As a promising new micro-physiological system, organ-on-a-chip has been widely utilized for in vitro pharmaceutical study and tissues engineering based on the three-dimensional constructions of tissues/organs and delicate replication of in vivo-like microenvironment. To better observe the biological processes, a variety of sensors have been integrated to realize in-situ, real-time, and sensitive monitoring of critical signals for organs development and disease modeling. Herein, we discuss the recent research advances made with respect to sensors-integrated organ-on-a-chip in this overall review. Firstly, we briefly explore the underlying fabrication procedures of sensors within microfluidic platforms and several classifications of sensory principles. Then, emphasis is put on the highlighted applications of different types of organ-on-a-chip incorporated with various sensors. Last but not least, perspective on the remaining challenges and future development of sensors-integrated organ-on-a-chip are presented.

Bioadhesive hydrogels have demonstrated great potential in bone regeneration. However, the relatively simple adhesion mechanism and lack of intricate structural design restrict their further applications. Herein, inspired by multiple adhesion mechanisms of pollen particles and marine mussels, we present a novel type of dual-adhesive hydrogel particles fabricated from microfluidic electrospray for bone regeneration. As the particles are rapidly solidified via liquid nitrogen-assisted cryogelation, they exhibit pollen-mimicking hierarchical porous morphology and gain structure-related adhesion. Besides, the particles are further coated by polydopamine (PDA) to achieve molecular-level adhesion especially to physiological wet surfaces of bone issues. Benefiting from such dual-adhesion mechanisms, the particles can strongly adhere to bone tissue defects, and function as porous scaffolds. Moreover, the dual-adhesive particles can serve as effective vehicles to release key growth factors more than two weeks. In vitro experiments showed that the growth factors-loaden particles have excellent biocompatibility and more significantly promote angiogenesis (~ 2-fold) and osteogenic differentiation (~ 3-fold) than control. In vivo experiments indicated that the dual-adhesive particles could significantly enhance bone regeneration (~ 4-fold) than control by coupling osteogenesis and angiogenesis effects. Based on these features, the bio-inspired dual-adhesive particles have great potentials for bone repair and wound healing applications.

Developing a biocompatible and multifunctional adhesive hydrogel with injectability and self-healing ability for promoting wound healing is highly anticipated in various clinical applications. In this paper, we present a novel natural biopolymer-derived hydrogel based on the aldehyde-modified oxidized guar gum (OGG) and the carboxymethyl chitosan (CMCS) for efficiently improving wound healing with the encapsulation of vascular endothelial growth factor (VEGF). As the hydrogels are synthesized via the dynamically reversible Schiff base linkages, it is imparted with excellent self-healing ability and good shear thinning behavior, which make the hydrogel be easily and conveniently injected through a needle. Besides, the physiochemical properties, including porous structure, mechanical strength and swelling ratio of the hydrogel can be well controlled by regulating the concentrations of the OGG. Moreover, the hydrogel can attain strong adhesion to the tissues at physiological temperature based on the Schiff base between the aldehyde group on the hydrogel and the amino group on the tissue. Based on these features, we have demonstrated that the VEGF encapsulated hydrogel can adhere tightly to the defect tissue and improve wound repair in the rat model of defected skin by promoting cell proliferation, angiogenesis, and collagen secretion. These results indicate that the multifunctional hydrogel is with great scientific significance and broad clinical application prospects.

Structural color materials with the property of angle-independence have attracted increasing interest in recent years because of their applications in various research fields. In this paper, inspired by the anisotropic lattice microstructure of the Parides sesostris butterfly, we present a novel angle-independent structural material by simply doping spinous pollen particles into the colloidal crystal arrays to interfere their self-assembling process. The resultant composited materials have anisotropic close-packed colloidal crystal domains around the spikes of the pollens. These differently oriented domains could reflect the light to a wide range of viewing angles, and thus imparted the composite materials with the same wide angle of structural colors. Attractively, the materials were endowed with light-controlled reversible structural color changing behavior by incorporating photothermal responsive graphene-tagged hydrogels. These features of the bioinspired angle- independent structural color materials showed their potential values in constructing intelligent sensors, anti-counterfeiting barcode labels, and so on.