Abstract

Introduction:

Over the last decades, advanced biomaterials have been widely developed for medical applications. Tailoring of their surface functionalities determines the interactions between the abiotic material and an organism. For instance, the spatially controlled distribution of proteins, the synthesis of non-fouling polymers and the development of cell culture substrates require stable, yet designable surfaces. In this context, Chemical Vapor Deposition (CVD) is a versatile, solvent-free process that enables surface modification of substrates. Originally developed by Gorham¹, vapor-based polymerization of [2.2]paracyclophanes is today approved by the FDA for biomedical coatings. However the lack of anchor groups in these commercial parylene coatings limits their potential applications. Therefore, our group has focused on CVD (co)polymerization of substituted [2.2]paracyclophanes using a custom-designed CVD system in order to obtain bioactive surfaces².

Experimental

Typically, substituted [2.2]paracyclophane is sublimated under low pressure (<0.5mbar) before entering a furnace (540-800°C), where pyrolysis of the dimer generates quinodimethane intermediates. Polymerization of substituted [2.2]paracyclophanes by vapor-deposition then occurs in the deposition chamber on the desired sample maintained at or below room temperature.

Results and Discussion:

A wide variety of mono- and di-substituted [2.2]paracyclophanes has been synthesized and used as precursors in order to provide anchor groups onto surfaces. For instance, aldehyde-, amino- or carbonyl- functionalized poly-p-xylylenes have been coated² by CVD polymerization of the corresponding precursors. Mechanical and chemical stable coatings, possibly exhibiting a chemical gradient when copolymers are synthesized, have been obtained by the use of our custom-designed system². This process is versatile, since it has enabled functionalizing various materials, such as metals, polymers or glass, even thermo-sensitive or with complex geometries like microfluidic devices. Efficient chemical reactions, such as click-chemistry reactions, can be carried out from the resulting reactive CVD coatings³. Immobilization of biomolecules (proteins, sugars) has been performed via hydrazone linkers⁴. Non-fouling surfaces have also been designed by anchoring polymerization initiators onto substrates and subsequent graft-polymerization. Engineering CVD coatings finally leads to potential applications for medicine, when spatially controlled surface modification is considered. Various surface engineering methods have already been successfully applied to CVD coated substrates to generate patterned surfaces. For instance, micro-contact printing, vapor-assisted micropatterning in replica structures and dip-pen nanolithography have enabled micro-/nano-structuring² of CVD reactive coatings, which is particularly interesting for the combination of various immobilization strategies.

Conclusions:

A wide variety of functional polymer coatings have been successfully obtained by our versatile CVD (co)polymerization process. Biomedical applications, possibly requiring micro-/nano-structuring, can therefore be considered to tailor bioactive surfaces and to design on-demand multi-reactive coatings.

References

¹ Gorham, W.F. J. Polym. Sci Part A-1: Polym. Chem 1966, 4, 3027–3039

² Chen, H.Y.; Lahann, J. Langmuir 2011, 14, 326–334

³ Deng, X.; Friedmann, C.; Lahann, J. Angew. Chem. Int. Ed. 2011, 50, 6522–6526

⁴ Nandivada, H.; Chen, H.Y.; Lahann, J. Macromol. Rapid Commun. 2005, 26, 1794–1799