Femtosecond-Laser Preparation of Hydrogel with Micro/Nano-Structures and their Biomedical Applications

Hydrogels with micro/nano-structures precisely prepared by femtosecond-laser processing technology are biomaterials that mimic the natural extracellular matrix and can achieve the precise regulation of biological properties, such as cell behavior and structural-mechanical properties. They also play a crucial role in biomedical fields such as regenerative medicine, bionanostructural construction, drug transport, and particle manipulation. This study summarizes the central role of the nonlinear absorption property of femtosecond lasers in the preparation of hydrogel micro/nano-structures. Based on the electron-dynamics model and electron-density flood theory, the two main processing types of the femtosecond laser-processed hydrogel, additive and subtractive manufacturing, are discussed in depth. The modification mechanisms such as the photon-electron energy-field conversion, multiphoton absorption effect, and bubble-driven bio-link molding are analyzed. Additionally, the stimulus-response diversification and functional biomimicry properties of the structural hydrogels under the influences of different laser action modes and hydrogel composition ratios are investigated for their biomedical applications, such as microactuators, drug delivery, microscaffolds, and the in vitro simulation of vascular networks. On this basis, the advantages and limitations of the current technology are summarized and a reasonable prediction for future research on the law of action of the femtosecond-laser preparation of hydrogel micro/nano-structures is made.