Wavelength Selective Multi‐Material 3D Printing of Soft Active Devices Using Orthogonal Photoreactions

Abstract

Orthogonal photoreactions provide a unique way to locally and independently control (thermo)mechanical properties and functionality of polymer networks simply by choice of the wavelength. Herein, a library of acrylate functional coumarin monomers is synthesized, which are cured by sequence‐dependent wavelength orthogonality. In the presence of a long wavelength absorbing photoinitiator, the monomers undergo rapid curing by visible light induced radical chain growth polymerization. Subsequent irradiation with light in the UV‐A region selectively initiates the [2+2] photocycloaddition of the coumarin chromophores, which is confirmed by FTIR and UV–vis experiments. Through a well‐targeted design, acrylate‐based and thiol‐acrylate resin formulations are prepared, whose fast curing rate, low viscosity, and prolonged storage stability enable the one‐step fabrication of multi‐material structures by digital light processing (DLP) 3D printing. By using a dual‐wavelength printer, which operates at two different wavelengths (405 and 365 nm), objects comprising soft (ε = 22%, σ = 7.5 MPa) and stiff (ε = 2%, σ = 8.3 MPa) domains are printed with a single resin vat. Along with tensile properties, the wavelength selective change in the network structure features a local control of the glass transition temperature (ΔTg = 17 °C) in the 3D‐printed objects. Soft active devices are fabricated by dual‐wavelength DLP 3D printing, with distinct domains having a higher Tg and the local programming of multi shapes is demonstrated.

Photochemically Activated 3D Printing Inks: Current Status, Challenges, and Opportunities

“…[102,103,121,147,151,152] A more elegant approach toward fabricating advanced materials is to use a single 𝜆orthogonal multi-material photoresist (Figure 12a). [153] The ability to print material A with 𝜆 1 and material B with 𝜆 2 -in any order-would be considered a major breakthrough. [154] However, it is common that the absorption profiles of different chromophores partially overlap since most visible-light active species also show absorbance in the UV region.…”

Directing network degradability using wavelength-selective thiol-acrylate photopolymerization

“…6,7 For example, wavelength-selective photopolymerization has been used to incorporate various building blocks and functionalities into a single polymeric matrix, including thiol-ene/thiolepoxy, [8][9][10] epoxy/acrylate, [11][12][13][14][15] thiol-acrylate/acrylate, [16][17][18] and many other hybrid systems. [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] Wavelength-selective photopolymerization can fabricate these multimaterials through both simultaneous and sequential polymer network formations. For example, Hawker and coworkers employed photochromic dyes to enable wavelengthselective photopolymerization of a hybrid epoxy/acrylate resin and successfully 3D printed a multimaterial comprising patterned rigid and soft domains in a single step.…”

“…6,7 For example, wavelength-selective photopolymerization has been used to incorporate various building blocks and functionalities into a single polymeric matrix, including thiol–ene/thiol-epoxy, 8–10 epoxy/acrylate, 11–15 thiol-acrylate/acrylate, 16–18 and many other hybrid systems. 19–33…”

Unusual Stress Upturn in Elastomers Prepared Using Macro Cross‐Linkers with Multiple Vinyl Side Groups

“…The elastomer samples are prepared by photo-induced polymerization using a macro cross-linker polymers bearing multiple vinyl side groups as the key component (Figure 1). Such photo-curable elastomers have been rekindled recently due to the development of photo-curing 3D printers, [21][22][23] and thus studies on versatile physical property modification of such elastomers should be meaningful in terms of practical application. Using the proposed macro cross-linker allows tuning of tensile stress exclusively in the large elongation region, unlike the conventional molecular designs.…”