Although poly(L-lactide) (PLLA) based porous scaffolds have been widely fabricated through 3D printing, their poor mechanical properties and osteogenic activity still do not meet the needs of bone tissue repair....

To date, designing a perfect poly(D,L-lactide) (PDLLA) bone repair material still remains a major challenge. Inspired by the superior cell affinity, osteogenic activity, and mechanical properties of polysaccharide chitin whiskers, here, positively charged chitin whiskers (HCHW) and negatively charged maleated chitin whiskers (mCHW) are prepared for strengthening and biofunctionalizing the PDLLA membrane via a layer-by-layer (LBL) electrostatic self-assembly method. At a pH value of 4.3, the process of LBL electrostatic self-assembly between the HCHW and mCHW on the membranes is successfully performed, which can be directly proved by the cross-sectional morphology, light transmittance, surface composition, and topography of the membranes. Especially, polydopamine, as an intermediate layer, can greatly enhance the stability and adhesion of the first chitin whisker layer on the PDLLA substrate. Compared with the PDLLA membrane, the mechanical properties of self-assembly membranes are highly enhanced and controllable by adjusting the number of self-assembly whisker layers. Furthermore, in vitro biological evaluations indicate that the HCHW-assembled surface has a higher cell affinity than that of the mCHW-assembled one, which may be attributed to different protein adsorption. Meanwhile, interesting directional cell migration behavior is observed on the HCHW-assembled surface, which can be explained by the guiding effect of surface ordered topology and collective cell migration. These findings provide a new strategy for designing bioactive PDLLA composites with superior and tunable mechanical properties for bone regeneration materials.

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The liquid crystal properties and viscoelasticity of the natural bone extracellular matrix (ECM) play a decisive role in guiding cell behavior, conducting cell signals, and regulating mineralization. Here, we develop a facile approach for preparing a novel polysaccharide hydrogel with liquid crystal properties and viscoelasticity similar to those of natural bone ECM. First, a series of chitin whisker/chitosan (CHW/CS) hydrogels were prepared by chemical cross-linking with genipin, in which CHW can self-assemble to form cholesteric liquid crystals under ultrasonic treatment and CS chains can enter into the gaps between the helical layers of the CHW cholesteric liquid crystal phase to endow morphological stability and good mechanical properties. Subsequently, the obtained chemically cross-linked liquid crystal hydrogels were immersed into the desired concentration of the NaCl solution to form physical cross-linking. Due to the Hofmeister effect, the as-prepared dual-cross-linked liquid crystal hydrogels showed an enhanced modulus, viscoelasticity similar to that of natural ECM with relatively fast stress relaxation behavior, and fold surface morphology. Compared to both CHW/CS hydrogels without liquid crystal properties and CHW/CS liquid crystal hydrogels without further physical cross-linking, the dual-cross-linked CHW/CS liquid crystal hydrogels are more favorable for the adhesion, proliferation, and osteogenic differentiation of bone marrow mesenchymal stem cells. This approach could inspire the design of hydrogels mimicking the liquid crystal properties and viscoelasticity of natural bone ECM for bone repair.

The multiple-sugar metabolism regulator (MsmR), a transcription factor belonging to the AraC/XylS family, participates in polysaccharide metabolism and virulence. However, the transcriptional regulatory mechanisms of MsmR1 in Paenibacillus polymyxa remain unclear. In this study, knocking out msmR1 was found to reduce polymyxin synthesis by the SC2-M1 strain. Chromatin immunoprecipitation assay with sequencing (ChIP-seq) revealed that most enriched pathway was that of carbohydrate metabolism. Additionally, electromobility shift assays (EMSA) confirmed the direct interaction between MsmR1 and the promoter regions of oppC3, sucA, sdr3, pepF, yycN, PPSC2_23180, pppL, and ydfp. MsmR1 stimulates polymyxin biosynthesis by directly binding to the promoter regions of oppC3 and sdr3, while also directly regulating sucA and influencing the citrate cycle (TCA cycle). In addition, MsmR1 directly activates pepF and was beneficial for spore and biofilm formation. These results indicated that MsmR1 could regulate carbohydrate and amino acid metabolism, and indirectly affect biological processes such as polymyxin synthesis, biofilm formation, and motility. Moreover, MsmR1 could be autoregulated. Hence, this study expand the current knowledge of MsmR1 and will be beneficial for the application of P. polymyxa SC2 in the biological control against the certain pathogens in pepper.