Closed-Loop Controlled Photopolymerization of Hydrogels.

Area of Science:

• Polymer Science
• Materials Engineering
• Biomedical Engineering

Background:

• Hydrogel fabrication often lacks precise control over mechanical properties.
• Photopolymerization is a common method for hydrogel synthesis.
• Achieving consistent and tunable hydrogel mechanics is crucial for applications.

Purpose of the Study:

• To develop a closed-loop controlled photopolymerization process for hydrogel fabrication.
• To control the storage moduli of hydrogels using advanced control algorithms.
• To investigate the influence of control strategies on hydrogel structure and properties.

Main Methods:

• Utilized a piezoelectric cantilever sensor to monitor hydrogel crosslinking in real-time.
• Employed bang-bang and fuzzy logic controllers to manage the photopolymerization process.
• Characterized hydrogel composition, structure, and mechanical properties using Raman spectroscopy, SEM, and DMA.

Main Results:

• Demonstrated successful control over storage moduli for poly(ethylene glycol) dimethacrylate (PEGDMA) and poly(N-isopropylacrylamide) (PNIPAm) hydrogels.
• Identified that bang-bang control led to overshoot, which was improved by fuzzy logic and setpoint correction.
• Showed that cure time and UV exposure profile significantly impact PEGDMA hydrogel network structure and storage modulus.

Conclusions:

• Closed-loop control enables reproducible fabrication of hydrogels with desired mechanical properties.
• Fuzzy logic control offers enhanced precision in achieving target storage moduli compared to bang-bang control.
• This approach advances hydrogel engineering for pulsed and continuous photopolymerization processes.