Volumetric Photopolymerization Confinement through Dual-Wavelength Photoinitiation and Photoinhibition

Abstract

Conventional photolithographic rapid prototyping approaches typically achieve reaction confinement in depth through patterned irradiation of a photopolymerizable resin at a wavelength where the resin strongly absorbs, such that only a very thin layer of material is solidified. Consequently, three-dimensional objects are fabricated by progressive, two-dimensional addition of material, curtailing fabrication rates and necessitating the incorporation of support structures to ensure the integrity of overhanging features. Here, we examine butyl nitrite as a UV-active photoinhibitor of blue light-induced photopolymerizations and explore its utilization to confine in depth the region polymerized in a volume of resin. By employing two perpendicular irradiation patterns at blue and near-UV wavelengths to independently effect either polymerization initiation or inhibition, respectively, we enable three-dimensional photopolymerization patterning in bulk resin, thereby complementing emergent approaches to volumetric 3D printing.

Dual-Wavelength (UV and Blue) Controlled Photopolymerization Confinement for 3D-Printing: Modeling and Analysis of Measurements

“…As reported by by van der Laan et al [11], the effectiveness of a photoinhibitor is strongly monomer-dependent, which also requires: (i) a high conversion of blue-photoinitiation in the absence of the UV-active inhibitor; (ii) a strong chain termination with significant reduction of blue and UV conversion in the presence of UV-active inhibitor; and (iii) short induction time or rapid elimination of the inhibitor species in the dark (or absence of UV-light), such that the initiation-inhibition cycles may be switched on and off rapidly. Fast switching-time may be achieved by high conversion rate, or high blue-light intensity, the triple-state quantum yield, and the absorption constant of the monomer resin.…”

“…initiator, co-initiator and inhibitor, and the dual-wavelength light intensity and dose (or exposure time). The advantages of dual-wavelength concurrent inhibition and initiation photopolymerization include: controllable high vertical print speeds, eliminating the need for thin, oxygen-permeable projection windows, single-step fabrication of cured materials, rapid generation of personalized products, and the reflow into the inhibition volume during printing can be optimized for large cross-sectional area parts, Dual-wavelength photopolymerization confinement (PC) were reported in both parallel [10] and perpendicular [11] concurrent irradiation schemes. In the parallel scheme, the volumetric PC was achieved by inhibition volume depth controlled by varying the ratio of the intensities of the UV and blue lights, where print speeds of 2 m/hour have been achieved in a wide variety of resins including acrylates, methacrylates, and vinyl ethers.…”

Enhancing UV Photopolymerization by a Red‐light Preirradiation: Kinetics and Modeling Strategies for Reduced Oxygen Inhibition

“…Two different mechanisms of dual-wavelength selectively controlled photoinitiation and photoinhabitation have been reported experimentally: (a) oxygen inhibition reported by Childress et al 16 and (b) radical inhibition reported by de Beer et al 20 and van der Laan et al 21 In the first mechanism using red light and UV light, the preirradiation time of red light could be controlled to tailor the induction time, such that photosensitization and photoinitiation can be independently achieved for reduced oxygen inhibition for faster and more efficient UV-light polymerization.…”

“…Concurrent with the blue-light photoorthogonal, patterned irradiation, the blue-light-produced initiation radical could be reduced/inhibited by [N], such that photopolymerization confinement (PC) is achieved. 21 For PC application, large polymerization inhibition depth adjacent to the projection window and continuous part production at high translation speeds are desired. More detailed kinetics and modeling of PC were published elsewhere.…”

“…Higher PS initial concentration will improve the efficacy, but there is an optimal value. 21 Additive enhancer monomer were proposed to improve the curing (crosslink) efficacy by either reducing the oxygen inhibition effect by stable monomer, or increase the lifetime of radicals in clinical applications. 18,23…”