A Brief History of Neuromodulation Devices: How Parylene coatings improve

For over 40 years, SCS Parylene conformal coatings have provided protection to numerous medical devices and components, including those used in neuromodulation. Neuromodulation, the electric stimulation of a specific nerve or set of nerves, for an intended purpose, has been successfully used for many years to improve a wide range of medical conditions. As researchers and manufacturers reflect on successes achieved, they are continually challenged to improve current technologies as well as discover applicability for other medical conditions.

In the early years of neuromodulation, neurostimulation devices were often only considered after pharmacological or surgical options were exhausted. However more recently, there has been movement in the industry to introduce these less invasive options sooner as patients desire less pain and shorter recovery times. In most cases, neurostimulation devices do not cure the conditions they treat, rather they work to modify the nerves programmed response to lessen or alleviate the condition. A host of medical conditions have benefitted from neurostimulation treatments and many more are emerging as potential successes. The conditions include:

• Epilepsy
• Depression
• Urinary and fecal incontinence
• Pain management
• Parkinson disease
• Essential tremor
• Anxiety
• Obesity
• Migraines
• Alzheimer disease
• Stroke recovery
• Sleep apnea
• Hearing impairment

Depending on the medical condition, neurostimulation devices can be implanted, such as in the case of spinal cord, deep brain, vagus and sacral nerve stimulation, or can be used externally on the skin’™s surface, such as in transcranial magnetic stimulation and transcutaneous electrical stimulation treatments. In most implanted neurostimulation devices, electrode-containing leads are placed near the nerve that is to be stimulated. A pulse generator is responsible for managing electrical current to the leads, continuously or on demand, and then a programming unit communicates with the power source to start and stop stimulation and to codify the treatment regimen.

SCS Parylene coatings are applied through a vapor deposition process in which the Parylene raw material (dimer) vaporizes into a gas, which is then pyrolized into reactive monomer molecules. The Parylene monomer enters the ambient temperature chamber and polymerizes on the substrate. Parylene conformal coatings offer reliable protection to many critical components in neurostimulation devices, including circuit boards, batteries, capacitors, leads, electrodes and needles, to name a few.

Ultra-thin and lightweight

Since the Parylene coating material enters the deposition chamber as a gas, its penetration power is high which enables the film to uniformly grow on all surfaces and edges, including inside the smallest crevices of a substrate. Thus, these ultra-thin coatings are well suited for medical devices that continue to grow smaller and more compact in nature.

Biocompatibility and biostability

SCS Parylenes N, C and HT comply with biological testing requirements per ISO-10993. Testing included cytotoxicity, sensitization, intracutaneous reactivity, acute systemic toxicity, implantation (2, 12 and 26 weeks), hemocompatibility (hemolysis and PPT) and pyrogenicity. SCS Parylenes N, C and Parylene HT are also certified to comply with the biological testing requirements for USP Class VI Plastics. The results of these evaluations are maintained in SCS’ FDA Device and Drug Master Files.

Barrier properties

SCS Parylene coatings are effective moisture and chemical barriers for medical device components. Applied much thinner than alternatice coatings, Parylene provides a pinhole-free barrier to protect against bodily fluids as well as moisture, chemicals and common gases.

Dielectric properties

SCS Parylenes have valuable dielectric properties as they can formed as thin, continuous films, free from defects and fillers that are commonly found in conventional coatings. Parylene coatings have low dielectric constants and dissipation factors, and high dielectric strengths, enabling electrical and communication signal transfer without absorption or loss.

RF properties

As electronics used in medical devices continue to advance, they are often required to operate reliably at higher frequencies than their predecessors. Some materials, however, lose some of their key performance properties when they are subjected to high frequency ranges. It has been demonstrated that SCS Parylenes N, C and Parylene HT do not experience a reduction in dielectric constant or dissipation factor properties under high frequency (6 GHz) conditions. Thus, SCS Parylenes are well suited to protect devices that operate in such environments.

Advanced adhesion promotion technologies

While Parylene coatings commonly achieve optimal adhesion to a wide variety of substrates with a treatment with A-174 silane prior to coating, newer methods of adhesion promotion have been introduced to improve the adhesion of Parylene to metallic and polymeric substrates. SCS AdPro Plus adhesion promotion technology enhances adhesion of Parylene coatings to metallic substrates, including titanium, stainless steel, gold, chromium and solder mask, to name a few. SCS AdPro Poly was specially engineered to solve the adhesion challenges of many polymeric materials, including polyimide substrates. Both AdPro Plus and AdPro Poly adhesion technologies are biocompatible and available to SCS commercial coating service customers.

As designers look to develop next generation neurostimulation devices, SCS recognizes the challenges they encounter, including smaller, more compact designs, higher concentration of electronic content, leadless designs and device-to-device communications. SCS Parylene coatings are unmatached in their ability to protect critical components, while enhancing the overall reliability of neurostimulation devices.

SCS Speciality Coating Systems
www.scscoatings.com