Biocompatible cracked reduced graphene oxide strain sensors: enhancing implantable strain sensing performance and durability

Implantable strain sensors that reliably detect various biomechanical signals in vivo are essential electronic devices for advanced biomedical and bioengineering technologies. However, it is a challenge to prepare soft implantable strain sensors with high linear sensitivity, good mechanical/chemical stability, and proper biological compatibility. Here, we report the preparation, mechanics, and applications of soft and implantable cracked reduced graphene oxide-based electro-mechanical strain sensors for monitoring internal tissue or organ dynamics that also address the aforementioned limitations. These skin-like strain sensors are composed of a high-quality microwaved reduced graphene oxide multilayer and a microcracked polymer substrate. By adopting both prestrain and hybrid reduction strategies, we successfully developed novel implantable graphene strain sensors that exhibit a set of unique properties, including high strain linear sensitivity (∼876.7 GF over a range of 0% to 30% strain), excellent mechanical durability (10 000 strain cycles at a strain of 20%) and chemical stability in biological fluids (a saline solution for 7 days), and excellent in vitro and in vivo biocompatibility. We also demonstrated the use of our implantable sensors for reliably measuring the strain associated with in vivo dynamic cardiac activity and for assessing preclinical cardiovascular drugs.