Enzymatic depolymerization of polyurethanes: discovery, mechanisms, and engineering of hydrolases

Area of Science:

• Polymer Science
• Biotechnology
• Biocatalysis

Background:

• Polyurethane (PU) recycling is difficult due to its complex structure and limited enzymatic accessibility.
• Sustainable plastic recycling necessitates novel approaches like enzymatic depolymerization for polymer circularity.

Purpose of the Study:

• To review recent advancements in discovering, understanding, and engineering PU-degrading enzymes.
• To highlight challenges and future opportunities in enzymatic polyurethane biorecycling.

Main Methods:

• Screening approaches: culture-based assays, high-throughput screening, omics mining, machine learning.
• Enzyme classification: targeting polyester soft-segment ester bonds (cutinases, lipases, esterases) and hard-segment carbamate linkages (urethanases).
• Engineering strategies: active-site remodeling, loop engineering, computational simulations (QM/MM).

Main Results:

• Progress in identifying and characterizing PU-degrading enzymes, including esterases and urethanases.
• Engineering efforts have enhanced enzyme activity and specificity for PU components.
• Integrated chemo-enzymatic processes, like glycolysis followed by urethanase hydrolysis, show practical potential for monomer recovery.

Conclusions:

• Enzymatic PU depolymerization is a promising strategy for sustainable recycling.
• Challenges remain in degrading bulk PU due to its heterogeneity and crosslinking.
• Future directions include AI-aided discovery, enzyme engineering, and modular bioprocess design for scalable PU biorecycling.