Tuesday, December 29, 2015

Applying Thin Film Coatings Used in Medical Devices: White Paper

Courtesy of Brooks Instrument
Society has benefited tremendously from the development and utilization of mechanical devices which are implanted inside the body and are used to replace bones and joints, increase blood flow, and even measure blood chemistry. To further enhance the performance of these devices, the application of thin films to the external surfaces is an ongoing research and development interest at many companies.
Engineers have a choice of a variety of technologies to apply these liquid coatings to these often complex surfaces ranging from vacuum technology to direct liquid application. The decision on what technology to use is a function of the liquid precursor used, the mechanism of coating formation and the geometry of the object to be coated. A critical quality and process control criterion is the consistency of the coating on the surface. Fluid delivery technology can play an important part in maintaining coating consistency. Pumps and liquid flow controllers are technologies being used today. For vapor coating processes, liquid vaporization technology is a critical link in the fluid delivery system. New flow and vaporization technology is available that can be applied to fluid delivery to improve the application of medical device coatings.

Why Coating

The human body has defense mechanisms that normally treat foreign objects as a threat. This is great when the foreign body is a bacteria or a virus, but in relation to medical devices, this response can affect their performance. Certain metals and plastics have surface properties that make them somewhat compatible in the body. In many applications, these materials don’t have the proper physical properties to make them useful for a specific function. Other materials might be better from a mechanical standpoint, but are more irritating to the body. Coatings are also used to extend the useful life of the device in the body. Here are just some of the uses of medical coatings.
  • To reduce friction of the medical device in the body to improve the placement of the device and also minimize irritation and inflammation 
  • To reduce the formation of scar tissue surrounding implanted devices 
  • To encourage the growth of tissues to help the healing process 
  • To reduce the chance of infection related to the implanted device 
  • To “hide” the device from the body’s self defense mechanism 
  • To measure body chemistry in real time
  • The coatings applied to the surface can be as simple as a thin metal coating or as complex as polymer coating interlaced with precise pores that time-release drugs. 
Coating Challenges and Solutions

Applying a coating to a device that is placed in the body is a very critical process. The potential detrimental affects of the coating must be thoroughly investigated prior to official approval for market introduction. Here are some of the many challenges facing an engineer when designing techniques for coating medical device structures.
  • Complex substrate geometry 
  • Even coating over the complete surface 
  • Consistent thickness and mass of coating across a production lot 
  • Eliminating bridging across web structures 
  • Coating adhesion and eliminating post implant particle generation 
  • Applying high molecular weight active drug molecules 
  • Creating porous films that allow time release of drugs
See the entire white paper here: