Poly(lactic acid)/Poly(ethylene glycol) Polymer Nanocomposites: Effects of Graphene Nanoplatelets

Gadolinium-Doped Gallic Acid-Zinc/Aluminium-Layered Double Hydroxide/Gold Theranostic Nanoparticles for a Bimodal Magnetic Resonance Imaging and Drug Delivery System

We have developed gadolinium-based theranostic nanoparticles for co-delivery of drug and magnetic resonance imaging (MRI) contrast agent using Zn/Al-layered double hydroxide as the nanocarrier platform, a naturally occurring phenolic compound, gallic acid (GA) as therapeutic agent, and Gd(NO₃)₃ as diagnostic agent. Gold nanoparticles (AuNPs) were grown on the system to support the contrast for MRI imaging. The nanoparticles were characterized using techniques such as Hi-TEM, XRD, ICP-ES. Kinetic release study of the GA from the nanoparticles showed about 70% of GA was released over a period of 72 h. The in vitro cell viability test for the nanoparticles showed relatively low toxicity to human cell lines (3T3) and improved toxicity on cancerous cell lines (HepG2). A preliminary contrast property test of the nanoparticles, tested on a 3 Tesla MRI machine at various concentrations of GAGZAu and water (as a reference) indicates that the nanoparticles have a promising dual diagnostic and therapeutic features to further develop a better future for clinical remedy for cancer treatment.

Polylactide/graphene oxide nanosheets/clove essential oil composite films for potential food packaging applications

Antimicrobial nanopackaging films were developed by incorporating clove essential oil (CLO) (15-30% w/w) and graphene oxide (GO) nanosheets (1% w/w) into polylactide (PLA), suitable for use as food packaging, via solution casting. Addition of CLO into PLA matrix improved the flexibility of the composite films by lowering tensile stress, complex viscosity (η*), and glass transition temperature (T_g). GO improved the T_g, η* and lowered the oxygen permeability of the plasticized PLA matrix. Optical and anti-UV properties of the film were influenced by both GO and CLO incorporation. FTIR spectra exhibited a change in the molecular organization of the plasticized PLA film after incorporation with CLO. Microstructural studies revealed that the reinforcement of GO prevented porosity of plasticized PLA/CLO film surface. The developed composite film showed excellent antibacterial activity against Staphylococcus aureus and Escherichia coli and therefore, has a potential to be used as active packaging material for food safety and preservation.

Triethyl Citrate (TEC) as a Dispersing Aid in Polylactic Acid/Chitin Nanocomposites Prepared via Liquid-Assisted Extrusion

The production of fully bio-based and biodegradable nanocomposites has gained attention during recent years due to environmental reasons; however, the production of these nanocomposites on the large-scale is challenging. Polylactic acid/chitin nanocrystal (PLA/ChNC) nanocomposites with triethyl citrate (TEC) at varied concentrations (2.5, 5.0, and 7.5 wt %) were prepared using liquid-assisted extrusion. The goal was to find the minimum amount of the TEC plasticizer needed to enhance the ChNC dispersion. The microscopy study showed that the dispersion and distribution of the ChNC into PLA improved with the increasing TEC content. Hence, the nanocomposite with the highest plasticizer content (7.5 wt %) showed the highest optical transparency and improved thermal and mechanical properties compared with its counterpart without the ChNC. Gel permeation chromatography confirmed that the water and ethanol used during the extrusion did not degrade PLA. Further, Fourier transform infrared spectroscopy showed improved interaction between PLA and ChNC through hydrogen bonding when TEC was added. All results confirmed that the plasticizer plays an important role as a dispersing aid in the processing of PLA/ChNC nanocomposites.

Poly(lactic acid) Composites Containing Carbon-Based Nanomaterials: A Review

Poly(lactic acid) (PLA) is a green alternative to petrochemical commodity plastics, used in packaging, agricultural products, disposable materials, textiles, and automotive composites. It is also approved by regulatory authorities for several biomedical applications. However, for some uses it is required that some of its properties be improved, namely in terms of thermo-mechanical and electrical performance. The incorporation of nanofillers is a common approach to attain this goal. The outstanding properties of carbon-based nanomaterials (CBN) have caused a surge in research works dealing with PLA/CBN composites. The available information is compiled and reviewed, focusing on PLA/CNT (carbon nanotubes) and PLA/GBM (graphene-based materials) composites. The production methods, and the effects of CBN loading on PLA properties, namely mechanical, thermal, electrical, and biological, are discussed.

Effect of Preparation Methods on the Tensile, Morphology and Solar Energy Conversion Efficiency of RGO/PMMA Nanocomposites

In this study, reduced graphene oxide (RGO)/polymethyl methacrylate (PMMA) nanocomposites were prepared by employing in situ polymerization and solution blending methods. In terms of mechanical properties, RGO loading increased the Young's modulus but decreased the elongation at break for RGO/PMMA nanocomposites. Tensile strength for solution blended RGO/PMMA nanocomposites increased after adding 0.5 wt % RGO, which was attributed to the good dispersion of RGO in the nanocomposites as evidenced from SEM and TEM. Solar energy conversion efficiency measurement results showed that the optimum concentration of RGO in the RGO/PMMA nanocomposites was found to be 1.0 wt % in order to achieve the maximum solar energy conversion efficiency of 25%. In the present study, the solution blended nanocomposites exhibited better overall properties than in situ polymerized nanocomposites owing to the better dispersion of RGO in solution blending. These findings would contribute to future work in search of higher conversion efficiency using nanocomposites.

Epoxidized Jatropha Oil as a Sustainable Plasticizer to Poly(lactic Acid)

A renewable resource, epoxidized jatropha oil (EJO), was used as a green plasticizer and added to poly(lactic acid) (PLA). EJO was compounded into PLA at different contents. The addition of 3 wt % EJO to the PLA demonstrates significant improvement in flexibility, which leads to a percentage increase of about 7000% in elongation at break. This tensile result was confirmed by surface morphology analysis with clear proof of plastic deformation in EJO-plasticized PLA. EJO imparts a good heat stabilization effect. Thermal stability of PLA was enhanced upon addition of EJO, which is due to their good interaction and plasticizer dispersion within the PLA matrix. This EJO-plasticized PLA has wide applications in various industries, such as packaging of food and non-food products.

Effect of Maleic Anhydride-Modified Poly(lactic acid) on the Properties of Its Hybrid Fiber Biocomposites

This work investigated the effect of maleic anhydride (MA)-modified poly(lactic acid) (PLA), which is melt-blended with different untreated and aqueous borax (BR)-treated hybrid oil palm empty fruit bunch fibers (EFBF)/Kenaf core fibers (KCF), and compression-molded into corresponding hybrid biocomposites. These hybrid systems includes BR-treated EFBF/BR-treated KCF reinforced MA-modified PLA i.e., BR(EFBF-KCF)-MAPLA, BR-treated EFBF/BR-treated KCF reinforced unmodified PLA i.e., BR(EFBF-KCF)-PLA, untreated EFBF/untreated KCF reinforced MA-modified PLA i.e., EFBF-KCF-MAPLA, and untreated EFBF/untreated KCF reinforced unmodified PLA i.e., EFBF-KCF-PLA respectively. Characterizations of the hybrid systems revealed that optimal mechanical, physical, morphological, thermal and dynamic mechanical properties were provided by the BR(EFBF-KCF)-MAPLA, resulting from improved interface adhesion, consequent of the synergistic influence of BR treatment of natural fibers, and the compatibilization effect provided by the MA-modified PLA. The grafting degree and efficiency of MA onto the PLA backbone was appreciable, as indicated by direct titration, and through monitoring using Fourier Transform Infrared Spectroscopy (FTIR); thus the MA-modified PLA facilitated the formation of strong interface adhesion with the BR-treated hybrid fibers. The BR(EFBF-KCF)-MAPLA showed promising properties for usage as a bio-inspired, and sustainable alternative fiberboard article.

Comparative effects of untreated and 3-methacryloxypropyltrimethoxysilane treated ZnO nanoparticle reinforcement on properties of polylactide-based nanocomposite films

Polylactide (PLA) nanocomposites characterized by antimicrobial properties are gaining increasing attention for food packaging. In this contribution, the PLA based nanocomposite films with multifunctional end-use properties were achieved by incorporating ZnO nanoparticles (NPs) [untreated: ZnO(UT) and 3-methacryloxypropyltrimethoxysilane treated: ZnO(ST)] into polymer matrix via solvent casting method. The ZnO(ST) prevented the degradation of PLA at higher temperature and improved the mechanical property. Color, transparency, and anti-UV properties of composite films were influenced by the incorporation of ZnO NPs. Contrary to untreated ZnO, the treated NPs were more effective in enhancing the tortuosity of the diffusive path for the oxygen molecules to diffuse through the film. The glass transition (T_g) and crystallization (T_c) temperatures of composites were improved by the addition of ZnO, whereas a higher T_g was recorded for ZnO(ST) loaded films. XRD demonstrated the change in crystallinity of the films with NPs addition. Nanoparticles well distributed in the composite films as observed through SEM however spots of agglomeration were observed for PLA/ZnO(UT) films. Developed films especially incorporated with ZnO(ST) were found to be active against both Gram-negative (Salmonella Typhimurium) and Gram-positive (Listeria monocytogenes) bacteria. Therefore, PLA/ZnO nanocomposite films could be considered as environment-friendly active packaging material for food preservation.

Antibacterial Property and Cytotoxicity of a Poly(lactic acid)/Nanosilver-Doped Multiwall Carbon Nanotube Nanocomposite

A novel method was used to synthesize a nanosilver-doped multiwall carbon nanotube (MWCNT-Ag), and subsequently, the novel poly(lactic acid) (PLA)- and MWCNT-Ag-based biocompatible and antimicrobial nanocomposites were prepared by melt blending. Based on energy dispersive X-ray spectrometry images, an MWCNT-Ag was successfully synthesized. The effect of the MWCNT-Ag on the PLA bionanocomposites was investigated by evaluating their thermal and mechanical properties, antifungal activity, and cytotoxicity. The nanocomposites exhibited a high degree of biocompatibility with the MWCNT-Ag content, which was less than 0.3 phr. Furthermore, tensile strength testing, thermogravimetric analysis, differential scanning calorimetry, and antibacterial evaluation revealed that the tensile strength, thermostability, glass transition temperature, and antibacterial properties were enhanced by increasing the MWCNT-Ag content. Finally, hydrolysis analysis indicated that the low MWCNT-Ag content could increase the packing density of PLA.

Preparation and characterization of polyethylene glycol/poly(L-lactic acid) blends

The effect of incorporation of poly(ethylene glycol) (PEG) on thermomechanical and hydrophilicity properties of poly(L-lactic acid) (PLLA) was investigated. PEG/PLLA blends, containing 10, 20, 30 and 40 wt% PEG, were prepared by melt-extrusion in a co-rotating twin-screw extruder. By DSC analysis, it was observed that the Tg of PLLA phase in PEG/PLLA blends decreased accompanied by a significant decrease in Tcc and increase in their melting enthalpy. Therefore, the addition of PEG enhances the crystallization ability of PLLA phase due to its lubricating effect which increased mobility of PLLA chains. From TGA it was observed that low concentrations of PEG (10 & 20 wt%) increase the Tonset of thermal degradation, probably due to improved heat resistance of the crystalline phase. At higher PEG content, the Tonset decreases, as the lubricating effect becomes the controlling mechanism for the initiation of degradation process. Decrease in tensile strength and modulus was recorded especially in PLLA blends with PEG content higher than 20 wt%. The elongation at break decreases reaching a maximum at 20 wt% PEG and then dropped again. To investigate the effect of PEG on the wetting ability of PLLA, water contact angle measurements were performed. The results indicate that the introduction of PEG lowers the contact angle values in PEG/PLLA film surfaces, as compared to pure PLLA, suggesting improved hydrophilic properties.

Polyethylene glycol oligomers as siloxane modificators in consolidation of carbonate stones

The overall performance of alkoxysilanes as stone consolidants is constrained by stone mineralogy (particularly in the carbonate varieties) and by their tendency to crack during drying. In an attempt to overcome these problems, polyethylene glycol “chains” with two carboxylic acid end-groups (PEG-CA) were introduced in siloxane sols obtained by sol-gel chemistry using tetraethoxysilane (TEOS) as precursor. Different pre-condensation degrees (by varying the stirring times of sol-gel reaction: 10 min, 2, and 24 h) and PEG-CA chains with different molecular weights were studied as variables affecting the initial efficacy of the consolidants when applied into a limestone. The sol containing siloxanes with the lowest pre-condensation degree (10 min stirring) was quite susceptible to the carbonate media and thus a poor consolidation was achieved. The sol with the highest pre-condensation degree (24 h stirring) together with the PEG-CA chains with intermediate molecular weight produced significant and uniform strength gains along the stone depth. The consolidation also showed to be highly dependent on the molecular weight of the PEG-CA chains, the PEG-CA with highest molecular weight produced a non-uniform strength increase with potential harmful side effects. The results confirmed the role of carboxylic acid end-groups as efficient sol-gel catalysts and their ability to be incorporated into the silica matrix in the presence of carbonate stone.

Hydrogels based on poly(ethylene glycol) as scaffolds for tissue engineering application: biocompatibility assessment and effect of the sterilization process

Hydrogels are suitable materials to promote cell proliferation and tissue support because of their hydrophilic nature, porous structure and sticky properties. However, hydrogel synthesis involves the addition of additives that can increase the risk of inducing cytotoxicity. Sterilization is a critical process for hydrogel clinical use as a proper scaffold for tissue engineering. In this study, poly(ethylene glycol) (PEG), poly(ethylene glycol)-chitosan (PEG-CH) and multi-arm PEG hydrogels were synthesized by free radical polymerization and sterilized by gamma irradiation or disinfected using 70 % ethanol. The biocompatibility assessment in human fibroblasts and hemocompatibility studies (hemolysis, platelet aggregation, morphology of mononuclear cells and viability) in peripheral blood from healthy volunteers (ex vivo), were performed. The sterilization or disinfection effect on hydrogel structures was evaluated by FT-IR spectroscopy. Results indicated that hydrogels do not induce any damage to fibroblasts, erythrocytes, platelets or mononuclear cells. Moreover, there was no significant difference in the biocompatibility after the sterilization or disinfection treatment. However, after gamma irradiation, several IR spectroscopic bands were shifted to higher or lower energies with different intensity in all hydrogels. In particular, several bands associated to carboxyl or hydroxyl groups were slightly shifted, possibly associated to scission reactions. The disinfection treatment (70 % ethanol) and γ-irradiation at 13.83 ± 0.7 kGy did not induce morphological damages and yielded sterile and biocompatible PEG hydrogels potentially useful for clinical applications.

Physical and mechanical characterization of PLLA interference screws produced by two stage injection molding method

The purpose of this study was to produce and evaluate different mechanical, physical and in vitro cell culture characteristics of poly(L-lactic) acid (PLLA) interference screws. This work will focus on evaluating the effect of two important parameters on operation of these screws, first the tunnel diameter which is one of the most important parameters during the operation and second the thermal behavior, the main effective characteristic in production process. In this work, PLLA screws were produced by a two-stage injection molding machine. For mechanical assessment of the produced screws, Polyurethane rigid foam was used as cancellous bone and polypropylene rope as synthetic graft to simulate bone and ligament in real situation. Different tunnel diameters including 7-10 mm were evaluated for fixation strength. When the tunnel diameter was changed from 10 to 9 mm, the pull-out force has increased to about 12 %, which is probably due to the aforementioned frictional forces, however, by reducing the tunnel diameter to 8 and 7 mm, the pull-out force reduced to 16 and 50 % for 8 and 7 mm tunnel diameter, respectively. The minimum and maximum pull-out force was obtained 160.57 and 506.86 N for 7 and 9 mm tunnel diameters, respectively. For physicochemical assay, Fourier transform infrared spectroscopy (FTIR), degradation test and differential scanning calorimetry (DSC) were carried out. The crystallinity (Xc) of samples were decreased considerably from 64.3 % before injection to 32.95 % after injection with two different crystallographic forms α' and α. probably due to the fast cooling rate at room temperature. In addition, MTT and cell attachment assays were utilized by MG63 osteoblast cell line, to evaluate the cytotoxicity of the produced screws. The results revealed no cytotoxicity effect.

Effect of Microwave Treatment of Graphite on the Electrical Conductivity and Electrochemical Properties of Polyaniline/Graphene Oxide Composites

Polyaniline (PANI)/graphene oxide (GO) composites were synthesized via in situ polymerization of aniline in the presence of GO. The effect of microwave treatment of graphite on the electrical conductivity and electrochemical properties of PANI/GO composites was highlighted, and the morphology and microstructure were subsequently characterized using transmission electron microscopy, scanning electron microscopy, Fourier-transformed infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis. The results demonstrated that microwave treatment of graphite imparted a well-dispersed, highly ordered layered structure to the as-prepared GO, and in turn facilitated strong bonding between the GO and PANI nanosheets, which may be responsible for the improved electrical conductivity and electrochemical properties of the resulting PANI/GO composites. The desired PANI/GO composites possessed an electrical conductivity of 508 S/m, an areal capacitance of 172.8 mF/cm², and a retained capacitance of 87.4% after cycling, representing percentage increases of 102, 232, and 112, respectively, as a result of the microwave treatment of graphite. The resulting composites are promising electrode materials for high-performance and ecofriendly electrical energy storage devices.

Quantitative Determination of Fluorine Content in Blends of Polylactide (PLA)-Talc Using Near Infrared Spectroscopy

Near-infrared spectroscopy (NIRS) has been widely used for quantitative and/or qualitative determination of a wide range of matrices. The objective of this study was to develop a NIRS method for the quantitative determination of fluorine content in polylactide (PLA)-talc blends. A blending profile was obtained by mixing different amounts of PLA granules and talc powder. The calibration model was built correlating wet chemical data (alkali digestion method) and NIR spectra. Using FT (Fourier Transform)-NIR technique, a Partial Least Squares (PLS) regression model was set-up, in a concentration interval of 0 ppm of pure PLA to 800 ppm of pure talc. Fluorine content prediction (R²cal = 0.9498; standard error of calibration, SEC = 34.77; standard error of cross-validation, SECV = 46.94) was then externally validated by means of a further 15 independent samples (R²EX.V = 0.8955; root mean standard error of prediction, RMSEP = 61.08). A positive relationship between an inorganic component as fluorine and NIR signal has been evidenced, and used to obtain quantitative analytical information from the spectra.

Stimulatory effect of cobalt ions incorporated into calcium phosphate coatings on neovascularization in an in vivo intramuscular model in goats

Rapid vascularization of bone graft substitutes upon implantation is one of the most important challenges to overcome in order to achieve successful regeneration of large, critical-size bone defects. One strategy for stimulating vascularization during the regeneration process is to create a hypoxic microenvironment by either directly lowering the local oxygen tension, or by applying hypoxia-mimicking factors. Cells compensate for the hypoxic condition by releasing angiogenic factors leading to new blood vessel formation. In the present study, we explored the potential of cobalt ions (Co(2+)), known chemical mimickers of hypoxia, to stimulate vascularization within a bone graft substitute in vivo. To this end, Co(2+) ions were incorporated into calcium phosphate (CaPs) coatings deposited on poly(lactic acid) (PLA) particles with their effect on the formation of new blood vessels studied upon intramuscular implantation in goats. PLA particles and CaP-coated particles without Co(2+) ions served as controls. Pathological scoring of the inflammatory response following a 12-week implantation period showed no significant differences between the four types of materials. Based on histological and immunohistochemical analyses, both blood vessel area and number of blood vessels in CaP-coated PLA particles containing Co(2+) were higher than in the uncoated PLA particles and CaP-coated PLA particles without Co(2+). Analysis of blood vessel size distribution indicated abundant formation of small blood vessels in all the samples, while large blood vessels were predominantly found in PLA particles coated with CaP containing Co(2+) ions. The results of this study support the use of CaPs containing Co(2+) ions to enhance vascularization in vivo.

STATEMENT OF SIGNIFICANCE

In this work, we have investigated the potential of cobalt ions, incorporated into thin calcium phosphate (CaP) coatings that were deposited on particles of poly(lactic acid) (PLA), to induce neovascularization in vivo. Qualitative and quantitative histological and immunohistochemical analyses showed that both the number of blood vessels and the total blood vessel area were higher in CaP-coated PLA particles containing cobalt ions as compared to the uncoated PLA particles and CaP-coated PLA particles without the metallic additive. Furthermore, a wider distribution of blood vessel sizes, varying from very small to large vessels was specifically observed in samples containing cobalt ions. This in vivo study will significantly contribute to the existing knowledge on the use of bioinorganics, which are simple and inexpensive inorganic factors that can be used to control relevant biological process during tissue regeneration, such as vascularization. As such, we are convinced that this manuscript will be of interest to the readers of Acta Biomaterialia.

Monolithic calcium phosphate/poly(lactic acid) composite versus calcium phosphate-coated poly(lactic acid) for support of osteogenic differentiation of human mesenchymal stromal cells

Calcium phosphates (CaPs), extensively used synthetic bone graft substitutes, are often combined with other materials with the aim to overcome issues related to poor mechanical properties of most CaP ceramics. Thin ceramic coatings on metallic implants and polymer-ceramic composites are examples of such hybrid materials. Both the properties of the CaP used and the method of incorporation into a hybrid structure are determinant for the bioactivity of the final construct. In the present study, a monolithic composite comprising nano-sized CaP and poly(lactic acid) (PLA) and a CaP-coated PLA were comparatively investigated for their ability to support proliferation and osteogenic differentiation of bone marrow-derived human mesenchymal stromal cells (hMSCs). Both, the PLA/CaP composite, produced using physical mixing and extrusion and CaP-coated PLA, resulting from a biomimetic coating process at near-physiological conditions, supported proliferation of hMSCs with highest rates at PLA/CaP composite. Enzymatic alkaline phosphatase activity as well as the mRNA expression of bone morphogenetic protein-2, osteopontin and osteocalcin were higher on the composite and coated polymer as compared to the PLA control, while no significant differences were observed between the two methods of combining CaP and PLA. The results of this study confirmed the importance of CaP in osteogenic differentiation while the exact properties and the method of incorporation into the hybrid material played a less prominent role.

Recent advances in graphene/polyamide 6 composites: a review

This paper reviews recent years’ (2009–2015) advances in graphene/PA6 nanocomposites for the first time.

Space charge-induced unusually-high mobility of a solution-processed indium oxide thin film transistor with an ethylene glycol incorporated aluminum oxide gate dielectric

Undecomposed ethylene glycol residuals in solution processed aluminum oxide gate dielectric result in the frequency-dependent capacitance.

Core-Shell Structured Electro- and Magneto-Responsive Materials: Fabrication and Characteristics

Core-shell structured electrorheological (ER) and magnetorheological (MR) particles have attracted increasing interest owing to their outstanding field-responsive properties, including morphology, chemical and dispersion stability, and rheological characteristics of shear stress and yield stress. This study covers recent progress in the preparation of core-shell structured materials as well as their critical characteristics and advantages. Broad emphasises from the synthetic strategy of various core-shell particles to their feature behaviours in the magnetic and electric fields have been elaborated.