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Additional file 1: Figure S1. SEM images of (a) the silica colloidal crystal template, (b) the PS hybrid colloidal crystal template, (c) the PS inverse opal film. Scale bars are 500 nm. Figure S2. Different stretching degrees. (a) 3-times, (b) 6-times, (c) 9-times, (d) 12-times stretched PS inverse opal films. Scale bars are 1 ��m. Figure S3. (a) MTT assays and (b) adhesion properties of PC12 cells cultured on ordinary glass slides, PS substrates stretched at 0��, 15��, 30��, 45�� for 1 day, 2 days, and 3 days, respectively. Error bars represent SD. Figure S4. (a) Immunofluorescence image, (b) SEM image, (c) angle distribution of neurites of PC12 cells cultured on ordinary glass slides. Scale bars are 50 ��m. Figure S5. Orientation angle frequency distribution of PC12 cells cultured on PS inverse opal films stretched at different angles. �� or ����� means the angle between the direction of neurite (the red dotted line) and the stretching orientation (the black solid line), respectively. Figure S6. Raman spectrum of PEDOT:PSS-doped PAAm hydrogels. Figure S7. (a) MTT assays and (b) adhesion properties of PC12 cells cultured on ordinary glass slides, PS inverse opal films, composite films for 1 day, 2 days, and 3 days, respectively. Error bars represent SD. Figure S8. (a) Differentiation rates of PC12 cells cultured on ordinary glass slides, PS inverse opal films and composite films on the 7th day. (b) Orientation angle frequency distribution of PC12 cells on PS inverse opal films and composite films.

Here the acoustic gradient composites were developed by using epoxy resin as matrix and aluminum and iron powders as filling components, respectively, and the density and acoustic properties of the composites in the gradient direction were investigated. When the mass ratio of epoxy resin and aluminum and iron powders is between 1:0.5 and 1:2, the density of aluminum and iron filled composites is 1.4–1.9 gcm−3 and 1.5–4.0 gcm−3, respectively. The density of all the aluminum filled composites presents linear variation in the gradient direction of the composites, however, that of the iron filled composites shows obvious linear variation in the gradient direction of the composites only when the mass ratio of epoxy resin and iron powder is 1:2. The acoustic impedance values of aluminum and iron filled composites are 3–6 Mrayl and 3–9 Mrayl, respectively, and show exponential variations in the gradient direction of the composite.

The 2–2 cement/polymer based piezoelectric composites containing inorganic fillers were prepared. The influences of filler content and composite thickness on the composite properties were investigated. The results show that graphite powder shows larger effect on dielectric property of the composites than silicon powder and strontium ferrite (Sr-ferrite) powder, especially when graphite powder is larger than 10 wt.%. The Sr-ferrite can improve the thickness electromechanical coupling properties of the composites. When Sr-ferrite powder content is 15 wt.%, the composite has a k t value of 68.6% at a 2 mm thickness. The electromechanical quality factor ( Q m ) of the composites shows fluctuation variation between 10 and 60 with increasing the composite thickness, which is far less than that of the pure ceramic. The coupling resonance effects between planar mode and thickness mode of the composites was reduced by decreasing the composite thickness, and the pure thickness mode resonance can be obtained at a small composite thickness.

Here the 1–3 connectivity cement/polymer based piezoelectric composites with varied piezoelectric phase distribution were designed. The dielectric, piezoelectric and electromechanical properties of the composites were studied. The results indicate that the composite with varied distribution of piezoelectric ceramic has large relative permittivity, piezoelectric strain constant and electromechanical coupling coefficient at the thickness vibration mode. The composites with varied distribution of matrix phase have larger piezoelectric voltage constant, smaller mechanical quality factor and acoustic impedance value than those with varied distribution of piezoelectric ceramic phase. The electromechanical coupling property of the composites at the planar vibration mode shows obvious dependence on matrix phase distribution. The novel piezoelectric composites show potential applications in fabricating ultrasonic transducers with specific surface vibration amplitude.

A novel piezo-damping composite was designed and fabricated by using cement/polymer as matrix, PZT ceramic as piezoelectric phase, and graphite as conductive component. The piezoelectric, electromechanical and damping properties of the composite were investigated. The results show that the piezo-damping composite has larger piezoelectric voltage constant ( g 33 ) and thickness electromechanical coupling coefficient ( k t ), and smaller mechanical quality factor ( Q m ) than the pure PZT ceramic. When the graphite percentage is 1 wt.%, the cement/polymer based 1–3 connectivity piezo-damping composite has a g 33 value of 133 mV m N −1 , k t value of 58%, and Q m value of 9.6. The damping property of the piezo-damping composite is also obviously larger than that of the epoxy resin, and the largest damping dissipation factor of the composite is 0.51 at a glass transition temperature of 70 °C when the graphite percentage is 1 wt.%.

The piezoelectric composite transducers were fabricated by using different types of piezoelectric composites as core elements, and mixtures of cement, epoxy resin and hardener as packaging material. The performance testing results show that piezoelectric composite transducers have characteristics of broad band, high sensitivity and good matching ability with cement material, etc. Based on ultrasonic wave technique, the hydration reaction process of Portland cement was monitored by using the piezoelectric composite transducers as ultrasonic probes. Through analyzing the relationship between waveform and wave parameters of received ultrasonic wave and cement hydration reaction time, the cement hydration reaction rule is obtained. The cement hydration reaction process could be divided into about four periods, that is, induction period, acceleration period, attenuation period and steady period. Especially in initial 24 h of cement hydration reaction, the changes of wave velocity, head wave amplitude and dominant frequency value of received ultrasonic wave are very obvious.

This paper presents a quantitative analysis of the relations of the occurrence of polymetallic nodules with the geochemical actions of microbes in the seawater, pore water and sediments at the bottom of the eastern Pacific Ocean basin. Emphasis is laid on the relations of the activity intensity and biochemical transformation rate of aerobic bacteria (iron bacteria, Thiobacillus thioparus, halobacteria and manganese—oxidizing bacteria) and anaerobic bacteria (sulphate—reducing bacteria, denitrifying bacteria, Thiobacillus denitrificans) with mineralization. The experimental research on the migration and accumulation of ore-forming elements caused by microbial and chemical actions shows that the microbes have changed the conditions of oxidation and reduction in the system, and their effect on the element precipitation is much stronger than the chemical actions and accelerates the enrichment of Fe and Ma It demonstrates that the microbes can change the environment to promote the accumulation of ore-forming elements, thus leading to indirect mineralization. It is first found under the scanning electron microscope (SEM) and transmission electron microscope (TEM) that there are fossil microbes of various sizes and forms in the shells of polymetallic nodules, and even ultramicrofossil bacteria at the cores. On the walls of some mineralized microbes there are sheaths of Fe and Mn oxides. After the death of the microbes, their bodies are accumulated on the interface of seawater-sediments and form polymetallic nodules. Microstructures of polymetallic nodules formed by microbes are also discussed, and two modes of microbial minerogenesis of polymetallic nodules, both direct and indirect, are suggested in the paper.

Cement-based piezoelectric composites with 2—2 connectivity were fabricated from lead magnesium niobate—lead zirconate—lead titanate (PMN) and sulfoaluminate cement by a dice-and-fill technique. The influences of PMN volume fraction and frequency on the piezoelectric and dielectric properties of the composite were analyzed. The results indicated that with increasing the PMN volume fraction, both the piezoelectric strain factor d33 and the relative dielectric factor εr of the composite increased, while the piezoelectric voltage factor g33 decreased. The dielectric resonance peaks, antiresonance absorption peaks, and the dielectric loss peaks of the composites commonly appeared around 200 kHz. With increasing the PMN volume fraction, both the dielectric resonance peaks value and the antiresonance absorption peaks value increased, while the dielectric loss peaks value decreased. At the high frequency zone, the relative dielectric factor εr and dielectric loss tan δ of the composite changed smoothly with increasing frequency.

Cement-based piezoelectric composites with 0–3 connectivity pattern were fabricated from lead lithium niobate-lead zirconate-lead titanate (PLN) and sulphoaluminate cement. The influences of PLN particle size on the electromechanical coupling and piezoelectric properties of composites were discussed in detail. The results show that under the conditions of the same PLN content and fabrication technique, the piezoelectric strain factor d 33 and piezoelectric voltage factor g 33 increase with increasing the PLN particle size. When the PLN particle size is larger than 100 μ m, d33 and g 33 are hardly influenced by the PLN particle size. Electromechanical coupling coefficient K p and K t are shown to be independent of the PLN particle size, while mechanical quality factor Q m decreases with increasing the PLN particle size.

In this study carbon fiber reinforced cement-based composites (CFRC) are fabricated by compressing, and the smart properties of the composites are studied. The results show that there exists a remarkable negative temperature coefficient (NTC) and a positive temperature coefficient (PTC) in the composite. The resistivities of the composites formed under 10 MPa are more sensitive to temperature than that of the composites formed under 2 MPa, and the critical temperature zone of the composites formed under 10 MPa (100-130°C) is narrower than that of the composites formed under 2 MPa (50-100°C). The fractional change in resistance of CFRC shows obvious one-to-one correspondence with cyclic load. The amplitude of the fractional change in resistance of the composites formed under 10 MPa is obviously larger than that of the composites formed under 2 MPa, which is more suitable for the application of important buildings such as bridges, dams, and so on to realize the real-time, dynamic and health monitoring, and damnification evaluation.

Composites with 2–2 connectivity were fabricated from plates of “PMN” ceramic embedded in a sulphoaluminate cement matrix by a cut-filling process. The influences of the water–cement ratio in the matrix on the properties of the composite were analyzed. The results show that when the water–cement ratio is less than 0.4, the piezoelectric stain factor d33 and piezoelectric voltage factor g33 increase smoothly. When the water–cement ratio is larger than 0.4, d33 and g33 increase obviously with increasing the water–cement ratio. This is attributed to a more effective contact between the active and matrix phases. d33 = 322 pc N− 1 and g33 = 20.9 mV mN− 1 at a water–cement ratio of 0.45. The planar electromechanical coupling coefficient Kp of the composite is nearly independent of the water–cement ratio. With increasing the water–cement ratio, the thickness electromechanical coupling coefficient Kt of the composite increases, while the mechanical quality factor Qm exhibits the trend of decrease.

Here, a strip-shaped 2-2 cement/polymer-based piezoelectric composite was designed and fabricated. The dielectric, piezoelectric and electromechanical coupling properties of the composite were investigated as well as the coupling effects between the thickness and lateral modes of the piezoelectric composites. The dielectric and piezoelectric properties of the composites can be greatly influenced by variations of the piezoelectric ceramic volume fraction and the structural dimensions of the composites. Excellent properties have been achieved for ultrasonic transducer applications in civil engineering monitoring fields, such as large piezoelectric voltage constants, high thickness electromechanical coupling coefficients and low acoustic impedance. The damping property of the composites was especially studied. The maximum damping loss factor of the composites is between 0.28–0.32, and the glass transition temperature is between 55°–66 °C.