Laser forward transfer processes incorporating thin absorbing films can be used to deposit robust organic and inorganic materials but the deposition of more delicate materials has remained elusive due to contamination and stress induced during the transfer process. Here, we present the approach to high resolution patterning of sensitive materials by incorporating a thick film polymer absorbing layer that is able to dissipate shock energy through mechanical deformation. Multiple mechanisms for transfer as a function of incident laser energy are observed and we show viable and contamination-free deposition of living mammalian embryonic stem cells.

Articles you may be interested inIn-situ characterization of femtosecond laser-induced crystallization in borosilicate glass using time-resolved surface third-harmonic generation Blister-actuated laser-induced forward transfer ͑BA-LIFT͒ is a versatile, direct-write process capable of printing high-resolution patterns from a variety of sensitive donor materials without damage to their functionality. In this work, we use time-resolved imaging to study the laser-induced formation of blisters on polyimide films in order to understand and optimize their role in BA-LIFT. We find that the initial blister expansion occurs very rapidly ͑Ͻ100 ns͒, followed by a brief oscillation ͑100-500 ns͒, and then a longer time contraction to steady-state dimensions ͑0.5-50 s͒. This behavior is explained by kinetic and thermal effects that occur during the process. We further probe the influence of polyimide thickness, laser beam diameter, and laser fluence on blister formation characteristics. Results indicate that the presence of a thin layer of donor material on the polyimide surface does not have a significant effect on the size and shape of the blisters which form.

Laser-induced forward transfer (LIFT) is a high-resolution direct-write technique, which can print a wide range of liquid materials without a nozzle. In this process, a pulsed laser initiates the expulsion of a highvelocity micro-jet of fluid from a thin donor film. LIFT involves a novel regime for impulsively driven free-surface jetting in that viscous forces developed in the thin film become relevant within the jet lifetime. In this work, timeresolved microscopy is used to study the dynamics of the laser-induced ejection process. We consider the influence of thin metal and thick polymer laser-absorbing layers on the flow actuation mechanism and resulting jet dynamics. Both films exhibit a mechanism in which flow is driven by the rapid expansion of a gas bubble within the liquid film. We present high-resolution images of the transient gas cavities, the resulting ejection of high aspect ratio external jets, as well as the first images of re-entrant jets formed during LIFT. These observations are interpreted in the context of similar work on cavitation bubble formation near free surfaces and rigid interfaces. Additionally, by increasing the laser beam size used on the polymer absorbing layer, we observe a transition to an alternate mechanism for jet formation, which is driven by the rapid expansion of a blister on the polymer surface. We compare the dynamics of these blister-actuated jets to those of the gas-actuated mechanism. Finally, we analyze these results in the context of printing sensitive ink materials.

Intraocular pressure (IOP) initially increases when an individual enters microgravity compared with baseline values when an individual is in a seated position. This has been attributed to a headward fluid shift that increases venous pressures in the head. The change in IOP exceeds changes measured immediately after moving from seated to supine postures on Earth, when a similar fluid shift is produced. Furthermore, central venous and cerebrospinal fluid pressures are at or below supine position levels when measured initially upon entering microgravity, unlike when moving from seated to supine postures on Earth, when these pressures increase. To investigate the effects of altering gravitational forces on the eye, we made ocular measurements on 24 subjects (13 men, 11 women) in the seated, supine, and prone positions in the laboratory, and upon entering microgravity during parabolic flight. IOP in microgravity (16.3 ± 2.7 mmHg) was significantly elevated above values in the seated (11.5 ± 2.0 mmHg) and supine (13.7 ± 3.0 mmHg) positions, and was significantly less than pressure in the prone position (20.3 ± 2.6 mmHg). In all measurements,P< 0.001. Choroidal area was significantly increased in subjects in a microgravity environment (P< 0.007) compared with values from subjects in seated (increase of 0.09 ± 0.1 mm(2)) and supine (increase of 0.06 ± 0.09 mm(2)) positions. IOP results are consistent with the hypothesis that hydrostatic gradients affect IOP, and may explain how IOP can increase beyond supine values in microgravity when central venous and intracranial pressure do not. Understanding gravitational effects on the eye may help develop hypotheses for how microgravity-induced visual changes develop.

We examine the effects of three laser direct-write ͑LDW͒ printing techniques on 9-anthracenemethanol and tris͑8-hydroxyquinoline͒aluminum ͑Alq 3 ͒ organic luminophores in order to link the differences in transfer mechanism to the resulting material properties. Degradation can occur where laser light and elevated temperatures are transferred to the molecules, such as those printed via matrix-assisted or thin metal absorptive layer LDW. In contrast, thick film polyimide absorbing layer techniques eliminate damage in these sensitive materials by shielding them from excessive heat and laser illumination.