Enzymatically stable, non-cell adhesive, implantable polypyrrole/thiolated hyaluronic acid bioelectrodes for in vivo signal recording.

Implantable bioelectrodes have attracted significant attention for precise in vivo signal transduction with living systems. Conductive polymers, including polypyrrole (PPy), have been widely used as bioelectrodes due to their large surface areas, high charge injections, and versatilities for modification. Especially, several natural biopolymers, such as hyaluronic acid (HA), can be incorporated into conductive polymers to produce biomimetic electrodes with better biocompatibility. However, HA-incorporated PPy electrodes (PPy/HA) frequently lose their original performances after implantation in the body because of the deterioration of material properties, such as degradation of natural biopolymers in the electrode. Here, thiolated HA (HA-SH) was synthesized and introduced into PPy electrodes (PPy/HA-SH) to enhance the enzymatic stabilities of PPy electrodes against hyaluronidase (HAase) and endow these electrodes with robust resistances to non-specific cell adhesion, thereby enabling prolonged signal transmission. Unlike PPy/HA, PPy/HA-SH resisted cell adhesion even in the presence of HAase. Subcutaneous implantation studies revealed that PPy/HA-SH formed less fibrotic scar tissue and permitted more sensitive and stable signal recording for up to 15 days after implantation as compared to PPy/HA. These findings hold significance for the design and advancement of biocompatible implantable bioelectrodes for a wide range of applications, such as neural electrodes, cardiac pacemakers, and biosensors.