An ionic crosslinking nanocellulose/sodium alginate (BC/SA) hybrid hydrogel was prepared as a dual-stimuli responsive release system. The drug release rate of BC/SA hybrid hydrogels in vitro not only depend on pH value but also depend on the presence of electric stimulus.

With the rapid development of the wearable detector and medical devices, flexible biosensing materials have received more and more attention. In this work, a novel flexible and conductive biocompatible composite with electronic and ionic bioconductive ability was demonstrated to fabricate a new flexible bioelectrode used for electrophysiological signal detection. This composite was prepared by the in situ self-polymerization of dopamine on the nanofiber of bacterial cellulose (BC) under the neutral pH condition. By using this method, poly(dopamine) (PDA) could form a uniform and continuous wrapped layer on the BC nanofiber that can prevent the aggregation of PDA caused by rapid polymerization under the conventional alkaline condition. In addition, a fabricated film with a special structure is suitable for the transportation of electrons and ions existing in it. Moreover, the flexible conductive film (FCF) reveals an extremely tensile strength, which is 2 times higher than the pure BC in addition to a high electric conductivity, which reaches a value of 10 S/cm with a high PDA content. Furthermore, the result of electrocardiogram signal testing shows that the antibacterial property of the FCF bioelectrode has an excellent stability, which is comparable to or better than the commercially available electrode. The BC/PDA-FCF provides a platform for the creation of flexible conductive biomaterials for wearable response devices.

A novel biodegradable PHBV-based polyurethane was designed and synthesized by using PHBV, MDI and PEG.

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Mechanical flexibility, faster processing, lower fabrication cost and biocompatibility enable poly (vinylidene fluoride) (PVdF) to have a wide range of applications. This work investigated the use of a piezoelectric polymeric material, PVdF, in combination with 3D printing, to explore new strategies for the fabrication of smart materials with embedded functions, namely sensing. The motivation behind this research was to design and fabricate PVdF thin films that will be used to build pressure sensors with applications in active intelligent structures. In this work, 3D printed PVdF thin films with thickness values in the range of 250 to 350 μm were poled under high direct current electrical fields, which were varied from 0.4 to 12 MV/m and temperatures from 80 to 140 °C. Copper electrodes were applied, forming a standard capacitor layered structure, to facilitate poling and to collect piezoelectric output voltage. The poling process enabled the piezoelectric crystalline phase transition of printed PVdF films to transfer from the non-active a α-phase to the piezoelectric active β-phase and rearranged the dipole alignments of the β-phase. The efficiency of poling was evaluated through the piezoelectric constant calculated from measured calibration curves. These calibration curves demonstrated the PVdF sensing device have a positive linear correlation between mechanical input and voltage output. We found that a peak value in piezoelectric constant correlated with poling voltages and temperatures. The highest piezoelectric constant achieved through contact poling was 32.29 pC/N poled at 750 V and 120 °C, and temperature was deemed the most important factors to influence piezoelectric constant. We believe that the present work demonstrates a path towards fully 3D printed smart, functional materials.

This work presents a new process to print piezoelectric polymer-based sensors through additive manufacturing via three-dimensional (3D) printing technology. 3D printing has become an efficient method to fabricate devices with complex geometric structures and embedded functionalities. The motivation of this research was to explore a path towards fully 3D printed multifunctional thin and flexible sensing devices. The 3D printed methods used were Fused Deposition Modelling and Direct Ink Writing. A fully 3D printed sensor consisting of a (2.54 cm × 2.54 cm) poly(vinylidene fluoride) (PVdF) film with thickness in the range of ∼250 μm to 350 μm was sandwiched between two fast-drying silver paint printed electrodes with thickness ranging from ∼10 μm to 50 μm. The arithmetic average roughness, Ra, of typical printed PVdF profiles with and without printed silver electrodes was ∼12.9 μm and ∼7.3 μm, respectively. Silver electrodes were printed to facilitate contact poling and to collect charges generated due to piezoelectricity. The average piezoelectric activity of printed unpoled films was 7.13 pC/N. The polarization in the printed PVdF films was realized by conventional contact poling at elevated temperatures (100, 110, 120 and 130 °C, respectively) with step increased electric fields, which were varied from 0.4 MV/m to 14 MV/m at 1 MV/m increments. To perform contact poling, PVdF films were immersed in mineral oil and a controlled voltage was applied to electrodes on one side while electrodes on the opposite side were grounded. The extrusion process during 3D printing and the subsequent contact poling process enabled the phase transition from the thermally stable α-phase to the piezoelectric active β-phase and the rearranging of the dipole alignments. The efficiency of poling was evaluated through measurement of the average value of the charge generated by six poled PVdF films in response to mechanical input increasing from 0.29 N to 1.91 N with ∼0.27 N increments. The highest average piezoelectric activity obtained was 59.2 pC/N, and a single device of 96.44 pC/N, at step increased poling voltages up to 3.5 kV under a fixed temperature 120 °C. The results demonstrate that by increasing the poling voltages and time, a higher piezoelectric activity (about 8 times compared to unpoled films) was achieved, indicating improvement of the β-phase content. This study provides a new method for continuous and direct printing of piezoelectric devices from PVdF polymeric filament. This technology opens a new path towards fully 3D printed free-form structured functional materials for sensing applications.

Schematic of the PtNPs/MWCNTs/BC anode membrane.