A signal amplification for Trp isomers electrochemical recognition based on PEDOT:PSS and CS/PAA multilayers

In this work, enhanced tryptophan (Trp) isomers recognition was successfully demonstrated on (CS/PAA)3.5@PEDOT:PSS/GCE, a multilayer chiral sensor with good stability and reproducibility. The (CS/PAA)n multilayers chiral interface was first fabricated via alternating self-assembly of chiral chitosan (CS) and achiral polyacrylic acid (PAA). Conductive PEDOT:PSS was then compounded with (CS/PAA)n multilayers to obtain the chiral sensor for the electrochemical recognition of Trp isomers. The structure of the sensor and its chirality properties for Trp isomers were characterized by fourier transform infrared spectroscopy (FT-IR)，scanning electron microscopy (SEM) and electrochemical methods. The SEM images showed uniform distribution of PEDOT:PSS in the multilayer films, which changed the internal structure of the (CS/PAA)3.5. Consequently, (CS/PAA)3.5@PEDOT:PSS multilayers rendered more chiral centers in addition to improved good conductivity, which significantly amplified the oxidation peak current ratio of D-Trp to L-Trp (ID/IL) up to 6.71 at 25 °C. In addition, a linear relationship was observed between the peak current and Trp enantiomer concentration in the range of 0.002-0.15 mM, and the detection limits of D-Trp and L-Trp were 0.33 and 0.67 μM, respectively. More importantly, the percentage of D-Trp in non-racemic Trp enantiomers mixture solutions were successfully determined on the chiral interface, showing its effectiveness and promising potential in practical applications.

Development of an anti-infective coating on the surface of intraosseous implants responsive to enzymes and bacteria

Background

Bacterial proliferation on the endosseous implants surface presents a new threat to the using of the bone implants. Unfortunately, there is no effective constructed antibacterial coating which is bacterial anti-adhesion substrate-independent or have long-term biofilm inhibition functions.

Methods

Drug release effect was tested in Chymotrypsin (CMS) solution and S. aureus. We used bacterial inhibition rate assays and protein leakage experiment to analyze the in vitro antibacterial effect of (Montmorillonite/Poly-l-lysine-Chlorhexidine)₁₀ [(MMT/PLL-CHX)₁₀] multilayer film. We used the CCK-8 assay to analyze the effect of (MMT/PLL-CHX)₁₀ multilayer films on the growth and proliferation of rat osteoblasts. Rat orthopaedic implant-related infections model was constructed to test the antimicrobial activity effect of (MMT/PLL-CHX)₁₀ multilayer films in vivo.

Results

In this study, the (MMT/PLL-CHX)₁₀ multilayer films structure were progressively degraded and showed well concentration-dependent degradation characteristics following incubation with Staphylococcus aureus and CMS solution. Bacterial inhibition rate assays and protein leakage experiment showed high levels of bactericidal activity. While the CCK-8 analysis proved that the (MMT/PLL-CHX)₁₀ multilayer films possess perfect biocompatibility. It is somewhat encouraging that in the in vivo antibacterial tests, the K-wires coated with (MMT/PLL-CHX)₁₀ multilayer films showed lower infections incidence and inflammation than the unmodified group, and all parameters are close to SHAM group.

Conclusion

(MMT/PLL-CHX)₁₀ multilayer films provides a potential therapeutic method for orthopaedic implant-related infections.

Optimized PAH/Folic acid layer-by-layer films as an electrochemical biosensor for the detection of folate receptors

Folate receptor alpha (FR-α) is a glycoprotein overexpressed in tumor cell surfaces, especially in gynecologic cancers, and can be used as a biomarker for diagnostics. Currently, FRα is quantified by positron emission tomography (PET) or fluorescence imaging techniques. However, these methods are costly and time-consuming. We report on the development of an electrochemical biosensor for FRα detection based on the use of nanostructured layer-by-layer (LbL) films as modified electrodes. Multilayer films were deposited on indium tin oxide (ITO) electrodes by the alternately assembling of positively charged polyallylamine hydrochloride (PAH) and negatively charged folic acid (FA), used as the biorecognition element. UV-vis and FTIR spectroscopies revealed the successful PAH and FA adsorption on ITO. Devices performance was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The [PAH/FA] films presented a good reproducibility (RSD of 1.12%) and stability when stored in the Tris-HCl solution (RSD 6.7%). The biosensor electrochemical response exhibited a linear relationship with FRα concentration in the range from 10 to 40 nM. The limit of detection reached for CV and EIS measurements were 0.7 and 1.5 nM, respectively. As a proof-of-concept, we show that the devices can differenciate tumor cells from healthy cell, showing an excellent selectivity. The biosensor device based on [PAH/FA] films represents a promising strategy for a simple, rapid, and low-cost cancer diagnosis through FRα quantification on the surface of cancer cells.

Engineering the surface of prostate tumor cells and hyaluronan/chitosan multilayer films to modulate cell-substrate adhesion properties

This paper explores different film assembly conditions of the polyelectrolyte solutions of hyaluronan (HA) and chitosan (CHI), as well as both substrate and cell surface modifications, to investigate PC3 cells adhesion properties. UV-Visible, AFM-IR and Zeta potential techniques indicate that the solution ionic strength is a relevant parameter to modulate the free carboxylic groups of HA on the film surface. In addition, capacitive coupling measurements suggest that assembly conditions that favor surface charge mobility inhibit cell adhesion due to polymer rearrangements that support non-specific electrostatic interactions of positively charged CHI residues and the negatively charged cell moieties, rather than specific CD44-hyaluronan interactions. Moreover, the PC3 cells treatment with hyaluronidase and anti-CD44 antibody also highlighted the importance of CD44 binding site availability on the tumor cell adhesion properties. Finally, the conjugation of wheat germ agglutinin on the film surface proved to be a suitable strategy to boost the PC3 cell adhesion properties. Our results reveal the remarkable capacity of HA/CHI films to modulate cell-substrate properties, which pave the road for the development of surfaces suitable for several applications based on biosensing.

Enzyme-free glucose sensor based on layer-by-layer electrodeposition of multilayer films of multi-walled carbon nanotubes and Cu-based metal framework modified glassy carbon electrode

A high-performance nonenzymatic glucose sensor was successfully prepared by a layer by layer strategy through electrodeposition assembling multilayer films of Cu-metal-organic frameworks/multi-walled carbon nanotubes (Cu-MOF/MWNTs) modified glassy carbon electrodes (GCE). Different multilayer films of Cu-MOF/MWNTs modified GCE (Cu-MOF/MWNTs/GCE) were prepared by repeating the electrodeposition of MWNTs onto the GCE in an MWNTs solution (MWNTs/GCE) and electrodeposition of the Cu-MOF layer onto the MWNTs film surface to form a Cu-MOF/MWNTs composite layer in the crystallization solution of Cu-MOF. Results confirmed that this method to fabricate multilayer composite films on the GCE was fast and convenient, and that multilayer composite films were stable and unified. The electrode modified by the multilayer composite films could effectively increase the exposure of active sites and increase the surface area of reactive contact. The GCE modified by eight layers (four multilayers Cu-MOF/MWNTs films) showed the optimum catalytic performance in the oxidation of glucose. The novel glucose sensor exhibited a wider detection linear range of 0.5 μM-11.84 mM, with a detection limit of 0.4 μM and a sensitivity of 3878 μA cm^-2 mM^-1. Moreover, the electrochemical response of the sensor on glucose was fast (within 0.3 s) and stable, exhibited good selectivity and was free of interference.

Influence of compatibilizer on the properties of low-density polyethylene/polyamide 6 blends obtained by mechanical recycling of multilayer film waste

Polymeric wastes have caused increasing environmental problems, mainly in oceans that accumulate large amounts of non-degradable plastic waste. Particularly, waste of polymeric multilayer films for packaging presents low interest for mechanical recycling due to the poor properties and low commercial value of the recycled material generated as polymeric blends. Multilayer films of low-density polyethylene (LDPE) and polyamide 6 (PA6) is a typical material used for packaging applications. The aim of this study was to evaluate the action of the concentration of maleic anhydride grafted polyethylene (PE- g-MA) on the compatibilization of LDPE/PA6 blends generated from mechanical recycling of multilayer films containing both polymers. The action of the PE- g-MA on the properties of the LDPE/PA6 blends was evaluated by tensile tests, optical microscopy, melt flow rate, and scanning electron microscopy. The use of PE- g-MA at 2.5 wt% as a compatibilizer during reactive extrusion of the multilayer films waste has showed the best result for production of the respective recycled LDPE/PA6 blends.

Synthesis of chitosan-based micelles for pH responsive drug release and antibacterial application

The over- and inefficient release of antibiotics from common delivery systems causes the development of drug-resistant bacteria. In the present work, methoxy poly(ethylene glycol)-poly(ε-caprolactone)-chitosan/montmorillonite (MPC/MMT) hybrid multilayer films were constructed for bacterial infections and pH-dependent release of the hydrophobic drug triclosan (TCA). The thickness of the (MPC-T/MMT)₁₀ multilayer films was 384.4 ± 26.5 nm, and the TCA loading dosage was 2.4 μg/cm². Staphylococcus aureus, Escherichia coli and Staphylococcus epidermidis were used in the antibacterial tests. pH responsive TCA release from the prepared multilayer films was examined by measuring the bactericidal activity of the films after immersion in PBS (pH 7.4) or MES (pH 5.5) and zone of inhibition on nutrient agar. In vitro bacterial shake-flask, zone of inhibition and live/dead staining results demonstrated the high sterilization efficiency of the films. Furthermore, cell biocompatibility measurements toward L929 fibroblasts and human lens epithelial cells showed no adverse effects of the multilayer film.

Protein-tannic acid multilayer films: A multifunctional material for microencapsulation of food-derived bioactives

The benefits of various functional foods are often negated by stomach digestion and poor targeting to the lower gastrointestinal tract. Layer-by-Layer assembled protein-tannic acid (TA) films are suggested as a prospective material for microencapsulation of food-derived bioactive compounds. Bovine serum albumin (BSA)-TA and pepsin-TA films demonstrate linear growth of 2.8±0.1 and 4.2±0.1nm per bi-layer, correspondingly, as shown by ellipsometry. Both multilayer films are stable in simulated gastric fluid but degrade in simulated intestinal fluid. Their corresponding degradation constants are 0.026±0.006 and 0.347±0.005nm^-1min^-1. Milk proteins possessing enhanced adhesion to human intestinal surface, Immunoglobulin G (IgG) and β-Lactoglobulin (BLG), are explored to tailor targeting function to BSA-TA multilayer film. BLG does not adsorb onto the multilayer while IgG is successfully incorporated. Microcapsules prepared from the multilayer demonstrate 2.7 and 6.3 times higher adhesion to Caco-2 cells when IgG is introduced as an intermediate and the terminal layer, correspondingly. This developed material has a great potential for oral delivery of numerous active food-derived ingredients.

Performance properties, lactic acid specific migration and swelling by simulant of biodegradable poly(lactic acid)/nanoclay multilayer films for food packaging

The aim of the study was the development of a multifunctional, high-performance, fully biodegradable multilayer polylactic acid (PLA) film for food packaging applications. In particular, sealable multilayer PLA-clay nanocomposite systems with different layouts in terms of composition and relative thickness of the layers, all consisting of a PLA-clay nanocomposite layer between two pure PLA layers for direct food contact, were designed and produced by blown film co-extrusion. The films obtained were analysed for their morphology, functional properties and lactic acid (LA)-specific migration in 50% ethanol. The results showed that, with respect to the unfilled multilayer system, taken as a reference, the nanocomposite films had significant improvements, up to about 40%, in their barriers to oxygen and tensile strengths, and resulted in being more easily sealable over a wide heat-sealing temperature range (80-100°C) with higher seal strength. Moreover, all films had LA migrations always well below the former generic overall migration limit of 60 mg kg^-1 food (10 mg dm^-2) of European Union Regulation No. 10/2011 (deleted by the amending Regulation No. 2016/1416), even if their morphology was strongly modified during the migration tests due to the strong swelling action of the used simulant (simulant D1 = 50% ethanol (aq.) (v/v)) towards PLA.

Transport, mechanical and global migration data of multilayer copolyamide nanocomposite films with different layouts

Transport, mechanical and global migration data concern multilayer food packaging films with different layouts, all incorporating a layered silicate/polyamide nanocomposite as oxygen barrier layer, and a low-density polyethylene (LDPE) as moisture resistant layer in direct contact with food. The data are related to "Tuning of co-extrusion processing conditions and film layout to optimize the performances of PA/PE multilayer nanocomposite films for food packaging" by Garofalo et al. (2017) [1]. Nanocomposite multilayer films, with different relative layer thicknesses and clay types, were produced using a laboratory scale co-extrusion blown-film equipment and were analyzed in terms of transport to oxygen and water vapor, mechanical properties and overall migration. The results have shown that all the multilayer hybrid films, based on the copolyamide layer filled with Cloisite 30B, displayed the most significant oxygen barrier improvements and the best mechanical properties compared to the unfilled films. No significant alteration of the overall migration values was observed, as expectable [2], [3], [4]. The performance improvement was more relevant in the case of the film with the thinner nanocomposite layer.

Hydrophobization and smoothing of cellulose nanofibril films by cellulose ester coatings

The Cellulose nanofibrils (CNF), also referred to as nanocellulose, is one of the most studied bio-based material in recent year, which has good potential in the future for packaging applications due to its excellent mechanical strength and oxygen barrier properties. In the future, CNF films may also find new applications for example in printed electronics, if the surface smoothness of CNF films can be improved. One way to improve surface smoothness is to use thin coating solutions with zero porosity, such as molar mass controlled cellulose ester coatings. In this study, we have coated CNF films using molar mass controlled cellulose esters with different side chain lengths forming 3-layer film (ester-CNF-ester). These coatings improved significantly the smoothness of CNF films. The 3-layer films have also good water vapor barrier and mechanical properties and the films are heat-sealable, which enable various new applications in the future.

Enhancing proliferation and osteogenic differentiation of HMSCs on casein/chitosan multilayer films

Creating a bioactive surface is important in tissue engineering. Inspired by the natural calcium binding property of casein (CA), multilayer films ((CA/CS)n) with chitosan (CS) as polycation were fabricated to enhance biomineralization, cell adhesion and differentiation. LBL self-assembly technique was used and the assembly process was intensively studied based on changes of UV absorbance, zeta potential and water contact angle. The increasing content of chitosan and casein with bilayers was further confirmed with XPS and TOF-SIMS analysis. To improve the biocompatibility, gelatin was surface grafted. In vitro mineralization test demonstrated that multilayer films had more hydroxyapatite crystal deposition. Human mesenchymal stem cells (HMSCs) were seeded onto these films. According to fluorescein diacetate (FDA) and cell cytoskeleton staining, MTT assay, expression of osteogenic marker genes, ALP activity, and calcium deposition quantification, it was found that these multilayer films significantly promoted HMSCs attachment, proliferation and osteogenic differentiation than TCPS control.

Graphene-polyelectrolyte multilayer film formation driven by hydrogen bonding

A method for preparing hydrogen bonded multilayer thin films comprised of layer pairs of surfactant stabilized graphene and an anionic polyelectrolyte is described. The films were constructed at low pH using the Layer-By-Layer (LbL) technique, where the adsorption of the cationic polyelectrolyte, polyethyleneimine (PEI) is followed by the sequential alternating adsorption of the anionic polyelectrolyte, polyacrylic acid (PAA) and anionic graphene sheets modified with Pluronic® F108, a polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) surfactant. Quartz Crystal Microbalance (QCM) measurements indicate that film formation was driven by hydrogen bonding between the carboxylic acid group of the PAA and ethylene oxide unit present in the surfactant. QCM measurements and Raman spectra showed evidence of non-linear and linear growth at low and high numbers of adsorbed layers respectively, suggesting overall superlinear film growth. Atomic Force Microscopy (AFM) Quantitative Nanomechanical Mapping (QNM) measurements of the films indicated that the reduced Young's Modulus of the films decreased with increasing numbers of adsorbed layers, reaching a bulk value of 6.07-32.3 MPa for samples with greater than 300 layers of surfactant stabilized graphene and PAA. The films were also shown to deteriorate partially with aqueous solutions at neutral and basic pH. The thin films exhibited features advantageous for use in coatings, such as pH responsiveness in addition to different mechanical properties, surface roughness, and internal structures based on the number of layers adsorbed.