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Abstract
Therapeutic growth factor delivery typically requires supraphysiological dosages, which can cause undesirable off-target effects. The aim of this study was to 3D bioprint implants containing spatiotemporally defined patterns of growth factors optimized for coupled angiogenesis and osteogenesis. Using nanoparticle functionalized bioinks, it was possible to print implants with distinct growth factor patterns and release profiles spanning from days to weeks. The extent of angiogenesis in vivo depended on the spatial presentation of vascular endothelial growth factor (VEGF). Higher levels of vessel invasion were observed in implants containing a spatial gradient of VEGF compared to those homogenously loaded with the same total amount of protein. Printed implants containing a gradient of VEGF, coupled with spatially defined BMP-2 localization and release kinetics, accelerated large bone defect healing with little heterotopic bone formation. This demonstrates the potential of growth factor printing, a putative point of care therapy, for tightly controlled tissue regeneration.

Abstract
Abstract Electrically conductive materials that mimic physical and biological properties of tissues are urgently required for seamless brain–machine interfaces. Here, a multinetwork hydrogel combining electrical conductivity of 26 S m−1, stretchability of 800%, and tissue-like elastic modulus of 15 kPa with mimicry of the extracellular matrix is reported. Engineering this unique set of properties is enabled by a novel in-scaffold polymerization approach. Colloidal hydrogels of the nanoclay Laponite are employed as supports for the assembly of secondary polymer networks. Laponite dramatically increases the conductivity of in-scaffold polymerized poly(ethylene-3,4-diethoxy thiophene) in the absence of other dopants, while preserving excellent stretchability. The scaffold is coated with a layer containing adhesive peptide and polysaccharide dextran sulfate supporting the attachment, proliferation, and neuronal differentiation of human induced pluripotent stem cells directly on the surface of conductive hydrogels. Due to its compatibility with simple extrusion printing, this material promises to enable tissue-mimetic neurostimulating electrodes.

Abstract
Physical entrapment of enzymes within a porous matrix is a fast and gentle process to immobilize biocatalysts to enable their recycling and long‐term use. This study introduces the development of a biocompatible 3D‐printing material suitable for enzyme entrapment, while having good rheological and UV‐hardening properties. Three different viscosity‐enhancing additives have been tested in combination with a polyethylenglycol‐diacrylate‐based hydrogel system. The addition of polyxanthan or hectorite clay particles results in hydrogels that degrade over hours or days, releasing entrapped compounds. In contrast, the addition of nanometer‐sized silicate particles ensures processability while preventing disintegration of the hydrogel. Lattice structures with a total height of 6 mm consisting of 40 layers were 3D‐printed with all materials and characterized by image analysis. Rheological measurements identified a shear stress window of 200 < τ < 500 Pa at shear rates of 25 s−1 and 25°C for well‐defined geometries with an extrusion‐based printhead. Enzymes immobilized in these long‐term stable hydrogel structures retained an effective activity of approximately 10% compared to the free enzyme in solution. It could be shown that the reduction of effective activity isn't caused by a significant reduction of the intrinsic enzyme activity but by mass transfer limitations within the printed hydrogel structures. This article is protected by copyright. All rights reserved