Polydopamine is the first adhesive polymer that can functionalize surfaces made of virtually all material chemistries. The material‐independent surface modification properties of polydopamine allow the functionalization of various types of medical and energy devices. However, the mechanism of dopamine polymerization has not yet been clearly demonstrated. Covalent oxidative polymerization via 5,6‐dihydroxyindole (DHI), which is similar to the mechanism for synthetic melanin synthesis, has been the clue. Here, it is reported that a physical, self‐assembled trimer of (dopamine)2/DHI exists in polydopamine, which has been known to be formed only by covalent polymerization. It is also found that the trimeric complex is tightly entrapped within polydopamine and barely escapes from the polydopamine complex. The result explains the previously reported in vitro and in vivo biocompatibility. The study reveals a different perspective of polydopamine formation, where it forms in part by the self‐assembly of dopamine and DHI, providing a new clue toward understanding the structures of catecholamines such as melanin.

Capture and release: The material‐independent surface chemistry of a poly(norepinephrine) (pNE) which exhibits perfect smoothness at the nanometer scale is controlled by 3,4‐dihydroxybenzaldehyde‐norepinephrine (DHBA‐NE) conjugates. The pNE layer containing DHBA‐NE serves to store and release small therapeutics such as nitric oxide.

Recreating heterotypic cell–cell interactions in vitro is key to dissecting the role of cellular communication during a variety of biological processes. This is especially relevant for stem cell niches, where neighbouring cells provide instructive inputs that govern cell fate decisions. To investigate the logic and dynamics of cell–cell signalling networks, we prepared heterotypic cell–cell interaction arrays using DNA-programmed adhesion. Our platform specifies the number and initial position of up to four distinct cell types within each array and offers tunable control over cell-contact time during long-term culture. Here, we use the platform to study the dynamics of single adult neural stem cell fate decisions in response to competing juxtacrine signals. Our results suggest a potential signalling hierarchy between Delta-like 1 and ephrin-B2 ligands, as neural stem cells adopt the Delta-like 1 phenotype of stem cell maintenance on simultaneous presentation of both signals.

Setzt glatt NO frei: Die materialunabhängige Oberflächenchemie von nanoskopisch glattem Poly(norepinephrin) (pNE) wird durch 3,4‐Dihydroxybenzaldehyd‐Norepinephrin‐Konjugate (DHBA‐NE) bestimmt. pNE‐Schichten mit DHBA‐NE können kleine Wirkstoffe wie Stickstoffmonoxid speichern und freisetzen.

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