Fabrication and Functionalization of 3D Printed Polydimethylsiloxane-Based Microfluidic Devices Obtained through Digital Light Processing

This work reports the preparation and 3D printing of a custom-made photopolymer based on acrylate-polydimethylsiloxane (PDMS), for the fabrication of complex-shaped 3D printed microfluidic chips. By selecting and combining the proper materials during the preparation of the resins along with the freedom of design of light-based 3D printers, 3D microfluidic PDMS-like chips are obtained with excellent optical features, high chemical stability, and good mechanical properties. Furthermore, taking advantage of unreacted functional groups exposed on the sample's surface after the 3D printing step, the surface properties of the devices are easily and selectively modified during the postcuring step through UV-induced grafting polymerization techniques, giving an added value to the printed devices in terms of surface treatment compared to conventional methods. The 3D printing of the PDMS-based resins developed here may potentially transforms the fabrication methodology of PDMS microfluidic devices by decreasing manufacturing costs and time, allowing the production of complex-shaped and truly 3D microdevices

Stimuli-responsive thiol-epoxy networks with photo-switchable bulk and surface properties

In the present work, the versatile nature of o-nitrobenzyl chemistry is used to alter bulk and surface properties of thiol-epoxy networks. By introducing an irreversibly photocleavable chromophore into the click network, material properties such as wettability, solubility and crosslink density are switched locally by light of a defined wavelength. The synthesis of photo-responsive thiol-epoxy networks follows a photobase-catalyzed nucleophilic ring opening of epoxy monomers with photolabile o-nitrobenzyl ester (o-NBE) groups across multi-functional thiols. To ensure temporal control of the curing reaction, a photolatent base is employed releasing a strong amidine-type base upon light exposure, which acts as an efficient catalyst for the thiol epoxy addition reaction. The spectral sensitivity of the photolatent base is extended to the visible light region by adding a selected photosensitizer to the resin formulation. Thus, in the case of photoactivation of the crosslinking reaction the photorelease of the base does not interfere with the absorbance of the o-NBE groups. Once the network has been formed, the susceptibility of the o-NBE groups towards photocleavage reactions is used for a well-defined network degradation upon UV exposure. Sol–gel analysis evidences the formation of soluble species, which is exploited to inscribe positive tone micropatterns by photolithography. Along with the localized tuning of network structure, the irreversible photoreaction is exploited to change the surface wettability of thiol-epoxy networks. The contact angle of water significantly decreases upon UV exposure due to the photo-induced formation of hydrophilic cleavage products enabling the inscription of domains with different surface wettability by photolithography

NIR Sensitizer Operating under Long Wavelength (1064 nm) for Free Radical Photopolymerization Processes

International audienceFree radical polymerization upon near‐infrared (NIR) light is still the subject of intense research efforts and remains a huge challenge particularly for long wavelengths (>1000 nm). In this study, a NIR sensitizer operating upon long wavelength (1064 nm) is proposed for an efficient polymerization of acrylate monomers. A new three‐component photoinitiating system is developed comprising the NIR sensitizer in combination with an Iodonium salt (Iod) and an amine. Remarkably, the NIR sensitizer (IR 1064) absorbing strongly in all the near infrared region (700–1200 nm) offers the possibility to use a broad range of irradiation wavelengths, i.e., examples are provided at 785 and 1064 nm. Such long wavelengths are characterized by many advantages such as a deeper penetration of light and therefore a better curing of the monomer but it is also much safer than UV light. Excellent performance is observed for the three‐component IR 1064/Iod/Amine system under air: high conversion of acrylate functions associated with a fast polymerization time. The use of IR 1064 as NIR sensitizer with a broad NIR absorption is—to the best of current knowledge—never proposed in the literature. The photoinitiating performances are studied using real‐time Fourier transform infrared spectroscopy