Implantable probe with integrated reference electrode for in situ neural signal and calcium ion monitoring

Monitoring the electrophysiology activity of neurons and blood calcium signals can enable a better understanding of disease-related neural system circuits.However,currently,in situ calcium ion monitoring tools are scarce and exhibit low integration and limited sensitivity.In this letter,we propose an implantable probe with an integrated in situ Ag/AgCl reference electrode(ISA/ARE)that can monitor action potential(AP)and Ca^(2+) concentrations.

A flexible neural implant with ultrathin substrate for low-invasive brain–computer interface applications

Implantable brain–computer interface(BCI)devices are an effective tool to decipher fundamental brain mechanisms and treat neural diseases.However,traditional neural implants with rigid or bulky cross-sections cause trauma and decrease the quality of the neuronal signal.Here,we propose a MEMS-fabricated flexible interface device for BCI applications.The microdevice with a thin film substrate can be readily reduced to submicron scale for low-invasive implantation.An elaborate silicon shuttle with an improved structure is designed to reliably implant the flexible device into brain tissue.The flexible substrate is temporarily bonded to the silicon shuttle by polyethylene glycol.On the flexible substrate,eight electrodes with different diameters are distributed evenly for local field potential and neural spike recording,both of which are modified by Pt-black to enhance the charge storage capacity and reduce the impedance.The mechanical and electrochemical characteristics of this interface were investigated in vitro.In vivo,the small cross-section of the device promises reduced trauma,and the neuronal signals can still be recorded one month after implantation,demonstrating the promise of this kind of flexible BCI device as a low-invasive tool for brain–computer communication.

Brainmask:an ultrasoft and moist microelectrocorticography electrode for accurate positioning and long-lasting recordings

Bacterial cellulose(BC),a natural biomaterial synthesized by bacteria,has a unique structure of a cellulose nanofiberweaved three-dimensional reticulated network.BC films can be ultrasoft with sufficient mechanical strength,strong water absorption and moisture retention and have been widely used in facial masks.These films have the potential to be applied to implantable neural interfaces due to their conformality and moisture,which are two critical issues for traditional polymer or silicone electrodes.In this work,we propose a micro-electrocorticography(micro-ECoG)electrode named“Brainmask”,which comprises a BC film as the substrate and separated multichannel parylene-C microelectrodes bonded on the top surface.Brainmask can not only guarantee the precise position of microelectrode sites attached to any nonplanar epidural surface but also improve the long-lasting signal quality during acute implantation with an exposed cranial window for at least one hour,as well as the in vivo recording validated for one week.This novel ultrasoft and moist device stands as a next-generation neural interface regardless of complex surface or time of duration.

Stretchable Parylene-C electrodes enabled by serpentine structures on arbitrary elastomers by silicone rubber adhesive

The delicate serpentine structures are widely used in high-performance stretchable electronics over the past decade.The metal interconnects encapsulated in biocompatible polymer Parylene-C film is a superior choice for long-term implantation in vivo,especially as neural interface to acquire electrophysiological signals or apply electrical stimulation.To avoid the physical contact damages from the neural tissues such as the brain or peripheral nerves,serpentine interconnects are utilized as stretchable electrodes and usually bonded to the soft elastomer substrate.The adhesion strength between the serpentine interconnects and the elastomer substrate becomes a considerable issue to ensure reliability and structural integrity.In this paper,the stretchable Parylene-C electrodes can be transfer printed onto arbitrary elastomer substrates by a thin layer of silicone rubber adhesive with low modulus for electrocorticogram(ECoG)recording.Mechanical simulation of serpentine structures consisting of same periodic arcs and different straight segments is investigated by uniaxial stretching.Then,the elastic stretchability of serpentine electrodes is further studied by simulation and experiments.After 5000 repetitive stretching cycles,the electrochemical impedance of microelectrodes remains in steady states.These results prove that the silicone rubber adhesive facilitates the interfacial bonding in the structure of stretchable electrodes as the compliant and reliable neural interface.