Development of free-standing polymer nanosheets for advanced medical and health-care applications

Nanomaterial strategies in wound healing: A comprehensive review of nanoparticles, nanofibres and nanosheets

Wound healing is a complex process that orchestrates the coordinated action of various cells, cytokines and growth factors. Nanotechnology offers exciting new possibilities for enhancing the healing process by providing novel materials and approaches to deliver bioactive molecules to the wound site. This article elucidates recent advancements in utilizing nanoparticles, nanofibres and nanosheets for wound healing. It comprehensively discusses the advantages and limitations of each of these materials, as well as their potential applications in various types of wounds. Each of these materials, despite sharing common properties, can exhibit distinct practical characteristics that render them particularly valuable for healing various types of wounds. In this review, our primary focus is to provide a comprehensive overview of the current state-of-the-art in applying nanoparticles, nanofibres, nanosheets and their combinations to wound healing, serving as a valuable resource to guide researchers in their appropriate utilization of these nanomaterials in wound-healing research. Further studies are necessary to gain insight into the application of this type of nanomaterials in clinical settings.

Ultraconformable Capacitive Strain Sensor Utilizing Network Structure of Single-Walled Carbon Nanotubes for Wireless Body Sensing

Capture and real-time recording of precise body movements using strain sensors provide personal information for healthcare monitoring and management. To acquire this information, a sensor that conforms to curved irregular surfaces, including biological tissue, is desired to record complex body movements while acting like a second skin to avoid interference with the movements. In this study, we developed a thin-film-type capacitive strain sensor that is flexible and stretchable on the surface of a living body. We fabricated conductive polymeric ultrathin films ("nanosheets") comprising polystyrene-block-polybutadiene (SB) elastomers and single-walled carbon nanotubes (SWCNTs) (i.e., SWCNT-SB nanosheets) via gravure coating; the SWCNT-SB-coated nanosheets were used as the flexible electrode in a capacitive strain sensor. The dielectric (DE) layer was then prepared using the silicone elastomer Ecoflex 00-30 because its Young's modulus is comparable to that of the epidermis. The normalized capacitance changes (ΔC/C0) in the sensor increased with increasing tensile strain over a range from 0-100%, indicating that the proposed sensor can measure the strain of biological movements, including those of skin and blood vessels. To improve sensor conformability further, the effect of sensor thickness on the gauge factor (GF) was investigated using thinner DE layers by focusing on their flexural rigidity. As a result, the GF increased from 0.64 to 1.13 as the DE layer thickness decreased from 260 to 40 μm. Finally, we evaluated the fabricated sensor's signal stability and mechanical durability, including during wireless sensing when applied to human skin and a vascular model. The ΔC/C0 values varied in response to the bending motion of a finger, dilation of a blood vessel, and the swallowing movement of the throat. These results indicate that our capacitive strain sensor is conformable and functional on biological tissue to enable monitoring of dynamic biological movements (e.g., pulse rate and arterial dilation) without wearer discomfort.

Advances in Functionalization of Bioresorbable Nanomembranes and Nanoparticles for Their Use in Biomedicine

Bioresorbable nanomembranes (NMs) and nanoparticles (NPs) are powerful polymeric materials playing an important role in biomedicine, as they can effectively reduce infections and inflammatory clinical patient conditions due to their high biocompatibility, ability to physically interact with biomolecules, large surface area, and low toxicity. In this review, the most common bioabsorbable materials such as those belonging to natural polymers and proteins for the manufacture of NMs and NPs are reviewed. In addition to biocompatibility and bioresorption, current methodology on surface functionalization is also revisited and the most recent applications are highlighted. Considering the most recent use in the field of biosensors, tethered lipid bilayers, drug delivery, wound dressing, skin regeneration, targeted chemotherapy and imaging/diagnostics, functionalized NMs and NPs have become one of the main pillars of modern biomedical applications.

Nanoscale Control of the Surface Functionality of Polymeric 2D Materials

Typically, 2D nanosheets have a homogeneous surface, making them a major challenge to structure. This study proposes a novel concept of 2D organic nanosheets with a heterogeneously functionalized surface. This work achieves this by consecutively crystallizing two precisely synthesized polymers with different functional groups in the polymer backbone in a two-step process. First, the core platelet is formed and then the second polymer is crystallized around it. As a result, the central area of the platelets has a different surface functionality than the periphery. This concept offers two advantages: the resulting polymeric 2D platelets are stable in dispersion, which simplifies further processing and makes both crystal surfaces accessible for subsequent functionalization. Additionally, a wide variety of polymers can be used, making the process and the choice of surface functionalization very flexible.

Sumac (Rhus coriaria) Extract-Loaded Polymeric Nanosheets Efficiently Protect Human Dermal Fibroblasts from Oxidative Stress

Under healthy physiological conditions, living organisms possess a variety of antioxidant mechanisms to scavenge overproduced reactive oxygen species (ROS). However, under pathological circumstances, endogenous antioxidant systems may not be adequate to eliminate the excessive amount of oxidants, and thus, a continuous exogenous antioxidant income is required. In this regard, sumac (Rhus coriaria) extract is a good candidate for therapeutic applications, because of its high content of antioxidant polyphenolic compounds. In this work, sumac extract-loaded nanosheets (sumac-nanosheet) have been exploited for loading and controlled release of sumac extract, envisioning topical drug delivery applications. Sumac extract has been obtained through the solvent extraction method, and polymeric nanosheets have been thereafter prepared through the spin coating-assisted layer-by-layer deposition of polycaprolactone (PCL), sumac extract, and poly(d,l-lactic acid) (PDLLA). The collected data show a rich content of the sumac extract in terms of polyphenolic compounds, as well as its strong antioxidant properties. Moreover, for the first time in the literature, we demonstrated the possibility of efficiently loading such extract in polymeric nanosheets and the suitability of this nanoplatform as a reactive oxygen species scavenger in human dermal fibroblasts treated with a pro-oxidant insult.

Study of Polymer Nanofilms Using for High-Throughput Screening in the Development of Transdermal Therapeutic System

We investigated polymer nanofilm (PNF) for use in high-throughput screening (HTS) to promote the development of transdermal therapeutic systems (TTS). The drug permeability of PNF with a 1 : 1 weight mix ratio of poly(L-lactic acid) (PLLA) and poly(methylhydrosiloxane) (PMHS) (PLLA/PMHS (1/1) PNF) and Strat-M^® of the transdermal diffusion test membrane, was evaluated using 12 kinds of drugs with the logarithmic value of n-octanol/water partition coefficients of -4.70 to 3.86. The lag time of PLLA/PMHS (1/1) PNF made via polymer alloying was significantly shorter than that of Strat-M^® for 10 drug types, and the formation of a highly diffusible PMHS-rich phase accompanying the formation of a sea-island structure was suggested as a contributing factor. Additionally, a high correlation was confirmed between the measured value for the logarithm of the apparent permeability coefficient of PLLA/PMHS (1/1) PNF and the literature values for the logarithm of the apparent permeability coefficient of human skin (r = 0.929). This study shows that PLLA/PMHS (1/1) PNF can reliably predict drug permeability in human skin and can potentially be used in HTS for developing TTS.

When 2D nanomaterials meet biomolecules: design strategies and hybrid nanostructures for bone tissue engineering

2D nanomaterials show great potential in biomedical applications due to their unique physical and chemical surface properties. This review includes typical 2D nanomaterials used in bone tissue engineering (BTE), such as graphene oxide, hexagonal boron nitride, molybdenum disulfide, black phosphorus, and MXenes. Moreover, the construction methods of BTE materials with 2D nanosheets are analyzed. Before designing a BTE material, it is essential to understand the relationship between the material structure and properties. Notably, 2D nanomaterials can be hybridized with biomaterials, such as polypeptides, proteins, and polysaccharides, to improve biocompatibility and host responses. The effects of the surface properties and size of 2D nanomaterials on cellular behavior, gene expression, antibacterial properties, and cytotoxicity in BTE applications are also discussed. This work provides new design ideas and directions for constructing 2D nanomaterial-based BTE scaffolds.

Hydrogel Nanosheets Confined 2D Rhombic Ice: A New Platform Enhancing Chondrogenesis

Nanoconfinement within flexible interfaces is a key step towards exploiting confinement effects in several biological and technological systems wherein flexible 2D materials are frequently utilized but are arduous to prepare. Hitherto unreported, the synthesis of 2D Hydrogel nanosheets (HNS) using a template- and catalyst-free process is developed representing a fertile ground for fundamental structure-property investigations. In due course of time, nucleating folds propagating along the edges trigger co-operative deformations of HNS generating regions of nanoconfinement within trapped water islands. These severely constricting surfaces force water molecules to pack within the nanoscale regime of HNS almost parallel to the surface bringing about phase transition into puckered rhombic ice with AA and AB Bernal stacking pattern, which was mostly restricted to Molecular dynamics (MD) studies so far. Interestingly, under high lateral pressure and spatial inhomogeneity within nanoscale confinement, bilayer rhombic ice structures were formed with an in-plane lattice spacing of 0.31 nm. In this work, a systematic exploration of rhombic ice formation within HNS has been delineated using High-resolution transmission electron microscopy (HRTEM), and its ultrathin morphology was examined using Atomic Force Microscopy (AFM). Scanning Electron Microscopy (SEM) images revealed high porosity while mechanical testing presented young's modulus of 155 kPa with ~84% deformation, whereas contact angle suggested high hydrophilicity. The combinations of nanosheets, porosity, nanoconfinement, hydrophilicity, and mechanical strength, motivated us to explore their application as a scaffold for cartilage regeneration, by inducing chondrogenesis of human Wharton Jelly derived mesenchymal stem cells (hWJ MSCs). HNS promoted the formation of cell aggregates giving higher number of spheroid formation and a marked expression of chondrogenic markers (ColI, ColII, ColX, ACAN and S-100), thereby providing some cues for guiding chondrogenic differentiation.

Progress in recycling and valorization of waste silk

Due to the improvements in living standards and the "throw away" culture of mankind, large amount of waste textiles is constantly generated. In particular, silk is an abundant high-grade textile material with characteristics of wear comfort, high profit, and low supply with high demand, but it transforms into waste when discarded. This paper reviews the current progress of recycling and reuse of waste silk from the aspects of energy, yarn and fabric, reinforcement of composites, silk fibroin, biological tissue engineering, filtration of air and water, and electrode. The modification, optimization and application of regenerated silk fibroin extracted from waste silk are promising to industrialization and sustainable development. Making waste silk functional and intelligently wearable are two ways of recycling waste silk with low cost and high return value in the near future. The recovery and utilization of waste silk provide a paradigm for valorization of other fiber-based waste such as wool, cotton, bast and synthetic fibers.

Polymer Brush Formation Assisted by the Hierarchical Self-Assembly of Topological Supramolecules

The development of methods for the polymer brush layer formation on material surfaces to improve the surface properties has been researched for decades. Here, we report a novel approach for the formation of a polymer brush layer on materials and the alteration of the surface properties using a pseudo-polyrotaxane nanosheet (PPRNS). In the PPRNS, β-cyclodextrin (CD) selectively covered the central poly(propylene oxide)₂₉ segment of the carboxyl-terminated poly(ethylene oxide)₇₅-b-poly(propylene oxide)₂₉-b-poly(ethylene oxide)₇₅ (COOH-EO₇₅PO₂₉EO₇₅) triblock copolymer to form columnar crystals. The EO chains of COOH-EO₇₅PO₂₉EO₇₅ then adopt polymer brush conformations and exhibit an oil-repellent property on the material surfaces. Based on the flexibility derived from the nanosheet structure, the PPRNS showed high adhesion to the Blu-ray disk substrate (1D bending), polystyrene spherical beads (2D bending), and random rough surface of pork skin. The PPRNS is expected to become a new method for obtaining polymer brush layers and improving the surface properties irrespective of the material type.

Emerging 2D Nanomaterials for Biomedical Applications

Two-dimensional (2D) nanomaterials are an emerging class of biomaterials with remarkable potential for biomedical applications. The planar topography of these nanomaterials confers unique physical, chemical, electronic and optical properties, making them attractive candidates for therapeutic delivery, biosensing, bioimaging, regenerative medicine, and additive manufacturing strategies. The high surface-to-volume ratio of 2D nanomaterials promotes enhanced interactions with biomolecules and cells. A range of 2D nanomaterials, including transition metal dichalcogenides (TMDs), layered double hydroxides (LDHs), layered silicates (nanoclays), 2D metal carbides and nitrides (MXenes), metal-organic framework (MOFs), covalent organic frameworks (COFs) and polymer nanosheets have been investigated for their potential in biomedical applications. Here, we will critically evaluate recent advances of 2D nanomaterial strategies in biomedical engineering and discuss emerging approaches and current limitations associated with these nanomaterials. Due to their unique physical, chemical, and biological properties, this new class of nanomaterials has the potential to become a platform technology in regenerative medicine and other biomedical applications.

Robust, self-adhesive, reinforced polymeric nanofilms enabling gas-permeable dry electrodes for long-term application

Robust polymeric nanofilms can be used to construct gas-permeable soft electronics that can directly adhere to soft biological tissue for continuous, long-term biosignal monitoring. However, it is challenging to fabricate gas-permeable dry electrodes that can self-adhere to the human skin and retain their functionality for long-term (>1 d) health monitoring. We have succeeded in developing an extraordinarily robust, self-adhesive, gas-permeable nanofilm with a thickness of only 95 nm. It exhibits an extremely high skin adhesion energy per unit area of 159 μJ/cm² The nanofilm can self-adhere to the human skin by van der Waals forces alone, for 1 wk, without any adhesive materials or tapes. The nanofilm is ultradurable, and it can support liquids that are 79,000 times heavier than its own weight with a tensile stress of 7.82 MPa. The advantageous features of its thinness, self-adhesiveness, and robustness enable a gas-permeable dry electrode comprising of a nanofilm and an Au layer, resulting in a continuous monitoring of electrocardiogram signals with a high signal-to-noise ratio (34 dB) for 1 wk.

Wetting-Induced Polyelectrolyte Pore Bridging

Active layers of ion separation membranes often consist of charged layers that retain ions based on electrostatic repulsion. Conventional fabrication of these layers, such as polyelectrolyte deposition, can in some cases lead to excess coating to prevent defects in the active layer. This excess deposition increases the overall membrane transport resistance. The study at hand presents a manufacturing procedure for controlled polyelectrolyte complexation in and on porous supports by support wetting control. Pre-wetting of the microfiltration membrane support, or even supports with larger pore sizes, leads to ternary phase boundaries of the support, the coating solution, and the pre-wetting agent. At these phase boundaries, polyelectrolytes can be complexated to form partially freestanding selective structures bridging the pores. This polyelectrolyte complex formation control allows the production of membranes with evenly distributed polyelectrolyte layers, providing (1) fewer coating steps needed for defect-free active layers, (2) larger support diameters that can be bridged, and (3) a precise position control of the formed polyelectrolyte multilayers. We further analyze the formed structures regarding their position, composition, and diffusion dialysis performance.

Spin-coated freestanding films for biomedical applications

Spin-coating is a widely employed technique for the fabrication of thin-film coatings over large areas with smooth and homogeneous surfaces. In recent years, research has extended the scope of spin-coating by developing methods involving the interface of the substrate and the deposited solution to obtain self-supported films, also called freestanding films. Thereby, such structures have been developed for a wide range of areas. Biomedical applications of spin-coated freestanding films include wound dressings, drug delivery, and biosensing. This review will discuss the fundamental physical and chemical processes governing the conventional spin-coating as well as the techniques to obtain freestanding films. Furthermore, developments within this field with a primary focus on tissue engineering applications will be reviewed.

Enhanced cellular engraftment of adipose-derived mesenchymal stem cell spheroids by using nanosheets as scaffolds

The short survival time of transplanted adipose-derived mesenchymal stem cells (ASCs) is a problem for skin wound healing. Transplantation after the formation of cellular spheroids has been investigated as a promising method for prolonging cellular survival. However, there have been technical restrictions for transplantation of spheroids in clinical practice. Here, we show an effective method for transplantation of ASC spheroids onto skin wounds in order to efficiently cure refractory ulcers. To assist anchoring of spheroids onto skin wounds, we used a 120-nm-thick free-standing film (nanosheet) that has a highly adhesive property. Bioluminescence imaging showed that ASC spheroids carried by the nanosheet survived for 14 days, which is about two-times longer than that previously reported. Wounds treated with a nanosheet carrying ASC spheroids were 4-times smaller than untreated wounds on day 14. This method for transplantation of spheroids could be applied to cell therapy for various refractory skin wounds.

Ultra-Thin Porous PDLLA Films Promote Generation, Maintenance, and Viability of Stem Cell Spheroids

Three-dimensional (3D) culture bridges and minimizes the gap between in vitro and in vivo states of cells and various 3D culture systems have been developed according to different approaches. However, most of these approaches are either complicated to operate, or costive to scale up. Therefore, a simple method for stem cell spheroid formation and preservation was proposed using poly(D,L-lactic acid) porous thin film (porous nanosheet), which were fabricated by a roll-to-roll gravure coating method combining a solvent etching process. The obtained porous nanosheet was less than 200 nm in thickness and had an average pore area of 6.6 μm² with a porosity of 0.887. It offered a semi-adhesive surface for stem cells to form spheroids and maintained the average spheroid diameter below 100 μm for 5 days. In comparison to the spheroids formed in suspension culture, the porous nanosheets improved cell viability and cell division rate, suggesting the better feasibility to be applied as 3D culture scaffolds.

Fabrication of Quasi-2D Shape-Tailored Microparticles using Wettability Contrast-Based Platforms

The ability to fabricate materials with ultrathin architectures enables the breakthrough of low-dimensional structures with high surface area that showcase distinctive properties from their bulk counterparts. They are exploited in a wide range of fields, including energy harvesting, catalysis, and biomedicine. Despite such versatility, the fine tuning of the lateral dimensions and geometry of these structures remains challenging. Prepatterned platforms gain significant attention as enabling technologies to process materials with highly controlled shapes and dimensions. Herein, different nanometer-thick particles of various lateral sizes and geometries (e.g., squares, circles, triangles, hexagons) are processed with high precision and definition, taking advantage of the wettability contrast of oleophilic-oleophobic patterned surfaces. Quasi-2D polymeric microparticles with high shape- and size-fidelity can be retrieved as freestanding objects in a single step. These structures show cell-mediated pliability, and their integration in gravity-enforced human adipose-derived stem cell spheroids leads to an enhanced metabolic activity and a modulated secretion of proangiogenic factors.

Ultra-thin, transparent, porous substrates as 3D culture scaffolds for engineering ASC spheroids for high-magnification imaging

Three-dimensional (3D) culture is expected to reproduce biological tissues more representatively than monolayer culture, which is important for in vitro research such as drug screening. Recently, various cell culture substrates for spheroid engineering have been developed based on the prevention of cell adhesion. However, despite the expanded usability these substrates provide, they remain limited in terms of optical microscopy imaging of spheroids with high magnification lenses. This is because almost all substrates generated by nanoimprinting hamper the light passing through them owing to their low optical transparency caused by the thickness and surface structure. In this study, we achieved the preparation of spheroids from adipose-tissue derived stem cells (ASCs) on free-standing porous polymeric ultrathin films ("porous nanosheets") consisting of poly(d,l-lactic acid) (PDLLA) with thickness of 120 nm and average pore diameter of 4 μm. ASCs migrated on the porous nanosheet, leading to the spontaneous organization of spheroids anchored via a cell monolayer. The porous nanosheet also provided more than twice the optical transparency in confocal and holographic microscopy observation compared to conventional nanoimprinted substrates for 3D cell culture (NanoCulture Dish). The internal structure of the organized spheroids could be clearly observed with 40× magnification. In addition, the engineered spheroids showed bioactivities indicated by mRNA expression of fibroblast growth factor (FGF-2) and vascular endothelial growth factor (VEGF). Thus, porous nanosheets offer a unique cell culture substrate, not only for engineering 3D cellular organization from stem cells, but also for imaging detailed structure using light microscopy.

Novel Ultrathin Films Based on a Blend of PEG-b-PCL and PLLA and Doped with ZnO Nanoparticles

In this paper, a novel nanofilm type is proposed based on a blend of poly(ethylene glycol)-block-poly(ε-caprolactone) methyl ether (PEG-b-PCL) and poly(l-lactic acid), doped with zinc oxide nanoparticles (ZnO NPs) at different concentrations (0.1, 1, and 10 mg/mL). All nanofilm types were featured by a thickness value of ∼500 nm. Increasing ZnO NP concentrations implied larger roughness values (∼22 nm for the bare nanofilm and ∼67 nm for the films with 10 mg/mL of NPs), larger piezoelectricity (average d₃₃ coefficient for the film up to ∼1.98 pm/V), and elastic modulus: the nanofilms doped with 1 and 10 mg/mL of NPs were much stiffer than the nondoped controls and nanofilms doped with 0.1 mg/mL of NPs. The ZnO NP content was also directly proportional to the material melting point and crystallinity and inversely proportional to the material degradation rate, thus highlighting the stabilization role of ZnO particles. In vitro tests were carried out with cells of the musculoskeletal apparatus (fibroblasts, osteoblasts, chondrocytes, and myoblasts). All cell types showed good adhesion and viability on all substrate formulations. Interestingly, a higher content of ZnO NPs in the matrix demonstrated higher bioactivity, boosting the metabolic activity of fibroblasts, myoblasts, and chondrocytes and enhancing the osteogenic and myogenic differentiation. These findings demonstrated the potential of these nanocomposite matrices for regenerative medicine applications, such as tissue engineering.

Advanced Artificial Electronic Skin Based pH Sensing System for Heatstroke Detection

Heatstroke is a serious illness that can potentially damage many victims every year. Many intelligent physical sensors have been developed to prevent heatstroke fatalities. However, it remains a challenge to fabricate skin-adhesive, small, and low-cost sensors for in situ heatstroke detection to overcome the weaknesses of the physical sensors. As far as we know, this is the first breakthrough for exploiting a PDMS based freestanding nanosheet skin patch consisting of pH sensing elements (antimony/antimony oxide and silver/silver iodate) to achieve high pH sensitivity and repeatability. The sensing elements were investigated for structural and morphological properties. The easy to use and easy to fabricate nanosheet sensor exhibited a linear pH response of -43 mV/pH. Overall, the developed sensor showed high sensitivity, repeatability, and stability. Our initial results indicate that the developed sensor adhered well to a skin surface. It is expected that this proof of concept approach gives reliable fabrication and measurement unlike other physical sensors.

Biofunctional Silk Kirigami With Engineered Properties

The fabrication of multifunctional materials that interface with living environments is a problem of great interest. A variety of structural design concepts have been integrated with functional materials to form biodevices and surfaces for health monitoring. In particular, approaches based on kirigami-inspired cuts can engineer flexibility in materials through the creation of patterned defects. Here, the fabrication of a biodegradable and biofunctional "silk kirigami" material is demonstrated. Mechanically flexible, free-standing, optically transparent, large-area biomaterial sheets with precisely defined and computationally designed microscale cuts can be formed using a single-step photolithographic process. Using modeling techniques, it is shown how cuts can generate remarkable "self-shielding" leading to engineered elastic behavior and deformation. As composites with conducting polymers, flexible, intrinsically electroactive sheets can be formed. Importantly, the silk kirigami sheets are biocompatible, can serve as substrates for cell culture, and be proteolytically resorbed. The unique properties of silk kirigami suggest a host of applications as transient, "green", functional biointerfaces, and flexible bioelectronics.

All-Polymer Conducting Fibers and 3D Prints via Melt Processing and Templated Polymerization

Because of their attractive mechanical properties, conducting polymers are widely perceived as materials of choice for wearable electronics and electronic textiles. However, most state-of-the-art conducting polymers contain harmful dopants and are only processable from solution but not in bulk, restricting the design possibilities for applications that require conducting micro-to-millimeter scale structures, such as textile fibers or thermoelectric modules. In this work, we present a strategy based on melt processing that enables the fabrication of nonhazardous, all-polymer conducting bulk structures composed of poly(3,4-ethylenedioxythiophene) (PEDOT) polymerized within a Nafion template. Importantly, we employ classical polymer processing techniques including melt extrusion followed by fiber spinning or fused filament 3D printing, which cannot be implemented with the majority of doped polymers. To demonstrate the versatility of our approach, we fabricated melt-spun PEDOT:Nafion fibers, which are highly flexible, retain their conductivity of about 3 S cm-1 upon stretching to 100% elongation, and can be used to construct organic electrochemical transistors (OECTs). Furthermore, we demonstrate the precise 3D printing of complex conducting structures from OECTs to centimeter-sized PEDOT:Nafion figurines and millimeter-thick 100-leg thermoelectric modules on textile substrates. Thus, our strategy opens up new possibilities for the design of conducting, all-polymer bulk structures and the development of wearable electronics and electronic textiles.

Syringe-Injectable, Self-Expandable, and Ultraconformable Magnetic Ultrathin Films

Syringe-injectable biomaterials and medical devices are important as minimally invasive implants for diagnosis, therapy, and regenerative medicine. Free-standing polymeric nanosheets with a thickness less than 1 μm and a flexural rigidity less than 10^-2 nN m are a promising platform of syringe-injectable, implantable devices that provide conformable and long-term stable adhesion to the target biological tissues for in situ delivery of therapeutic materials. Here, we developed free-standing ultrathin films (<1 μm thick) based on polyurethane-based shape-memory polymer (SMP) and magnetic nanoparticles (MNP), termed MNP-SMP nanosheets. With the temperature-mediated shape-memory effect of SMP, we overcome the limitation in the manipulation of the conventional polymer nanosheets. In particular, we demonstrated the following four capabilities using the 710 nm thick MNP-SMP nanosheet with the glass transition temperature (T_g) of 25 °C: (1) syringe-injectability through the medical needles, (2) self-expandability after ejection, (3) conformability and removability on the biological surfaces, and (4) guidability in an external magnetic field. The MNP-SMP nanosheets were readily interfaced with an additional layer of poly(lactic-co-glycolic acid) (PLGA) to extend their functionality as a carrier of molecular and cellular drugs. The MNP-SMP nanosheets will contribute to the development of advanced syringe-injectable medical devices as a platform to deliver drugs, sensors, cells, and engineered tissues to the specific site or lesion in the body for minimally invasive diagnosis and therapy.

Fabrication, Characterization, and Properties of Poly (Ethylene-Co-Vinyl Acetate) Composite Thin Films Doped with Piezoelectric Nanofillers

Ethylene vinyl acetate (EVA) is a copolymer comprehending the semi-crystalline polyethylene and amorphous vinyl acetate phases, which potentially allow the fabrication of tunable materials. This paper aims at describing the fabrication and characterization of nanocomposite thin films made of polyethylene vinyl acetate, at different polymer concentration and vinyl acetate content, doped with piezoelectric nanomaterials, namely zinc oxide and barium titanate. These membranes are prepared by solvent casting, achieving a thickness in the order of 100-200 µm. The nanocomposites are characterized in terms of morphological, mechanical, and chemical properties. Analysis of the nanocomposites shows the nanofillers to be homogeneously dispersed in EVA matrix at different vinyl acetate content. Their influence is also noted in the mechanical behavior of thin films, which elastic modulus ranged from about 2 to 25 MPa, while keeping an elongation break from 600% to 1500% and tensile strength from 2 up to 13 MPa. At the same time, doped nanocomposite materials increase their crystallinity degree than the bare ones. The radiopacity provided by the addition of the dopant agents is proven. Finally, the direct piezoelectricity of nanocomposites membranes is demonstrated, showing higher voltage outputs (up to 2.5 V) for stiffer doped matrices. These results show the potentialities provided by the addition of piezoelectric nanomaterials towards mechanical reinforcement of EVA-based matrices while introducing radiopaque properties and responsiveness to mechanical stimuli.

Printed nanofilms mechanically conforming to living bodies

It is anticipated that flexible wearable/implantable devices for biomedical applications will be established for the development of medical diagnostics and therapeutics. However, these devices need to be compatible with the physical and mechanical properties of the living body. In this minireview, we introduce free-standing polymer ultra-thin films (referred to as "polymer nanosheets"), for which a variety of polymers can be selected as building blocks (e.g., biodegradable polymers, conductive polymers, and elastomers), as a platform for flexible biomedical devices that are mechanically compatible with the living body, and then we demonstrate the use of "printed nanofilms" by combining nanosheets and printing technologies with a variety of inks represented by drugs, conductive nanomaterials, chemical dyes, bio-mimetic polymers, and cells. Owing to the low flexural rigidity (<10-2 nN m) of the polymer nanosheets, which is within the range of living brain slices (per unit width), the flexible printed nanofilms realize bio-integrated structure and display various functions with unique inks that continually monitor or detect biological activities, such as performing surface electromyography, measuring epidermal strain, imaging tissue temperature, organizing cells, and treating lesions in wounds and tumors.

Ultrathin and Stretchable Rechargeable Devices with Organic Polymer Nanosheets Conformable to Skin Surface

Ultrathin flexible electronic devices have been attracting substantial attention for biomonitoring, display, wireless communication, and many other ubiquitous applications. In this article, organic robust redox-active polymer/carbon nanotube hybrid nanosheets with thickness of just 100 nm are reported as power sources for ultrathin devices conformable to skin. Regardless of the extreme thinness of the electrodes, a moderately large current density of 0.4 mA cm^-2 is achieved due to the high output of the polymers (>10 A g^-1 ). For the first time, the use of mechanically robust yet intrinsically soft electrodes and polymer nanosheet sealing leads to the fabrication of rechargeable devices with only 1-µm thickness and even with stretchable properties.

The ABC Guide to Fluorescent Toolsets for the Development of Future Biomaterials

In recent decades, diversified approaches using nanoparticles or nano-structured scaffolds have been applied to drug delivery and tissue engineering. Thanks to recent interdisciplinary studies, the materials developed have been intensively evaluated at animal level. Despite these efforts, less attention has been paid to what is really going on at the subcellular level during the interaction between a nanomaterial and a cell. As the proposed concept becomes more complex, the need for investigation of the dynamics of these materials at the cellular level becomes more prominent. For a deeper understanding of cellular events, fluorescent imaging techniques have been a powerful means whereby spatiotemporal information related to cellular events can be visualized as detectable fluorescent signals. To date, several excellent review papers have summarized the use of fluorescent imaging toolsets in cellular biology. However, applying these toolsets becomes a laborious process for those who are not familiar with imaging studies to engage with owing to the skills gap between them and cell biologists. This review aims to highlight the valuable essentials of fluorescent imaging as a tool for the development of effective biomaterials by introducing some cases including photothermal and photodynamic therapies. This distilled information will be a convenient short-cut for those who are keen to fabricate next generation biomaterials.

In situ transplantation of adipose tissue-derived stem cells organized on porous polymer nanosheets for murine skin defects

Stem cell transplantation is expected to be an effective early-phase treatment for deep burn injuries and intractable ulcers. Localizing and proliferating stem cells on the lesion utilizing engineered scaffolds is important for this treatment. In this study, we demonstrated in situ transplantation of adipose-tissue derived stem cells (ASCs) organized on free-standing porous polymer ultrathin films (referred to as "porous nanosheets") to a skin defect model in diabetic mice. Porous nanosheets were prepared by a combination of micro-gravure coating with macrophase separation of poly(d,l-lactic acid) and polystyrene under a roll-to-roll process and solvent etching process with cyclohexane. The permeable structure of porous nanosheets (thickness of 150 nm, average pore diameter of 4 μm) allowed for proliferation of ASCs and also provided sufficient nutrient inflow into multilayered ASC constructs. Then, transplantation of a trilayered ASC-laden porous nanosheet achieved homogeneous transference of ASCs onto the skin lesion. Transplanted ASCs contributed to wound healing in a dorsal skin defect model in diabetic mice. Thus, cell transplantation using porous nanosheets will be a new method for promoting wound healing in diabetic and other kinds of refractory ulcers. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1363-1371, 2019.

Bio-industrial Waste Silk Fibroin Protein and Carbon Nanotube-Induced Carbonized Growth of One-Dimensional ZnO-based Bio-nanosheets and their Enhanced Optoelectronic Properties

High performance UV/Visible photodetectors are successfully fabricated from ZnO/fibroin protein-carbon nanotube (ZFP_CNT ) composites using a simple hydrothermal method. The as-fabricated ZnO nanorods (ZnO NRs) and ZFP_CNT nanostructures were measured under different light illuminations. The measurements showed the UV-light photoresponse of the as-fabricated ZFP_CNT nanostructures (55,555) to be approximately 26454 % higher than that of the as-prepared ZnO NRs (210). This photodetector can sense photons with energies considerably smaller (2.75 eV) than the band gap of ZnO (3.22 eV). It was observed that the finest distribution of fibroin and CNT into 1D ZnO resulted in rapid electron transportation and hole recombination via carbon/nitrogen dopants from the ZFP_CNT . Carbon dopants create new energy levels on the conduction band of the ZFP_CNT , which reduces the barrier height to allow for charge carrier transportation under light illumination. Moreover, the nitrogen dopants increase the adsorptivity and amount of oxygen vacancies in the ZFP_CNT so that it exhibits fast response/recovery times both in the dark and under light illumination. The selectivity of UV light among the other types of illumination can be ascribed to the deep-level energy traps (E_T ) of the ZFP_CNT . These significant features of ZFP_CNT lead to the excellent optical properties and creation of new pathways for the production of low-cost semiconductors and bio-waste protein based UV/Visible photodetectors.

Macroscopic Freestanding Nanosheets with Exceptionally High Modulus

Macroscopic single-wall carbon nanotube (SWCNT) films of nanoscale thickness have significant potential for an array of applications that demand thin, transparent, conductive coatings. Using macroscopic micrometer thick polystyrene sheets as a reference, we characterize the elastic response of freestanding multifunctional SWCNT nanosheets possessing both exceptionally high Young's modulus and good durability. Thin SWCNT films (20-200 nm thick) asymmetrically "doped" with dilute concentrations of superparamagnetic colloids were suspended in ethanol as freestanding nanosheets. Through repeated and controlled deformation in an external magnetic field, we measure the temporal relaxation of nanosheet curvature back to equilibrium. From the relaxation time and its dependence on nanosheet thickness and length, we extract the SWCNT nanosheet modulus through a simple viscoelastic model. Our results are consistent with nearly ideal SWCNT rigidity percolation with moduli approaching 200 GPa and limited plasticity for sufficiently thick sheets, which we attribute to the screening of van der Waals interactions by the surrounding solvent and the macroscopic nature of the deformation.

Extracellular pH imaging of a plant leaf with a polyelectrolyte multilayered nanosheet

We have developed a sheet-like pH imaging sensor based on a flexible and physically adhesive polymer thin film (referred to as a “pH sensing nanosheet”). The pH sensing nanosheet was composed of two films: one is a pH-sensitive layer-by-layer (LbL) film constructed from fluorescein-conjugated poly(acrylic acid) and poly(allylamine hydrochloride) and the other is a pH-insensitive film made from Nile red-embedded poly(d,l-lactic acid). The pH sensing nanosheet enabled the ratiometric imaging of pH changes in a leaf (500 × 500 μm²), namely the apoplastic ion milieu responding to an external NaCl stress. It was successfully mapped out that the alkalization of the leaf apoplast spread from the leaf base to the tip at 20 min after the stimulation and the pH value increased up to approximately pH 6.3 from less than pH 4.5 within 60 min when a 100 mM NaCl aqueous solution was added. The pH sensing nanosheet should be useful for energy metabolic mapping in tissue biology.

We have developed a sheet-like pH imaging sensor based on a flexible and physically adhesive polymer thin film (referred to as a “pH sensing nanosheet”).

Polymer Nanosheets from Supramolecular Assemblies of Conjugated Linoleic Acid-High Surface Area Adsorbents from Renewable Materials

We present a strategy for robustly cross-linking self-assembled lamellar mesophases made from plant-derived materials to generate polymer nanosheets decorated with a high density of functional groups. We formulate a supramoleclar complex by hydrogen-bonding conjugated linoleic acid moieties to a structure-directing tribasic aromatic core. The resulting constructs self-assemble into a thermotropic lamellar mesophase. Photo-cross-linking the mesophase with the aid of an acrylate cross-linker yields a polymeric material with high-fidelity retention of the lamellar mesophase structure. Transmission electron microscopy images demonstrate the preservation of the large area, highly ordered layered nanostructures in the polymer. Subsequent extraction of the tribasic core and neutralization of the carboxyl groups by NaOH result in exfoliation of polymer nanosheets with a uniform thickness of ∼3 nm. The nanosheets have a large specific area of ∼800 m²/g, are decorated by negatively charged carboxylate groups at a density of 4 nm^-2, and exhibit the ability to readily adsorb positively charged colloidal particles. The strategy as presented combines supramolecular self-assembly with the use of renewable or sustainably derived materials in a scalable manner. The resulting nanosheets have potential for use as adsorbents and, with further development, rheology modifiers.

Mini Review: Nanosheet Technology towards Biomedical Application

The fabrication technique of ultrathin film (commonly known as nanosheets) has been significantly developed over the years. Due to the mechanical properties of nanosheets, such as high levels of adhesion and flexibility, this made nanosheets the ideal candidate in biomedical applications. In this review, innovative biomedical applications of nanosheets are discussed, which include, drug delivery, wound treatment, and functional nanosheets towards flexible biodevices, etc. Finally, the future outlook of nanosheet technology towards a biomedical application is discussed.

Thin polymeric films for building biohybrid microrobots

This paper aims to describe the disruptive potential that polymeric thin films have in the field of biohybrid devices and to review the recent efforts in this area. Thin (thickness  <  1 mm) and ultra-thin (thickness  <  1 µm) matrices possess a series of intriguing features, such as large surface area/volume ratio, high flexibility, chemical and physical surface tailorability, etc. This enables the fabrication of advanced bio/non-bio interfaces able to efficiently drive cell-material interactions, which are the key for optimizing biohybrid device performances. Thin films can thus represent suitable platforms on which living and artificial elements are coupled, with the aim of exploiting the unique features of living cells/tissues. This may allow to carry out certain tasks, not achievable with fully artificial technologies. In the paper, after a description of the desirable chemical/physical cues to be targeted and of the fabrication, functionalization and characterization procedures to be used for thin and ultra-thin films, the state-of-the-art of biohybrid microrobots based on micro/nano-membranes are described and discussed. The research efforts in this field are rather recent and they focus on: (1) self-beating cells (such as cardiomyocytes) able to induce a relatively large deformation of the underlying substrates, but affected by a limited controllability by external users; (2) skeletal muscle cells, more difficult to engineer in mature and functional contractile tissues, but featured by a higher controllability. In this context, the different materials used and the performances achieved are analyzed. Despite recent interesting advancements and signs of maturity of this research field, important scientific and technological steps are still needed. In the paper some possible future perspectives are described, mainly concerning thin film manipulation and assembly in multilayer 3D systems, new advanced materials to be used for the fabrication of thin films, cell engineering opportunities and modelling/computational efforts.

Molecular Engineering of the Peptoid Nanosheet Hydrophobic Core

The relationship between the structure of sequence-defined peptoid polymers and their ability to assemble into well-defined nanostructures is important to the creation of new bioinspired platforms with sophisticated functionality. Here, the hydrophobic N-(2-phenylethyl)glycine (Npe) monomers of the standard nanosheet-forming peptoid sequence were modified in an effort to (1) produce nanosheets from relatively short peptoids, (2) inhibit the aggregation of peptoids in bulk solution, (3) increase nanosheet stability by promoting packing interactions within the hydrophobic core, and (4) produce nanosheets with a nonaromatic hydrophobic core. Fluorescence and optical microscopy of individual nanosheets reveal that certain modifications to the hydrophobic core were well tolerated, whereas others resulted in instability or aggregation or prevented assembly. Importantly, we demonstrate that substitution at the meta and para positions of the Npe aromatic ring are well tolerated, enabling significant opportunities to tune the functional properties of peptoid nanosheets. We also found that N-aryl glycine monomers inhibit nanosheet formation, whereas branched aliphatic monomers have the ability to form nanosheets. An analysis of the crystal structures of several N,N'-disubstituted diketopiperazines (DKPs), a simple model system, revealed that the preferred solid-state packing arrangement of the hydrophobic groups can directly inform the assembly of stable peptoid nanosheets.

Polymeric Microporous Nanofilms as Smart Platforms for in Vitro Assessment of Nanoparticle Translocation and Caco-2 Cell Culture

The study of nanomaterial translocation across epithelial barriers is often hindered by the low permeability of transwell membranes to nanoparticles. To address this issue ultra-thin poly(L-lactic acid) nanofilms with zero tortuosity micropores were developed for use in nanoparticle passage tests. In this study we demonstrate that microporous polymeric nanofilms allow a significantly higher passage of silver nanoparticles in comparison with commercial membranes normally used in transwell inserts. A reliable procedure for collecting free-standing nanofilms which enables their manipulation and use in lab-on-chip systems is described. We also demonstrate the cytocompatibility of porous nanofilms and their ability to sustain the adhesion and proliferation of Caco-2 cells. Ultra-thin microporous membranes show promise as low-cost nanomaterial screening tools and may be used as matrices for the development of bioengineered systems for mimicking the intestinal epithelium.