Hydrophilic crosslinked polymer networks, or hydrogels, are commonly studied systems for many biological applications ranging from corneal implants to drug delivery and wound dressings. The key attributes of hydrogels that make them particularly well-suited to biological applications are their high water content, biological stability, optical transparency, permeability to metabolites, and sufficient crosslinking to prevent dissolution. In order to expand the scope of hydrogels’ impact in the biomedical arena, several challenges must be addressed, primarily improving mechanical properties, without reducing its high water content and permeability.
Hydrogels made from zwitterionic materials have many interesting properties. Zwitterionic hydrogels have been studied as superabsorbants, with particular attention being paid to their swelling properties. We have previously reported low protein adhesion on sulfobetaine methacrylate and mixed charge hydrogels and low cell adhesion on carboxybetaine methacrylate gels. The zwitterionic gels studied so far have shown low mechanical strength,3, which limits their potential biological uses, but we have achieved high mechanical properties by designing and synthesizing a carboxybetaine dimethacrylate crosslinker. Thermally polymerized hydrogels with a compressive modulus of 8 MPa and 60% water content were made.
Photopolymerizing these hydrogels, on the other hand, improves the uniformity of the polymer network and results in an order-of-magnitude improvement in compressive modulus. With 50% water, hydrogels were made with a compressive modulus of 90 MPa. Furthermore, a redesign of the crosslinker to enable it to be more functionalizable allows for uniformly functionalizable hydrogels regardless of crosslinker content or physical properties, with a completely nonfouling background. These hydrogels were implanted subcutaneously into mice for 4 weeks to monitor their ability to reduce the foreign body response and minimize capsule formation. pHEMA hydrogels were used as a control.
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