Parylene for Medical Sensors

Many medical devices rely on sensors to detect and measure conditions affecting patient health. These sensors often record and transmit data on physical properties like heartbeat, blood pressure, breath rate, temperature and more to medical personnel and technology, enabling continuous physiological monitoring of health-specific disorders and improving the quality of diagnosis and treatment.

Sensors are often components of devices implanted directly into the body. Miniaturization, customization, and integration of multiple sensors into a single device allow for easier positioning within the body and generate more and better data to enhance diagnosis and treatment options. Wearable sensor devices can be surprisingly unobtrusive, providing dependable information from articles like wristbands, watches, headphones, smartphones, hats, or shoes. A third category of medical-grade sensors are stand-alone devices.

Implantable sensors must function without fail within the body and require exceptional protection to maintain performance through harsh environments. The polymer Parylene is well-suited to provide the necessary protective capabilities. It’s biocompatible, pinhole-free and offers truly conformal coverage that resists water, body sweat, fluids, cleaning agents, chemicals, corrosives, and solvents. Parylene’s ultra-thin film layers (IPC standard/10-50 microns) also support implantable positioning within minute bodily spaces.

Rapid progress in sensor and conformal coating technology has contributed to the evolution of Parylene-protected medical sensors. Until recently, sensors’ physical size made it difficult for implantable or wearable tech-use. Newer miniaturized circuits and enhanced microcontroller functions have led to the development of micro electro-mechanical (MEMS) and nano (NT) systems, small enough to be readily positioned throughout the body’s interior. Parylene micro-thin films offer coating protection without jeopardizing sensor location at critically confined sites within the body, enabling the acquisition of real-time physiological and movement data that expands the capabilities of digital health monitoring systems and patient care.

In addition to biocompatibility and biostability, Parylene is extremely lightweight and chemically inert and can be precisely deposited on virtually all available sensor materials. Its unique vapor deposition polymerization (VDP) process allows for the creation of a durable, pinhole-free conformal film on complex implant shapes and a successful covering of a wide range of substrate/product materials, including ceramic, composite and metallic substances.

The process begins with a granulated starting material called “dimer” which is sublimated under vacuum, polymerized in a high temperature region and introduced to the parts to be coated as a highly reactive monomer species that deposits onto surfaces and grows the film on device surfaces at a molecular level. The resultant conformal film covers all sensor surfaces, including the smallest crevices. Only microns thick, the biocompatible barrier tightens all areas on multi-layer sensor elements with a uniform coating, supporting the device’s performance requirements.

Other beneficial properties of Parylene that support sensor encapsulation include:

• In-process synthesis — no catalysts, fillers, plasticizers, solvents or stabilizers are used
• No additional curing, cross-linking or related processes after VDP is complete
• Excellent pinhole-free, secure barrier protection
• Micro-thin film layers controlled to precise thickness specifications
• Exceptional hydrophobic properties
• Ultra-low outgassing
• Functional stability in the presence of bodily fluids
• Chemically inert and non-reactant with the carrier polymers or drugs

In addition to meeting IPC standards, Parylene thicknesses typically vary between 500 angstroms and 25 microns. Parylene coating provides an electrical insulating capability of up to 7,000 volts at a thickness of 25 microns, far exceeding the protection levels of liquid coating materials at that thickness.

Biomedical sensors and related hybrid flexible sensing platforms require long-term functionality through corrosion resistance, film durability, enhanced lubricity and sufficient surface consolidation so they can continue to record real-time physiological activities of organs and tissues at sites ranging from the brain to the bladder. Ultra-thin Parylene coatings provide sensors this exceptional resilience and protection without adding significant dimension or weight. MEMS/NT diagnostic monitoring sensors are especially well served by its insulating, pinhole-free conformal protection, minimizing tissue response while allowing sensors to operate as needed.