Short Oxygen Plasma Treatment Leading to Long-Term Hydrophilicity of Conductive PCL-PPy Nanofiber Scaffolds

Chemically Polymerized Polypyrrole on Glucose-Porcine Skin Gelatin Nanofiber as Multifunctional Electrochemical Actuator-Sensor-Capacitor

Multifunctional materials requiring low functional voltages are the main goal of new industrial smart technologies. Polypyrrole (PPy) was chemically synthesized by a simple dip-coating process on glucose-porcine skin gelatin nanofibers, accelerating mass production, here shown on nanofiber scaffolds (NFs) with those consisting of composites. The isometric and isotonic characterizations by electro-chemo-mechanical deformation (ECMD) of NFS-PPy are obtained from cyclic voltammetric and chronoamperometric responses in lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium triflouromethanesulfonate (LiTF) and sodium perchlorate (NaClO4) in propylene carbonate (PC). The results indicate a prevalent anion-driven actuation of the linear actuator (expansion by oxidation and contraction by reduction). Different stress (4-2 kPa) and strain (0.7-0.4%) gradients are a function of the anion Van der Waals volume. During reversible actuation (expansion/contraction), the material stores/releases energy, obtaining greater specific capacitance, 68 F g-1, in LiTFSI solutions, keeping 82% of this capacity after 2000 cycles. The sensitivity (the slope of the linear sensing equation) is a characteristic of the exchanged anion. The reaction of the PPy-coated nanofiber is multifunctional, developing simultaneous actuation, sensing, and energy storage. The materials were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, and Fourier transform infrared (FTIR) spectroscopy.

Optimizing Electroconductive PPy-PCL Scaffolds for Enhanced Tissue Engineering Performance

The integration of electrically conductive materials is a promising approach in tissue regeneration research. The study presented focuses on the creation of electroconductive scaffolds made from polypyrrole-polycaprolactone (PPy-PCL) using optimal processing parameters. Utilizing Box-Behnken response surface methodology for in situ chemical polymerization of PPy, the scaffolds exhibited a maximum conductivity of 2.542 mS/cm. Morphological examination via scanning electron microscopy (SEM) indicated uniform dispersion of PPy particles within PCL fibers. Fourier transform infrared spectroscopy (FTIR) and energy dispersive x-ray (EDX) analysis validated the composition of the scaffolds, while mechanical testing revealed that the optimized scaffolds exhibit superior tensile strength and Young's modulus compared to scaffolds comprised only of PCL. The hydrophilicity of the scaffolds was improved considerably, transitioning from initially hydrophobic to fully hydrophilic for the optimum scaffold, making it suitable for tissue engineering applications. Cell viability assays, including MTT with L929 fibroblasts and Alamar Blue with bone marrow mesenchymal stem cells (bmMSCs), reflected no cytotoxicity. They showed an increase in metabolic activity, suggesting the capability of the scaffolds to support cellular functions. In conclusion, the in situ synthesis of PPy in the PCL matrix by optimizing the fabrication parameters resulted in conductive scaffolds with promising structural and functional properties for tissue engineering.

Electrically conductive coatings in tissue engineering

Recent interest in tissue engineering (TE) has focused on electrically conductive biomaterials. This has been inspired by the characteristics of the cells' microenvironment where signalling is supported by electrical stimulation. Numerous studies have demonstrated the positive influence of electrical stimulation on cell excitation to proliferate, differentiate, and deposit extracellular matrix. Even without external electrical stimulation, research shows that electrically active scaffolds can improve tissue regeneration capacity. Tissues like bone, muscle, and neural contain electrically excitable cells that respond to electrical cues provided by implanted biomaterials. To introduce an electrical pathway, TE scaffolds can incorporate conductive polymers, metallic nanoparticles, and ceramic nanostructures. However, these materials often do not meet implantation criteria, such as maintaining mechanical durability and degradation characteristics, making them unsuitable as scaffold matrices. Instead, depositing conductive layers on TE scaffolds has shown promise as an efficient alternative to creating electrically conductive structures. A stratified scaffold with an electroactive surface synergistically excites the cells through active top-pathway, with/without electrical stimulation, providing an ideal matrix for cell growth, proliferation, and tissue deposition. Additionally, these conductive coatings can be enriched with bioactive or pharmaceutical components to enhance the scaffold's biomedical performance. This review covers recent developments in electrically active biomedical coatings for TE. The physicochemical and biological properties of conductive coating materials, including polymers (polypyrrole, polyaniline and PEDOT:PSS), metallic nanoparticles (gold, silver) and inorganic (ceramic) particles (carbon nanotubes, graphene-based materials and Mxenes) are examined. Each section explores the conductive coatings' deposition techniques, deposition parameters, conductivity ranges, deposit morphology, cell responses, and toxicity levels in detail. Furthermore, the applications of these conductive layers, primarily in bone, muscle, and neural TE are considered, and findings from in vitro and in vivo investigations are presented. STATEMENT OF SIGNIFICANCE: Tissue engineering (TE) scaffolds are crucial for human tissue replacement and acceleration of healing. Neural, muscle, bone, and skin tissues have electrically excitable cells, and their regeneration can be enhanced by electrically conductive scaffolds. However, standalone conductive materials often fall short for TE applications. An effective approach involves coating scaffolds with a conductive layer, finely tuning surface properties while leveraging the scaffold's innate biological and physical support. Further enhancement is achieved by modifying the conductive layer with pharmaceutical components. This review explores the under-reviewed topic of conductive coatings in tissue engineering, introducing conductive biomaterial coatings and analyzing their biological interactions. It provides insights into enhancing scaffold functionality for tissue regeneration, bridging a critical gap in current literature.

Comparative study of iodine-doped and undoped pyrrole grafting with plasma on poly (glycerol sebacate) scaffolds and its human dental pulp stem cells compatibility

This study addresses the morphological and chemical characterization of PGS scaffolds after (6, 12, 18, 24, and 30 min) residence in undoped pyrrole plasma (PGS-PPy) and the evaluation of cell viability with human dental pulp stem cells (hDPSCs). The results were compared with a previous study that used iodine-doped pyrrole (PGS-PPy/I). Analyses through SEM and AFM revealed alterations in the topography and quantity of deposited PPy particles. FTIR spectra of PGS-PPy scaffolds confirmed the presence of characteristic absorption peaks of PPy, with higher intensities observed in the nitrile and -C≡C- groups compared to PGS-PPy/I scaffolds, while raman spectra indicated a lower presence of polaron N+ groups. On the other hand, PGS scaffolds modified with PPy exhibited lower cytotoxicity compared to PGS-PPy/I scaffolds, as evidenced by the Live/Dead assay. Furthermore, the PGS-PPy scaffolds at 6 and 12 min, and particularly the PGS-PPy/I scaffold at 6 min, showed the best results in terms of cell viability by the fifth day of culture. The findings of this study suggest that undoped pyrrole plasma modification for short durations could also be a viable option to enhance the interaction with hDPSCs, especially when the treatment times range between 6 min and 12 min.

Polycaprolactone in Bone Tissue Engineering: A Comprehensive Review of Innovations in Scaffold Fabrication and Surface Modifications

Bone tissue engineering has seen significant advancements with innovative scaffold fabrication techniques such as 3D printing. This review focuses on enhancing polycaprolactone (PCL) scaffold properties through structural modifications, including surface treatments, pore architecture adjustments, and the incorporation of biomaterials like hydroxyapatite (HA). These modifications aim to improve scaffold conformation, cellular behavior, and mechanical performance, with particular emphasis on the role of mesenchymal stem cells (MSCs) in bone regeneration. The review also explores the potential of integrating nanomaterials and graphene oxide (GO) to further enhance the mechanical and biological properties of PCL scaffolds. Future directions involve optimizing scaffold structures and compositions for improved bone tissue regeneration outcomes.

Advanced Hollow Cathode Discharge Plasma Treatment of Unique Bilayered Fibrous Nerve Guidance Conduits for Enhanced/Oriented Neurite Outgrowth

Despite all recent progresses in nerve tissue engineering, critical-sized nerve defects are still extremely challenging to repair. Therefore, this study targets the bridging of critical nerve defects and promoting an oriented neuronal outgrowth by engineering innovative nerve guidance conduits (NGCs) synergistically possessing exclusive topographical, chemical, and mechanical cues. To do so, a mechanically adequate mixture of polycaprolactone (PCL) and polylactic-co-glycolic acid (PLGA) was first carefully selected as base material to electrospin nanofibrous NGCs simulating the extracellular matrix. The electrospinning process was performed using a newly designed 2-pole air gap collector that leads to a one-step deposition of seamless NGCs having a bilayered architecture with an inner wall composed of highly aligned fibers and an outer wall consisting of randomly oriented fibers. This architecture is envisaged to afford guidance cues for the extension of long neurites on the underlying inner fiber alignment and to concurrently provide a sufficient nutrient supply through the pores of the outer random fibers. The surface chemistry of the NGCs was then modified making use of a hollow cathode discharge (HCD) plasma reactor purposely designed to allow an effective penetration of the reactive species into the NGCs to eventually treat their inner wall. X-ray photoelectron spectroscopy (XPS) results have indeed revealed a successful O2 plasma modification of the inner wall that exhibited a significantly increased oxygen content (24 → 28%), which led to an enhanced surface wettability. The treatment increased the surface nanoroughness of the fibers forming the NGCs as a result of an etching effect. This effect reduced the ultimate tensile strength of the NGCs while preserving their high flexibility. Finally, pheochromocytoma (PC12) cells were cultured on the NGCs to monitor their ability to extend neurites which is the base of a good nerve regeneration. In addition to remarkably improved cell adhesion and proliferation on the plasma-treated NGCs, an outstanding neural differentiation occurred. In fact, PC12 cells seeded on the treated samples extended numerous long neurites eventually establishing a neural network-like morphology with an overall neurite direction following the alignment of the underlying fibers. Overall, PCL/PLGA NGCs electrospun using the 2-pole air gap collector and O2 plasma-treated using an HCD reactor are promising candidates toward a full repair of critical nerve damage.

Sonochemical Deposition of Gentamicin Nanoparticles at the PCV Tracheostomy Tube Surface Limiting Bacterial Biofilm Formation

BACKGROUND

The use of nanotechnology in the production of medical equipment has opened new possibilities to fight bacterial biofilm developing on their surfaces, which can cause infectious complications. In this study, we decided to use gentamicin nanoparticles. An ultrasonic technique was used for their synthesis and immediate deposition onto the surface of tracheostomy tubes, and their effect on bacterial biofilm formation was evaluated.

METHODS

Polyvinyl chloride was functionalized using oxygen plasma followed by sonochemical formation and the embedment of gentamicin nanoparticles. The resulting surfaces were characterized with the use of AFM, WCA, NTA, FTIR and evaluated for cytotoxicity with the use of A549 cell line and for bacterial adhesion using reference strains of S. aureus (ATCC® 25923™) and E. coli (ATCC® 25922™).

RESULTS

The use of gentamicin nanoparticles significantly reduced the adhesion of bacterial colonies on the surface of the tracheostomy tube for S. aureus from 6 × 105 CFU/mL to 5 × 103 CFU/mL and for E. coli from 1.655 × 105 CFU/mL to 2 × 101 CFU/mL, and the functionalized surfaces did not show a cytotoxic effect on A549 cells (ATTC CCL 185).

CONCLUSIONS

The use of gentamicin nanoparticles on the polyvinyl chloride surface may be an additional supporting method for patients after tracheostomy in order to prevent the colonization of the biomaterial by potentially pathogenic microorganisms.

Highly Stretchable PPy/PDMS Strain Sensors Fabricated with Multi-Step Oxygen Plasma Treatment

We present highly stretchable polypyrrole (PPy)/polydimethylsiloxane strain sensors of highly improved sensitivity and durability fabricated by a chemical oxidative polymerization with oxygen plasma treatment (O₂ PT). In this study, O₂ PT was performed for 30, 60, and 90 s at each growth stage of the PPy film in three steps to investigate the effects on the sensor performance as well as the microstructural properties of the PPy films. Bonding characteristics with underlying layers and resistance to microcrack generation of the multi-layer PPy films under our given strained state were significantly enhanced by the O₂ PT. The best sensor performance in terms of sensitivity and stability were achieved by PT for 30 s with a maximum gauge factor of ~438 at a uniaxial strain of 50%, excellent durability over 500 stretching/release cycles, and a fast response time of ~50 ms.

Understanding and utilizing textile-based electrostatic flocking for biomedical applications

Electrostatic flocking immobilizes electrical charges to the surface of microfibers from a high voltage-connected electrode and utilizes Coulombic forces to propel microfibers toward an adhesive-coated substrate, leaving a forest of aligned fibers. This traditional textile engineering technique has been used to modify surfaces or to create standalone anisotropic structures. Notably, a small body of evidence validating the use of electrostatic flocking for biomedical applications has emerged over the past several years. Noting the growing interest in utilizing electrostatic flocking in biomedical research, we aim to provide an overview of electrostatic flocking, including the principle, setups, and general and biomedical considerations, and propose a variety of biomedical applications. We begin with an introduction to the development and general applications of electrostatic flocking. Additionally, we introduce and review some of the flocking physics and mathematical considerations. We then discuss how to select, synthesize, and tune the main components (flocking fibers, adhesives, substrates) of electrostatic flocking for biomedical applications. After reviewing the considerations necessary for applying flocking toward biomedical research, we introduce a variety of proposed use cases including bone and skin tissue engineering, wound healing and wound management, and specimen swabbing. Finally, we presented the industrial comments followed by conclusions and future directions. We hope this review article inspires a broad audience of biomedical, material, and physics researchers to apply electrostatic flocking technology to solve a variety of biomedical and materials science problems.

Comparison of Surface Modification Methods for Improving the Compatibility of Recycled Plastic Film-Based Aggregates

The surface modification of recycled plastic film-based aggregates was investigated to improve the compatibility between the aggregates and a cement paste. Surface modification was performed using ultraviolet–ozone treatment (UV-O₃), a silane coupling agent, O₂ atmospheric pressure plasma, and acrylic binder coating methods. The surface properties of the modified aggregates were analyzed using a contact angle measuring instrument. The results revealed that for all surface modification methods, the contact angle decreased with an increase in the treatment time. According to the comparative evaluation results of the changes in the surface characteristics of the aggregates through various surface modification methods, the contact angle reduction rates were 58.9%, 51.4%, 25.5%, and 24.5% for the O₂ atmospheric pressure plasma, the acrylic binder coating, the silane coupling agent, and the UV-O₃ method, respectively. After 48 h, the contact angle had increased by 110.9%, 29.9%, 16.4%, and 5.9% for the O₂ atmospheric pressure plasma, UV-O₃, the silane coupling agent, and the acrylic binder coating, respectively. Namely, the surface modification using the acrylic binder coating method was found to be the most effective method in terms of the wettability increase effect and the long-term storage stability.

Microtubular PEDOT-Coated Bricks for Atmospheric Water Harvesting

Atmospheric water harvesting is a promising technology for alleviating global water scarcity. Current water sorption materials efficiently capture water vapor from ubiquitous air; however, they are difficult to scale up due to high costs, complex device engineering, and intensive energy consumption. Fired red brick, a low-cost masonry construction material, holds the potential for developing large-scale functional architectures. Here, we utilize fired red brick for atmospheric water harvesting by integrating a microtubular coating of the conducting polymer PEDOT within its inorganic microstructure. This microtubular polymer coating affords hygroscopicity and high surface area for water nucleation, enables capillary forces to promote water transport, and enhances the water harvesting efficiency. Our brick composite achieves a maximum water vapor uptake of ∼200 wt % versus polymer mass at 95% relative humidity, decreasing to ∼15 wt % at 40% relative humidity. Facile water release is demonstrated via thermal, electrical, and illuminative heating. This proof-of-concept study demonstrates the potential of masonry construction materials for large-scale atmospheric water harvesting.

Poly (ε-caprolactone)-based electrospun nano-featured substrate for tissue engineering applications: a review

The restoration of normal functioning of damaged body tissues is one of the major objectives of tissue engineering. Scaffolds are generally used as artificial supports and as substrates for regenerating new tissues and should closely mimic natural extracellular matrix (ECM). The materials used for fabricating scaffolds must be biocompatible, non-cytotoxic and bioabsorbable/biodegradable. For this application, specifically biopolymers such as PLA, PGA, PTMC, PCL etc. satisfying the above criteria are promising materials. Poly(ε-caprolactone) (PCL) is one such potential candidate which can be blended with other materials forming blends, copolymers and composites with the essential physiochemical and mechanical properties as per the requirement. Nanofibrous scaffolds are fabricated by various techniques such as template synthesis, fiber drawing, phase separation, self-assembly, electrospinning etc. Among which electrospinning is the most popular and versatile technique. It is a clean, simple, tunable and viable technique for fabrication of polymer-based nanofibrous scaffolds. The design and fabrication of electrospun nanofibrous scaffolds are of intense research interest over the recent years. These scaffolds offer a unique architecture at nano-scale with desired porosity for selective movement of small molecules and form a suitable three-dimensional matrix similar to ECM. This review focuses on PCL synthesis, modifications, properties and scaffold fabrication techniques aiming at the targeted tissue engineering applications.

Utilizing Radio Frequency Plasma Treatment to Modify Polymeric Materials for Biomedical Applications

Studies that utilize radio frequency plasma modification as a strategy to tune the surface properties of polymeric constructs with the goal of enhancing their use as biomedical devices have grown considerably in number over the past decade. In this Review, we present the importance of plasma surface treatment to biomedical applications, including tissue engineering and wound healing. First, we introduce several key polymeric materials of interest for use as biomaterials, including those that are naturally derived and synthetic. We, then, provide an overview of possible outcomes of plasma modification, such as surface activation, etching, and deposition of a thin film, all of which can be used to alter the surface properties of a given polymer. Following this discussion, we review the methods used to characterize plasma-treated polymer surface properties, as well as the techniques used to evaluate their interactions with biological species of interest such as mammalian cells, bacteria, and blood components. To close, we provide a perspective on future outlooks of this exciting and rapidly evolving field.

Basic Principles of Emulsion Templating and Its Use as an Emerging Manufacturing Method of Tissue Engineering Scaffolds

Tissue engineering (TE) aims to regenerate critical size defects, which cannot heal naturally, by using highly porous matrices called TE scaffolds made of biocompatible and biodegradable materials. There are various manufacturing techniques commonly used to fabricate TE scaffolds. However, in most cases, they do not provide materials with a highly interconnected pore design. Thus, emulsion templating is a promising and convenient route for the fabrication of matrices with up to 99% porosity and high interconnectivity. These matrices have been used for various application areas for decades. Although this polymer structuring technique is older than TE itself, the use of polymerised internal phase emulsions (PolyHIPEs) in TE is relatively new compared to other scaffold manufacturing techniques. It is likely because it requires a multidisciplinary background including materials science, chemistry and TE although producing emulsion templated scaffolds is practically simple. To date, a number of excellent reviews on emulsion templating have been published by the pioneers in this field in order to explain the chemistry behind this technique and potential areas of use of the emulsion templated structures. This particular review focusses on the key points of how emulsion templated scaffolds can be fabricated for different TE applications. Accordingly, we first explain the basics of emulsion templating and characteristics of PolyHIPE scaffolds. Then, we discuss the role of each ingredient in the emulsion and the impact of the compositional changes and process conditions on the characteristics of PolyHIPEs. Afterward, current fabrication methods of biocompatible PolyHIPE scaffolds and polymerisation routes are detailed, and the functionalisation strategies that can be used to improve the biological activity of PolyHIPE scaffolds are discussed. Finally, the applications of PolyHIPEs on soft and hard TE as well as in vitro models and drug delivery in the literature are summarised.

Bioengineering Vascular Networks to Study Angiogenesis and Vascularization of Physiologically Relevant Tissue Models in Vitro

Angiogenesis assays are essential for studying aspects of neovascularization and angiogenesis and investigating drugs that stimulate or inhibit angiogenesis. To date, there are several in vitro and in vivo angiogenesis assays that are used for studying different aspects of angiogenesis. Although in vivo assays are the most representative of native angiogenesis, they raise ethical questions, require considerable technical skills, and are expensive. In vitro assays are inexpensive and easier to perform, but the majority of them are only two-dimensional cell monolayers which lack the physiological relevance of three-dimensional structures. Thus, it is important to look for alternative platforms to study angiogenesis under more physiologically relevant conditions in vitro. Accordingly, in this study, we developed polymeric vascular networks to be used to study angiogenesis and vascularization of a 3D human skin model in vitro. Our results showed that this platform allowed the study of more than one aspect of angiogenesis, endothelial migration and tube formation, in vitro when combined with Matrigel. We successfully reconstructed a human skin model, as a representative of a physiologically relevant and complex structure, and assessed the suitability of the developed in vitro platform for studying endothelialization of the tissue-engineered skin model.

Effects of an Acetic Acid and Acetone Mixture on the Characteristics and Scaffold–Cell Interaction of Electrospun Polycaprolactone Membranes

Green electrospinning has attracted great interest since non-toxic solvents were shown to be applicable in the fabrication of fibrous materials while ensuring health safety and environmental protection. Less harmful reagents such as acetone (AC) and acetic acid (AA) have been employed in this field in recent years. However, research in this area is still rare, yielding only preliminary results. In this study, two different types of solvents (pure AC and an AA/AC mixture) were used to fabricate electrospun polycaprolactone (PCL) membranes. Sample morphology, wettability, tensile strength, and chemical composition were compared between two types of membranes. Cell–scaffold interaction was also examined by cell adhesion and proliferation assays. The results demonstrate that the two types of solvents had significant effects on membrane morphology, physical strength, and cell adherence behaviors, which should be considered for different application purposes.

A Novel Bilayer Polycaprolactone Membrane for Guided Bone Regeneration: Combining Electrospinning and Emulsion Templating

Guided bone regeneration is a common dental implant treatment where a barrier membrane (BM) is used between epithelial tissue and bone or bone graft to prevent the invasion of the fast-proliferating epithelial cells into the defect site to be able to preserve a space for infiltration of slower-growing bone cells into the periodontal defect site. In this study, a bilayer polycaprolactone (PCL) BM was developed by combining electrospinning and emulsion templating techniques. First, a 250 µm thick polymerised high internal phase emulsion (polyHIPE) made of photocurable PCL was manufactured and treated with air plasma, which was shown to enhance the cellular infiltration. Then, four solvent compositions were investigated to find the best composition for electrospinning a nanofibrous PCL barrier layer on PCL polyHIPE. The biocompatibility and the barrier properties of the electrospun layer were demonstrated over four weeks in vitro by histological staining. Following in vitro assessment of cell viability and cell migration, cell infiltration and the potential of PCL polyHIPE for supporting blood vessel ingrowth were further investigated using an ex-ovo chick chorioallantoic membrane assay. Our results demonstrated that the nanofibrous PCL electrospun layer was capable of limiting cell infiltration for at least four weeks, while PCL polyHIPE supported cell infiltration, calcium and mineral deposition of bone cells, and blood vessel ingrowth through pores.