Enhancing piezoelectric properties of bacterial cellulose films by incorporation of MnFe2O4 nanoparticles.

Low-cost and highly sensitive piezoelectric sensors were fabricated from bacterial cellulose (BC)/MnFe2O4 nanocomposite films via a co-precipitation method, followed by hot-pressing. MnFe2O4 nanoparticles were homogeneously distributed in the BC structure. The piezoelectric sensitivity measurements in the normal mode showed that the pristine BC film exhibited a sensitivity of ∼5 pC/N, whereas this value was increased to 23 pC/N for the composite film, which is comparable to the PVDF reference film. In the bending mode, the piezoelectric response increased to 25 pC/N and 57 pC/N for the BC film and the composite film, respectively. Moreover, the piezoelectric sensitivity was significantly enhanced using carbon tape electrodes attached directly to the films instead of sandwiched electrodes. This produced a sensitivity of greater than 50 pC/N for the MBC nanocomposite film in the normal mode measurement. Our work demonstrates the potential of using MBC composite films as inexpensive and highly sensitive flexible piezoelectric sensors.

Engineering and Characterization of Bacterial Nanocellulose Films as Low Cost and Flexible Sensor Material.

Some bacterial strains such as Komagataeibacter xylinus are able to produce cellulose as an extracellular matrix. In comparison to wood-based cellulose, bacterial cellulose (BC) holds interesting properties such as biodegradability, high purity, water-holding capacity, and superior mechanical and structural properties. Aiming toward improvement in BC production titer and tailored alterations to the BC film, we engineered K. xylinus to overexpress partial and complete bacterial cellulose synthase operon that encodes activities for BC production. The changes in cell growth, end metabolite, and BC production titers from the engineered strains were compared with the wild-type K. xylinus. Although there were no significant differences between the growth of wild-type and engineered strains, the engineered K. xylinus strains demonstrated faster BC production, generating 2-4-fold higher production titer (the highest observed titer was obtained with K. xylinus-bcsABCD strain producing 4.3 ± 0.46 g/L BC in 4 days). The mechanical and structural characteristics of cellulose produced from the wild-type and engineered K. xylinus strains were analyzed with a stylus profilometer, in-house built tensile strength measurement system, a scanning electron microscope, and an X-ray diffractometer. Results from the profilometer indicated that the engineered K. xylinus strains produced thicker BC films (wild type, 5.1 µm, and engineered K. xylinus strains, 6.2-10.2 µm). Scanning electron microscope revealed no principal differences in the structure of the different type BC films. The crystallinity index of all films was high (from 88.6 to 97.5%). All BC films showed significant piezoelectric response (5.0-20 pC/N), indicating BC as a promising sensor material.

Cellulose Nanofibril Film as a Piezoelectric Sensor Material.

Self-standing films (45 µm thick) of native cellulose nanofibrils (CNFs) were synthesized and characterized for their piezoelectric response. The surface and the microstructure of the films were evaluated with image-based analysis and scanning electron microscopy (SEM). The measured dielectric properties of the films at 1 kHz and 9.97 GHz indicated a relative permittivity of 3.47 and 3.38 and loss tangent tan Î´ of 0.011 and 0.071, respectively. The films were used as functional sensing layers in piezoelectric sensors with corresponding sensitivities of 4.7-6.4 pC/N in ambient conditions. This piezoelectric response is expected to increase remarkably upon film polarization resulting from the alignment of the cellulose crystalline regions in the film. The CNF sensor characteristics were compared with those of polyvinylidene fluoride (PVDF) as reference piezoelectric polymer. Overall, the results suggest that CNF is a suitable precursor material for disposable piezoelectric sensors, actuators, or energy generators with potential applications in the fields of electronics, sensors, and biomedical diagnostics.