Mao-Hua Zhang

Properties and biocompatibility of chitosan films modified by blending with PEG.

Chitosan (beta-1,4-D-glucosamine), a polysaccharide with excellent biological properties, has been widely used in biomedical fields, but many barriers still exist to its broader usage due to its chemical and physical limitations. Further work is needed to improve these properties, but changes of the chemical and physical properties will influence its biocompatibility, so the biological attribute of modified chitosan must be evaluated. In this study, the biocompatibility of chitosan modified by several methods was carefully evaluated at the cellular and protein levels using different physical and biological methods. The results provide a theoretical basis for screening biomaterials. We studied the properties of five kinds of materials made by blending chitosan with different types of polyethylene glycol (PEG). The properties included physical and chemical properties, such as mechanical strength, static contact angle, spectroscopy, thermodynamic attributes and so on. The mechanical properties were slightly improved with the proper amount of PEG, but the improvement was not obvious and was destroyed by the wrong proportion of PEG. Cultures of the cells and amounts and structures of the adsorbed proteins on different materials showed that the PEG effectively improved the biocompatibility of the materials. The PEG enhanced the protein adsorption, cell adhesion, growth and proliferation, but the effects were impaired by excessive PEG. The experiments also demonstrated that the optimum PEG concentration helped to maintain the natural structure of the protein adsorbed on the materials and that maintaining the natural structure benefited cell growth. Analysis of the results based on the intramolecular and intermolecular interaction forces leads to a basic theory for the modification of biomaterials.

High and Temperature-Insensitive Piezoelectric Strain in Alkali Niobate Lead-free Perovskite

With growing concern over world environmental problems and increasing legislative restriction on using lead and lead-containing materials, a feasible replacement for lead-based piezoceramics is desperately needed. Herein, we report a large piezoelectric strain (d33*) of 470 pm/V and a high Curie temperature (Tc) of 243 °C in (Na0.5K0.5)NbO3-(Bi0.5Li0.5)TiO3-BaZrO3 lead-free ceramics by doping MnO2. Moreover, excellent temperature stability is also observed from room temperature to 170 °C (430 pm/V at 100 °C and 370 pm/V at 170 °C). Thermally stimulated depolarization currents (TSDC) analysis reveals the reduced defects and improved ferroelectricity in MnO2-doped piezoceramics from a macroscopic view. Local poling experiments and local switching spectroscopy piezoresponse force microscopy (SS-PFM) demonstrates the enhanced ferroelectricity and domain mobility from a microscopic view. Distinct grain growth and improvement in phase angle may also account for the enhancement of piezoelectric properties.

Poling engineering of (K,Na)NbO3-based lead-free piezoceramics with orthorhombic–tetragonal coexisting phases

(K,Na)NbO3 (KNN) is considered as one of the most promising candidates for lead-free piezoelectric ceramics, due to its large piezoelectric response as well as high Curie temperature. In the present study, the effect of various poling conditions on CaZrO3-modified KNN-based lead-free piezoceramics was investigated. Featured by a polymorphic phase transition around ambient temperature, the samples differ from conventional Pb(Zr,Ti)O3-based (PZT) ceramics in phase constitution, which inevitably influences the optimal poling conditions. It is found that the KNN ceramics can reach a saturated polarization state under reduced poling field and at short times, compared with PZT. Besides, poling at a relatively high temperature of 120 °C can yield an enhanced piezoelectric constant d33 of up to 345 pC N−1. The poling behavior of CaZrO3-modified KNN-based ceramics is rationalized by the competition between domain reorientation and space charge accumulation.

Identifying phase transition behavior in Bi1/2Na1/2TiO3-BaTiO3 single crystals by piezoresponse force microscopy

Using piezoresponse force microscopy (PFM) and Raman spectroscopy, we studied the local temperature-dependent piezoelectric properties and phase structures of 0.95(Bi0.5Na0.5)TiO3-0.05BaTiO3 (BNT-BT) single crystals. Local-area PFM revealed non-ergodic relaxor behavior around 160 °C. Switching spectroscopy-PFM (SS-PFM) results also supported the transition around 160 °C, with a gradual decrease in hysteresis width and nucleation bias. Moreover, Raman spectroscopy provided structural evidence of a phase transition in the same temperature region. These results are consistent with other theories of phase transitions in BNT-BT-based materials and verify the existence of a phase transition from a non-ergodic relaxor to ergodic relaxor of BNT-5.0%BT near 160 °C.

Temperature-Insensitive Piezoelectric Performance in Pb(Zr0.52Ti0.42Sn0.02Nb0.04)O3 Ceramics Prepared by Spark Plasma Sintering

Dense Pb(Zr0.52Ti0.42Sn0.02Nb0.04)O3 high-performance piezoceramics were prepared by spark plasma sintering. Phase structure, domain structure, and temperature-dependent electrical properties were systematically investigated. The spark-plasma-sintered ceramics possess a pure perovskite structure with rhombohedral-tetragonal (R-T) phase boundaries and a high Curie temperature of 347 °C. Reliable performance against temperature was observed. First, high strain behavior with a normalized strain d33* of 640 and 710 pm/V occurred at 25 and 150 °C, respectively, varying less than 11%. Besides, a large remnant polarization Pr of 36.9 μC/cm2 is observed at room temperature and varies less than 18% within the temperature range of 25-150 °C. In addition, an enhanced piezoelectric coefficient d33 of ∼460 pm/V was attained at a high temperature of 150 °C, manifesting a 40% enhancement with respect to the d33 value (330 pm/V) obtained at room temperature.

Refreshing Piezoelectrics: Distinctive Role of Manganese in Lead-Free Perovskites

Driven by an ever-growing demand for environmentally compatible materials, the past two decades have witnessed the booming development in the field of piezoelectrics. To maximally explore the potential of lead-free piezoelectrics, chemical doping could be an effective approach, referenced from tactics adopted in lead-based piezoelectrics. Herein, we reveal the distinct role of manganese in a promising lead-free perovskite (K, Na)NbO3 (denoted by KNN) in comparison to that in market-dominating lead-based counterparts [Pb(Zr, Ti)O3, PZT]. In contrast to the scenario in PZT, manganese doping in KNN results in tremendously improved piezoelectric coefficient d33 by nearly 200%, whereas the same doping species in PZT deteriorates the d33 down to less than 30% of its original value. The result is rationalized from macroscopic and local electrical characterizations down to atomic-scale visualization. This study demonstrates that there is enormous space to further enhance piezoelectricity in lead-free systems because the chemical doping effect may completely differ in lead-containing and lead-free perovskites.