrication of miniaturized analytical devices and microfluidic molds using 3D printing and PDMS.

Main Methods:

• Systematic study of 16 commercial SLA resins.
• Analysis of 3D-printed structures using Raman spectroscopy, nuclear magnetic resonance (NMR), and high-resolution mass spectrometry (HRMS).
• Evaluation of UV and/or thermal post-curing treatments to assess their efficacy in supporting PDMS replication.

Main Results:

• Phosphine oxide-based photo-initiators leaching from 3D-printed SLA structures were identified as the cause of PDMS catalyst poisoning.
• UV and/or thermal post-curing treatments effectively eliminated or sequestered these photo-initiators.
• Post-curing resulted in the formation of high molecular weight species, preventing catalyst inhibition and enabling accurate PDMS replication.

Conclusions:

• Post-curing treatments are crucial for overcoming PDMS curing inhibition caused by SLA resins.
• Understanding the chemical nature of inhibitors (phosphine oxides) allows for targeted remediation strategies.
• This study provides a straightforward method to enable reliable PDMS replication from 3D-printed molds, advancing microfabrication techniques.