Sealing effect of a polysaccharide nanosheet for murine cecal puncture

Large-scale cranial window for in vivo mouse brain imaging utilizing fluoropolymer nanosheet and light-curable resin

Two-photon microscopy enables in vivo imaging of neuronal activity in mammalian brains at high resolution. However, two-photon imaging tools for stable, long-term, and simultaneous study of multiple brain regions in same mice are lacking. Here, we propose a method to create large cranial windows covering such as the whole parietal cortex and cerebellum in mice using fluoropolymer nanosheets covered with light-curable resin (termed the 'Nanosheet Incorporated into light-curable REsin' or NIRE method). NIRE method can produce cranial windows conforming the curved cortical and cerebellar surfaces, without motion artifacts in awake mice, and maintain transparency for >5 months. In addition, we demonstrate that NIRE method can be used for in vivo two-photon imaging of neuronal ensembles, individual neurons and subcellular structures such as dendritic spines. The NIRE method can facilitate in vivo large-scale analysis of heretofore inaccessible neural processes, such as the neuroplastic changes associated with maturation, learning and neural pathogenesis.

Layer-by-layer assembly methods and their biomedical applications

Various biomedical applications arising due to the development of different LbL assembly methods with unique process properties.

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.

The Efficacy of Posttreatment with Synthetic C-Reactive Protein in Murine Bacterial Peritonitis via Activation of FcγRI-Expressing Kupffer Cells

Pretreatment with synthetic C-reactive protein (CRP), a functional CRP peptide, has the potential to augment macrophage phagocytosis by bacterial challenge. However, the posttreatment is clinically ideal. We investigated the efficacy of posttreatment with synthetic CRP on murine cecal ligation and puncture (CLP), focusing on liver macrophages. Mice received CLP, and 1 h later, synthetic CRP or saline was intraperitoneally administered. Posttreatment with synthetic CRP increased the murine survival after CLP. It reduced viable bacterial counts in the liver 24 h after CLP with an increase in the number of Kupffer cells but not monocyte-derived liver macrophages. Posttreatment with synthetic CRP increased the phagolytic activity of Kupffer cells against Escherichia coli (E. coli) as well as capsulated Klebsiella pneumoniae at 3 h after CLP. Synthetic CRP therapy augmented TNF production by E. coli-phagocytosing Kupffer cells, resulting in an increase in tissue TNF levels in the liver at 24 h. Kupffer cells substantially expressed FcγRI, which is a ligand of CRP, and their FcγRI expression was further increased after CLP. In contrast, synthetic CRP therapy affected neither the phagocytic function of monocyte-derived liver macrophages (showing a weak FcγRI expression) nor their TNF production. Depletion of Kupffer cells in mice inhibited these beneficial effects of synthetic CRP in CLP mice. Conclusion: Posttreatment with synthetic CRP effectively improves murine bacterial peritonitis via the activation of phagocytosis of FcγRI-expressing Kupffer cells.

PEO-CYTOP Fluoropolymer Nanosheets as a Novel Open-Skull Window for Imaging of the Living Mouse Brain

In vivo two-photon deep imaging with a broad field of view has revealed functional connectivity among brain regions. Here, we developed a novel observation method that utilizes a polyethylene-oxide-coated CYTOP (PEO-CYTOP) nanosheet with a thickness of ∼130 nm that exhibited a water retention effect and a hydrophilized adhesive surface. PEO-CYTOP nanosheets firmly adhered to brain surfaces, which suppressed bleeding from superficial veins. By taking advantage of the excellent optical properties of PEO-CYTOP nanosheets, we performed in vivo deep imaging in mouse brains at high resolution. Moreover, PEO-CYTOP nanosheets enabled to prepare large cranial windows, achieving in vivo imaging of neural structure and Ca²⁺ elevation in a large field of view. Furthermore, the PEO-CYTOP nanosheets functioned as a sealing material, even after the removal of the dura. These results indicate that this method would be suitable for the investigation of neural functions that are composed of interactions among multiple regions.

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PEO-CYTOP nanosheet enables in vivo deep brain imaging in a vast field of view

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The 130 nm thickness and the hydrophilized surface realize the strong adhesiveness

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Suppressions of bleeding from the surface and inflammation in long-term are achieved

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The vast and transparent cranial window with natural curvature of the surface

Pires R, Botelho G, Reis RL, Alves NM. Spin-Coated Polysaccharide-Based Multilayered Freestanding Films with Adhesive and Bioactive Moieties

Freestanding films based on catechol functionalized chitosan (CHI), hyaluronic acid (HA), and bioglass nanoparticles (BGNPs) were developed by spin-coating layer-by-layer assembly (SA-LbL). The catechol groups of 3,4-dihydroxy-l-phenylalanine (DOPA) present in the marine mussels adhesive proteins (MAPs) are the main factors responsible for their characteristic strong wet adhesion. Then, the produced films were cross-linked with genipin to improve their stability in wet state. Overall, the incorporation of BGNPs resulted in thicker and bioactive films, hydrophilic and rougher surfaces, reduced swelling, higher weight loss, and lower stiffness. The incorporation of catechol groups onto the films showed a significant increase in the films' adhesion and stiffness, lower swelling, and weight loss. Interestingly, a synergetic effect on the stiffness increase was observed upon the combined incorporation of BGNPs with catechol-modified polymers, given that such films were the stiffest. Regarding the biological assays, the films exhibited no negative effects on cellular viability, adhesion, and proliferation, and the BGNPs seemed to promote higher cellular metabolic activity. These bioactive LbL freestanding films combine enhanced adhesion with improved mechanical properties and could find applications in the biomedical field, such as guided hard tissue regeneration membranes.

Bio-inspired swellable hydrogel-forming double-layered adhesive microneedle protein patch for regenerative internal/external surgical closure

Significant tissue damage, scarring, and an intense inflammatory response remain the greatest concerns for conventional wound closure options, including sutures and staples. In particular, wound closure in internal organs poses major clinical challenges due to air/fluid leakage, local ischemia, and subsequent impairment of healing. Herein, to overcome these limitations, inspired by endoparasites that swell their proboscis to anchor to host's intestines, we developed a hydrogel-forming double-layered adhesive microneedle (MN) patch consisting of a swellable mussel adhesive protein (MAP)-based shell and a non-swellable silk fibroin (SF)-based core. By possessing tissue insertion capability (7-times greater than the force for porcine skin penetration), MAP-derived surface adhesion, and selective swelling-mediated physical entanglement, our hydrogel-forming adhesive MN patch achieved ex vivo superior wound sealing capacity against luminal leaks (139.7 ± 14.1 mmHg), which was comparable to suture (151.0 ± 23.3 mmHg), as well as in vivo excellent performance for wet and/or dynamic external and internal tissues. Collectively, our bioinspired adhesive MN patch can be successfully used in diverse practical applications ranging from vascular and gastrointestinal wound healing to transdermal delivery for pro-regenerative or anti-inflammatory agents to target tissues.

Adhesive free-standing multilayer films containing sulfated levan for biomedical applications

This work is the first reporting the use of layer-by-layer to produce adhesive free-standing (FS) films fully produced using natural-based macromolecules: chitosan (CHI), alginate (ALG) and sulfated levan (L-S). The deposition conditions of the natural polymers were studied through zeta potential measurements and quartz crystal microbalance with dissipation monitoring analysis. The properties of the FS films were evaluated and compared with the control ones composed of only CHI and ALG in order to assess the influence of levan polysaccharide introduced in the multilayers. Tensile tests, dynamic mechanical analysis and single lap shear strength tests were performed to evaluate the mechanical properties of the prepared FS films. The presence of L-S conferred both higher tensile strength and shear strength to the developed FS membranes. The results showed an adhesion strength 4 times higher than the control (CHI/ALG) FS films demonstrating the adhesive character of the FS films containing L-S. Morphological and topography studies were carried out revealing that the crosslinking reaction granted the L-S based FS film with a higher roughness and surface homogeneity. Preliminary biological assays were performed by cultivating myoblasts cells on the surface of the produced FS films. Both crosslinked and uncrosslinked FS films containing L-S were cytocompatible and myoconductive.

STATEMENT OF SIGNIFICANCE

Sutures remain as the "gold standard" for wound closure and bleeding control; however they still have limitations such as, high infection rate, inconvenience in handling, and concern over possible transmission of blood-borne disease through the use of needles. One of the challenges of tissue engineering consist on the design and development of biocompatible tissue adhesives and sealants with high adhesion properties to repair or attach devices to tissues. In this work, the introduction of sulfated levan (L-S) on multilayered free-standing membranes was proposed to confer adhesive properties. Moreover, the films were myoconductive even in the absence of crosslinking just by the presence of L-S. This study provides a promising strategy to develop biological adhesives and for cardiac tissue engineering applications.

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.

Polylactic acid nanosheets in prevention of postoperative intestinal adhesion and their effects on bacterial propagation in an experimental model

Background

Ultrathin films (nanosheets) adhere tightly to organ surfaces but prevent adhesion to other organs. The antiadhesive effect of nanosheets and their effect on bacterial propagation were investigated in a murine intestinal adhesion model.

Methods

Polylactic acid nanosheets (approximately 80 nm thick) were produced. Serosal defects were created by peeling off the intestinal serosa; these were left open or covered with nanosheets or Seprafilm® and the formation of intestinal adhesions was analysed. To examine bacterial propagation, a nanosheet or Seprafilm® was placed on intact murine jejunum followed by Escherichia coli inoculation at the site.

Results

Treatment both with nanosheets and with Seprafilm® reduced postoperative intestinal adhesion (mean adhesion score 0·67 for nanosheets, 0·43 for Seprafilm® and 2·87 for no antiadhesive treatment; P < 0·001 for nanosheets or Seprafilm® versus no adhesive treatment). Nanosheet treatment did not affect bacterial propagation in the peritoneal cavity, whereas Seprafilm®-treated mice showed bacterial propagation, leading to increased mortality.

Conclusion

Nanosheets may be effective novel antiadhesive agents even in the presence of bacterial contamination. Surgical relevanceIntra-abdominal adhesions following surgical contamination can trigger postoperative complications and lead to deterioration in long-term quality of life. However, currently there are no effective antiadhesion materials to prevent the formation of adhesions.Treatment with ultrathin nanosheets effectively reduced postoperative intestinal adhesion in an experimental mouse model, and did not affect bacterial propagation in the peritoneal cavity.These nanosheets are potent novel antiadhesive materials that potentially can be applied even in contaminated conditions.

Sustainable antimicrobial effect of silver sulfadiazine-loaded nanosheets on infection in a mouse model of partial-thickness burn injury

Partial-thickness burn injury has the potential for reepithelialization and heals within 3weeks. If the wound is infected by bacteria before reepithelization, however, the depth of disruption increases and the lesion easily progresses to the full-thickness dermal layers. In the treatment of partial-thickness burn injury, it is important to prevent the wound area from bacterial infection with an antimicrobial dressing. Here, we have tested the antimicrobial properties of polymeric ultra-thin films composed of poly(lactic acid) (termed "PLA nanosheets"), which have high flexibility, adhesive strength and transparency, and silver sulfadiazine (AgSD), which exhibits antimicrobial efficacy. The AgSD-loaded nanosheet released Ag(+) for more than 3days, and exerted antimicrobial efficacy against methicillin-resistant Staphylococcus aureus (MRSA) in an in vitro Kirby-Bauer test. By contrast, a cell viability assay indicated that the dose of AgSD used in the PLA nanosheets did not show significant cytotoxicity toward fibroblasts. In vivo evaluation using a mouse model of infection in a partial-thickness burn wound demonstrated that the nanosheet significantly reduced the number of MRSA bacteria on the lesion (more than 10(5)-fold) and suppressed the inflammatory reaction, thereby preventing a protracted wound healing process.

Development of a ubiquitously transferrable silver-nanoparticle-loaded polymer nanosheet as an antimicrobial coating

Ultra-thin polymer films (nanosheets) fabricated by a layer-by-layer (LbL) method possess unique properties such as high flexibility, adhesive strength, and transparency, and can be peeled off from a substrate and attached to various surfaces via a water-soluble supporting film. Therefore, flexible and transferrable LbL nanosheets are convenient tools as coating materials. Here, we fabricated a novel antimicrobial coating material by embedding silver nanoparticles (AgNPs) in an LbL nanosheet composed of layers of chitosan and sodium alginate (Ag-LbL nanosheet) by means of a photo-reduction method. Optimizing the amount of irradiated energy applied led to robust antimicrobial efficacy against methicillin-resistant Staphylococcus aureus (MRSA), sufficient to meet ISO standards (ISO 22196), while maintaining the flexibility and adhesive potency of the LbL nanosheet. Thus, the Ag-LbL nanosheet is a promising coating material that can provide antimicrobial efficacy to various surfaces.

Spatio-Temporal Control of LbL Films for Biomedical Applications: From 2D to 3D

Introduced in the '90s by Prof. Moehwald, Lvov, and Decher, the layer-by-layer (LbL) assembly of polyelectrolytes has become a popular technique to engineer various types of objects such as films, capsules and free standing membranes, with an unprecedented control at the nanometer and micrometer scales. The LbL technique allows to engineer biofunctional surface coatings, which may be dedicated to biomedical applications in vivo but also to fundamental studies and diagnosis in vitro. Initially mostly developed as 2D coatings and hollow capsules, the range of complex objects created by the LbL technique has greatly expanded in the past 10 years. In this Review, the aim is to highlight the recent progress in the field of LbL films for biomedical applications and to discuss the various ways to spatially and temporally control the biochemical and mechanical properties of multilayers. In particular, three major developments of LbL films are discussed: 1) the new methods and templates to engineer LbL films and control cellular processes from adhesion to differentiation, 2) the major ways to achieve temporal control by chemical, biological and physical triggers and, 3) the combinations of LbL technique, cells and scaffolds for repairing 3D tissues, including cardio-vascular devices, bone implants and neuro-prosthetic devices.

Insulating and semiconducting polymeric free-standing nanomembranes with biomedical applications

Free-standing nanomembranes, which are emerging as versatile elements in biomedical applications, are evolving from being composed of insulating (bio)polymers to electroactive conducting polymers.

PMMA/polysaccharides nanofilm loaded with adenosine deaminase inhibitor for targeted anti-inflammatory drug delivery

A novel drug delivery vector, a free-standing polymeric ultrathin film (nanofilm) composed of PMMA and a polysaccharides multilayer, is presented. Chitosan and sodium alginate are alternatively deposited by spin-assisted LbL assembly onto a plasma-treated PMMA thin film. Hydrophobic anti-inflammatory drugs, an adenosine deaminase inhibitor (APP) and its fluorescent dansyl derivate (APP-Dns), are encapsulated inside the LbL multilayer using a simple casting deposition procedure. The resulting drug loaded nanofilm can be suspended in water upon dissolution of a PVA sacrificial layer. Morphological characterization of the nanofilm shows that PMMA/LbL nanofilms possess nanometric thickness (<200 nm) and very low surface roughness (1-2 nm for drug loaded nanofilms and <1 nm for blank nanofilm). Drug loaded films exhibit a diffusion controlled release mechanism following the Korsmayer-Peppas release model, confirmed by the fit of release data with a characteristic power law. Drug release is impaired through the PMMA layer, which acts effectively as a barrier for drug transport. This ultrathin polymer film can find application as a nanopatch for targeted inflammatory drug delivery to treat localized pathologies as inflammatory bowel disease.

Application of poly-L-lactic acid nanosheet as a material for wound dressing

The authors evaluated the efficacy of an ultrathin nanosheet consisting of poly-L-lactic acid (75 nm thick) as a wound dressing material. A full-thickness skin defect was made on the backs of mice and overlapped with or without the poly-L-lactic acid nanosheet. Wound healing was more rapidly improved by overlapping with the nanosheet, especially in the early healing period (at 4 to 6 days). The remaining wound area in the treatment group was significantly smaller at 4 days than in the control group. Histologically, a clear layer was observed over the granulation layer by the nanosheet therapy at 4 days. Thus, overlapping therapy with the poly-L-lactic acid nanosheet accelerated wound healing and formed a clear layer just above the granulation tissue. The poly-L-lactic acid nanosheet may have potential as a novel wound dressing to promote wound healing.

Asymmetric free-standing film with multifunctional anti-bacterial and self-cleaning properties

A superhydrophobic/hydrophilic asymmetric free-standing film has been created using layer-by-layer assembly technique. Poly(ethylene-imine)-Ag(+) complex (PEI-Ag(+)) at pH 9.0 was assembled with poly(acrylic acid) (PAA) at pH 3.2 on a Teflon substrate to yield a micronanostructured surface that can be turned to be superhydrophobic after being coated with a low surface energy compound. Silver nanoparticle loaded free-standing film with one surface being superhydrophobic while the other surface is hydrophilic was then obtained after detachment from the substrate. The superhydrophobicity enabled the upper surface with anti-adhesion and self-cleaning properties and the hydrophilic bottom surface can release silver ions as antibiotic agent. The broad-spectrum antimicrobial capability of silver ions released from the bottom surface coupled with superhydrophobic barrier protection of the upper surface may make the free-standing film a new therapy for open wound.

Therapeutic efficacy of an antibiotic-loaded nanosheet in a murine burn-wound infection model

Polymeric ultra-thin films (nanosheets) possess unique properties that make them suitable materials for various biomedical applications. In our previous study, we assessed the use of an antibiotic (tetracycline, TC)-loaded nanosheet (or "TC-nanosheet") for the treatment of gastrointestinal tissue defects. The nanosheet consisted of three functional layers: layer-by-layer nanosheet as a stable platform, TC as an antimicrobial agent with autofluorescence for tracing, and a poly(vinyl acetate) nanosheet to act as a protecting layer. The TC-nanosheet has high flexibility, adhesive strength and transparency. Here, we evaluated the effectiveness of the TC-nanosheet in preventing full thickness burn-wound infections. In an in vivo study, murine dorsal skin was injured by full-thickness burns and then infected with Pseudomonas aeruginosa (P. aeruginosa), a common bacterium causing burn-associated infections. The wound site was treated either with a TC-nanosheet, TC-unloaded nanosheet or left untreated. Wound management was facilitated by the high transparency of the TC-nanosheet. The TC-nanosheet significantly improved burn-wound infection by P. aeruginosa in mice. Indeed, all mice treated with the TC-nanosheet survived, whereas the other treatment groups displayed increased rates of mortality due to bacterial infection. According to histological analyses and viable bacterial counting in the liver (bacterial translocation), the TC-nanosheets were able to prevent not only the local inflammation but also systemic inflammation. We conclude that the TC-nanosheet can act as an effective treatment for full-thickness burn-wound infection. Hence, the TC-nanosheet is a promising therapeutic tool for burn-wound management in severely burn-injured patients.

Evaluation of substrata effect on cell adhesion properties using freestanding poly(L-lactic acid) nanosheets

Investigation of the interactions between cells and material surfaces is important not only for the understanding of cell biology but also for the development of smart biomaterials. In this study, we investigated the substrate-related effects on the interaction between cell and polymeric ultrathin film (nanosheet) by modulating the mechanical properties of the nanosheet with a metal substrate or mesh. A freestanding polymeric nanosheet with tens-of-nanometers thickness composed of poly(L-lactic acid) (PLLA nanosheet) was fabricated by combination of a spin-coating technique and a water-soluble sacrificial layer. The freestanding PLLA nanosheet was collected on a stainless steel mesh (PLLA-mesh) and subsequently used for cell adhesion studies, comparing the results to the ones on a control SiO(2) substrate coated with an ultrathin layer of PLLA (PLLA-substrate). The adhesion of rat cardiomyocytes (H9c2) was evaluated on both samples after 24 h of culture. The PLLA-mesh with the tens-of-nanometers thick nanosheets induced an anisotropic adhesion of H9c2, while H9c2 on the PLLA-substrate showed an isotropic adhesion independent from the nanosheet thickness. Interestingly, an increment in the nanosheet thickness in the PLLA-mesh samples reduced the cellular anisotropy and led to a similar morphology to the PLLA-substrate. Considering the huge discrepancy of Young's modulus between PLLA nanosheet (3.5-4.2 GPa) and metal substrate (hundreds of GPa), cell adhesion was mechanically regulated by the Young's modulus of the underlying substrate when the thickness of the PLLA nanosheet was tens of nanometers. Modulation of the stiffness of the polymeric nanosheet by utilizing a rigid underlying material will allow the constitution of a unique cell culture environment.

Dual therapeutic action of antibiotic-loaded nanosheets for the treatment of gastrointestinal tissue defects

An ultra-thin polymer film (nanosheet) composed of polysaccharides (i.e., polysaccharide nanosheet) provides sufficient adhesiveness, flexibility and robustness to act as an effective wound dressing. We have recently demonstrated the sealing effect of a nanosheet on a murine cecal puncture. Nevertheless, a small percentage of bacteria penetrated the nanosheet because of its ultra-thin structure. Here, we have developed an antibiotic-loaded nanosheet to inhibit bacterial penetration and investigated its therapeutic efficacy using a model of a murine cecal puncture. Tetracycline (TC) was sandwiched between a poly(vinylacetate) (PVAc) layer and the polysaccharide nanosheet (named PVAc-TC-nanosheet). Under physiological conditions, TC was released from the nanosheet for 6 h. Microscopic observation between the interface of the PVAc-TC-nanosheet and bacteria demonstrated how its potent anti-microbial effect was achieved. In vivo studies show that overlapping therapy with the PVAc-TC-nanosheet (thickness: 177 nm) significantly increases mouse survival rate after cecal puncture as well as suppressing an increase in the intraperitoneal bacterial count and leukocyte count.