Patterned and switchable surfaces for biomaterial applications

Chapter 2 – Spatially controlled electro-stimulated DNA adsorption and desorption for biodeviceapplicationsPolymerisation conditions used were a frequency of 200 kHz, a power of 20 W andan initial monomer pressure of 0.188 mbar. Deposition time was 25 s.2.2.3. Poly(ethylene glycol) graftingPEG monoaldehyde (Shearwater Polymers, Huntsville AL, USA) with amolecular weight of 5000 was grafted onto freshly deposited ALAPP layers byreductive amination. Grafting was performed under ‘cloud point’ conditions in 20 mlof a 0.1 M sodium phosphate buffer containing K 2 SO 4 (2.2 mg), NaCNBH 3 (60 mg)and PEG (50 mg) at pH 6.2. Freshly deposited ALAPP films were incubated in thePEG grafting solution at 60 °C for 16 hr.2.2.4. Excimer laser ablationAblation experiments were conducted using a 248 nm KrF excimer laser Series8000 (Exitech Limited, UK) equipped with a Lambda Physik LPX210i laser source.The beam delivery system contained beam shaping and homogenisation optics tocreate a uniform, square beam at the plane of a mask held on an open frame CNCcontrolled X-Y stage set. The square beam was passed through a chrome-on-quartzmask pattern. The beam was then passed through a 1:10 demagnification lens, NA of0.3, a 1.5 mm diameter field with a theoretical resolution of 0.8 m. PEG graftedALAPP samples on silicon substrates were ablated at an energy density of 60 mJ/cm 2and 4 pulses of 20 ns duration per area to form a spatially patterned substrate. Thelaser ablated pattern is shown in Figure 2.2. Light microscope images of the ablatedpattern were taken with an Olympus SZ-STS light microscope and a charge coupleddetector (CCD) colour video camera. Images were captured using Data translation,Inc. DT Acquire v3.3.0 software.2-68