Fire Retardant Action of Layered Double Hydroxides and Zirconium Phosphate Nanocomposites Fillers in Polyisocyanurate Foams

Modern day energy codes are driving the design and multi-layered configuration of exterior wall systems with a significant emphasis on achieving high performance insulation towards improving energy performance of building envelopes. Use of highly insulating polyisocyanurate (PIR) based materials enhanced with eco-friendly lamellar inorganic fillers reinforces energy performance requirements, environmental challenges and cost reduction without compromising the overall building fire safety. The current work assessed the fire behaviour of PIR modified with three layered fillers, namely MgAlCO3 (PIR-LDH1), MgAl Stearate (PIR-LDH2) and Zirconium Phosphate octadecylamine (PIR-ZrP3). For each of the fillers, three loadings (2, 4 and 6% by weight) were used. Optical analysis by X-ray diffraction patterns (XRD), cone calorimeter (CC), thermogravimetric (TGA) analysis, post-burning morphological evaluation using field emission scanning electron microscope (FESEM) and diffuse reflectance infrared spectroscopy (DRIFT) analysis, were performed. The results indicated that fire reaction properties and thermal stability of foam samples were enhanced with all three different lamellar inorganic smart fillers. The initial degradation temperature of PIR-layered filler samples was increased, demonstrating that incorporation of flame retardants decelerated the degradation of the PIR foam and contributed to significant char formation, from 19.5% in pure PIR samples to 33% in PIR-6%LDH1 samples. Increasing the filler content also resulted in improved char properties and decreased peak Heat Release Rates (HRR) in the cone calorimeter. Due to the development of a stable char layer, samples containing 6% of ZrP3 did not ignite at 20 kW/m2 and a reduction of up to 40% in the peak HRR was achieved in PIR-2%ZrP3 samples

3D additive manufactured composite scaffolds with antibiotic-loaded lamellar fillers for bone infection prevention and tissue regeneration

Bone infections following open bone fracture or implant surgery remain a challenge in the orthopedics field. In order to avoid high doses of systemic drug administration, optimized local antibiotic release from scaffolds is required. 3D additive manufactured (AM) scaffolds made with biodegradable polymers are ideal to support bone healing in non-union scenarios and can be given antimicrobial properties by the incorporation of antibiotics. In this study, ciprofloxacin and gentamicin intercalated in the interlamellar spaces of magnesium aluminum layered double hydroxides (MgAl) and α-zirconium phosphates (ZrP), respectively, are dispersed within a thermoplastic polymer by melt compounding and subsequently processed via high temperature melt extrusion AM (~190 °C) into 3D scaffolds. The inorganic fillers enable a sustained antibiotics release through the polymer matrix, controlled by antibiotics counterions exchange or pH conditions. Importantly, both antibiotics retain their functionality after the manufacturing process at high temperatures, as verified by their activity against both Gram + and Gram - bacterial strains. Moreover, scaffolds loaded with filler-antibiotic do not impair human mesenchymal stromal cells osteogenic differentiation, allowing matrix mineralization and the expression of relevant osteogenic markers. Overall, these results suggest the possibility of fabricating dual functionality 3D scaffolds via high temperature melt extrusion for bone regeneration and infection prevention.We are grateful to the FAST project funded under the H2020-NMP- PILOTS-2015 scheme (GA n. 685825) for financial support. Some of the materials used in this work were provided by the Texas A&M Health Science Center College of Medicine Institute for Regenerative Medicine at Scott & White through a grant from NCRR of the NIH (Grant #P40RR017447)

Additive Manufactured Scaffolds for Bone Tissue Engineering: Physical Characterization of Thermoplastic Composites with Functional Fillers

Thermoplastic polymer–filler composites are excellent materials for bone tissue engineering (TE) scaffolds, combining the functionality of fillers with suitable load-bearing ability, biodegradability, and additive manufacturing (AM) compatibility of the polymer. Two key determinants of their utility are their rheological behavior in the molten state, determining AM processability and their mechanical load-bearing properties. We report here the characterization of both these physical properties for four bone TE relevant composite formulations with poly(ethylene oxide terephthalate)/poly(butylene terephthalate (PEOT/PBT) as a base polymer, which is often used to fabricate TE scaffolds. The fillers used were reduced graphene oxide (rGO), hydroxyapatite (HA), gentamicin intercalated in zirconium phosphate (ZrP-GTM) and ciprofloxacin intercalated in MgAl layered double hydroxide (MgAl-CFX). The rheological assessment showed that generally the viscous behavior dominated the elastic behavior (G″ > G′) for the studied composites, at empirically determined extrusion temperatures. Coupled rheological–thermal characterization of ZrP-GTM and HA composites showed that the fillers increased the solidification temperatures of the polymer melts during cooling. Both these findings have implications for the required extrusion temperatures and bonding between layers. Mechanical tests showed that the fillers generally not only made the polymer stiffer but more brittle in proportion to the filler fractions. Furthermore, the elastic moduli of scaffolds did not directly correlate with the corresponding bulk material properties, implying composite-specific AM processing effects on the mechanical properties. Finally, we show computational models to predict multimaterial scaffold elastic moduli using measured single material scaffold and bulk moduli. The reported characterizations are essential for assessing the AM processability and ultimately the suitability of the manufactured scaffolds for the envisioned bone regeneration application.The work was supported by a Horizon 2020 Research and Innovation Programme grant from the European Union, called the FAST project (grant no. 685825, project website: http:// project-fast.eu). The authors acknowledge the support of the FAST project consortium for the various aspects of this wor

Caffeic Acid-layered Double Hydroxide Hybrid: A New Raw Material for Cosmetic Applications

Bioactive ingredients from natural sources possess well-known positive effects in cosmetic applications. Among them, phenolic acids have emerged with very interesting potential. Caffeic acid (CAF) is one of the most promising active compounds because it possess antioxidant, anti-inflammatory, antitumoral and anti-wrinkle effects. In order to increase its local bioavailability in topical applications, the vehiculation of caffeic acid can lead to a new raw material of cosmetic interest. For this purpose, clay minerals possess excellent properties, such as low or null toxicity and good biocompatibility. Clays are able to host a wide range of active ingredients in the interlayer region, using a green process known as intercalation reaction. The hosting of cosmetic actives into the layered structure of anionic clays allows the preparation of new materials with enhanced stability towards oxidation and photodegradation, better local bioavailability, and easier workability. In this paper, the successful vehiculation of caffeic acid into anionic clay is presented. The obtained hybrid is very promising for the cosmetic market because of its higher bioavailability and prolonged antioxidant activity

The Rheology of PEOT/PBT Block Copolymers in the Melt State and in the Thermally-Induced Sol/Gel Transition. Implications on the 3D-Printing Bio-Scaffold Process

Poly(ethyleneoxideterephthalate)/poly(butyleneterephthalate) (PEOT/PBT) segmented block copolymers are widely used for the manufacturing of 3D-printed bio-scaffolds, due to a combination of several properties, such as cell viability, bio-compatibility, and bio-degradability. Furthermore, they are characterized by a relatively low viscosity at high temperatures, which is desired during the injection stages of the printing process. At the same time, the microphase separated morphology generated by the demixing of hard and soft segments at intermediate temperatures allows for a quick transition from a liquid-like to a solid-like behavior, thus favoring the shaping and the dimensional stability of the scaffold. In this work, for the first time, the rheology of a commercial PEOT/PBT material is studied over a wide range of temperatures encompassing both the melt state and the phase transition regime. Non-isothermal viscoelastic measurements under oscillatory shear flow allow for a quantitative determination of the material processability in the melt state. Additionally, isothermal experiments below the order–disorder temperature are used to determine the temperature dependence of the phase transition kinetics. The importance of the rheological characterization when designing the 3D-printing scaffold process is also discussed

Innovative Composites Based on Organic Modified Zirconium Phosphate and PEOT/PBT Copolymer

Polymers are key building blocks in the development of smart materials for biomedical applications, and many polymers offer unique properties for specific applications. A wide range of materials is available through the use of polymer compounds. These compounds can incorporate performance-enhancing fillers, which provide properties not reachable with ordinary neat polymers (e.g., bending stiffness, tensile strength, elongation, torque, biological activity such as antimicrobial properties, cell differentiation). In this work, the preparation of functional biocomposites containing organic modified zirconium phosphate (ZrP) as drug carrier is presented. The composites were prepared by melt compounding, which offers significant promise since it allows an easy customization of the plastic compounds that well suit biomedical applications (devices, long-term implantable polymers, bioresorbable polymers). The obtained polymer composites based on ZrP intercalated with gentamicin (GMT) and poly(ethylene oxide terephthalate)/poly(butylene terephthalate) (PEOT/PBT) were characterized

Determination of Pb(II) Ions in Water by Fluorescence Spectroscopy Based on Silver Nanoclusters

In this work, a method to determine Pb(II) ions in model water is presented; the method is based on the fluorescence emission of a silver nanoclusters (AgNCs) colloidal solution, which is sensitive to lead ions. The presence of Pb(II) ions causes a photoemission enhancement of the AgNCs solution dependent on the pollutant concentration. The functional dependence is logarithmic in the range from 2.5 to 40 µM, and through the linearization of the calibration points, a linear function is determined and exploited for the extrapolation of the test Pb(II) concentrations with a precision estimated by relative standard deviation (RSD) ranging from 21% to 10% from the highest to the lowest Pb(II) quantity, respectively. Finally, inductively coupled plasma–optical emission spectroscopy (ICP-OES) successfully validated the described method. The accuracy of the method is also studied for intentionally polluted mineral waters, revealing the same trend of the model water: the lower the concentration, the higher the precision of the method