Table 2.
Sterilization methods used and their effect on Parylene. “No adverse effects recorded” indicates the sterilization method was used in literature but no adverse effects on adhesion or bulk properties was recorded, while “n/a” indicates no use of the sterilization method was found in literature.
| Sterilization Method | Effect on Bulk Parylene | Effect on Parylene-Parylene Adhesion | Effect on Parylene to Metal Adhesion | Effect on Parylene Adhesion to Other Materials | Reference |
|---|---|---|---|---|---|
| Electron beam ISO 11137 |
Chemical structure changed: partial breakage of C-Cl bonds, ionization of polymer, crystallinity decrease | No adverse effects recorded | No adverse effects recorded | n/a | [92,93] |
| Gamma radiation ISO 11137 |
Recombination, cross-linking (increases strength and decreases elongation), loss in bond strength | n/a | Decreased adhesion, causing loss of electrical insulation capabilities | To silicon wafer: Crystallinity increased, no change in Young’s modulus |
[91,94] |
| Ethylene oxide ISO 11135 |
Formation of inorganic chlorides, reduction of chlorine amount. EtO is toxic, carcinogenic, flammable, explosive | For sterilization after thermal annealing, no adverse effects recorded | Decreased electrical insulation capabilities (but not as damaging as gamma sterilization | To glass: No adverse effects recorded |
[93,95,96] |
| Autoclave (steam) ISO 17665 |
Parylene became brittle and hard, decreased adhesion, changed chemical stability, did not contaminate | Decreased adhesion | Decreased adhesion | To silicon: Significant decrease in adhesion, Parylene crystallinity increased, electrical stability decreased |
[57,91,97,98,99] |
| H2O2 Plasma ISO/NP 22441 * |
No change in adhesion. Recommended “best suitability for Parylene” (based on XRD testing), successfully killed bacteria without degradation of Parylene coating | n/a | n/a | To Silastic: Parylene withstood implantation and was unaffected. However, coating was easily peeled off after implantation, suggesting poor Parylene-Silastic adhesion |
[93,100,101] |
| Antibiotic coating No standard |
0.5–0.75 mg/mL concentration of tetracycline nanoparticles completely eradicated E. coli but not aureus bacteria | n/a | n/a | n/a | [102] |
* NP: the standard is a new proposal and is still under consideration by the ISO.