Filamented Light (FLight) Biofabrication of Highly Aligned Tissue‐Engineered Constructs

Abstract

Cell‐laden hydrogels used in tissue engineering generally lack sufficient 3D topographical guidance for cells to mature into aligned tissues. A new strategy called filamented light (FLight) biofabrication rapidly creates hydrogels composed of unidirectional microfilament networks, with diameters on the length scale of single cells. Due to optical modulation instability, a light beam is divided optically into FLight beams. Local polymerization of a photoactive resin is triggered, leading to local increase in refractive index, which itself creates self‐focusing waveguides and further polymerization of photoresin into long hydrogel microfilaments. Diameter and spacing of the microfilaments can be tuned from 2 to 30 µm by changing the coherence length of the light beam. Microfilaments show outstanding cell instructive properties with fibroblasts, tenocytes, endothelial cells, and myoblasts, influencing cell alignment, nuclear deformation, and extracellular matrix deposition. FLight is compatible with multiple types of photoresins and allows for biofabrication of centimeter‐scale hydrogel constructs with excellent cell viability within seconds (<10 s per construct). Multidirectional microfilaments are achievable within a single hydrogel construct by changing the direction of FLight projection, and complex multimaterial/multicellular tissue‐engineered constructs are possible by sequentially exchanging the cell‐laden photoresin. FLight offers a transformational approach to developing anisotropic tissues using photo‐crosslinkable biomaterials.

Multiscale Hybrid Fabrication: Volumetric Printing Meets Two-Photon Ablation

“…In order to successfully combine these two techniques, we first developed a strategy to remove the VP-generated microdefects. As recently shown by Liu et al, 19 optical modulation instability (OMI) results in the formation of hydrogel microfilaments and microchannels (void spaces between microfilaments) in the range of 2 −30 μm propagating via self-focusing waveguides (Figure 1A). Therefore, although commonly described as defect-free due to the layer-less printing modality, VP printed constructs have in microfilaments and microchannels a major source of defects which can limit their applications.…”

“…When the light-dose exceeds the material’s critical gelation threshold, the desired 3D model is formed and can be retrieved with the removal of the uncrosslinked photoresin. However, when reaching the photoresin, the laser beam featuring a speckle-pattern intensity noise causes the formation of microfilaments and microchannels, 19 herein also generally described as microdefects. This phenomenon originates from the non-linear nature of the photosensitive material which shows a change in refractive index (RI) between its uncrosslinked to crosslinked state.…”

“…In fact, while on one hand microchannels can improve diffusion of nutrients into the printed construct, they can also act as physical guidance cues for cells to spread, migrate, align and deposit extracellular matrix (ECM). 19 Although optimal for anisotropic tissues such as muscle and tendon, this unidirectional microarchitecture is not desirable for all applications requiring an isotropic cell spreading without preferential outgrowth direction or cell confinement in a defined region (i.e., channel wall). In particular for the combination with 2PA, the presence of microchannels hinders high-resolution printing which requires a homogeneous, defect-free material substrate to fully guarantee precise control over hollow architectures.…”

Instantly adhesive and ultra-elastic patches for dynamic organ and wound repair

“…Resolution could be further improved by reducing the voxel size of the incident light beam ( 17 ). While the current system used chain-growth polymerization of the GelMA matrix in the presence of LAP, future research could use step-growth polymerization using thiol-ene photoclick chemistry ( 65, 66 ) to allow for both higher resolution fabrication and quicker fabrication times. One could also deploy higher resolution techniques such as volumetric printing ( 67, 68 ) or stereolithography ( 69 ) to achieve resolutions of up to 50 μm.…”

Bioprinting on Organ-on-Chip: Development and Applications

“…Flight biofabrication utilizes the phenomenon of optical modulation instability of filament light beams inside a photosensitive biomaterial, for bioprinting highly aligned hydrogel microfilaments [ 46 ].…”