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The use of conductive polymer composites (CPCs) as strain sensors has been widely investigated and various resistivity-strain sensitivities are desirable for different applications. In this study, the use of mixed carbon fillers and functionalized carbon nanotubes was demonstrated to be vital for preparing thermoplastic polyurethane (TPU)-based strain sensors with tunable sensitivity. To understand the strain sensing behavior, we carried out scanning electron microscopy (SEM), Raman spectroscopy, wide-angle X-ray diffraction (WAXD), mechanical test, and rheology-electrical measurement. Hybrid fillers of multi-walled carbon nanotubes (MWNTs) and carbon black (CB) could reduce the entanglement in conductive network structure, thus increase the resistivity-strain sensitivity. Furthermore, incorporation of additional functionalized MWNTs in the CPCs could enhance the interfacial interaction between nanofillers and TPU, leading to further increase in sensitivity. Through such a simple method, strain sensors could be efficiently fabricated with large strain-sensing capability (strain as large as 200%) and a wide range of strain sensitivity (gauge factor ranging from 5 to 140238). Finally, the exponential revolution of resistive response to strain was fitted with a model based on tunneling theory by Simmons. It was observed that the change in tunneling distance and the number of conductive pathways could be accelerated significantly by adjusting conductive network structure and interfacial interaction. This study provides a guideline for the preparation of high-performance CPC strain sensors with a large range of resistivity-strain sensitivity.

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We present a new way of combining polymer blends and pre-stretching to design strain sensing polymer composites. Fibrillization and “slippage” between conductive phases are proposed to explain the resistivity–strain behavior.

In this work, novel bioactive organic–inorganic composite bone cements consisting of tricalcium silicate (C3S), sodium alginate (SA), and calcium sulfate hemihydrate (CS) were successfully fabricated for the first time via a special method designing material composition and internal structure simultaneously, which was intended to enhance mechanical performance by combining progressive hydration process of C3S with distinctive gelation capacity of SA and further improve degradability and self‐setting properties with the addition of CS. Depending on the synergistic combination of hydration and gelation, the C3S/SA/CS composite cements (45/45/10 wt %) obtained extremely higher compressive strength up to 92.41 MPa as compared with each single component. The reinforcing mechanisms involving interfacial interaction and interior microstructure were proposed to explain this enhancement phenomenon. Additionally, the final setting time could be reduced from 68 min to 21 min with the increasing CS content. The composite cements possessed good apatite mineralization ability in simulated body fluid solution and moderate degradation rate in phosphate buffer solution. What's more, the composite cements exhibited excellent cytocompatibility and increased proliferation of rat bone‐marrow stem cells. This study could provide guidelines for the preparation of bioactive composite cements with enhanced mechanical performance, which may be suitable for load‐bearing bone repair. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2365–2377, 2019.

Vitamin D3 (VD3), an important regulator of calcium and phosphate ion concentrations in blood serum, participates in bone formation by promoting calcium and citrate deposition at defect sites while further stimulating bone calcification and osteoblast function. In this study, VD3-loaded calcium sulfate (VD3/CS) and calcium citrate/calcium sulfate (VD3/ CC/CS) cements were successfully fabricated for the first time. The incorporation of VD3 into the cements did not alter their structures or physicochemical properties. Additionally, compared with the VD3/CS cement, the VD3/CC/CS composite cement showed higher mechanical strength (28.87 MPa), better injectability (94.48%), and more appropriate setting time (23.7 min). Depending on the method by which the loaded VD3 was adsorbed, both VD3/CS and VD3/CC/ CS cements could achieve sustained drug release. However, due to their different compositions, VD3/CS cement samples, owing to the dissolution of their matrix, showed faster VD3 release rates, while VD3/CC/CS composite cement samples showed more controlled VD3 release rates, owing to the presence of a physical barrier created by calcium citrate. The VD3/CC/CS composite cement samples also demonstrated excellent bioactivity at cellular level, indicating that the VD3/CC/CS composite cement might be beneficial for the localised treatment of bone defects, especially osteoporotic bone.

Many studies about fabricating organic-inorganic composite materials have been carried out in order to mimic the natural structure of bone. Pearl, which has a special block-and-mortar hierarchical structure, is a superior bone repair material with high osteogenic activity, but it shows few applications in the clinical bone repair and reconstruction because of its brittle and uneasily shaped properties. In this work, pearl powder (P)/poly (amino acid) (PAA) composites were successfully prepared by a method of in situ melting polycondensation to combine the high osteogenic activity of the pearl and the pliability of the PAA. The mechanical properties, in vitro bioactivity and biocompatibility as well as osteogenic activity of the composites were investigated. The results showed that P/PAA composites have both good mechanical properties and bioactivity. The compressive strength, bending strength and tensile strength of the composites reached a maximum of 161 MPa, 50 MPa and 42 MPa, respectively; in addition, apatite particles successfully deposited on the composites surface after immersion in simulated body fluid (SBF) for 7 days indicated that P/PAA composites showed an enhanced mineralization capacity and bioactivity due to incorporation of pearl powder and PAA. The cell culture results revealed that higher cell proliferation and better adhesion morphology of mouse bone marrow mesenchymal stem cells (MSCs) appeared on the composite surface. Moreover, cells growing on the surface of the composites exhibited higher alkaline phosphatase (ALP) activity, more calcium nodule-formation, and higher expression levels of osteogenic differentiation-related genes (COL 1, RunX2, OCN, and OPN) than cells grown on PAA surface. The P/PAA composites exhibited both superior mechanical properties to the pearl powder, higher bioactivity and osteogenic capability compared with those of PAA.

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