Materials
Hydrophobic Coatings
- Introduction
- The hydrophobic effect is the observed tendency of nonpolar substances to aggregate in aqueous solution and exclude water molecules. The word hydrophobic literally means “water-fearing,” and it describes the segregation and apparent repulsion between water and nonpolar substances.
- The hydrophobic effect is responsible for the separation of a mixture of oil and water into its two components. The hydrophobic effect is also responsible for the stability of cell membranes, drives protein folding as well as the insertion of membrane proteins into the nonpolar lipid environment and finally stabilizes protein-small molecule interactions. Hence the hydrophobic effect is essential to medical device.
- Properties
Self-Cleaning/Anti-Dust , Prevent surface contamination, Organic pollution prevention, Water Contact Angle: < 150°
PO Coatings
Teflon Coatings
Parylene Coatings
PO Coatings
- Introduction
- Simple Hydrophobic coatings of simple and moderate performance
- Advantages
- Simple, single coatings
- Hydrophobic, high contact angle
- Biocompatible polymer
- Shorter heat cure, 10 min.
- Low cure temperature, 60°C
Teflon Coatings
- Teflon Coating
One of the most common processes for coating medical devices is Hydrophobic Coating for PTFE.
There are generally five steps to it:
- 1) Surface preparation/washing
- 2) Submersion of the device in a coating liquid (with a certain dwelling time in some instances)
- 3) Dip coating machine Withdrawal from the coating liquid, i.e. coating application/deposition
- 4) Drying and/or Curing of the coating (via heat or UV)
- 5) Post processing, if any. Especially with heat curing, this is a batch process. With proper equipment, the batches can be quite large, giving a decent effective throughput.
- Applications
medical equipment, textiles and all sorts of surfaces and substrates. However, the current state of the art for this technology is
hindered in terms of the weak durability of the coating making it unsuitable for most applications. Newer engineered surface textures
on stainless steel are extremely durable and permanently hydrophobic. Optically these surfaces appear a smooth matte surface but
microscopically they consist of rounded depressions one to two microns deep over 25% to 5
Parylene Coatings
- Parylene Coating
Powder Parylene in the vacuum condition is vaporised into coated onto the substrates in the form of polymer.
It is kind of CVD(Chemical-Vapor Deposition)
- Process
Parylene Vaporisation → Decomposition → Evaporation
- Coating System Setting
- Vaporiser : Parylene Dimer is vaporised with 80-175℃
- Pyrolyser : Dimer in gas into Monomer with 650~690℃
- Evaporation Chamber : Parylene in the form of polymer is coated on the target substrates
- Benefits
- Hydrophobic, Chemically resistant
- Low leakage current and low dielectric constant
- A biostable, biocompatible, FDA approved
- Dense pinhole free, with thickness above 1.4nm
- Coating without temperature load of the substrates as coating takes place at ambient temperature in a vacuum
- Completely homogeneous surface
- Stable to oxidation up to 350℃(Parylene AF-4, SF, HT)
- Low intrinsic thin film stress due to its room temperature deposition
- Very low permeability to gases