Control of deposition processes and structures of fibroin nanofilms by IR pulsed laser ablation

Control of structural and morphological features of silk fibroin (SF), one of the most popular and stable structural proteins, prepared by near infrared (1064 nm) pulsed laser deposition (PLD) are discussed, based mainly on the recent experimental studies made in the authors' laboratory. The small deposition rate and mingling of much larger units, called chunks or debris, are the main problems. The structure and properties of irradiation targets are highlighted, in an attempt to make the protein PLD technique affordable for practical purposes. Firm adhesion among fibroin powder particles is a straightforward way to avoid pull-out of the particles from the powder-consolidated target, being one of the main sources of debris. This alone cannot, however, satisfactorily increase the homogeneity of the nanostructures and increase the deposition rate. Finer control of the properties of grain-boundary in the target was therefore devised by using binders, including an autogenous one. A unique feature of the ablation mechanisms of fibroin was also discussed by taking account of the optical properties of fibroin, being transparent to a 1064 nm laser beam.