Norbornene Homopolymerization Limits Cell Spreading in Thiol-Ene Photoclick Hydrogels

Area of Science:

• Biomaterials Science
• Tissue Engineering
• Polymer Chemistry

Background:

• Thiol-ene click chemistry is vital for creating 3D cell-spreading hydrogels.
• Thiol-norbornene reactions offer precise crosslinking but may cause unintended norbornene homopolymerization, hindering cell behavior.

Purpose of the Study:

• Investigate unintended norbornene homopolymerization in guest-host crosslinked norbornene-modified hyaluronic acid (NorHA) hydrogels.
• Determine the impact of norbornene density on hydrogel properties and cell morphology.

Main Methods:

• Fabrication of NorHA hydrogels with varying norbornene densities (f).
• Quantification of norbornene conversion and hydrogel stress relaxation.
• Culture of encapsulated human mesenchymal stromal cells (hMSCs) to assess morphology and spreading.

Main Results:

• Norbornene conversion exceeded stoichiometric thiol-ene expectations, indicating homopolymerization.
• Hydrogels with lower norbornene density (NorHA, f=8) showed significantly higher stress relaxation (93.0%) compared to higher density (NorHA, f=40, 42.3%).
• NorHA (f=8) hydrogels promoted hMSC spreading into spindle-like shapes, while NorHA (f=40) constrained cells into spherical morphologies.

Conclusions:

• Thiol-norbornene crosslinking is not fully stoichiometric in dilute systems, with homopolymerization occurring.
• Network topology, controlled by the number of norbornenes per chain (f), critically influences hydrogel permissivity for cell spreading.
• Optimizing polymer architecture is essential for developing advanced biomaterials for tissue engineering applications.