Three dimensional microstructuring of biopolymers by femtosecond laser irradiation

Abstract

A sequence of single femtosecond pulses is used to create a pattern of laser affected spots at increasing depths below the surface of transparent biopolymer samples. Materials with different water contents and mechanical strengths, gelatine, chitosan, synthetic polyvinyl pyrrolidone, and biopolymer-polymer blends, are irradiated near the edge of the sample with an amplified Titanium:Sapphire laser ͑800 nm͒ delivering 30 fs pulses through a 0.45 numerical aperture objective with energies of 100-3000 nJ. The micrometric modified region is observed by optical microscopy perpendicularly to irradiation. Self-focusing and optical aberration are major factors controlling morphology and size of the created spots.

3D features of modified photostructurable glass–ceramic with infrared femtosecond laser pulses

“…Above a critical power value, the Gaussian intensity profile of the beam induces a refractive-index variation within the material that acts as a converging lens that promotes additional focusing. At 1027 nm wavelength the critical power for self-focusing in Foturan can be estimated in between 1.3 and 2.6 MW [16][17][18][19]. Thus, for pulse energies above 0.6 J this mechanism may compensate for the spherical aberration one, allowing the photomodification of material at depths and energies that otherwise should not occur.…”

“…Moreover, self-focusing can be also involved in counteracting the intensity dispersion produced by spherical aberration. Self-focusing is a non-linear process that takes into account the refractive index dependence with light intensity and that often appears when working with femtosecond laser pulses [14][15][16][17][18][19]. Above a critical power value, the Gaussian intensity profile of the beam induces a refractive-index variation within the material that acts as a converging lens that promotes additional focusing.…”

Laser-based three-dimensional multiscale micropatterning of biocompatible hydrogels for customized tissue engineering scaffolds

“…We further find that it is possible to form voids within the gels nearly 1 cm below the gel surface. To our knowledge, this represents the greatest depth of multiphoton-induced void generation reported, exceeding by 1.5 orders of magnitude the deepest ablation in any material yet tested (12).…”

“…Extremely high light intensities found in these amplified pulses can locally change a material's refractive index, resulting in self-focusing of the beam. Self-focusing limits the depth at which a tight focal spot can be formed and has limited MPA-induced void formation to less than 200 μm below the surface of the material (12). Some natural proteins including amyloid (16) and silk fibroin (17) are much more efficient multiphoton absorbers than their amino acid composition would suggest.…”

“…If the material is transparent to the low-energy photons, very little of the light is absorbed at the surface, allowing a focal spot to be formed, and MPA to occur, deep within the material. Multiphotoninduced structural modification leading to void formation has been investigated in a variety of biocompatible materials including collagen, poly(vinyl-alcohol) (PVA), poly(methyl methacrylate), and gelatin hydrogels (11)(12)(13). Poly(ethylene glycol) hydrogels crosslinked with a photolabile bond can be selectively degraded to induce 3D structures (14).…”