![]() ![]() The full IPNs are formed through covalent bonds, based on photocuring of the complementary photoreactive groups o-methyl benzaldehyde (UV light) and styrylpyrene (visible light). Light gated control over materials properties of IPNs is assessed theoretically by applying the general rule of mixture and experimentally by using a multifunctional polymer resist. Herein, control is exerted over network material properties of a single polymer blend through the spatiotemporally controlled incorporation of secondary polymer networks resulting in interpenetrating polymer networks (IPNs). ![]() Light-induced curing of photoresists is a well-established technique to fabricate polymer networks with precise control over the material properties. By changing the colour of light, photopolymers can be recycled and reshaped, allowing these macromolecular precursors to be applied to reversible and photodegradable material design. Size exclusion chromatography provides additional offline analysis of both the polymerisation and photodegradation over time. The process was monitored online via a photoflow-high resolution electrospray ionisation mass spectrometry setup (ESI-MS). Violet blue light at 415 nm triggers -cycloadditions of a pyrene-chalcone derivative to grow linear step-growth polymers, while subsequent UV-B light irradiation triggers the depolymerisation. Both a batch approach and a continuous photoflow setup are employed to investigate the degree of polymerisation and scalability. Herein, we demonstrate the scalable synthesis of catalyst-free, visible-light mediated photo-oligomers and-polymers via a step-growth mechanism. Light as a non-invasive and clean external stimulus provides a facile route towards macromolecular design. Specifically, hydrogel softening can be achieved in a stepwise fashion according to the chromophores’ activation wavelength, enabling fine control over the hydrogel's mechanical properties. The highly selective photochemical behavior of three chromophores with distinct degradation wavelengths is exploited for the construction of selectively degradable hydrogels. Furthermore, the materials and photodegradation processes are non‐toxic to cells, making this platform attractive for biomaterials engineering. The softening is shown to influence the spreading of pre‐osteoblastic cells adhering to the gels as a demonstration of their potential utility. Critically, this platform technology allows for the fabrication of various hydrogels, whose mechanical properties can be fine‐tuned using different colors of light to reach a predefined value, according to the chromophore ratios used. The wavelength‐selective addressability of individual photoreactive units is subsequently translated into hydrogel design, enabling wavelength‐dependent cleavage of the hydrogel networks on‐demand. By examining their photochemical action plots, the wavelength‐dependent reactivity of the photocleavable moieties is determined. Specifically, three chromophores are exploited, that is, ortho‐nitrobenzene, dimethyl aminobenzene, and bimane, each absorbing light at different wavelengths. Herein, the wavelength‐dependent degradation of bio‐orthogonal poly(ethylene glycol) hydrogels is reported, using three selective activation levels. Photoresponsive hydrogels hold key potential in advanced biomedical applications including tissue engineering, regenerative medicine, and drug delivery, as well as intricately engineered functions such as biosensing, soft robotics, and bioelectronics. ![]()
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