Advances in thin film technology could soon offer a less invasive and more cost-effective solution to enhance neurosurgery for people with neurological brain conditions, including epilepsy.

In the 1950s, Drs. Talariach and Bancaud developed a new methodology called stereoelectroencephalography (sEEG) to place depth electrodes into burr holes drilled into a patient’s skull rather than performing a craniotomy to place cortical electrodes. The less-invasive implant procedure of sEEG electrodes compared to cortical electrodes has been shown to have a lower morbidity.

While sEEG allows for a better understanding of the deep brain structures, cortical electrodes can cover large continuous areas of the cerebral cortex or surface of the brain to obtain a holistic view of the neural network. In addition, there have not been any major changes to the manufacturing process or to the materials used in any commercially available electrodes.

Due to the cost and inefficiencies of labor-intensive manufacturing processes for cortical electrodes, companies began to explore the manufacturing of thin film electrodes leveraging modern microfabrication techniques in the late 1990s.

If the pharmacological therapy is not successful, the patient may then undergo an invasive surgical procedure to help identify the areas of the brain that are causing the seizures. (Credit: NeuroOne)

Today, designers and engineers of medical devices should be aware of the potential benefits of the latest patented thin film technology. Evo™ Cortical Electrodes (“Evo”), the first FDA-cleared thin film flexible electrodes for recording, monitoring, and stimulating brain tissue for up to 30 days, have demonstrated a reduction in the brain’s immunological response, potentially improving patient comfort and reducing signal artifacts.1,2, 3

Snapshot of Stakeholder Benefits

Designed to record brain activity and stimulate brain tissue for up to 30 days, the developers of this technology expect that it will generate substantial interest from neurologists and neurosurgeons managing patients with epilepsy and brain tumors.

With its thin film properties, this cortical electrode technology may enable minimally invasive delivery through a reduced size craniotomy. This capability is an important improvement because today’s commercially available silicone electrodes are heavier and thicker than the new thin film electrodes and are typically placed through a large craniotomy. In addition, silicone electrodes are handmade, making them costly and time-consuming to manufacture versus the current automated processes used to manufacture thin film technology.

Thin film flexible electrodes have demonstrated a reduction in the brain’s immunological response, potentially improving patient comfort and reducing signal artifacts. (Credit: NeuroOne)

Patients — The potential to place the device minimally invasively could be more appealing in the same way percutaneous valve surgery is more attractive than open chest valve surgery procedures. Epilepsy patients, for example, have been reluctant to agree to surgery to treat their epilepsy due to the invasiveness of the procedure, risk of infection, long hospital stay, and uncertain success rate.

In addition, there’s potential to improve comfort during the surgical procedure and post-surgery due to the product being eight times lighter and seven times thinner than silicone electrodes.

Surgeons/physicians — This technology could provide enhanced clinical electro-physiological value with decreased immunological response, reduced cost, and potentially lower infection risk.2 In addition, the thin film characteristics of the electrode may allow for less-invasive surgery as discussed previously. Also, the electrode contacts may be scaled down in size, improving the ability to increase resolution, as well as customize electrode configurations to meet physician requests.

Furthermore, the potential to significantly increase the resolution of brain recordings may enable the usage of powerful computing techniques, such as machine learning and artificial intelligence.

Medical device manufacturers — This technology represents a significant improvement over current, commercially available silicone electrodes that require manual labor to manufacture. In contrast, thin film technology utilizes automated manufacturing processes, allowing for improved efficiency and potentially shorter lead times to customers.

Impact on Epilepsy Market

Thin film cortical and depth electrodes made with lithographic polymer film technology are an effective way to increase mechanical flexibility and reduce mass. (Credit: NeuroOne)

Epilepsy affects more than 1 percent of the world’s population — more than 70 million people worldwide. Epilepsy and seizures affect more than 3.4 million Americans of all ages and accounts for about $15.5 billion in direct costs (medical) and indirect costs (lost or reduced earnings and productivity) each year. 3

Approximately 30 percent (720,000) of people with epilepsy in the United States are not receptive to pharmaceutical treatment, making them appropriate candidates for surgical treatment. 4

Currently, a person with epilepsy is typically treated with medications. If the pharmacological therapy is not successful, the patient may then undergo an invasive surgical procedure to help identify the areas of the brain that are causing the seizures.

This procedure, referred to as iEEG, is the practice of recording electroencephalographic signals via cortical or depth electrodes. After the diagnostic procedure, a second therapeutic surgical procedure is performed to treat the seizure onset location. The success rate of seizure freedom after surgery ranges between 30 to 70 percent depending on the seizure location and surgical treatment.

Because of the invasiveness of a craniotomy, neurosurgeons that perform epilepsy surgery predominantly use sEEG electrodes since they can be placed less invasively through a stereotactic procedure. There are clinical scenarios where implanting cortical electrodes and sEEG would potentially provide a more complete map of the brain by obtaining recordings from the surface and deep structures of the cortex.

Physicians also recognize the potential of thin film electrodes for applications with Parkinson’s disease, dystonia, essential tremors, and pain management for failed back surgery syndrome.

Optimal Mapping for the Brain

Today about 30–40 percent of people with epilepsy are candidates for surgery but only 3 percent undergo surgery. Now that thin film electrode arrays are poised for clinical practice, this could lead to more people opting for surgery because of the potentially less invasive nature of the surgery.

Leveraging thin film technology could be a defining moment in the world of medical devices by allowing the patient to receive “optimal mapping” of the brain. This enables the evaluation of activity both deep in the brain and from the surface by utilizing both cortical and depth electrodes simultaneously.

Thin film cortical and depth electrodes made with lithographic polymer film technology are an effective way to increase mechanical flexibility and reduce mass. This is a welcomed improvement for patients because they weigh less than traditional electrodes and conform more completely to the brain for more direct contact.

Given their flexibility and versatility, this technological advance is attracting interest from hospitals and research centers around the world. Ultimately, this technology’s high-definition recording may enable a doctor to be more precise in identifying the problematic tissue.

While many designers have been focused on software and hardware rather than electrode innovation, thin film electrode technology shows potential to eclipse current commercially approved electrode technologies by:

  • Enhancing recording resolution.

  • Being capable of stimulating brain tissue during a procedure for intraoperative mapping, which is conducted during surgeries to help surgeons identify and preserve essential functional tissue.

  • Reducing inflammation or being more “brain friendly.”

  • Using a minimally invasive placement method.

  • Can be implanted to record and identify the problematic brain tissue and can remain implanted until after ablative treatment is conducted. Leaving the device in place both eliminates the need for another surgery and supports more precise ablation than if the surgeon were to subsequently re-drill and re-insert an electrode for ablation only.

Given its key advantages, designers of this technology anticipate that minimally invasive thin film electrodes may become the new gold standard when performing iEEG procedures.


  1. Commercial Scale Production of Thin-Film Electrode Arrays for Clinical Intracranial EEG,” American Epilepsy Society, Annual Meeting, 2019.
  2. Development of Polyimide Electrodes for High-Resolution Intracranial EEG Recordings,” American Epilepsy Society, Annual Meeting, 2017.
  3. Multi-Resolution Intracranial EEG Rodent Recording System,” American Epilepsy Society, Annual Meeting, 2017.
  4. Epilepsy by the Numbers,” Living Well with Epilepsy, Nov. 25, 2018.
  5. L. Rudzinski , K. Medor , “Epilepsy Five New Things,” Neurology , Feb. 15 , 2011.
  6. M. Meglio , “Several Factors Influence Seizure Freedom After Epilepsy Surgery,” NeurologyLive, Feb. 11, 2020.

This article was written by Dave Rosa, President and CEO, NeuroOne Medical Technologies Corp., Eden Prairie, MN. For more information, visit here .