BackgroundThe fully developed adult skeleton adapts to mechanical forces by generating more bone, usually at the periosteal surface. Progenitor cells in the periosteum are believed to differentiate into bone-forming osteoblasts that contribute to load-induced adult bone formation, but in vivo evidence does not yet exist. Furthermore, the mechanism by which periosteal progenitors might sense physical loading and trigger differentiation is unknown. We propose that periosteal osteochondroprogenitors (OCPs) directly sense mechanical load and differentiate into bone-forming osteoblasts via their primary cilia, mechanosensory organelles known to be involved in osteogenic differentiation.MethodsWe generated a diphtheria toxin ablation mouse model and performed ulnar loading and dynamic histomorphometry to quantify the contribution of periosteal OCPs in adult bone formation in vivo. We also generated a primary cilium knockout model and isolated periosteal cells to study the role of the cilium in periosteal OCP mechanosensing in vitro. Experimental groups were compared using one-way analysis of variance or student’s t test, and sample size was determined to achieve a minimum power of 80%.ResultsMice without periosteal OCPs had severely attenuated mechanically induced bone formation and lacked the mineralization necessary for daily skeletal maintenance. Our in vitro results demonstrate that OCPs in the periosteum uniquely sense fluid shear and exhibit changes in osteogenic markers consistent with osteoblast differentiation; however, this response is essentially lost when the primary cilium is absent.ConclusionsCombined, our data show that periosteal progenitors are a mechanosensitive cell source that significantly contribute to adult skeletal maintenance. More importantly, an OCP population persists in the adult skeleton and these cells, as well as their cilia, are promising targets for bone regeneration strategies.Electronic supplementary materialThe online version of this article (10.1186/s13287-018-0930-1) contains supplementary material, which is available to authorized users.

The development of white-light-emitting polymers has been actively pursued because of the importance of such polymers in various applications, such as lighting sources and displays. To generate white-light, numerous research efforts have focused on synthesizing multifluorophore-based random copolymers to effectively cover the entire visible region. However, due to their intrinsic synthetic and structural features, this strategy has limitations in securing color reproducibility and stability. Herein, we report the development of single-fluorophore-based white-light-emitting homopolymers with excellent color reproducibility. A powerful direct C–H amidation polymerization (DCAP) strategy enabled the synthesis of defect-free polysulfonamides that emit white-light via excited-state intramolecular proton-transfer (ESIPT). To gain structural insights for designing such polymers, we conducted detailed model studies by varying the electronic nature of substituents that allow facile tuning of the emission colors. Further analysis revealed precise control of the thermodynamics of the ESIPT process by fine-tuning the strength of the intramolecular hydrogen bond. By applying this design principle to polymerization, we successfully produced a series of well-defined polysulfonamides with single-fluorophore emitting white-light. The resulting polymers emitted consistent fluorescence, regardless of their molecular weights or phases (i.e., solution, powder, or thin film), guaranteeing excellent color reproducibility. With these advantages in hand, we also demonstrated practical use of our DCAP system by fabricating a white-light-emitting coated LED.

Cyclopolymerization is a powerful method for synthesizing polyacetylenes containing four-to sevenmembered rings. However, the structure of the repeat unit only consists of mono-cycloalkene due to the single cyclization of diyne monomers. Herein, we demonstrate a novel cascade cyclopolymerization to synthesize polyacetylenes containing fused bicyclic rings from triyne monomers containing bulky dendrons via sequential cascade ring-closing metathesis. These dendrons provided solubility and stability to the rigid bicyclic polyacetylene backbone. In addition, we controlled the regioselectivity of the catalyst approach by altering its structure and synthesized polymers containing fused bicyclo [4,3,0] or [4,4,0] rings with high molecular weights of up to 120 kg mol À 1 . Interestingly, the resulting polymers showed narrower band gaps (down to 1.6 eV) than polymers with mono-cycloalkene repeat units due to the planarization of the conjugated segment resulting from the fused bicyclic structure.

The bottom-up synthesis of graphene nanoribbons (GNRs) offers a promising approach for designing atomically precise GNRs with tuneable photophysical properties, but controlling their length remains a challenge. Herein, we report an efficient synthetic protocol for producing length-controlled armchair GNRs (AGNRs) through living Suzuki–Miyaura catalyst-transfer polymerization (SCTP) using RuPhos–Pd catalyst and mild graphitization methods. Initially, SCTP of a dialkynylphenylene monomer was optimized by modifying boronates and halide moieties on the monomers, affording poly­(2,5-dialkynyl-p-phenylene) (PDAPP) with controlled molecular weight (M n up to 29.8k) and narrow dispersity (Đ = 1.14–1.39) in excellent yield (>85%). Subsequently, we successfully obtained N = 5 AGNRs by employing a mild alkyne benzannulation reaction on the PDAPP precursor and confirmed their length retention by size-exclusion chromatography. In addition, photophysical characterization revealed that a molar absorptivity was directly proportional to the length of the AGNR, while its highest occupied molecular orbital (HOMO) energy level remained constant within the given AGNR length. Furthermore, we prepared, for the very first time, N = 5 AGNR block copolymers with widely used donor or acceptor-conjugated polymers by taking advantage of the living SCTP. Finally, we achieved the lateral extension of AGNRs from N = 5 to 11 by oxidative cyclodehydrogenation in solution and confirmed their chemical structure and low band gap by various spectroscopic analyses.

No abstract