Patterning the inner part of a biomaterial without alterning its surface may seem an impossible task, but exactly this kind of internal microstructuring of materials is now possible using two-photon (2ph) excitation. With 2ph excitation, materials can be patterned by photopolymerization (cross-linking solid structures out of liquid precursors), photoablation (creating empty spaces in a solid structure), or photografting (chemically modifying local regions of the material without altering its shape).
This technique relies on the simultaneous absorption of two photons to trigger an electronic transition (Fig1a), a phenomenon which only happens at very high photon densities. This is generated by a pulsed laser, which provides a high number of photons during the pulses while still delivering a reasonable average power. Also, to trigger transitions which would normally be in the visible range, photons of half the energy have to be used, which locates them in the infrared. In patterning conditions, the light intensity is high enough in the focal spot only, and the material is not modified at any other depth (Fig1b/c).
Our group is working on the development of:
- biocompatible hydrogels that can be processed by two-photon methods,
- scripts for simultaneous imaging and patterning on a multiphoton microscope,
- applications of two-photon patterning in tissue engineering.
HPL J 15.2
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