Ultrafast fiber laser for biomaterial processing
60 years ago, the first laser was demonstrated using a small ruby rod placed between reflecting mirrors, surrounded by a flash lamp. Back then, it was described as “a solution looking for a problem”. Today, lasers are everywhere, and there have been significant developments in terms of laser performance. The vast improvements in laser performance realized applications from particle acceleration to material processing.
Hydrogels are cross-linked polymeric biomaterials with human tissue-like water content and physiochemical resemblance. Hence, they have been widely accepted as tissue analogs in cell therapy, tissue engineering and regenerative medicine research. Topographical properties such as porosity, surface roughness, micro- and macro-patterns influence cell adhesion, direct cell growth and in some cases cell differentiation.
Laser-based topographical modification of biomaterials has gained popularity in recent years due to its high-resolution control and flexibility in altering the biomaterial simply by steering the laser beam and varying laser parameters such as fluence, and pulse duration.
Fig. 1 (a) Schematic of laser scanner setup on dried hydrogel films. Inset: Schematic of foam formation due to water absorption within film causing laser-induced expansion. (b) Scanning electron microscopy images of foamed hydrogel films with decreasing photon flux.
Recently, Professor Yu Xia from Beihang University and Professor Wang Qijie from Nanyang Technological University reported their collaborative work on a high-energy ultrafast fiber laser system at 2 μm wavelength regime, enabling high-speed direct-writing on biomaterials. The work was done when Prof. Yu was working at Singapore Institute of Manufacturing Technology, Agency for Science Technology and Research (A*STAR). The 2 μm wavelength eliminated the need to add photolabile materials as most biomaterials are inherently water-rich and absorb this wavelength strongly. Furthermore, the picosecond pulse property of the laser makes it suitable to process temperature-sensitive materials, such as biomaterials, as less heat is produced when compared to long-pulse or continuous-wave lasers. The watt-level average power coupled with the laser’s 100 kHz repetition rate facilitate high-speed processing of up to 1 m/s scanning speeds. Manipulation of the photon flux allowed topographical engineering of the hydrogel, creating features such as microchannels, foam structures and pores, with micrometer-level precision.
The compact fiber laser system was build based on chirped pulse amplification (CPA) principle. The all-fiber configuration was realized by a flexible large-mode area photonic crystal fiber. It offers excellent beam quality and could also be used to process other materials such as semiconductors and clear polymers. Moreover, it demonstrated potential usage of fiber lasers with specific wavelength and specific photon flux for minimal damage laser surgery.
About The Group
Professor Yu Xia’s technical background is in fiber optics and fiber lasers. Her research interest focuses on developing microstructured waveguide to enable high sensitivity sensor devices, and large mode area fiber to realize high power lasers. She built her mid-infrared fiber laser lab when she was working as a senior scientist in A*STAR. The collaborative work of high power mid-infrared fiber laser between Prof. Yu’s group in A*STAR and Prof. Wang’s group in NTU has been recognized as IES Prestigious Engineering Achievement Award 2017. Yu extended her research area from photonics to biomedical photonics especially neurophotonics after she joined Beihang University as a full professor. She aims to develop multi-modality instrument for deep brain research, by integrating optical/electrical/magnetic technologies.
Lee E, Sun B, Luo J Q, Singh S, Choudhury D et al. Compact pulsed thulium-doped fiber laser for topographical patterning of hydrogels. Opto-Electron Adv 3, 190039 (2020).