Rapidly prototyping biocompatible surfaces with designed wetting properties via photolithography and plasma polymerization
The testing and manufacturing of lab-on-a-chip devices increasingly require lower lead times from conception to market. In order to supply a potential answer to this burgeoning demand, the work herein explores a design and prototyping process for biocompatible surfaces with designed wetting states ranging from slightly hydrophilic behavior to superhydrophobicity. Direct laser writing was used to fabricate geometrically parameterized base structures out of an acrylic photopolymer (IP-Dip) for eventual coating of samples with hexamethyldisiloxane (HMDSO) via plasma polymerization, with numerical methods validating candidate geometries. After manufacturing, samples were examined for structural and/or coating integrity via scanning electron microscopy and optical microscopy; subsequent wetting property evaluation was performed with a contact angle goniometer. Beginning with the slight hydrophilicity of the planar-coated base polymer, surfaces were shown displaying wetting behavior from the 'mushroomed' Wenzel state, the metastable Cassie-Baxter state, and superhydrophobicity with the non-wetting rolling predicted by literature. The combination of methods used in this work creates a parameter space for the rapid fabrication of 'designer' or 'programmable' surfaces, that is, the attainment of a specific wetting state through parametric variation with fast prototype processing times on the order of hours or days instead of weeks or months, and is typified by a presented microarray section. Of further specific relevance to the lab-on-a-chip community is the biocompatible nature of the HMDSO coatings. All structures presented in this work can be used as printed on any substrate or transferred for further processing into media more applicable for large-scale manufacturing.