Biocompatibility and adsorption properties of hydrogels obtained by graft polymerization of acrylic acid on cellulose from rice hulls

Hydrogels constitute a group of cross-linked polymeric materials with the capability of swelling and retaining large amounts of water without dissolving. In this work, the hydrogels were obtained by grafting the acrylic acid on cellulose from rice hulls and cross-linking it with glycerol, ethylene glycol, and polyethylene glycol (M_w?=?200 and 10,000 g mol^?1). The samples were characterized using IR and Raman spectroscopy, the absence of the bands at 1636 and 1614 cm^?1 (in IR) and at 1659 and 1637 cm^?1 (in Raman), in the spectra of grafted cellulose and assigned to ν(C=C), indicated the polymerization process and the absence of the monomer residual. The cross-linking process was verified by the appearance of bands at 1090 cm^?1 (IR) and 996 cm^?1 (Raman), attributed to ν(C–O–C). Thermogravimetric analysis showed that the cross-linked sample with glycerol presented the lowest thermal stability. The molecular mass of CDClCC-g-AA was 55.56?±?5.21 kDa with an R² of 0.9741 and the CDClCC average particle size of 694 nm. The topography and the average roughness of the samples were obtained by atomic force microscopy and the samples that were cross-linked with the polyethylene glycol presented greater roughness. The degree of swelling was lower in the sample cross-linked with ethylene glycol, which was related to its higher degree of cross-linking. Finally, the biocompatibility of the samples was studied by analyzing the toxic effect of the samples on human embryonic kidney cells, where results showed that samples cross-linked with ethylene glycol were non-toxic.     

Pillar[5]arene-stabilized Plasmonic Nanoparticles as Selective SERS Sensors

We present here a simple procedure for the surface modification of plasmonic nanoparticles (NPs) with a cationic water-soluble ammonium pillar[5]arene (AP[5]A) in order to create selective surface-enhanced Raman scattering (SERS) spectroscopy based sensors. The strategy is based on a ligand exchange reaction between the AP[5]A and the stabilizing agent of the as-prepared plasmonic NPs. The approach could be applied to plasmonic nanoparticles either negatively charged, stabilized by citrate ions (Au spheres) or positively charged, stabilized by cetyltrimethylammonium bromide (Au and Au@Ag nanorods). The SERS performance of all systems was studied as a function of NP size and excitation laser line by using an analyte with no affinity towards the metal surface such as pyrene. The analytical enhancement factor (AEF) for the different systems was estimated between 0.55×10⁴ and 1.49×10⁵. Finally the synergistic effect of combining supramolecular chemistry and plasmonic NPs is demonstrated through SERS-based detection, in aqueous media, of molecules with no affinity towards a bare plasmonic substrate such as the contaminant pyrene or the biomolecule pyocyanin with nanomolar limit of detection.     

Influence of the soft segment nature on the thermomechanical behavior of shape memory polyurethanes

Shape‐memory polyurethanes (SMPUs) represent a highly interesting class of materials due to their applications in different sectors such as biomedical, textile, and aerospace. Moreover, it is possible to synthesize a variety of polyurethanes with different molecular architectures just choosing properly the chemical structure of their components. In this work, it is described the influence of the soft segment on the thermomechanical properties and shape memory behavior of shape memory polyurethanes. The synthesis, based on two‐step polymerization, was prepared by two different soft segments: poly(oxytetramethylene) glycol (PTMG) or poly(ethylene glycol) (PEG). Depending on the molecular architecture achieved, the materials present different properties that were studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Furthermore, the shape memory response of thermally activated SMPUs is determined qualitative and quantitatively by visually monitoring the shape recovery process and by thermomechanical analysis (TMA), respectively. All developed compositions have shown good shape memory behavior, with recovery ratios higher than 99.8%. POLYM. ENG. SCI., 58:238–244, 2018. © 2017 Society of Plastics Engineers     

Spraying Cellulose Nanofibrils for Improvement of Tensile and Barrier Properties of Writing & Printing (W&P) Paper

An experimental spray coater was used to coat writing and printing (W&P) paper substrate with cellulose nanofibrils (CNFs) suspensions. The effects of spraying variables (i.e. concentration of suspension, spray pressure, distance and time of spray) on the coated sheets were analyzed in terms of the tensile strength, water vapor transmission rate (WVTR), and oxygen transmission rate (OTR). Basis weight and the thickness of coated layers in the different treatments were measured. In addition, image analysis of the microstructure examined the coating adhesion. The WVTR of the papers decreased, while tensile strength increased with one layer of CNF coating. The OTR was not changed with the CNF coating. The tensile strength and microstructure images of the coated papers indicate good adhesion between the CNF coating and the paper substrate when using the spray coater.     

Fabrication of citric acid crosslinked β‐cyclodextrin/hydroxyethylcellulose hydrogel films for controlled delivery of poorly soluble drugs

β‐cyclodextrin grafted hydroxyethylcellulose (βCD‐g‐HEC) hydrogel films were prepared for the controlled release of poorly soluble model drug (ketoconazole) using citric acid as crosslinking agent. The active βCD and carboxyl content of the hydrogel films were determined by phenolphthalein assay and acid–base titration. The films were characterized by solid state ¹³C NMR, ATR–FTIR, thermogravimetric analysis, and differential scanning calorimetric, and analyzed for tensile strength, swelling ratio, drug loading, release, hemocompatibility, in vitro cytotoxicity, and implantation test. An increase in the concentration of βCD in feed increased the active βCD content of the hydrogel films but reduced their extent of interpolymer crosslinking. The βCD‐g‐HEC hydrogel films with high active βCD content showed maximum drug loading whereas those with high crosslinking density were capable of controlling the drug release for long duration. Hemolysis assay and in vitro cytotoxicity study revealed the biocompatible nature of the hydrogel films whereas implantation test indicated their minimal inflammatory effect. From the overall results, βCD‐g‐HEC hydrogel films were found to be better alternative to the previously reported βCD‐HPMC and βCD‐CMC hydrogel films for enhanced loading and long‐term release, respectively, of the poorly soluble drugs. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46452.     

Vis-Near-Infrared Photodetectors Based on Methyl Ammonium Lead Iodide Thin Films by Pulsed Laser Deposition

Organic–inorganic hybrid perovskite materials are considered as promising candidates for emerging thin-film photodetectors. In this work, we discuss the application of the CH₃NH₃PbI₃ thin films by pulsed laser deposition for photodetection applications. With this method, we obtained good perovskite film coverage on fluorine-doped tin oxide-coated substrates and observed wel- developed grains. The films showed no sign of degradation over several months of testing. We investigated the surface morphology and surface roughness of the films by field emission scanning electron microscopy and atomic force microscopy. The optical response of the films was studied using ultraviolet–visible and photoluminescence spectroscopy. We carried out a study on the solar and infrared photodetection of CH₃NH₃PbI₃ thin films. The values of the responsivity, sensitivity, external quantum efficiency and specific detectivity under 1 sun illumination and 0.7 V bias were 105.4 A/W, 1.9, 2.38 × 10⁴% and 1.5 × 10¹² Jones, respectively.     

Internal inversion of thin-walled tubes using a die: experimental and theoretical investigation

The design of sound double-walled tubular parts by external inversion using a die is presently well established. Major parameters are identified, the influence of lubrication is sufficiently well understood and the typical modes of deformation that may occur during the forming process are fully characterized. In contrast to external inversion, there are almost no published works that comprehensively cover the conception of double-walled tubular parts by internal inversion using a die.This paper draws from fundamental research on the internal inversion of thin-walled tubes using a die to the establishment of formability diagrams in terms of the major process parameters. Fundamental research is based on a comprehensive theoretical and experimental investigation of a wide range of subjects, such as: development of plastic instability modes (local buckling), thickening of the tube-wall and occurrence of wrinkling phenomena at the free curved end of the inwardly inverted tubes. The influence of the frictional conditions prevailing at the contact interface between the tube and the die is also examined. The theoretical investigation is supported by numerical predictions based on the finite element flow formulation and the overall methodology is assessed by means of experimental tests on industrial Al6060 Aluminium alloy tubes (annealed and naturally aged) under laboratory-controlled conditions.     

Wall position and thickness estimation from sequences of echocardiographic images

Presents a new method for endocardial (inner) and epicardial (outer) contour estimation from sequences of echocardiographic images. The framework herein introduced is fine-tuned for parasternal short axis views at the papillary muscle level. The underlying model is probabilistic; it captures the relevant features of the image generation physical mechanisms and of the heart morphology. Contour sequences are assumed to be two-dimensional noncausal first-order Markov random processes; each variable has a spatial index and a temporal index. The image pixels are modeled as Rayleigh distributed random variables with means depending on their positions (inside endocardium, between endocardium and pericardium, or outside pericardium). The complete probabilistic model is built under the Bayesian framework. As estimation criterion the maximum a posteriori (MAP) is adopted. To solve the optimization problem, one is led to (joint estimation of contours and distributions' parameters), the authors introduce an algorithm herein named iterative multigrid dynamic programming (IMDP). It is a fully data-driven scheme with no ad-hoc parameters. The method is implemented on an ordinary workstation, leading to computation times compatible with operational use. Experiments with simulated and real images are presented.