Electrical stimulation/electrical microenvironment are known effect the process of bone regeneration by altering the cellular response and are crucial in maintaining tissue functionality. Piezoelectric materials, owing to their capability of generating charges/potentials in response to mechanical deformations, have displayed great potential for fabricating smart stimulatory scaffolds for bone tissue engineering. The growing interest of the scientific community and compelling results of the published research articles has been the motivation of this review article. This article summarizes the significant progress in the field with a focus on the fabrication aspects of piezoelectric materials. The review of both material and cellular aspects on this topic ensures that this paper appeals to both material scientists and tissue engineers.

Electrical stimulation for delivery of biochemical agents such as genes, proteins and RNA molecules amongst others, holds great potential for controlled therapeutic delivery and in promoting tissue regeneration. Electroactive biomaterials have the capability of delivering these agents in a localized, controlled, responsive and efficient manner. These systems have also been combined for the delivery of both physical and biochemical cues and can be programmed to achieve enhanced effects on healing by establishing control over the microenvironment. This review focuses on current state-of-the-art research in electroactive-based materials towards the delivery of drugs and other therapeutic signalling agents for wound care treatment. Future directions and current challenges for developing effective electroactive approach based therapies for wound care are discussed.

Poly(vinylidene fluoride) has attracted interest from the biomaterials community owing to its stimuli responsive piezoelectric property and promising results for application in the field of tissue engineering. Here, solution blow spinning and electrospinning were employed to fabricate PVDF fibres and the variation in resultant fibre properties assessed. The proportion of piezoelectric β-phase in the solution blow spun fibres was higher than electrospun fibres. Fibre production rate was circa three times higher for solution blow spinning compared to electrospinning for the conditions explored. However, the solution blow spinning method resulted in higher fibre variability between fabricated batches. Fibrous membranes are capable of generating different cellular response depending on fibre diameter. For this reason, electrospun fibres with micron and sub-micron diameters were fabricated, along with successful inclusion of hydroxyapatite particles to fabricate stimuli responsive bioactive fibres.

flow rate, nozzle diameter, and collector distance), as well as physicochemical properties of the fluid, induce different EHD effects, each one unique in terms of potential, limitations, and applicability. [7] A schematic showing selected examples of EHD techniques, and a summary grouping their general parameters are provided in Figure 1 and Table 1, respectively.By taking advantage of Rayleigh-Plateau instabilities, electrospraying and drop-on-demand EHD approaches allow particle generation, generally using lowconcentration polymer solutions. Electrospraying allows significant material volume processing but offers limited control in terms of size, shape, and particle placement accuracy (Figure 1a). [26] Drop-on-demand, in contrast, deals with smaller volumes but increases the control over the processed particle and printing resolution (Figure 1b). [27] As described by Taylor in 1969, by preventing Rayleigh-Plateau instabilities through the increase of fluid molecular entanglements, it is possible to achieve a continuous jet. [28,29] In electrospinning, small diameter fibers are achieved by taking advantage of bending or "whipping" instabilities, induced by large surface charge density. The non-woven mats obtained using electrospinning have been of great interest for nanotechnology research, however, accurate fiber deposition is challenging (Figure 1c). [29] In EHD writing (electrowriting [EW]), lower voltages prevent these whipping instabilities, and the EHD phenomenon results in the sustaining of a fluid jet at low flow rates, allowing for accurate control over fiber dimension and deposition (Figure 1e). [28] The control of material placement is a crucial feature for additive manufacturing since this permits the precise deposition of fibers forming 2D layers, which can be repeated to produce highly complex highresolution 3D structures. This becomes even more crucial for biomedicine where a key goal is to mimic the biological environment of native tissue to support and guide cellular growth or understand tissue regeneration mechanisms. [30,31] The use of jet-deflecting auxiliary electrodes allows the control of bending or "whipping" instabilities to achieve the accurate patterning of nanofibers, providing an intermediate approach between electrospinning and EW [32] (Figure 1d).EHD techniques have primarily focused on processing polymeric materials, although metals and ceramics have also been explored. [33,34] Polymeric melts provide a low-toxicity alternative avoiding the use of hazardous solvents, decreasing the material consumption, and reducing processing variables (e.g., evaporation), but have a limited selection of available materials. [35] Solution-based EHD processing can process a wider range of materials, however, commonly used organic solvents are often Among the various electrohydrodynamic (EHD) processing techniques, electrowriting (EW) produces the most complex 3D structures. Aqueous solution EW similarly retains the potential for additive manufacturing well-resolved 3D structures, while providing n...

Melt electrowriting, a high-resolution additive manufacturing technique, is used in this study to process a magnetic polymer-based blend for the first time. Carbonyl iron (CI) particles homogenously distribute into poly(vinylidene fluoride) (PVDF) melts to result in well-defined, highly porous structures or scaffolds comprised of fibers ranging from 30 to 50 μm in diameter. This study observes that CI particle incorporation is possible up to 30 wt% without nozzle clogging, albeit that the highest concentration results in heterogeneous fiber morphologies. In contrast, the direct writing of homogeneous PVDF fibers with up to 15 wt% CI is possible. The fibers can be readily displaced using magnets at concentrations of 1 wt% and above. Combined with good viability of L929 CC1 cells using Live/Dead imaging on scaffolds for all CI concentrations indicates that these formulations have potential for the usage in stimuli-responsive applications such as 4D printing.