Photo-activated materials have found widespread use in biological and medical applications and are playing an increasingly important role in the nascent field of three-dimensional (3D) bioprinting. Light can be used as a trigger to drive the formation or the degradation of chemical bonds, leading to unprecedented spatiotemporal control over a material's chemical, physical, and biological properties. With resolution and construct size ranging from nanometres to centimeters, light-mediated biofabrication allows multicellular and multimaterial approaches. It promises to be a powerful tool to mimic the complex multiscale organization of living tissues including skin, bone, cartilage, muscle, vessels, heart, and liver, among others, with increasing organotypic functionality. With this review, we comprehensively discuss photochemical reactions, photo-activated materials, and their use in state-of-the-art deposition-based (extrusion and droplet) and vat polymerization-based (one-and two-photon) bioprinting. By offering an up-to-date view on these techniques, we identify emerging trends, focusing on both the chemistry and instrument aspects, thereby allowing the readers to select the best-suited approach. Starting with photochemical reactions and photo-activated materials, we then discuss principles, applications, and limitations of each technique. With a critical eye to the most recent achievements, the reader is guided through this exciting, emerging field with special emphasis on cell-laden hydrogel constructs.

A combined experimental-computational approach was used to study the self-organization and microenvironment of 1-methylnaphthalene (1MN) deposited on the surface of artificial snow grains from vapors at 238 K. The specific surface area of this snow (1.1 × 10(4) cm(2) g(-1)), produced by spraying very fine droplets of pure water from a nebulizer into liquid nitrogen, was determined using valerophenone photochemistry to estimate the surface coverage by 1MN. Fluorescence spectroscopy at 77 K, in combination with molecular dynamics simulations, and density functional theory (DFT) and second-order coupled cluster (CC2) calculations, provided evidence for the occurrence of ground- and excited-state complexes (excimers) and other associates of 1MN on the snow grains' surface. Only weak excimer fluorescence was observed for a loading of 5 × 10(-6) mol kg(-1), which is ∼2-3 orders of magnitude below monolayer coverage. However, the results indicate that the formation of excimers is favored at higher surface loadings (>5 × 10(-5) mol kg(-1)), albeit still being below monolayer coverage. The calculations of excited states of monomer and associated moieties suggested that a parallel-displaced arrangement is responsible for the excimer emission observed experimentally, although some other associations, such as T-shape dimer structures, which do not provide excimer emission, can still be relatively abundant at this surface concentration. The hydrophobic 1MN molecules, deposited on the ice surface, which is covered by a relatively flexible quasi-liquid layer at 238 K, are then assumed to be capable of dynamic motion resulting in the formation of energetically preferred associations to some extent. The environmental implications of organic compounds' deposition on snow grains and ice are discussed.

Functional polymer coatings that combine the ability to resist nonspecific fouling from complex media with high biorecognition element (BRE) immobilization capacity represent an emerging class of new functional materials for a number of bioanalytical and biosensor technologies for medical diagnostics, security, and food safety. Here, we report on a random copolymer brush surface - poly(CBMAA-ran-HPMAA) - providing high BRE immobilization capacity while simultaneously exhibiting ultralow-fouling behavior in complex food media. We demonstrate that both the functionalization and fouling resistance capabilities of such copolymer brushes can be tuned by changing the surface contents of the two monomer units: nonionic N-(2-hydroxypropyl) methacrylamide (HPMAA) and carboxy-functional zwitterionic carboxybetaine methacrylamide (CBMAA). It is demonstrated that the resistance to fouling decreases with the surface content of CBMAA; poly(CBMAA-ran-HPMAA) brushes with CBMAA molar content up to 15 mol % maintain excellent resistance to fouling from a variety of homogenized foods (hamburger, cucumber, milk, and lettuce) even after covalent attachment of BREs to carboxy groups of CBMAA. The poly(CBMAA 15 mol %-ran-HPMAA) brushes functionalized with antibodies are demonstrated to exhibit fouling resistance from food samples by up to 3 orders of magnitude better when compared with the widely used low-fouling carboxy-functional oligo(ethylene glycol) (OEG)-based alkanethiolate self-assembled monolayers (AT SAMs) and, furthermore, by up to 2 orders of magnitude better when compared with the most successful ultralow-fouling biorecognition coatings - poly(carboxybetaine acrylamide), poly(CBAA). When model SPR detections of food-borne bacterial pathogens in homogenized foods are used, it is also demonstrated that the antibody-functionalized poly(CBMAA 15 mol %-ran-HPMAA) brush exhibits superior biorecognition properties over the poly(CBAA).

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In the current study, well-defined polymer brushes are shown as an effective surface modification to resist the adhesion of whole blood and its components. Poly[oligo(ethylene glycol)methylether methacrylate] (poly(MeOEGMA)), poly(hydroxyethyl methacrylate) (poly(HEMA)), poly[N-(2-hydroxypropyl) methacrylamide] (poly(HPMA)), and poly(carboxybetaine acrylamide) (poly(CBAA)) brushes were grown by surface initiated atom transfer radical polymerization (SI-ATRP) and subsequently characterized by Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), dynamic contact angle measurements, atomic force microscopy (AFM), and surface plasmon resonance (SPR) spectroscopy. All brushes decreased the fouling from blood plasma over 95% and prevented the adhesion of platelets, erythrocytes, and leukocytes as evidenced by SPR and SEM measurements.