Biocompatible Parylene Coated Implanted Medical Device


Parylene Biocompatibility — It Does A Body Good

The human body is like a fortress. It protects your organs on the inside while rejecting foreign invaders and pushing them outside. Typically, that’s exactly what you’d want it to do, but sometimes, we need foreign materials to be accepted, like in the case of transplants, rods in damaged bones and pacemakers. So, when designing antibacterial coatings for medical devices, it’s important that they meet guidelines for biocompatibility including cleanliness, consistency and stability. Parylene has many advantages that make it a great choice for implanted medical devices.

Figure 1. Image of an infant with a cochlear implant

Predictable, Safe, and Stable

Parylene has a long history of use as a protective coating for medical device biocompatibility and conforms to the USP Class VI and ISO 10993 standards. It is transparent, pin-hole free, and conforms precisely to any surface’s features. Parylene’s thickness is critically controlled and extremely consistent. It coats very thinly, on the order of microns, providing deep crevice penetration, and adds very little weight or volume. On the whole, Parylene works extremely well in most medical applications.

Download the Engineer’s Parylene Properties Comprehensive Guidebook to learn more about parylene’s biocompatibility attributes →

When a material is biocompatible it means the materials won’t interact with living tissue negatively, aren’t toxic, and are physiologically non-reactive. Parylene biobased coatings don’t evoke an immune response, are biologically stable and chemically inert, in that it survives being exposed to the chemicals found in the body, and those chemicals won’t react with it. The types of biocompatibility-related testing that parylene has passed is shown in Table 1 below:

Table 1. Parylene coating and dimer testing based on industry literature

Study Standard Parylene Type Result
ASTM Hemolysis Complete (Direct and Indirect) ISO 10993-4 C & N Meets Requirements
ISO Partial Thromboplastin Time ISO 10993-4 C & N Meets Requirements
ISO Lee & White Clotting Time – Human Blood (Direct) ISO 10993-4 C & N Meets Requirements
ISO Lee & White Clotting Time – Human Blood (Indirect) ISO 10993-4 C & N Meets Requirements
ISO In Vitro Hemocompatibility (Direct) ISO 10993-4 C & N Meets Requirements
ISO In Vitro Hemocompatibility (Indirect) ISO 10993-4 C & N Meets Requirements
ISO Cytotoxicity Test – Neutral Red Uptake 4 Concentrations ISO 10993-5 C & N Meets Requirements
ISO MEM Elution Cytotoxicity ISO 10993-5 C & N Extracts Confirm Suitability
ISO Implant/Muscle/2Weeks ISO 10993-6 C & N Classified as Non-Irritant
ISO Implant/Muscle/13Weeks ISO 10993-6 C & N Classified as Non-Irritant
ISO Implant/Muscle/26Weeks ISO 10993-6 C & N Classified as Non-Irritant
ISO Klingman Maximization/2 Extracts/35 Animals/Concurrent (+) controls ISO 10993-10 C & N Meets Requirements
ISO Rabbit Pyrogen-Material Mediated ISO 10993-11 C & N Meets Requirements
USP Physiochemical/Plastics USP C & N Meets Criteria
USP Physiochemical Test For Plastics – Non-Volatile Residue USP C & N Meets Criteria
USP Class VI Test Parylene C USP C Meets Criteria
USP Class VI Test Parylene N USP N Meets Criteria
RoHS Compliance Parylene Type C EU C Compliant
RoHS Compliance Parylene Type N EU N Compliant
Reach Compliance Testing Per Regulation 1907/2006 Parylene C ECHA C Passes
Reach Compliance Testing Per Regulation 1907/2006 Parylene N ECHA N Passes


In a hospital setting, antimicrobial coatings for medical devices and instruments are vital for keeping them free of contamination. Parylene can withstand sterilization by E-beam, gamma ray, EtO, and autoclave, with the effects shown in Table 2 below. It protects against chemicals, moisture, and bodily fluids. Overall, Parylene protects the device from the body and the body from the device, helping to prevent premature and critical use device failure in the long term.

Table 2. Effects of various sterilization methods on parylene biocompatibility

Sterilization Method Parylene N Parylene C
Dielectric Strength WVT Tensile Strength Tensile Modulus COF Dielectric Strength WVT Tensile Strength Tensile Modulus COF
Steam None Δ43% None Δ12% Δ38% None Δ5* Δ17% Δ9% None
EtO None Δ21% None None Δ33% None 8% None None None
E-beam NA None None None None NA None None None None
H2O2 plasma None None None None Δ48% Δ9% None None None Δ188%
Gamma None None None None None None Δ5% None None None

* 5% values aren’t likely to be statistically significant. NA = not applicable; COF = coefficient of friction; WVT = water vapor transmission.

A Low-Friction Biocompatible Lubricant

Lubricity is the measure of the reduction in the coefficient of friction (CoF) and/or wear by a biocompatible lubricant. In biomedical materials and implants, the wear performance may be related to their apparent CoF in the presence of biological fluids.

Parylene is a low-friction polymer coating which allows for easy sliding and serves as a dry lubricant. That slickness is important in many medical applications because increased friction typically means a procedure is more painful and takes longer to accomplish. Parylene is about as slippery as TeflonTM and has proven to be extremely useful for stents, syringes, catheters, needles, and other medical implants.

Parylene is used as a high flexibility and low friction coating that resists contamination and discoloration on catheters, medical seals, and related products that use medical grade silicone and rubber.  It has also been used to coat stylets and mandrels. A stylet is a malleable metal wire used to guide an endotracheal tube during a difficult intubation. Parylene has been used extensively with vascular therapy devices, such as stents, angioplasty catheters, guiding catheters and wires. A mandrel is used in the manufacturing of precision medical tubing, such as forming catheter tubing.

Inhospitable To Bacteria, Microbes, And Mold

Parylene inhibits the growth of bacteria and fungi. In fact, that’s one of the criteria for conformal biobased coatings to meet the qualification to IPC-CC-830 – Qualification and Performance of Electrical Insulating Compound for Printed Wiring Assemblies and tested in accordance with IPC-TM-650, Test Method – Fungus Resistance – Conformal Coating.  IPC-CC-830 says that “the cured conformal coating shall not contribute to or be attacked by biological growth.

Fungus resistant materials are desired because the presence of fungi can cause infections that lead to serious health problems. Other reasons included in the IPC-HDBK-830 – Guidelines for Design, Selection, and Application of Conformal Coatings are:

  • Microorganisms digest organic materials as a normal metabolic process, thus degrading the substrate, reducing surface tension, and increasing moisture penetration.
  • Enzymes and organic acids, produced during metabolism, diffuse out of cells and onto the substrate and cause metal corrosion, glass etching, hardening of grease, and other physical and chemical changes to the substrates.
  • The physical presence of microorganisms produces living bridges across components that may result in electrical failures.
  • The physical presence of fungi can produce aesthetically unpleasant situations in which users will reject the equipment.

Wrapping It Up

The US FDA has approved parylene with a Class VI biocompatibility rating suitable for human implantable devices, based on its performance in the USP Class VI grade and ISO 10993 group of standards. Not only does parylene meet FDA biocompatibility standards, it’s also chemically inert, highly conformable with very well controlled thickness, resistant to flaking, and is capable of withstanding the effects of multiple sterilization processes. With all of these capabilities and characteristics, parylene biobased polymer coatings are just what the doctor ordered.

Download the engineer's comprehensive parylene properties guidebook

About The Authors

Sean Clancy, Ph.D. is the CEO, Co-Founder, & Principal Consultant of Clancy & Associates Technical Services LLC. Sean has extensive experience as a scientist, project manager, and instructor with a strong background in product and process creation and modification, data, and instrumental analysis, & material science and engineering. Sean also serves as Associate Director and Program Manager of the Materials Characterization Lab in the Materials Science & Engineering Department at the University of Utah.

Melissa Clancy is the President, Co-Founder, & Project Manager of Clancy & Associates Technical Services LLC. Melissa’s background is in project management, research, writing, editing, and design.