Table 1.
Systematic evaluation of the main CVD techniques for synthesizing polymer thin films with respect to features important for various bioapplications.a
| Feature | Importance for Bioapplications | iCVD b | Parylene CVD | PECVD | oCVD |
|---|---|---|---|---|---|
| Rich monomer library | Diverse functional moieties attainable to meet the demands of various biological applications (e.g. antifouling, stimuli-responsive, antimicrobial, biocompatible, etc.) | Y [37] |
Y [191] |
Y [192] |
|
| Functional group retention | Ensuring high retention of functional groups and avoiding side reactions to achieve chemically tailored bio-interfaces | Y [44] |
Y [193] |
N c [42,44,65] |
Y [27,194] |
| Biofunctionalizability | Incorporation of bioactive molecules; Enabling more specific ligand-receptor binding | Y [52,104] |
Y [195] |
Y [196] |
|
| Electroconductivity | Often required for bioelectronics and biosensors | Y [87] |
Y [87,118] |
||
| Conformality over micro-/nano- structures | Engineering surface chemistry and/or surface mechanical properties of the substrates while preserving their nano- to microscale features | Y [62,197] |
Y [198] |
Y [199] |
|
| Thickness control with µm to nm precision | Controlling mechanical properties, mass transfer across coatings, swelling/actuation behavior | Y [41,50] |
Y [200] |
Y [201] |
Y [202] |
| Grafting | Long-term stability of the resulting thin films in complex biological environments | Y [114,203,204] |
Y [205,206] |
Y [207] |
Y [208] |
| Benign reaction conditions | Allowing for coating various sensitive (bio)materials | Y [165] |
Y [166] |
Y [209] |
Y [38] |
“Y” in a blue cell denotes that the feature (indicated by the row identity) has been demonstrated in the literature by using the CVD technique (indicated by column identity); “N” in a red cell denotes that existing literature support the lack of that feature; an empty grey cell denotes that the feature has not been demonstrated using the corresponding CVD technique. Examples are provided in “[ ]” for the marked cells.
Activated by heat or photons.
Variants of PECVD such as pulsed PECVD (PPECVD), initiated PECVD (iPECVD) have allowed higher monomer functionality retention and lower frequency of side reaction.89 Introducing monomers downstream of the plasma zone can also improve the retention of functional moieties.