Patterned and switchable surfaces for biomaterial applications

Chapter 1 - Introductionby controlling the addition of a particular nucleotide after each activation step, ahigh-density array of tailored sequences can be grown at the surface. This approachhas also been achieved with inkjet technology, enabling probe growth without therigorous protocols required of the photolithography strategy [82, 83]. In situ DNAgrowth enables the formation of an array with millions of probes per cm 2 , however,probes are limited to 25 bases due to low synthesis yields at higher lengths. Thisapproach also requires clean rooms and specialised equipment [82].Laser ablation is another useful approach for micropatterning and can beconsidered a specialised case of photolithography. Here, a high-energy laser beam isdirected on a surface through a patterned mask which leads to ablation of the surfaceunderneath the transparent regions of the photomask. This method suffers from thesame limitations as all photolithographic techniques, but is able to produce highlyresolved patterns of controlled depth at a fast rate, thus, being applicable to theproduction of patterned surface topographies as well as patterned surface chemistries.Thissen, et al. utilised laser ablation with the development of a plasma polymer basedsystem that was shown to spatially confine cell growth [33, 35]. A schematic of theapproach is shown in Figure 1.3. An allylamine plasma polymer (ALAPP) withamine functionality was formed and aldehyde terminated PEG was grafted to thesurface by reductive amination. Subsequent laser ablation produced micronresolution patterned PEG and ALAPP regions (Figure 1.3A and B). Cells wereshown to be confined to the ALAPP region to micron resolution over a four dayperiod using a bovine corneal epithelial cell line (BCEp) (Figure 1.3C) [33]. Thissystem was expanded to include a human embryonic kidney cell (HEK) line [35],and has recently been shown to spatially control protein adsorption [84].1-20