Patterned and switchable surfaces for biomaterial applications

Chapter 4 – Formation of a chemically patterned substrate for cell microarray applications4.2. Materials and methods4.2.1. Substrate preparationAllylamine plasma polymer (ALAPP) depositions onto glass slides wereperformed in a custom-built reactor described elsewhere [182]. In short, the plasmareactor consisted of two circular electrodes separated by 125 mm in a cylindricalreactor being 350 mm high with a diameter of 170 mm. Allylamine (Aldrich, 98%purity) was used as a monomer. Polymerisation conditions used were a frequency of200 kHz, a power of 20 W and an initial monomer pressure of 0.188 mbar.Deposition time was 25 s. PEG monoaldehyde (Shearwater Polymers, Huntsville AL,USA) with a molecular weight of 5000 was grafted onto freshly deposited ALAPPlayers by reductive amination. Grafting was performed under ‘cloud point’conditions in 20 ml of a 0.1 M sodium phosphate buffer containing K 2 SO 4 (2.2 mg),NaCNBH 3 (60 mg) and PEG monoaldehyde (50 mg) at pH 6.2. Freshly depositedALAPP films were incubated in the PEG grafting solution at 60 °C for 16 hr.4.2.2. Array formationFor optimisation of polymer printing, a 1 mg/ml poly(ethyleneimine) (PEI) (MW70,000, Fluka) solution was arrayed onto a (PEG) surface using a BioOdysseyCalligrapher MiniArrayer (Bio-Rad) with a 375 µm diameter solid pin (ArrayIt)delivering approximately 4.0 nL/spot. Initially, the formation of the PEI array on thePEG surface was optimised by altering the humidity in the range of 57-65% and thetemperature in the range of 3-37 °C. 65% humidity and 25 °C were determined toproduce optimum spot size and uniformity and were used for subsequent formation4-134