Deep brain stimulation implantable devices

PHOTOS: BOSTON SICENTIFIC

Parkinson’s disease (PD), a neurodegenerative disorder affecting millions of people worldwide, causes muscle stiffness, slow movements, and tremors, making everyday tasks difficult to perform. Although there is no known cure, various treatments make PD more manageable, including deep brain stimulation (DBS) therapy, which delivers mild electrical stimulation to specific regions in the brain through implants powered by an implantable pulse generator (IPG) that sits inside the chest. Therapies improve PD symptoms, but do not slow or stop disease progression, making it imperative to have options to adjust treatments as the disease worsens. As with any fixed surgical implant, changing DBS treatment parameters – such as simulating different areas of the brain – can be difficult.

“The progression of PD necessitates a therapy that can evolve with the patient,” says Dr. Francisco Ponce, director of the Barrow Center of Neuromodulation in Phoenix, Arizona.

Cochlear-implant-inspired approach

To deliver a solution that improves patient comfort and enables physicians to easily adjust treatment as a patient’s symptoms change or progress, Boston Scientific looked to cochlear implant technology for inspiration, implants that regenerate hearing and teach users to identify different sounds, voices, and music. Engineers at Boston Scientific strived to create a similar product that would target specific locations and produce specific levels of stimulation in the brain. The company released the Vercise Primary Cell (PC) and Vercise Gevia DBS systems, featuring the Vercise Cartesia directional lead. The systems, with development spanning back to 2004, allow physicians to control the range, shape, position, and direction of electrical stimulation.

“This type of stimulator is described by some as a brain pacemaker,” says Rafael Carbunaru, vice president of research and design at Boston Scientific. “However, the heart doesn’t require the same finesse as the brain, as it simply contracts in a particular sequence. The brain is different because each fiber may be carrying different information. You need to be careful where you stimulate because 1mm difference right or wrong can have a significant impact on the patient.”

To give neurologists better control of the shape and size of the stimulation field, Vercise directional DBS systems use eight individually controlled electrodes on each lead, providing stimulation adaptable to impedance changes within the brain.

“With the brain you want to stimulate the right target,” Carbunaru says. “And this stimulation has to be maintained over time.”

These requirements are addressed by:

Electrodes – Cartesia directional leads allow current to be delivered in any direction around the lead.

Electricity – Current directed to each of eight contact points within the lead enables a stimulation shape that matches the target area. Multiple independent current control (MICC) independently manages how much current flows on each electrode.

Software – STIMVIEW technology developed by Boston Scientific allows neurologists and physicians to view the stimulation field being created on a screen, allowing them to easily match the shape of the stimulation field with the target region in the brain.

Engineers designed both systems to maximize device lifespan and usability. The Vercise Gevia system uses a rechargeable battery with at least a 15-year lifespan. The Vercise PC system’s battery, although not rechargeable, should last approximately four and a half years using typical settings. Data collected on the first Vercise system in the U.S., which won FDA approval in late 2017, shows that patients treated with the system had a 49.2% improvement in symptoms.

Developing, upgrading technology

The Vercise PC and Vercise Gevia DBS systems include mechanical, electrical, and software aspects which constantly change as technology advances. This requires Boston Scientific to work on future generations of technology while they develop and launch the first versions of these systems.

“Boston Scientific has created an environment where we can have a strong, safe manufacturing procedure that is reliable but also has the flexibility to advance,” Carbunaru says.

As advancements appear, engineers upgrade the devices’ capabilities to match – making electronics and mechanical packaging smaller, improving power supplies, and adding software capabilities. Computer modeling and in vitro studies ensure upgrades work and produce efficient results. The Vercise directional DBS systems are currently being used in clinical studies such as the global DBS post-market registry and DIRECT-DBS, a study that evaluates the effectiveness of directional leads used to treat PD.

Material science is also important, as implants must be biocompatible and interface well with body tissue. This can be a long process, as the devices are designed to last at least 15 years and therefore must be capable of long-term biocompatibility.

For future iterations of their DBS systems, Boston Scientific hopes to one day develop a closed-loop Vercise system, a feat that has not yet been possible due to the need for a sensitive, specific signal.

“Our vision is for the systems to become smarter, more autonomous, and more natural as a neural prosthesis,” Carbunaru adds.

Boston Scientific
http://www.bostonscientific.com

About the author: Mara Bahmer is the editorial intern for Today’s Medical Developments, Today’s Motor Vehicles, and Aerospace Manufacturing and Design.