Nelson Castro

A promising method for directing cell behavior and tissue regeneration is the use of smart materials that can transform physical inputs into bioelectrical signals. In this study, the mechanoelectrical control of preosteoblast activity was investigated using a piezoelectric smart biointerface based on positively poled poly(vinylidene fluoride) (PVDF). Distinct mechanical regimes, including vibrational and cyclic stretching, were applied through customized bioreactors, enabling controlled mechanoelectrical inputs ranging from 63 to 227 μVpp mm^-2. The biological response of MC3T3-E1 cells was evaluated in terms of metabolic activity, intracellular calcium signaling, alkaline phosphatase (ALP) activity, matrix mineralization, and gene expression (RUNX2, ALP, OPN, and OCN). The results demonstrated that stretching stimulation combined with higher mechano electric inputs (113-227 μVpp mm^-2) enhanced calcium influx and enhanced osteogenic differentiation, while lower impulses (∼63 μVpp mm^-2) under vibrational circumstances increased cell proliferation. These findings highlight the intensity- and mode-dependent nature of mechanoelectrical signaling in regulating osteogenic commitment. All things considered, this study shows how piezoelectric smart materials can be used as bioresponsive platforms to precisely control cell proliferation and differentiation, creating avenues for bone tissue engineering's next-generation regenerative techniques.

Water scarcity and contamination are urgent issues to be addressed. In this context, different materials, techniques, and devices are being developed to mitigate contemporary and forthcoming water constraints. Photocatalysis-based approaches are suitable strategies to address water contamination by degrading contaminants and eliminating microbes. Photoreactors are usually designed to perform photocatalysis in a scalable and standardised way. Few or none have been developed to combine these characteristics with portability, flexibility, and cost effectiveness. This study reports on designing and producing a portable (490 g), low-cost, and multifunctional photoreactor that includes adjustable radiation intensity and two types of wavelengths (UV-A and visible), including combined agitation in a compact mechanism produced through 3D printing technology. The mechanical, electrical, and optical subsystems were designed and assembled into a robust device. It is shown that it is possible to apply radiations that can reach 65 mW/cm² and 110 mW/cm² using the installed visible and UV LEDs and apply mechanical agitation up to 200 rpm, all under a ventilated system. Regarding functionality, the photoreactor proof of concept indicated the ability to degrade ~80% and 30% ciprofloxacin under UV and visible irradiation of TiO₂ and Ag/TiO₂ nanoparticles. The device also showed the ability to eliminate E. coli bacteria, recurring to radiation set-ups and nanoparticles. Therefore, the originally designed and constructed photoreactor concept was characterised and functionally validated as an exciting and flexible device for lab-scaled or outdoor experiments, assuring standardised and comparable results.

Within the efforts of developing a new generation of biomedical electrodes with embedded switching logics, developing safe and simple procedures for testing these novel systems is tackled. The development and demonstration of an all‐printed flexible testbed for automated validation and testing of multi pad systems is presented. The system is based on a Human model equivalent circuit (HMEC), which, when connected to the electrical stimulation system, mirrors the electrical behavior of biomedical electrodes and their specific interface material as if they are placed on a human subject. A simulation model of the electrical stimulation system components was developed based on the experimental data, in order to optimize printed electronic components’ characteristics and design. The testbed is composed of five layers of different conductive and dielectric materials screen‐printed on a flexible poly(ethylene terephthalate) (PET) substrate. The system was prototyped with the characteristic values of the HMEC matching the average experimental data acquired from human subjects. Thus, it is demonstrated that an all printed flexible HMEC is a feasible approach to enabling the functional testing of transcutaneous electrical stimulation devices required for their fabrication, evaluation and optimization, reducing the need for tests on human subjects in the development phase of new systems.

Different polycarbonate materials have been reinforced with carbon nanotubes to tune electrical conductivity and to induce piezoresistive self-sensing capabilities. Further, the composites were processed by solvent casting and fused deposition modelling (filament for 3D printing) methods. An electrical conductivity percolation threshold of ≈0.3 wt.% has been found for solvent casted films, whereas samples processed by 3D printing show higher thresholds, ≈2 wt.%, presenting all samples a similar maximum electrical conductivity ( σ ≈ 1 × 10 ⁻³ S m ⁻¹ ), thermal and chemical properties. Overall mechanical properties are larger for the solvent cast films concerning the 3D printed ones, particularly the elongation at break. The piezoresistive sensitivity, obtained after four-point-bending and uniaxial strain experiments, shows gauge factors up to 1.7, independently of the processing method. The functionality of the materials has been demonstrated by the implementation of an airplane wing section model with self-sensing capabilities. Two implemented strategies showed the suitability of the developed materials for real-time monitoring of the wing mechanical deformation.

Energy harvesting systems for low-power devices are increasingly being a requirement within the context of the Internet of Things and, in particular, for self-powered sensors in remote or inaccessible locations. Triboelectric nanogenerators are a suitable approach for harvesting environmental mechanical energy otherwise wasted in nature. This work reports on the evaluation of the output power of different polymer and polymer composites, by using the triboelectric contact-separation systems (10 N of force followed by 5 cm of separation per cycle). Different materials were used as positive (Mica, polyamide (PA66) and styrene/ethylene-butadiene/styrene (SEBS)) and negative (polyvinylidene fluoride (PVDF), polyurethane (PU), polypropylene (PP) and Kapton) charge materials. The obtained output power ranges from 0.2 to 5.9 mW, depending on the pair of materials, for an active area of 46.4 cm². The highest response was obtained for Mica with PVDF composites with 30 wt.% of barium titanate (BT) and PA66 with PU pairs. A simple application has been developed based on vertical contact-separation mode, able to power up light emission diodes (LEDs) with around 30 cycles to charge a capacitor. Further, the capacitor can be charged in one triboelectric cycle if an area of 0.14 m² is used.

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.

Biomimetic bioreactor systems are increasingly being developed for tissue engineering applications, due to their ability to recreate the native cell/tissue microenvironment. Regarding bone-related diseases and considering the piezoelectric nature of bone, piezoelectric scaffolds electromechanically stimulated by a bioreactor, providing the stimuli to the cells, allows a biomimetic approach and thus, mimicking the required microenvironment for effective growth and differentiation of bone cells. In this work, a bioreactor has been designed and built allowing to magnetically stimulate magnetoelectric scaffolds and therefore provide mechanical and electrical stimuli to the cells through magnetomechanical or magnetoelectrical effects, depending on the piezoelectric nature of the scaffold. While mechanical bioreactors need direct application of the stimuli on the scaffolds, the herein proposed magnetic bioreactors allow for a remote stimulation without direct contact with the material. Thus, the stimuli application (23 mT at a frequency of 0.3 Hz) to cells seeded on the magnetoelectric, leads to an increase in cell viability of almost 30% with respect to cell culture under static conditions. This could be valuable to mimic what occurs in the human body and for application in immobilized patients. Thus, special emphasis has been placed on the control, design and modeling parameters governing the bioreactor as well as its functional mechanism.

This work reports on magnetoelectric biomaterials suitable for effective proliferation and differentiation of myoblast in a biomimetic microenvironment providing the electro-mechanical stimuli associated to this tissue in the human body. Magnetoelectric films are obtained by solvent casting through the combination of a piezoelectric polymer, poly(vinylidene fluoride-trifluoro-ethylene), and magnetostrictive particles (CoFe2O4). The non-poled and poled (with negative and positive surface charge) magnetoelectric composites are used to investigate their effect on C2C12 myoblast adhesion, proliferation and differentiation. It is demonstrated that the proliferation and differentiation of the cells is enhanced by the application of mechanical and/or electrical stimulation, with higher values of maturation index under mechano-electrical stimuli. These results show that magnetoelectric cell stimulation is a full potential approach for skeletal muscle tissue engineering applications.