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This study demonstrates how either a heated flat or cylindrical collector enables defect-free melt electrowriting (MEW) of complex geometries from high melting temperature polymers. The open-source "MEWron" printer uses nylon-12 filament and combined with a heated flat or cylindrical collector, produces well-defined fibers with diameters ranging from 33 ± 4 to 95 ± 3 µm. Processing parameters for stable jet formation and minimal defects based on COMSOL thermal modeling for hardware design are optimized. The balance of processing temperature and collector temperature is achieved to achieve auxetic patterns, while showing that annealing nylon-12 tubes significantly alters their mechanical properties. The samples exhibit varied pore sizes and wall thicknesses influenced by jet dynamics and fiber bridging. Tensile testing shows nylon-12 tubes are notably stronger than poly(ε-caprolactone) ones and while annealing has limited impact on tensile strength, yield, and elastic modulus, it dramatically reduces elongation. The equipment described and material used broadens MEW applications for high melting point polymers and highlights the importance of cooling dynamics for reproducible samples., (© 2023 Wiley-VCH GmbH.)

Neuronal diseases and trauma are among the current major health-care problems. Patients frequently develop an irreversible state of neuronal disfunction that lacks treatment, strongly reducing life quality and expectancy. Novel strategies are thus necessary and tissue engineering research is struggling to provide alternatives to current treatments, making use of biomaterials capable to provide cell supports and active stimuli to develop permissive environments for neural regeneration. As neuronal cells are naturally found in electrical microenvironments, the electrically active materials can pave the way for new and effective neuroregenerative therapies. In this work the influence of piezoelectric poly(vinylidene fluoride) with different surface charges and dynamic mechanoelectrical stimuli on neuron-like cells adhesion, proliferation and differentiation was addressed. It is successfully demonstrated that both surface charge and electrically active dynamic microenvironments can be suitable to improve neuron-like cells adhesion, proliferation, and differentiation. These findings provide new knowledge to develop effective approaches for preclinical applications.

The incidence of bone disorders worldwide is increasing. For this reason, new and more effective strategies for bone repair are needed. The most common strategy used for cell regeneration relies in biochemical stimulation while biophysical stimulation using mechanical, and electrical cues is a promising, however, still under-investigated field. This work reports on the development of piezoelectric 2D and 3D porous scaffolds for bone tissue regeneration strategies. While the porous scaffolds mimic the bone's structure, the piezoelectric activity of the scaffolds mimics the bone mechano-electric microenvironment. The piezoelectric activity is related to the electroactive β-phase of poly(vinylidene fluoride) (PVDF) in the scaffolds and was dynamically stimulated by cell culture in a custom-made mechanical bioreactor. These two factors combined provide an effective biomimetic environment for the proliferation of preosteoblasts. The electromechanically-responsive scaffolds are found to promote the enhancement of proliferation rate of MC3T3-E1 osteoblastic cells in about 20 % as well as an improved adhesion and proliferation over the materials, mainly when dynamically stimulated. These results prove that local piezoelectric effect, as the one existing in bone tissue, allows effective cell proliferation, which could be further translated in more efficient strategies for bone tissue regeneration., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Cardiac tissue regeneration strategies are increasingly taking advantage of electroactive scaffolds to actively recreate the tissue microenvironment. In this context, this work reports on advanced materials based on two different ionic liquids (ILs), 2-hydroxyethyl-trimethylammonium dihydrogen phosphate ([Ch][DHP]) and choline bis(trifluoromethylsulfonyl)imide ([Ch][TFSI]), combined with poly(vinylidene fluoride- co -trifluoroethylene) (P(VDF-TrFE)) for the development of ionic electroactive IL/polymer hybrid materials for cardiac tissue engineering (TE). The morphological, physico-chemical, thermal and electrical properties of the hybrid materials, as well as their potential use as scaffolds for cardiac TE applications, were evaluated. Besides inducing changes in surface topography, roughness and wettability of the composites, the incorporation of [Ch][DHP] and [Ch][TFSI] leads to the increase in surface ( σ surface ) and volume ( σ volume ) electrical conductivities. Furthermore, washing the hybrid samples with phosphate-buffered saline solution strongly decreases the σ surface , whereas σ surface and σ volume of the composites remain almost unaltered after exposure to ultraviolet sterilization treatment. Additionally, it is verified that the incorporation of IL influences the P(VDF-TrFE) microstructure and crystallization process, acting as a defect during its crystallization. Cytotoxicity assays revealed that hybrid films based on [Ch][DHP] alone are not cytotoxic. These films also support H9c2 myoblast cell adhesion and proliferation, demonstrating their suitability for cardiac TE strategies based on electroactive microenvironments.

The morphological clues of scaffolds can determine cell behavior and, therefore, the patterning of electroactive polymers can be a suitable strategy for bone tissue engineering. In this way, this work reports on the influence of poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) electroactive micropatterned scaffolds on the proliferation and differentiation of bone cells. For that, micropatterned P(VDF-TrFE) scaffolds were produced by lithography in the form of arrays of lines and hexagons and then tested for cell proliferation and differentiation of pre-osteoblast cell line. Results show that more anisotropic surface microstructures promote bone differentiation without the need of further biochemical stimulation. Thus, the combination of specific patterns with the inherent electroactivity of materials provides a promising platform for bone regeneration.

Tissue engineering (TE) is a strongly expanding research area. TE approaches require biocompatible scaffolds, cells, and different applied stimuli, which altogether mimic the natural tissue microenvironment. Also, the extracellular matrix serves as a structural base for cells and as a source of growth factors and biophysical cues. The 3D characteristics of the microenvironment is one of the most recognized key factors for obtaining specific cell responses in vivo, being the physical cues increasingly investigated. Supporting those advances is the progress of smart and multifunctional materials design, whose properties improve the cell behavior control through the possibility of providing specific chemical and physical stimuli to the cellular environment. In this sense, a varying set of bioreactors that properly stimulate those materials and cells in vitro, creating an appropriate biomimetic microenvironment, is developed to obtain active bioreactors. This review provides a comprehensive overview on the important microenvironments of different cells and tissues, the smart materials type used for providing such microenvironments and the specific bioreactor technologies that allow subjecting the cells/tissues to the required biomimetic biochemical and biophysical cues. Further, it is shown that microfluidic bioreactors represent a growing and interesting field that hold great promise for achieving suitable TE strategies., (© 2020 Wiley-VCH GmbH.)

Bone tissue repair strategies are gaining increasing relevance due to the growing incidence of bone disorders worldwide. Biochemical stimulation is the most commonly used strategy for cell regeneration, while the application of physical cues, including magnetic, mechanical, or electrical fields, is a promising, however, scarcely investigated field. This work reports on novel magnetoactive three-dimensional (3D) porous scaffolds suitable for effective proliferation of osteoblasts in a biomimetic microenvironment. This physically active microenvironment is developed through the bone-mimicking structure of the scaffold combined with the physical stimuli provided by a magnetic custom-made bioreactor on a magnetoresponsive scaffold. Scaffolds are obtained through the development of nanocomposites comprised of a piezoelectric polymer, poly(vinylidene fluoride) (PVDF), and magnetostrictive particles of CoFe 2 O 4 , using a solvent casting method guided by the overlapping of nylon template structures with three different fiber diameter sizes (60, 80, and 120 μm), thus generating 3D scaffolds with different pore sizes. The magnetoactive composites show a structure very similar to trabecular bone with pore sizes that range from 5 to 20 μm, owing to the inherent process of crystallization of PVDF with the nanoparticles (NPs), interconnected with bigger pores, formed after removing the nylon templates. It is found that the materials crystallize in the electroactive β-phase of PVDF and promote the proliferation of preosteoblasts through the application of magnetic stimuli. This phenomenon is attributed to both local magnetomechanical and magnetoelectric response of the scaffolds, which induce a proper cellular mechano- and electro-transduction process.

Polymer-based piezoelectric biomaterials have already proven their relevance for tissue engineering applications. Furthermore, the morphology of the scaffolds plays also an important role in cell proliferation and differentiation. The present work reports on poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), a biocompatible, biodegradable, and piezoelectric biopolymer that has been processed in different morphologies, including films, fibers, microspheres, and 3D scaffolds. The corresponding magnetically active PHBV-based composites were also produced. The effect of the morphology on physico-chemical, thermal, magnetic, and mechanical properties of pristine and composite samples was evaluated, as well as their cytotoxicity. It was observed that the morphology does not strongly affect the properties of the pristine samples but the introduction of cobalt ferrites induces changes in the degree of crystallinity that could affect the applicability of prepared biomaterials. Young's modulus is dependent of the morphology and also increases with the addition of cobalt ferrites. Both pristine and PHBV/cobalt ferrite composite samples are not cytotoxic, indicating their suitability for tissue engineering applications.

A novel approach for tissue engineering applications based on the use of magnetoelectric materials is presented. This work proves that magnetoelectric Terfenol-D/poly(vinylidene fluoride-co-trifluoroethylene) composites are able to provide mechanical and electrical stimuli to MC3T3-E1 pre-osteoblast cells and that those stimuli can be remotely triggered by an applied magnetic field. Cell proliferation is enhanced up to ≈ 25% when cells are cultured under mechanical (up to 110 ppm) and electrical stimulation (up to 0.115 mV), showing that magnetoelectric cell stimulation is a novel and suitable approach for tissue engineering allowing magnetic, mechanical and electrical stimuli., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Chondrogenesis of dedifferentiated chondrocytes and mesenchymal stem cells is influenced not only by soluble molecules like growth factors, but also by the cell environment itself. The latter is achieved through both mechanical cues - which act as stimulation factor and influences nutrient transport - and adhesion to extracellular matrix cues - which determine cell shape. Although the effects of soluble molecules and cell environment have been intensively addressed, few observations and conclusions about the interaction between the two have been achieved. In this work, we review the state of the art on the single effects between mechanical and biochemical cues, as well as on the combination of the two. Furthermore, we provide a discussion on the techniques currently used to determine the mechanical properties of materials and tissues generated in vitro, their limitations and the future research needs to properly address the identified problems., Statement of Significance: The importance of biomechanical cues in chondrogenesis is well known. This paper reviews the existing literature on the effect of mechanical stimulation on chondrogenic differentiation of mesenchymal stem cells in order to regenerate hyaline cartilage. Contradictory results found with respect to the effect of different modes of external loading can be explained by the different properties of the scaffolding system that holds the cells, which determine cell adhesion and morphology and spatial distribution of cells, as well as the stress transmission to the cells. Thus, this review seeks to provide an insight into the interplay between external loading program and scaffold properties during chondrogenic differentiation. The review of the literature reveals an important gap in the knowledge in this field and encourages new experimental studies. The main issue is that in each of the few cases in which the interplay is investigated, just two groups of scaffolds are compared, leaving intermediate adhesion conditions out of study. The authors propose broader studies implementing new high-throughput techniques for mechanical characterization of tissue engineering constructs and the inclusion of fatigue analysis as support methodology to more exhaustive mechanical characterization., (Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Polymeric scaffolds used in regenerative therapies are implanted in the damaged tissue and submitted to repeated loading cycles. In the case of articular cartilage engineering, an implanted scaffold is typically subjected to long-term dynamic compression. The evolution of the mechanical properties of the scaffold during bioresorption has been deeply studied in the past, but the possibility of failure due to mechanical fatigue has not been properly addressed. Nevertheless, the macroporous scaffold is susceptible to failure after repeated loading-unloading cycles. In this work fatigue studies of polycaprolactone scaffolds were carried by subjecting the scaffold to repeated compression cycles in conditions simulating the scaffold implanted in the articular cartilage. The behavior of the polycaprolactone sponge with the pores filled with a poly(vinyl alcohol) gel simulating the new formed tissue within the pores was compared with that of the material immersed in water. Results were analyzed with Morrow's criteria for failure and accurate fittings are obtained just up to 200 loading cycles. It is also shown that the presence of poly(vinyl alcohol) increases the elastic modulus of the scaffolds, the effect being more pronounced with increasing the number of freeze/thawing cycles., (© 2014 Wiley Periodicals, Inc.)

Abstract: Tissue engineering applications rely on scaffolds that during its service life, either for in-vivo or in vitro applications, are under loading. The variation of the mechanical condition of the scaffold is strongly relevant for cell culture and has scarcely been addressed. The fatigue life cycle of poly-ε-caprolactone, PCL, scaffolds with and without fibrin as filler of the pore structure were characterized both dry and immersed in liquid water. It is observed that the there is a strong increase from 100 to 500 in the number of loading cycles before collapse in the samples tested in immersed conditions due to the more uniform stress distributions within the samples, the fibrin loading playing a minor role in the mechanical performance of the scaffolds. [Copyright &y& Elsevier]

Electroactive materials can be taken to advantage for the development of sensors and actuators as well as for novel tissue engineering strategies. Composites based on poly(vinylidene fluoride), PVDF, have been evaluated with respect to their biological response. Cell viability and proliferation were performed in vitro both with Mesenchymal Stem Cells differentiated to osteoblasts and Human Fibroblast Foreskin 1. In vivo tests were also performed using 6-week-old C57Bl/6 mice. It was concluded that zeolite and clay composites are biocompatible materials promoting cell response and not showing in vivo pro-inflammatory effects which renders both of them attractive for biological applications and tissue engineering, opening interesting perspectives to development of scaffolds from these composites. Ferrite and silver nanoparticle composites decrease osteoblast cell viability and carbon nanotubes decrease fibroblast viability. Further, carbon nanotube composites result in a significant increase in local vascularization accompanied an increase of inflammatory markers after implantation. [ABSTRACT FROM AUTHOR]

Local piezoelectric properties of the poly(L-lactic acid) individual electrospun fibers have been studied by Piezoresponse Force Microscopy. Piezoelectric response, polarization switching, and nanoscale patterning of the fibers have been demonstrated in this important biomaterial, thus opening interesting possibilities for tissue engineering and sensing/actuating applications. [ABSTRACT FROM AUTHOR]

[Display omitted] Electroactive materials are increasingly being used in strategies to regenerate cardiac tissue. These materials, particularly those with electrical conductivity, are used to actively recreate the electromechanical nature of the cardiac tissue. In the present work, we describe a novel combination of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), a highly electroactive polymer, with graphene (G), exhibiting high electrical conductivity. G/P(VDF-TrFE) films have been characterized in terms of topographical, physico-chemical, mechanical, electrical, and thermal properties, and studied the response of cardiomyocytes adhering to them. The results indicate that the crystallinity and the wettability of the composites remain almost unaffected after G incorporation. In turn, surface roughness, Young modulus, and electric properties are higher in G/P(VDF-TrFE). Finally, the composites are highly biocompatible and able to support cardiomyocyte adhesion and proliferation, particularly surface treated ones, demonstrating the suitability of these materials for cardiac tissue engineering applications. [ABSTRACT FROM AUTHOR]

Replicating the natural cellular environment is a critical strategy when employing biomaterials to enhance tissue regeneration. However, effectively controlling physical cues, including electrical and mechanical stimuli, in the extracellular microenvironment to promote tissue regeneration, remains a challenging endeavor. This study presents the technological utilization of magnetoelectric (ME) composites, capable of delivering electrical and mechanical stimuli through remote activation using a magnetic field, for applications in bone-related tissue engineering. Poly(vinylidene fluoride-co-trifluoroethylene) scaffolds incorporating two types of magnetostrictive particles, namely Terfenol-D (TD) microparticles and CoFe 2 O 4 (CFO) nanoparticles, were used to investigate the impact of mechano-electrical stimuli on preosteoblast cells. The results demonstrate that when such stimuli are applied through a custom-made magnetic bioreactor, both proliferation rate and mineralization increase. Such outcomes are dependent on the specific magnetic particles incorporated in the composite. These findings underscore the significance of designing magnetostrictive properties in ME active biomaterials to achieve successful bone regeneration. Thus, a strategy is presented to emulate the electrical and cellular microenvironment, enabling precise, controlled, and effective bone regenerative therapies. [Display omitted] [ABSTRACT FROM AUTHOR]

This manuscript reports on the fabrication of silk fibroin (SF)-based magnetic electrospun fiber composites as scaffolds for tissue engineering applications. The magnetic responsiveness of the SF composite fibers was achieved by the inclusion of cobalt ferrite (CoFe 2 O 4 ) or magnetite (Fe 3 O 4 ) nanoparticles prior to processing the fibers via electrospinning. The influence of the processing parameters, including type and amount of nanoparticles in the composite, on the mean fiber size and size distribution was studied. Whereas the average diameter of pristine SF fibers was of 294 ± 53 nm, the inclusion of 5% of CoFe 2 O 4 and Fe 3 O 4 nanoparticles led to a slight increase in the fiber diameter. Nevertheless, the fiber diameter decreased with the higher nanoparticles loading. Regarding the physico-chemical properties of the fibrous mats, it was observed that the degree of crystallinity dropped from 67% of the pristine SF mats to 37% for the SF composites. On the other hand, the onset degradation temperature of the SF electrospun was not significantly altered by inclusion of ferrite nanoparticles. It is shown that the magnetization saturation increased with the nanoparticle filler content for both compositions (CoFe 2 O 4 /SF and Fe 3 O 4 /SF). Neither the SF pristine fibers nor the SF composites were cytotoxic, indicating their suitability for tissue engineering applications. [ABSTRACT FROM AUTHOR]