July/August_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | J U L Y / A U G U S T 2 0 2 0 2 3 a coated material. When the coating material gets heated up, a small vapor pocket is created at the interface of the quartz disc, which eventually expands and ejects a portion of coating mate- rial downwards to form a jet (Fig. 5). It presents multiple advantages, such as precise control over deposition of cells, growth factors, drugs, genes, and oth- er biological materials. This approach is nozzle-free, contactless, and is not limited by the rheology of feedstock material [27,28] . TWO-PHOTON POLYMERIZATION (2PP) Issues surrounding the problem of increasing the resolution of 3D printing can be solved using the two-photon ab- sorption (2PA) effect. This is described as a simultaneous absorption of two photons using less energy than in one photon absorption by increasing the wavelength of photon. It is worth say- ing, that 2PA occurs only if the laser power reaches the required high inten- sity, and this issue is solved by using femtosecond pulse lasers. Another fea- ture of the 2PP technique is the ability to print structures inside of a photores- in volume, whereas 1PA SLA can print Fig. 5 — Schematic view of (a) laser-induced forward transfer (LIFT) and (b) laser-induced backward transfer (LIBT). In LIFT mode the laser irradiates the metal film through the transparent donor substrate while in LIBT mode the laser irradiates the thin film through the receiver substrate. (c) Typical experimental setup for laser printing of nanoparticles is shown on the left side. SEM images of a single printed gold nanoparticle and nanoparticle array are shown at the right [29] . Fig. 6 — Schematic illustration of the experimental setup for two-photon polymerization and the principle of fabricating 3Dmicrostructures; longitudinal profile of a laser beam and a photopolymerizable region (voxel) formed by two-photon absorption (into the frame) [32] . (b) (a) (C)