Chemical patterning of ultrathin polymer films by direct-write multiphoton lithography.

We applied 2-photon laser ablation to write subdiffraction nanoscale chemical patterns into ultrathin polymer films under ambient conditions. Poly(ethylene glycol) methacrylate brush layers were prepared on quartz substrates via surface-initiated atom-transfer radical polymerization and ablated to expose the underlying substrate using the nonlinear 2-photon absorbance of a frequency-doubled Ti:sapphire femtosecond laser. Single-shot ablation thresholds of polymer films were ~1.5 times smaller than that of a quartz substrate, which allowed patterning of nanoscale features without damage to the underlying substrate. At a 1/e(2) laser spot diameter of 0.86 µm, the features of exposed substrate approached ~80 nm, well below the diffraction limit for 400 nm light. Ablated features were chemically distinct and amenable to chemical modification.

Self-standing aligned fiber scaffold fabrication by two photon photopolymerization.

Development of materials and fabrication techniques lead the growth of three-dimensional cell culture matrices in biomedical engineering. In this work, we present a method for fabricating self-standing fiber scaffolds by two-photon polymerization induced by a femtosecond laser. The aligned fibers are 330 microm long with a diameter of 6-9 microm. Depending on the pitch of the aligned fibers, various cell morphologies are distinguished via three-dimensional images. Furthermore, the morphologies of fibroblast cells (NIH-3T3) and epithelial cells (MDCK) on the fiber scaffolds are studied to show the effect of high curvature (3-4.5 microm radii) on cell morphology. NIH-3T3 cells that contain straight pattern of actin microfilament bundles are extended and partly wrap single fibers or tend to reside between fibers. On the other hand, MDCK cells that contain circular pattern of actin microfilament bundles cover the fiber peripheral surface exhibiting high aspect ratio elongation. These results indicate that cell morphology on fiber scaffolds is influenced by the pattern of actin microfilament bundles.

Fabrication of arbitrary polymer patterns for cell study by two-photon polymerization process.

Topographically patterned surfaces are known to be powerful tools for influencing cellular functions. Here we demonstrate a method for fabricating high aspect ratio ( approximately 10) patterns of varying height by using two-photon polymerization process to study contact guidance of cells. Ridge patterns of various heights and widths were fabricated through single laser scanning steps by low numerical aperture optics, hence at much higher processing throughput. Fibroblast cells were seeded on parallel line patterns of different height ( approximately 1.5-microm, approximately 0.8-microm, and approximately 0.5-microm) and orthogonal mesh patterns ( approximately 8-microm and approximately 4-microm height, approximately 5-microm and approximately 5.5-microm height, approximately 5-microm and approximately 6-microm height). Cells experienced different strength of contact guidance depending on the ridge height. Our results demonstrate that a height threshold of nearly 1 microm influences cell alignment on both parallel line and orthogonal mesh patterns. This fabrication technique may find wide application in the design of single cell traps for controlling cell behavior in microdevices and investigating signal transduction as influenced by surface topology.