Laser-induced Forward Transfer Hydrogel Printing: A Defined Route for Highly Controlled Process

Abstract

Laser-induced forward transfer is a versatile, non-contact, and nozzle-free printing technique which has demonstrated high potential for different printing applications with high resolution. In this article, three most widely used hydrogels in bioprinting (2% hyaluronic acid sodium salt, 1% methylcellulose, and 1% sodium alginate) were used to study laser printing processes. For this purpose, the authors applied a laser system based on a pulsed infrared laser (1064 nm wavelength, 8 ns pulse duration, 1 – 5 J/cm2 laser fluence, and 30 μm laser spot size). A high-speed shooting showed that the increase in fluence caused a sequential change in the transfer regimes: No transfer regime, optimal jetting regime with a single droplet transfer, high speed regime, turbulent regime, and plume regime. It was demonstrated that in the optimal jetting regime, which led to printing with single droplets, the size and volume of droplets transferred to the acceptor slide increased almost linearly with the increase of laser fluence. It was also shown that the maintenance of a stable temperature (±2°C) allowed for neglecting the temperature-induced viscosity change of hydrogels. It was determined that under room conditions (20°C, humidity 50%), the hydrogel layer, due to drying processes, decreased with a speed of about 8 μm/min, which could lead to a temporal variation of the transfer process parameters. The authors developed a practical algorithm that allowed quick configuration of the laser printing process on an applied experimental setup. The configuration is provided by the change of the easily tunable parameters: Laser pulse energy, laser spot size, the distance between the donor ribbon and acceptor plate, as well as the thickness of the hydrogel layer on the donor ribbon slide.

Evolution of Shock-Induced Pressure in Laser Bioprinting

“…The gel may contain biomolecules [28], living cells [29], or microorganisms [6,7]. The impact of tightly focused ns laser pulses leads to the local sharp heating of the thin metal layer and the generation of a rapidly expanding cavitation bubble in the gel layer [14]. This leads to the appearance of a thin jet (as in Figures 2 and 3).…”

“…To illustrate this process, we also used the gel with 1.5% hyaluronic acid. The detailed description of the viscosity role during LEMS could be found in [14].…”

“…A result of the impact of an infrared nanosecond laser pulse with a wavelength of 1064 nm on such a system is that the local area of the absorbing layer and the nearby thin layer of gel are abruptly heated to temperatures exceeding supercritical values for water. Such heating leads to the explosive appearance of a rapidly expanding vapor-gas bubble, at the top of which a thin jet of gel is formed, from which a microdroplet with cells or microorganisms is then separated [14].…”

A State‐of‐the‐Art Review of Laser‐Assisted Bioprinting and its Future Research Trends

“…Among various laser wavelengths, the infrared laser is preferred, because its wavelength generally causes less change in the chemical and physical properties of the bioink and also creates less damage to cells than the UV laser [25,61,62], which is not a good choice when processing living cells because it has potential risks of breaking the DNA double strand [63]. However, it is worth noting that the laser wavelength also plays an important role in the thermal effect, e.g., even though the infrared laser is preferred over the UV laser, it may cause more thermal damages to cells.…”

3D Bioprinting of Vascularized Tissues for in vitro and in vivo Applications

“…This technique can be used to generate scaffolds onto which cells can be built (digital light processing, DPL; Zhu et al, 2016 ) or alternatively, it can be used to print cells onto a surface ( Murphy and Atala, 2014 ; Zhu et al, 2016 ). This has been labeled laser induced forward transfer (LIFT; Yusupov et al, 2020 ). The cell laden bioink is placed on the surface of a plate or slide.…”