Weak two-photon absorption applied to the rapid prototyping of cell scaffolds

Abstract

Two-photon polymerization (TPP) has been employed to generate deep structures using the biocompatible and optically transparent monomer ethoxylated bisphenol A dimethacrylate (EO=6) (EBPADMA) and 4, 4'-Bis(diethylamino)benzophenon as the photoinitiator. The two-photon absorption cross section of the initiator was measured to be 1 GM (1 GM=1×10(-50) cm(4) s photon(-1)) in EBPADMA. Here we have explored a weak absorption regime whereby deep structures (∼300 μm) can be generated in a single pass. This allows rapid fabrication of structures suitable for cell scaffolds where the length scales are small, ∼10 μm, but are required over long ranges, ∼cm. The dependence of the TPP properties on the writing power, speed, exposure time and NA, of the focusing lens were studied in detail. Diffraction calculations for the focusing optics employed show that spherical aberration plays a significant role in determining the feature sizes achieved.

From Light to Structure: Photo Initiators for Radical Two‐Photon Polymerization

“…In addition to the photophysical properties of BDAB , the parameters for polymerization were determined by using EBPADMA with 1 % BDAB . The parameters like line widths, were investigated as a function of laser power, writing speed, exposure time, and numerical aperture [36] . Figure 2A displays the width of structured lines with different laser powers (0.4, 1.0, and 1.3 mW) versus the writing speed.…”

“…Even a slight increase of the exposure time leads to an enlargement of the voxel and, thus, to a broadening of the line, as shown in Figure 2C. To achieve high resolutions it is important to adjust the exposure time, as well as the intensity carefully [36] …”

“…The parameters like line widths, were investigated as a function of laser power, writing speed, exposure time, and numerical aperture. [36] Figure 2A displays the width of structured lines with different laser powers (0.4, 1.0, and 1.3 mW) versus the writing speed. It should be noted that the line width becomes significantly narrower as the writing speed increases.…”

“…To achieve high resolutions it is important to adjust the exposure time, as well as the intensity carefully. [36] 3D-microstructures manufactured for tissue engineering are facing high requirements like stability and degradability. In addition, biocompatibility and cytotoxicity play decisive roles in the development of such scaffolds.…”

“…Ovsianikov writing speed/velocity, (B) laser power and (C) laser exposure time. [36] Adapted with permission from Ref. [36] © The Optical Society.…”