Targeting micromotion for mimicking natural bone healing by using NIPAM/Nb_(2)C hydrogel

Natural fracture healing is most efficient when the fine-tuned mechanical force and proper micromotion are applied.To mimick this micromotion at the fracture gap,a near-infrared-II(NIR–II)–activated hydrogel was fabricated by integrating two-dimensional(2D)monolayer Nb2C nanosheets into a thermally responsive poly(Nisopropylacrylamide)(NIPAM)hydrogel system.NIR–II–triggered deformation of the NIPAM/Nb2C hydrogel was designed to generate precise micromotion for co-culturing cells.It was validated that micromotion at 1/300 Hz,triggering a 2.37-fold change in the cell length/diameter ratio,is the most favorable condition for the osteogenic differentiation of bone marrow mesenchymal stem cells(BMSCs).Moreover,mRNA sequencing and verification revealed that micromotion-induced augmentation was mediated by Piezo1 activation.Suppression of Piezo1 interrupts the mechano-sensitivity and abrogates osteogenic differentiation.Calvarial and femoral shaft defect models were established to explore the biocompatibility and osteoinductivity of the Micromotion Biomaterial.A series of research methods,including radiography,micro-CT scanning,and immunohistochemical staining have been performed to evaluate biosafety and osteogenic efficacy.The in vivo results revealed that tunable micromotion strengthens the natural fracture healing process through the sequential activation of endochondral ossification,promotion of neovascularization,initiation of mineral deposition,and combinatory acceleration of full-thickness osseous regeneration.This study demonstrated that Micromotion Biomaterials with controllable mechanophysical characteristics could promote the osteogenic differentiation of BMSCs and facilitate full osseous regeneration.The design of NIPAM/Nb2C hydrogel with highly efficient photothermal conversion,specific features of precisely controlled micromotion,and bionic-mimicking bone-repair capabilities could spark a new era in the field of regenerative medicine.

Mobility Pattern of Taxi Passengers at Intra-Urban Scale:Empirical Study of Three Cities

The study of human mobility patterns is of both theoretical and practical values in many aspects. For long-distance travel, a few research endeavors have shown that the displacements of human travels follow a power-law distribution. However, controversies remain regarding the issue of the scaling laws of human mobility in intra-urban areas. In this work, we focus on the mobility pattern of taxi passengers by examining five datasets of three metropolitans. Through statistical analysis, we find that the lognormal distribution with a power-law tail can best approximate both the displacement and the duration time of taxi trips in all the examined cities. The universality of the scaling laws of human mobility is subsequently discussed, in view of the analysis of the data. The consistency of the statistical properties of the selected datasets that cover different cities and study periods suggests that, the identified pattern of taxi-based intra-urban travels seems to be ubiquitous over cities and time periods.