**3. Comparing "Utah" electrode arrays versus "Michigan" neural probes**

Implantable probe designs have primarily focused on modifying the size, shape, or geometry to minimize reactive cell responses. For the *"Utah" electrode array* [24] and the *"Michigan" neural probe* [25], Section 3.1 compares the spatial distribution of neurons (as related to improving recording quality), Section 3.2 compares the initial penetrating profile (as related to minimizing the insertion kill-zone), Section 3.3 compares the reactive responses (as related to preventing glial encapsulation), Section 3.4 compares the anchoring of the probe's position in the tissue (as related to reducing electrode micromotion), Section 3.5 compares the embedding of bioactive reagents (as related to eluting growth factors, anti-inflammatory drugs, etc.).

*3.1.2. Michigan neural probe*

Unlike the Utah electrode array [23], the planar Michigan probe [27] was only designed to take advantage of photolithographic manufacturing techniques from the semiconductor industry (**Figure 9A**). The extensibility of this platform technology enables these micromachined probes to be built with batch fabrication, easy customization of recording site placements or substrate shape, high reproducibility of geometrical/electrical characteristics, and the ability to integrate with ribbon cables or to incorporate on-chip electronics for signal conditioning (**Figure 9B**). Unfortunately, the Michigan probes are known to induce a chronic breach of the blood–brain barrier [28] which leads to more chronic inflammation and culminates in neurodegeneration and ultimately to electrode failure (as described in Section 2). For instance, Michigan probes showed a significantly higher breach and worse wound-healing in comparison to microwires. Since there is a trade-off between the size (spatial selectivity) and quality of signal recordings (sensitivity) in a neural microelectrode, previous research have altered the electrical properties by synthesizing biocompatible conducting polymers (**Figure 10A**) such as polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT) directly onto the electrode. Electrochemical deposition (**Figure 10B**) allows polymer films to be formed in a one-step process with a high degree of control over the film thickness and surface properties (e.g. with nanotubes in [27]).

**Figure 10.** (A) Scanning electron microscope of deposited polymer and (B) uncoated vs. PEDOT nanotube (NT) electrodes.

**Figure 9.** (A) Silicon-substrate Michigan probe and (B) microfabrication borrows semiconductors manufacturing methods.

Controlling the Biocompatibility and Mechanical Effects of Implantable Microelectrodes…

http://dx.doi.org/10.5772/intechopen.72659

181

#### **3.1. Spatial distribution of neurons**

#### *3.1.1. Utah electrode array*

**Figure 8.** (A) The 100 microelectrode Utah electrode array and (B) the electrode probe tips implanted into the cortex.

The Utah array was designed from the ground up (with new manufacturing techniques [26]) to meet the specific needs of a multichannel neural interface [24]. Psychophysical experiments usually require evoking discriminable patterned percepts from many electrodes. Therefore, the Utah array (**Figure 8A**) was designed to possess a large number (~100) of large electrodes (~1.5 mm) that are typically in a square grid that projects out from a thin (~0.2 mm) substrate. **Figure 8B** shows the tapered electrodes suspended in a "sea of glass" substrate (that isolates each of the individual electrodes in the array from each other (~0.4 mm separation) to form a very effective dielectric insulating layer between the adjacent electrodes). The electrode probe tips are coated with platinum, gold, or iridium to facilitate the electronic to ionic transduction. The array's substrate was designed to be thick enough to prevent breaking upon insertion, but thin enough to rest on the cortical surface without producing a constant downward force on the array that could push it further into the cortex.

#### *3.1.2. Michigan neural probe*

**3. Comparing "Utah" electrode arrays versus "Michigan" neural** 

Implantable probe designs have primarily focused on modifying the size, shape, or geometry to minimize reactive cell responses. For the *"Utah" electrode array* [24] and the *"Michigan" neural probe* [25], Section 3.1 compares the spatial distribution of neurons (as related to improving recording quality), Section 3.2 compares the initial penetrating profile (as related to minimizing the insertion kill-zone), Section 3.3 compares the reactive responses (as related to preventing glial encapsulation), Section 3.4 compares the anchoring of the probe's position in the tissue (as related to reducing electrode micromotion), Section 3.5 compares the embedding of bioactive reagents (as related to eluting growth factors, anti-inflammatory

The Utah array was designed from the ground up (with new manufacturing techniques [26]) to meet the specific needs of a multichannel neural interface [24]. Psychophysical experiments usually require evoking discriminable patterned percepts from many electrodes. Therefore, the Utah array (**Figure 8A**) was designed to possess a large number (~100) of large electrodes (~1.5 mm) that are typically in a square grid that projects out from a thin (~0.2 mm) substrate. **Figure 8B** shows the tapered electrodes suspended in a "sea of glass" substrate (that isolates each of the individual electrodes in the array from each other (~0.4 mm separation) to form a very effective dielectric insulating layer between the adjacent electrodes). The electrode probe tips are coated with platinum, gold, or iridium to facilitate the electronic to ionic transduction. The array's substrate was designed to be thick enough to prevent breaking upon insertion, but thin enough to rest on the cortical surface without producing a constant downward force on

**Figure 8.** (A) The 100 microelectrode Utah electrode array and (B) the electrode probe tips implanted into the cortex.

**probes**

180 An Excursus into Hearing Loss

drugs, etc.).

**3.1. Spatial distribution of neurons**

the array that could push it further into the cortex.

*3.1.1. Utah electrode array*

**Figure 9.** (A) Silicon-substrate Michigan probe and (B) microfabrication borrows semiconductors manufacturing methods.

Unlike the Utah electrode array [23], the planar Michigan probe [27] was only designed to take advantage of photolithographic manufacturing techniques from the semiconductor industry (**Figure 9A**). The extensibility of this platform technology enables these micromachined probes to be built with batch fabrication, easy customization of recording site placements or substrate shape, high reproducibility of geometrical/electrical characteristics, and the ability to integrate with ribbon cables or to incorporate on-chip electronics for signal conditioning (**Figure 9B**).

Unfortunately, the Michigan probes are known to induce a chronic breach of the blood–brain barrier [28] which leads to more chronic inflammation and culminates in neurodegeneration and ultimately to electrode failure (as described in Section 2). For instance, Michigan probes showed a significantly higher breach and worse wound-healing in comparison to microwires.

Since there is a trade-off between the size (spatial selectivity) and quality of signal recordings (sensitivity) in a neural microelectrode, previous research have altered the electrical properties by synthesizing biocompatible conducting polymers (**Figure 10A**) such as polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT) directly onto the electrode. Electrochemical deposition (**Figure 10B**) allows polymer films to be formed in a one-step process with a high degree of control over the film thickness and surface properties (e.g. with nanotubes in [27]).

**Figure 10.** (A) Scanning electron microscope of deposited polymer and (B) uncoated vs. PEDOT nanotube (NT) electrodes.
