bioprinting is a technology to print materials (bioink) with cells into customized tissues for regeneration or organoids for drug screening applications. Herein, a series of biodegradable polyurethane (PU)-gelatin hydrogel with tunable mechanical properties and degradation rates were developed as the bioink. The PU-gelatin hydrogel demonstrated good printability in 24−31 °C and could print a complicated structure such as the nose-shaped construct. Due to the excellent shear thinning and fast strain recovery properties, the PU-gelatin hydrogel also had long working windows for bioprinting (over 24 h), stacking ability (up to 80 layers), and feasibility for high-resolution printing (through an 80 μm nozzle). The structure stability of the PU-gelatin hydrogel was maintained by two-stage double-network formation through Ca 2+ chelation and thermal gelation at 37 °C without any toxic cross-linking reagent. The compressive modulus of printed PU-gelatin hydrogel constructs increased in about 3-fold by the treatment of CaCl 2 solution for 15 min and enhanced further after incubation because of the thermal sensitivity of PU at 37 °C. Mesenchymal stem cells (MSCs) printed with the PU-gelatin hydrogel through the 80 μm nozzle showed good viability, high mobility, and ∼200% proliferation ratio (or an ∼300% proliferation ratio through a 200 μm nozzle) in 10 days. Furthermore, the MSC-laden PU-gelatin constructs containing small molecular drug Y27632 underwent chondrogenesis in 10 days. The novel series of PU-gelatin hydrogels with tunable modulus, long working window, convenient bioprinting process, and high-resolution printing possibilities may serve as new bioink for 3D bioprinting of various tissues.

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Ethylene diamine potentially causes dimension-dependent face-selective chemical etching of fullerene crystals based on a post-assembly method.

This Minireview presents sophisticated interfacial materials nanoarchitectonics for cell regulation as controls of advanced bio‐systems. In the nanoarchitectonics procedures, functional materials and systems can be architected with various actions and processes including atomic/molecular manipulation, organic synthesis, self‐assembly/self‐organization and structural regulation upon application of external physical stimuli. Based on nano‐level materials fabrications with this nanoarchiteconics concept, several recent research accomplishments on cell regulations are described as classified into (i) influences of physical mechanical factors such as elasticity and viscoelasticity on cell regulations at materials surfaces and liquid interfaces; (ii) regulation of cells upon dynamic changes of surface natures, stimuli by chemicals, and geometric factors; (iii) effects of surface structures prepared by microfabrications and assemblies of nanomaterials on cell regulations.

Three-dimensional (3D) bioprinting is a technology that can precisely fabricate customized tissues and organs. Hydrogel materials that can embed living cells for use in 3D printing are called bioinks. However, there are only limited options of bioinks currently because they require the following features at once, such as printability, repetitive layer-by-layer stacking (stackability), structure stabilization, and biological properties. A polyurethane–gelatin double network hydrogel bioink was previously reported to own tunable modulus through changing the solid content, but cell viability at the high solid content is inevitably reduced. In the present study, the reinforcement effects of a metal–organic framework (MOF), zeolitic imidazolate framework-8 (ZIF-8), in the PUG bioink were evaluated. The printability, stackability, thermoresponsiveness, and shear-thinning behavior of the PUG-ZIF-8 composite hydrogels were examined. It was found that the PUG composite hydrogel containing 1250 μg/mL ZIF-8 crystals showed significant structural stability and modulus enhancement (∼2.5-fold). However, the PUG bioink containing 1250 μg/mL ZIF-8 crystals may lead to cell senescence or death. The cytocompatible concentration of ZIF-8 crystals in the bioink was about 875 μg/mL, and this concentration was much higher than the reported tolerable amount (∼50 μg/mL) of ZIF-8 for biomedical applications. The strong reinforcement effect of ZIF-8 and the drug-loading/sensing possibilities of MOFs may open new opportunities for using MOFs in 3D bioprinting applications.

Poly(3-hydroxybutyrate) (PHB) is a biodegradable polymer with good biocompatibility.

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Wood plastic composite, known as green composite, combines natural vegetable fibers and plastic and thus acquires the properties of both. In this study, coir was subject to alkali treatment to eliminate pectin, hemicelluloses, fat and impurities. Alkali treatment reduces the weight of coir and the greater the concentration and longer the alkali treatment time, the greater is the loss of coir fibers. This study uses coir fibers and polypropylene to make wood plastic composite. Alkali treatment can increase the mechanical property of the resulting wood plastic composite. In particular, the optimum parameters of the treatment are 17.5 wt% for 1 h. As is demonstrated by scanning electron microscope images, methylmaleic anhydride-graft-polypropylene improves the interface binding force between the coir and polypropylene.