Electroactive Smart Materials: Novel Tools for Tailoring Bacteria Behavior and Fight Antimicrobial Resistance

Piezoelectric biomaterials with embedded ionic liquids for improved orthopedic interfaces through osseointegration and antibacterial dual characteristics

Orthopedic implant failures, primarily attributed to aseptic loosening and implant site infections, pose significant challenges to patient recovery and lead to revision surgeries. Combining piezoelectric materials with ionic liquids as interfaces for orthopedic implants presents an innovative approach to addressing both issues simultaneously. In this study, films of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) incorporated with 1-ethyl-3-methylimidazolium hydrogen sulfate ([Emim][HSO4]) ionic liquid were developed. These films exhibited strong antibacterial properties, effectively reducing biofilm formation, thereby addressing implant-related infections. Furthermore, stem cell-based differentiation assays exposed the potential of the composite materials to induce osteogenesis. Interestingly, our findings also revealed the upregulation of calcium channel expression as a result of electromechanical stimulation, pointing to a mechanistic basis for the observed biological effects. This work highlights the potential of piezoelectric materials with ionic liquids to improve the longevity and biocompatibility of orthopedic implants. Offering dual-functionality for infection prevention and bone integration, these advancements hold significant potential for advancing orthopedic implant technologies and improving patient outcomes.

Black Phosphorus-Based Conductive Hydrogels Assisted by Electrical Stimulus for Skin Tissue Engineering

Conductive hydrogels have shown great potential in wound healing and skin tissue engineering, owing to their electroactive, mechanical, and chemical properties. However, it still remains as a challenge to incorporate other functions into conductive hydrogels, such as antibacterial ability, controllable drug release, and biodegradability. In this study, a black phosphorus-based conductive hydrogel (HA-DA@BP) is prepared by an amidation reaction coupled with a coordination of Fe3+ -catechol. The hydrogel could be changed from the sol phase to the gel phase under electrical stimulus (ES). The results show that BP could be released under slight acidity, which is cell compatible but could achieve synergistic electrical antibacterial action and promote wound healing. This study proves that BP is a strong candidate for electroactive materials and provides a new insight for the development of BP-based biomedical materials in skin tissue engineering.

Smart and Multifunctional Materials Based on Electroactive Poly(vinylidene fluoride): Recent Advances and Opportunities in Sensors, Actuators, Energy, Environmental, and Biomedical Applications

From scientific and technological points of view, poly(vinylidene fluoride), PVDF, is one of the most exciting polymers due to its overall physicochemical characteristics. This polymer can crystalize into five crystalline phases and can be processed in the form of films, fibers, membranes, and specific microstructures, being the physical properties controllable over a wide range through appropriate chemical modifications. Moreover, PVDF-based materials are characterized by excellent chemical, mechanical, thermal, and radiation resistance, and for their outstanding electroactive properties, including high dielectric, piezoelectric, pyroelectric, and ferroelectric response, being the best among polymer systems and thus noteworthy for an increasing number of technologies. This review summarizes and critically discusses the latest advances in PVDF and its copolymers, composites, and blends, including their main characteristics and processability, together with their tailorability and implementation in areas including sensors, actuators, energy harvesting and storage devices, environmental membranes, microfluidic, tissue engineering, and antimicrobial applications. The main conclusions, challenges and future trends concerning materials and application areas are also presented.

Biodegradable Polymers and Polymer Composites with Antibacterial Properties

Antibiotic resistance is one of the greatest threats to global health and food security today. It becomes increasingly difficult to treat infectious disorders because antibiotics, even the newest ones, are becoming less and less effective. One of the ways taken in the Global Plan of Action announced at the World Health Assembly in May 2015 is to ensure the prevention and treatment of infectious diseases. In order to do so, attempts are made to develop new antimicrobial therapeutics, including biomaterials with antibacterial activity, such as polycationic polymers, polypeptides, and polymeric systems, to provide non-antibiotic therapeutic agents, such as selected biologically active nanoparticles and chemical compounds. Another key issue is preventing food from contamination by developing antibacterial packaging materials, particularly based on degradable polymers and biocomposites. This review, in a cross-sectional way, describes the most significant research activities conducted in recent years in the field of the development of polymeric materials and polymer composites with antibacterial properties. We particularly focus on natural polymers, i.e., polysaccharides and polypeptides, which present a mechanism for combating many highly pathogenic microorganisms. We also attempt to use this knowledge to obtain synthetic polymers with similar antibacterial activity.

Electroactive Biomaterials for Facilitating Bone Defect Repair under Pathological Conditions

Bone degeneration associated with various diseases is increasing due to rapid aging, sedentary lifestyles, and unhealthy diets. Living bone tissue has bioelectric properties critical to bone remodeling, and bone degeneration under various pathological conditions results in significant changes to these bioelectric properties. There is growing interest in utilizing biomimetic electroactive biomaterials that recapitulate the natural electrophysiological microenvironment of healthy bone tissue to promote bone repair. This review first summarizes the etiology of degenerative bone conditions associated with various diseases such as type II diabetes, osteoporosis, periodontitis, osteoarthritis, rheumatoid arthritis, osteomyelitis, and metastatic osteolysis. Next, the diverse array of natural and synthetic electroactive biomaterials with therapeutic potential are discussed. Putative mechanistic pathways by which electroactive biomaterials can mitigate bone degeneration are critically examined, including the enhancement of osteogenesis and angiogenesis, suppression of inflammation and osteoclastogenesis, as well as their anti-bacterial effects. Finally, the limited research on utilization of electroactive biomaterials in the treatment of bone degeneration associated with the aforementioned diseases are examined. Previous studies have mostly focused on using electroactive biomaterials to treat bone traumatic injuries. It is hoped that this review will encourage more research efforts on the use of electroactive biomaterials for treating degenerative bone conditions.

Scaffolds in the microbial resistant era: Fabrication, materials, properties and tissue engineering applications

Due to microbial infections dramatically affect cell survival and increase the risk of implant failure, scaffolds produced with antimicrobial materials are now much more likely to be successful. Multidrug-resistant infections without suitable prevention strategies are increasing at an alarming rate. The ability of cells to organize, develop, differentiate, produce a functioning extracellular matrix (ECM) and create new functional tissue can all be controlled by careful control of the extracellular microenvironment. This review covers the present state of advanced strategies to develop scaffolds with antimicrobial properties for bone, oral tissue, skin, muscle, nerve, trachea, cardiac and other tissue engineering applications. The review focuses on the development of antimicrobial scaffolds against bacteria and fungi using a wide range of materials, including polymers, biopolymers, glass, ceramics and antimicrobials agents such as antibiotics, antiseptics, antimicrobial polymers, peptides, metals, carbon nanomaterials, combinatorial strategies, and includes discussions on the antimicrobial mechanisms involved in these antimicrobial approaches. The toxicological aspects of these advanced scaffolds are also analyzed to ensure future technological transfer to clinics. The main antimicrobial methods of characterizing scaffolds’ antimicrobial and antibiofilm properties are described. The production methods of these porous supports, such as electrospinning, phase separation, gas foaming, the porogen method, polymerization in solution, fiber mesh coating, self-assembly, membrane lamination, freeze drying, 3D printing and bioprinting, among others, are also included in this article. These important advances in antimicrobial materials-based scaffolds for regenerative medicine offer many new promising avenues to the material design and tissue-engineering communities.

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Antibacterial, antifungal and antibiofilm scaffolds.

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Antimicrobial scaffold fabrication techniques.

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Antimicrobial biomaterials for tissue engineering applications.

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Antimicrobial characterization methods of scaffolds.

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Bone, oral tissue, skin, muscle, nerve, trachea, cardiac, among other applications.

Antimicrobial activity of piezoelectric polymer: piezoelectricity as the reason for damaging bacterial membrane

Cell stimulation using piezoelectric polymers, which is known as piezostimulation, is an innovative approach for designing antimicrobial protection. As an antibiotic-free and inorganic nanoparticle-free approach, it uses physical stimuli to target bacterial cells in a non-specific manner, which may be of great importance, particularly in the context of avoiding resistant bacterial strains. In this study, we prepared fully organic piezoelectric biodegradable films composed of poly-L-lactide (PLLA) and demonstrated their antimicrobial effect on S. epidermidis as a model of Gram-positive and E. coli as a model of Gram-negative bacteria. The PLLA films were either smooth and fabricated using simple melt- drawing or nanotextured, as self-standing nanotubes formed using the template-assisted method. The morphological differences between nanotextured and smooth films resulted in a larger surface area and better surface contact in nanotextured films, together with improved structural properties and better crystallinity, which were the main reasons for their better piezoelectric properties, and consequently stronger bactericidal effect. The comparison between the nanotextured surfaces with and without piezoelectric nature excluded the main role of morphology and directly confirmed piezoelectricity as the main reason for the observed antimicrobial affect. We also confirmed that piezo-stimulation using the antibacterial nanotextured film could damage the bacterial membrane as the main mechanism of action, while the contribution of pH changes and ROS generation was negligible. More importantly, the effect was selective toward the bacterial membrane and the same damage was not observed in human red blood cells, making the therapeutic use of these films possible.

Flexible TiCux Thin Films with Dual Antimicrobial and Piezoresistive Characteristics

The eradication of microorganisms from high traffic surfaces to prevent either viral or bacterial infections represents an urgent need, mainly in the scope of the present pandemic scenario. In this context, this work explores the dual functionality of titanium-copper thin films as pressure elements with antimicrobial properties, aiming for the implementation of touch and sensing capabilities in high traffic surfaces. Copper was employed as the antibacterial agent within a titanium matrix. The film's geometry and deposition parameters were varied in order to optimize antimicrobial and piezoresistive response. A considerable antimicrobial response has been obtained, increasing the copper amount (from 23 to 63 at. %) in the titanium matrix, leading to an outstanding 8 log₁₀ CFU bacterial reduction in the case of Escherichia coli. Moreover, for the same amount of copper, the piezoresistive sensibility of the thin films increases up to a maximum gauge factor of 5.18 ± 0.09, which indicates an adequate electromechanical behavior for sensing applications. Our findings demonstrate the best combined antimicrobial and piezoresistive characteristics for the films with a Cu content of 63 at. %, indicating a potential use of these films for electromechanical sensor applications.

Ag/Zn Galvanic Couple Cotton Nonwovens with Breath-Activated Electroactivity: A Possible Antibacterial Layer for Personal Protective Face Masks

The water vapor exhaled by the human body can severely accelerate the charge dissipation of commercial face masks, thereby reducing the electrostatic adsorption efficiency and increasing the bacterial invasion risk. This study developed an electroactive antibacterial cotton nonwoven (Ag/cotton/Zn) using eco-friendly magnetron sputtering technology. The Ag/Zn electrode constructed on the surface of cotton nonwovens could produce a microelectric field in the moist environment of human respiration, which endowed Ag/cotton/Zn with excellent electroactivity. When Ag/cotton/Zn was used as an additional layer of polypropylene melt-blown nonwovens or polylactic acid nanofibers, the prepared personal protective air filter had a filtration efficiency of up to 96.8% and an appropriate pressure drop and air permeability. The antibacterial results based on bacterial aerosols showed that the antibacterial efficiency against Escherichia coli and Staphylococcus aureus in 20 min was 99.74 and 99.79%, respectively, indicating an excellent electroactive killing efficiency against airborne bacteria. In addition, Ag/cotton/Zn showed excellent biological security. These results shed some light on the design and fabrication of next generation of personal protective air filter materials driven by human breathing.

Electroactive Smart Materials for Neural Tissue Regeneration

Repair in the human nervous system is a complex and intertwined process that offers significant challenges to its study and comprehension. Taking advantage of the progress in fields such as tissue engineering and regenerative medicine, the scientific community has witnessed a strong increase of biomaterial-based approaches for neural tissue regenerative therapies. Electroactive materials, increasingly being used as sensors and actuators, also find application in neurosciences due to their ability to deliver electrical signals to the cells and tissues. The use of electrical signals for repairing impaired neural tissue therefore presents an interesting and innovative approach to bridge the gap between fundamental research and clinical applications in the next few years. In this review, first a general overview of electroactive materials, their historical origin, and characteristics are presented. Then a comprehensive view of the applications of electroactive smart materials for neural tissue regeneration is presented, with particular focus on the context of spinal cord injury and brain repair. Finally, the major challenges of the field are discussed and the main challenges for the near future presented. Overall, it is concluded that electroactive smart materials play an ever-increasing role in neural tissue regeneration, appearing as potentially valuable biomaterials for regenerative purposes.

Fructose-coated Ångstrom silver prevents sepsis by killing bacteria and attenuating bacterial toxin-induced injuries

Serious infection caused by multi-drug-resistant bacteria is a major threat to human health. Bacteria can invade the host tissue and produce various toxins to damage or kill host cells, which may induce life-threatening sepsis. Here, we aimed to explore whether fructose-coated Ångstrom-scale silver particles (F-AgÅPs), which were prepared by our self-developed evaporation-condensation system and optimized coating approach, could kill bacteria and sequester bacterial toxins to attenuate fatal bacterial infections.

Methods: A series of in vitro assays were conducted to test the anti-bacterial efficacy of F-AgÅPs, and to investigate whether F-AgÅPs could protect against multi-drug resistant Staphylococcus aureus (S. aureus)- and Escherichia coli (E. coli)-induced cell death, and suppress their toxins (S. aureus hemolysin and E. coli lipopolysaccharide)-induced cell injury or inflammation. The mouse models of cecal ligation and puncture (CLP)- or E. coli bloodstream infection-induced lethal sepsis were established to assess whether the intravenous administration of F-AgÅPs could decrease bacterial burden, inhibit inflammation, and improve the survival rates of mice. The levels of silver in urine and feces of mice were examined to evaluate the excretion of F-AgÅPs.

Results: F-AgÅPs efficiently killed various bacteria that can cause lethal infections and also competed with host cells to bind with S. aureus α-hemolysin, thus blocking its cytotoxic activity. F-AgÅPs inhibited E. coli lipopolysaccharide-induced endothelial injury and macrophage inflammation, but not by directly binding to lipopolysaccharide. F-AgÅPs potently reduced bacterial burden, reversed dysregulated inflammation, and enhanced survival in mice with CLP- or E. coli bloodstream infection-induced sepsis, either alone or combined with antibiotic therapy. After three times injections within 48 h, 79.18% of F-AgÅPs were excreted via feces at the end of the 14-day observation period.

Conclusion: This study suggests the prospect of F-AgÅPs as a promising intravenous agent for treating severe bacterial infections.

Electroactive material-based biosensors for detection and drug delivery

Electroactive materials are employed at the interface of biology and electronics due to their advantageous intrinsic properties as soft organic electronics. We examine the most recent literature of electroactive material-based biosensors and their emerging role as theranostic devices for the delivery of therapeutic agents. We consider electroactive materials through the lens of smart drug delivery systems as materials that enable the release of therapeutic cargo in response to specific physiological and external stimuli and discuss the way these mechanisms are integrated into medical devices with examples of the latest advances. Studies that harness features unique to conductive polymers are emphasized; lastly, we highlight new perspectives and future research direction for this emerging technology and the challenges that remain to overcome.

Interactions Between 2D Materials and Living Matter: A Review on Graphene and Hexagonal Boron Nitride Coatings

Two-dimensional material (2DM) coatings exhibit complex and controversial interactions with biological matter, having shown in different contexts to induce bacterial cell death and contribute to mammalian cell growth and proliferation in vitro and tissue differentiation in vivo. Although several reports indicate that the morphologic and electronic properties of the coating, as well as its surface features (e.g., crystallinity, wettability, and chemistry), play a key role in the biological interaction, these kinds of interactions have not been fully understood yet. In this review, we report and classify the cellular interaction mechanisms observed in graphene and hexagonal boron nitride (hBN) coatings. Graphene and hBN were chosen as study materials to gauge the effect of two atomic-thick coatings with analogous lattice structure yet dissimilar electrical properties upon contact with living matter, allowing to discern among the observed effects and link them to specific material properties. In our analysis, we also considered the influence of crystallinity and surface roughness, detailing the mechanisms of interaction that make specific coatings of these 2DMs either hostile toward bacterial cells or innocuous for mammalian cells. In doing this, we discriminate among the material and surface properties, which are often strictly connected to the 2DM production technique, coating deposition and post-processing method. Building on this knowledge, the selection of 2DM coatings based on their specific characteristics will allow to engineer desired functionalities and devices. Antibacterial coatings to prevent biofouling, biocompatible platforms suitable for biomedical applications (e.g., wound healing, tissue repairing and regeneration, and novel biosensing devices) could be realized in the next future. Overall, a clear understanding on how the 2DM coating's properties may modulate a specific bacterial or cellular response is crucial for any future innovation in the field.

Magnetic Bioreactor for Magneto-, Mechano- and Electroactive Tissue Engineering 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.