The use of materials patterned on a nano - and micro-metric scale in cellular engineering

1. Objective The use of materials patterned on a nano- and micro-metric scale in cellular engineering • Cells are organized in different patterns according to the function they serve • This organization is dictated by chemical and physical signals such as topographical cues from the environment • Understanding cell response to topography is crucial for successful design of bioengineered implants (e.g. artificial heart) • This paper deals with cell response to topography at the micro- and nano-scale C.D.W. Wilkinson, M. Riehle, M. Wood, J. Gallagher, A.S.G. Curtis Department of Electrical Engineering and Centre for Cell Engineering, Glasgow G12 8QQ, Scotland, UK Materials Science and Engineering C 19 2002.263–269

2. Fabrication of patterned substrates additive or subtractive (etching)

3. Nature Reviews Microbiology 5, 209-218 • Master template can be used as mold to create several copies of patterned • substrate, thus reducing cost

4. Nature Reviews Microbiology 5, 209-218 • Molding, embossing and soft lithography are some techniques used for pattern transfer

5. Studying cell response to topography: Basic set-up • Cells are grown on the patterned substrate placed in a petri dish in the presence of aqueous growth medium consisting of glucose, potassium and sodium salts and other factors • Culture dish is maintained in a controlled, sterile atmosphere at 37 C • Phase contrast microscopy and time lapse photography typically used to study cell behavior

6. 1. Simplest topographic feature: grooves • Most cell types align length-wise to the groove • Cell response dictated by groove dimensions and spacing Fig. 1. Grooves 7 um wide, 3 um deep and spaced by 14 um.

7. 2. Cell response to adhesive patterning 6 h 24 h • Specific cues (adhesion molecules such as certain proteins) can be patterned on the substrate • Alternative to topographic patterning • Example: can be used to selectively trap bacteria for pathogen detection 36 h 48 h

8. 3. Response to nano-patterning Regular vs. irregular spaced features Fig. 7. Rat tendon cells in the upper half of micrograph while no cell in the lower nano-patterned area. Substratum was a silica wafer, patterned with 100-nm pillars on 300-nm centre to centre spacing. Micrograph taken after 21 days in culture. • Lack of cell growth on nano-patterned region • Useful for applications like stent engineering Fig. 8. Array of pillars in silicon. a. Gold beads, 50 nm in diameter deposited onto a silicon wafer. b. Relief patterns of pillars made by dry etching gold beads

9. Conclusion • Surface microstructure mediates cellular organization and cell migration • Fabrication techniques such as soft lithography in particular offer immense scope for further exploring cell-surface interactions and manipulating single cells • Huge potential for several bioengineering applications such as implant design, drug delivery, biosensors etc.