Understanding the BA-LIFT process window
BA-LIFT is a laser-assisted bioprinting approach in which a polymer energy-absorbing layer shields the bioink from direct laser exposure. A laser pulse creates a rapidly expanding blister in the polymer layer, mechanically ejecting a small bioink droplet toward the receiving substrate.
The thesis systematically investigated three central variables in this process: laser pulse energy, the thickness of the polyimide energy-absorbing layer and the rheological behaviour of the bioink. The experimental work was carried out using a prototype laser bioprinter developed by AM Technologies by Brinter as part of the KeratOPrinter development environment.
Material and process parameters interact
The results showed that thicker polyimide layers tolerated higher laser pulse energies before blister rupture, while accurate laser focusing was critical for efficient and consistent blister formation. Blister size increased with pulse energy before rupture, but blister size alone did not reliably predict the size of the transferred bioink droplet.
Bioink composition and rheological behaviour had a strong influence on transfer. The highest-viscosity formulation tested did not transfer at any of the evaluated laser pulse energies, while lower-viscosity formulations could be deposited successfully. Increasing pulse energy also tended to increase droplet irregularity and splashing rather than simply increasing droplet size.
- Thicker polyimide layers withstood higher laser pulse energies before rupture.
- Accurate laser focus was critical for efficient blister formation.
- Blister size alone did not determine transferred droplet size.
- Bioink composition and rheology strongly influenced successful droplet transfer.
- Higher pulse energies increased the risk of irregular droplets and splashing.
Supporting KeratOPrinter process development
The work provides practical process-development evidence for the KeratOPrinter laser-assisted bioprinting platform. It highlights why high-resolution biofabrication cannot be optimized through a single machine parameter: the laser, energy-absorbing layer, bioink properties, material-layer thicknesses and transfer geometry must be developed as an interacting manufacturing process.
The thesis was completed by Alma Kurki at Tampere University within the Horizon Europe KeratOPrinter project and forms part of the broader effort to develop controlled multi-process manufacturing technology for advanced corneal biofabrication.