(413b) Enzyme Pegylation Photo-Patternable Hydrogels for Long-Term Implantable Glucose Sensors

Enzyme PEGylation Photo-patternable Hydrogels for Long-term Implantable Glucose Sensors

Zhe Li¹, MS; Liangliang Qiang¹, PhD; Sagar Vaddiraju^1,2, PhD;

Fotios Papadimitrakopoulos^1,3, PhD^*

1 Nanomaterials Optoelectronics Laboratory, Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT 06269, United States

2 Biorasis Inc., 23 Fellen Road, Storrs, CT 06268, United States

3 Department of Chemistry, University of Connecticut, Storrs, CT 06269, United States

* E-mail address: papadim@mail.ims.uconn.edu

Abstract:

The function and lifetime of an implantable CGM device are intimately linked with the stability of the glucose oxidase (GO_x) enzyme, responsible for glucose detection.  Enzyme denaturation, loss due to imperfect immobilization and biofouling-induced pore-clogging gradually decrease device stability.  Poly(ethylene glycol (PEG)-ylated hydrogels offer an opportune venue to minimize biofouling, while retaining their highly hydrated state to prevent enzyme denaturation. These hydrogels, not only retain enzyme activity and provide good antifouling properties but also afford ease of fabrication via traditional photo-lithography methods.

A random copolymer based on PEGylated side chains together with cinnamyl ethyl methacrylate (CEMA) and glycidyl methacrylate (GMA) (namely poly(PEGMEM-CEMA-GMA)) was synthesized by free radical polymerization using azobisisobutyronitrile (AIBN) initiator.  The polymer was mixed with GO_x enzyme and drop-casted on the electrode, followed by UV exposure for crosslinking and 24 hour incubation for reaction between the GO_x-amine and hydrogel’s GMA-epoxide group. After enzyme PEGylation, GO_x showed 1.7 times higher activity at 37^oC, and when testing at 45^oC, PEGylated GO_x preserved 2 times higher activity comparing with GO_x only.

Glucose sensors utilizing GO_x-grafted, poly(PEGMEM-CEMA-GMA) hydrogels showed excellent stability during continuous testing for 30 days.  Control experiments with a hydrogel lacking the epoxide functionalities indicated that the majority of enzyme leached out within hours.  By retaining >65% mole ratio in PEG functionality, these hydrogels provide a good biofouling resistance against serum albumin.  The sensors exhibited a sensitivity of 320 nA mM^-1mm^-2 with an apparent Michealis-Menten constant of 25 mM of glucose and limit of detection of 1 µM. This hydrogel produces CGM sensors with long-term stability and optimal performance.