Multielectrode Array - Disadvantages

Disadvantages

In vitro MEAs are less suited for recording and stimulating single cells due to their low spatial resolution compared to patch clamp and dynamic clamp systems. The complexity of signals an MEA electrode could effectively transmit to other cells is limited compared to the capabilities of dynamic clamps.

There are also several biological responses to implantation of a microelectrode array, particularly in regards to chronic implantation. Most notable among these effects are neuronal cell loss, glial scarring, and a drop in the number of functioning electrodes. The tissue response to implantation is dependent among many factors including size of the MEA shanks, distance between the shanks, MEA material composition, and time period of insertion. The tissue response is typically divided into short term and long term response. The short term response occurs within hours of implantation and begins with an increased population of astrocytes and glial cells surrounding the device. The recruited microglia then initiate inflammation and a process of phagocytosis of the foreign material begins. Over time, the astrocytes and microglia recruited to the device begin to accumulate, forming a sheath surrounding the array that extends tens of micrometres around the device. This not only increases the space between electrode probes, but also insulates the electrodes and increases impedance measurements. Problems with chronic implantation of arrays have been a driving force in the research of these devices. One novel study examined the neurodegenerative effects of inflammation caused by chronic implantation. Immunohistochemical markers showed a surprising presence of hyperphosphorylated tau, an indicator of Alzheimer's disease, near the electrode recording site. The phagocytosis of electrode material also brings to question the issue of a biocompatibility response, which research suggests has been minor and becomes almost nonexistent after 12 weeks in vivo. Research to minimize the negative effects of device insertion includes surface coating of the devices with proteins that encourage neuron attachment, such as laminin, or drug eluting substances.