Laser-assisted printing such as laser-induced forward transfer has been well studied to pattern or fabricate two-dimensional constructs. In particular, laser printing has found increasing biomedical applications as an orifice-free cell and organ printing approach, especially for highly viscous biomaterials and biological materials. Unfortunately, there have been very few studies on the efficacy of three-dimensional printing performance of laser printing. This study has investigated the feasibility of laser tube printing and the effects of sodium alginate concentration and operating conditions such as the laser fluence and laser spot size on the printing quality during laser-assisted printing of alginate annular constructs (short tubes) with a nominal diameter of 3 mm. It is found that highly viscous materials such as alginate can be printed into well-defined long tubes and annular constructs. The tube wall thickness and tube outer diameter decrease with the sodium alginate concentration, while they first increase, then decrease and finally increase again with the laser fluence. The sodium alginate concentration dominates if the laser fluence is low, and the laser fluence dominates if the sodium alginate concentration is low.

Modified laser-induced forward transfer has emerged as a promising bioprinting technique. Depending on the operating conditions and cell properties, laser cell printing may cause cell injury and even death, which should be carefully elucidated for it to be a viable technology. This study has investigated the effects of alginate gelation, gelation time, alginate concentration, and laser fluence on the post-transfer cell viability of NIH 3T3 fibroblasts. Sodium alginate and calcium chloride are used as the gel precursor and gel reactant solution to form cell-laden alginate microspheres. It is found that the effects of gelation depend on the duration of gelation. Two-minute gelation is observed to increase the cell viability after 24 h incubation, mainly due to the protective cushion effect of the forming gel membrane during droplet landing. Despite the cushion effect from 10 min gelation, it is observed that the cell viability decreases after 24 h incubation because of the forming thick gel membrane that reduces nutrient and oxygen diffusion from the culture medium. In addition, the cell viability after 24 h incubation decreases as the laser fluence or alginate concentration increases.

Laser-induced forward transfer (LIFT) has been widely studied to print various structures. It is important to investigate the jet and droplet formation process under different LIFT operating conditions. The resulting knowledge will help to better control the resulting printing quality and feature resolution. This study aims to better understand the effects of fluid properties and laser fluence on the jet formation process using time resolved imaging analysis during LIFT of glycerol solutions. It is found that if the laser fluence is too low and/or the glycerol concentration is too high, it is less likely for a bubble to fully form and/or grow before it diminishes. If the laser fluence is too high and/or the glycerol concentration is too low, it is also difficult to form a well-developed jet since dramatic bubble expansion may lead to a bulgy shape and even splashing. Only under certain combinations of glycerol concentration and laser fluence, can a well-defined jet form. When a jetting fluid is given, its jettability (J) can be characterized as the inverse of the Ohnesorge number. It is observed that a good jet forms at 0.86 ≤ J ≤ 2.49 (corresponding to 75%–85% glycerol solutions) when the laser fluence is 717 ± 45 mJ/cm2.

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