Fabrication of Architectured Biomaterials by Multilayer Co-Extrusion and Additive Manufacturing

Tissue engineering benefits from advances in 3D printing and multi-material assembly to attain certain functional benefits over existing man-made materials. Multilayered tissue engineering constructs might unlock a unique combination of properties, but their fabrication remains challenging. Herein, a facile process is reported to manufacture biomaterials with an engineered multilayer architecture, via a combination of co-extrusion and 3D printing. Polymer filaments containing 5, 17, or 129 alternating layers of poly(lactic acid)/thermoplastic polyurethane (PLA/TPU) are produced, and explored for their use in fused deposition modeling (FDM) to fabricate scaffolds for cardiomyocyte culture. The co-extruded filaments exhibit a layered architecture in their cross-section with a continuous interface, and the integrity and alignment of the layers are preserved after 3D printing. The 17 alternating layers PLA/TPU composites exhibit excellent mechanical properties. It is envisaged that the multilayered architecture of the fabricated scaffolds can be beneficial for aligning cardiomyocytes in culture. It is found that the 17 alternating layers PLA/TPU significantly improve cardiomyocyte morphology and functionality compared to single phase materials. It is believed that this biomaterials fabrication scheme, combining a top-down and bottom-up approach, offers tremendous flexibility in producing a broad class of novel-architectured materials with tunable structural design for tissue engineering applications and beyond.     

Dual-Atom-Site Sn-Cu/C3N4 Photocatalyst Selectively Produces Formaldehyde from CO2 Reduction

The solar-driven catalytic reduction of CO₂ to value-added chemicals is under intensive investigation. The reaction pathway via *OCHO intermediate (involving CO₂ adsorbed through O-binding) usually leads to the two-electron transfer product of HCOOH. Herein, a single-atom catalyst with dual-atom-sites featuring neighboring Sn(II) and Cu(I) centers embedded in C₃N₄ framework is developed and characterized, which markedly promotes the production of HCHO via four-electron transfer through the *OCHO pathway. The optimized catalyst achieves a high HCHO productivity of 259.1 µmol g⁻¹ and a selectivity of 61% after 24 h irradiation, which is ascribed to the synergic role of the neighboring Sn(II)–Cu(I) dual-atom sites that stabilize the target intermediates for HCHO production. Moreover, adsorbed *HCHO intermediate is detected by in situ Fourier transform infrared spectroscopy (CO stretches at 1637 cm⁻¹). This study provides a unique example that controls the selectivity of the multi-electron transfer mechanisms of CO₂ photoconversion using heteronuclear dual-atom-site catalyst to generate an uncommon product (HCHO) of CO₂ reduction.     

Weakly-Supervised Action Localization,and Action Recognition Using Global–Local Attention of 3D CNN

International Journal of Computer Vision - 3D convolutional neural network (3D CNN) captures spatial and temporal information on 3D data such as video sequences. However, due to the convolution and...     

Automated classification of patients with coronary artery disease using grayscale features from left ventricle echocardiographic images

Coronary Artery Disease (CAD), caused by the buildup of plaque on the inside of the coronary arteries, has a high mortality rate. To efficiently detect this condition from echocardiography images, with lesser inter-observer variability and visual interpretation errors, computer based data mining techniques may be exploited. We have developed and presented one such technique in this paper for the classification of normal and CAD affected cases. A multitude of grayscale features (fractal dimension, entropies based on the higher order spectra, features based on image texture and local binary patterns, and wavelet based features) were extracted from echocardiography images belonging to a huge database of 400 normal cases and 400 CAD patients. Only the features that had good discriminating capability were selected using t-test. Several combinations of the resultant significant features were used to evaluate many supervised classifiers to find the combination that presents a good accuracy. We observed that the Gaussian Mixture Model (GMM) classifier trained with a feature subset made up of nine significant features presented the highest accuracy, sensitivity, specificity, and positive predictive value of 100%. We have also developed a novel, highly discriminative HeartIndex, which is a single number that is calculated from the combination of the features, in order to objectively classify the images from either of the two classes. Such an index allows for an easier implementation of the technique for automated CAD detection in the computers in hospitals and clinics.     

Biomechanical studies on aliphatic physically crosslinked poly(urethane urea) for blood contact applications

Hydrophobic and physically crosslinked (virtually crosslinked through hydrogen bonding) aliphatic poly(urethane urea)s were developed and characterized for its biomechanical properties. The aging under induced-stress (bend samples) condition reveals resistance of poly(urethane urea) to environmental stress corrosion cracking (ESC) in hydrolytic media, Ringer's solution and phosphate buffered saline at 50 degrees C. The strain-induced (20% tensile strain) and aged polymer in hydrolytic enzyme medium, papain and in buffer reveals increase of elastic modulus in papain enzyme and papain buffer. The increase of elastic modulus is attributed to unidirectional reorganisation of chains under continually strained conditions. The polymer exposed in boiling alcoholic potassium hydroxide solution (accelerated hydrolytic chemical degradation) reveals no degradation. A comparative evaluation of poly(ether urethane urea)s reveals inferior properties. Poly(ether urethane urea)s polymer undergo hydrolytic degradation in boiling alcoholic potassium hydroxide solution. The candidate poly(urethane urea) HFL 18-PUU is more promising elastomer for long-term biomechanically sensitive blood contact applications such as heart valve and blood pump diaphragm of left ventricular assist device.     

Enrichment of piezoelectric properties in Nb5+doped (0.94) (Na0.5Bi0.5)TiO3–(0.06) BaTiO3 ceramics across morphotropic phase boundary region

Lead-free piezoelectric compounds (0.94)(Na_0.5Bi_0.5)TiO₃–(0.06) BaTiO₃ [NBBT (94/06)]?+?x wt.% Nb⁵⁺ (x?=?0%, 1%, 1.5%, 2%, and 2.5%) were synthesized by the solid-state reaction route and these powders were pelletized and sintered for dielectric and piezoelectric characterization. The phase coexistence Monoclinic (Cc)?+?Rhombohedral (R3c) was affirmed using X-ray Powder diffraction analysis. The structural properties like cell parameters and space group of the synthesized ceramics were investigated by the Rietveld refinement analysis. The surface morphology and grain size of the fractured ceramics were explored using SEM imaging technique. The dielectric properties for all the ratios of NBBT (94/06) ceramics were examined using LCR meter. The piezoelectric coefficients such as d₃₃ and g₃₃ of Nb-doped NBBT (94/06) ceramics were investigated. The saturation polarization (P_s) and remanent polarization (P_r) were exhibited from the P–E hysteresis loop analysis at room temperature. The appropriate addition of Nb⁵⁺ (x?=?1.5%) in NBBT (94/06) material demonstrates eminent dielectric constant and piezoelectric coefficient d₃₃ than other wt.% of Nb. The replacement of Ti⁴⁺ with higher radius cations Nb⁵⁺ in B-site of ABO₃ composes tilting of polar BO₆ octahedra resulting in rhombohedra distortion (RD) (90° ? α), in addition, the polarizability of ions and various valance states of B-site cations could be responsible for RD (90° ? α) ensuing relatively high dielectric constant and piezoelectricity.

     

Improved mechanical and thermal properties of spent coffee bean particulate reinforced poly(propylene carbonate) composites

Using biodegradable polypropylene carbonate (PPC) as the polymer matrix and 5 to 25?wt% content of spent coffee bean powder (SCBP) as filler, completely biodegradable composite films of PPC/SCBP were prepared. These composite films were characterized by polarized optical microscopy (POM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis, differential scanning calorimetry (DSC), and tensile tests. The POM images indicated the uniform distribution of the SCBP in the composites. The FTIR spectra indicated that the PPC structure was retained by the composite films. The XRD analysis found that the composite films had lower crystallinity than the PPC due to the presence of amorphous hemicellulose containing SCBP. A significant enhancement in thermal stability of the filler reinforced composite was noticed which was more than 30% of the PPC matrix due to the presence of polyphenols in SCBP. A maximum increase of 35% of tensile strength was observed with the addition of 20?wt% SCBP filled composite films. These biodegradable composite films with higher thermal stability and tensile strength can be considered for packaging applications.     

Effect of nano ribbons formed by the amide segment on the solvent resistivity of segmented block copolymers based on polystyrene

A segmented block copolymer is synthesized using dihydroxy terminated polystyrene (PSt) (M_W = 2,500 g/mol) and crystallizable amide segments. PSt length in the copolymer is varied from 2,500 to 10,000 g/mol using dimethylterephthalate (T). Amide segment is synthesized in situ using diamine‐diamide 6X6 (X = A or T) (synthesized by dimethylterepthalate [T], adipic acid [A], and hexamethylenediamine [6]) and T. This work is to modify the high T_g amorphous PSt to a semicrystalline copolymers (‐(PSt‐T)_y‐6X6‐T‐)‐_n). These copolymers have a very high inherent viscosity and depending on the amide concentration, the melting temperature of the polymers was ranged between 129°C and 248°C. The crystallinity of the amide segments is up to 75%. The AFM analysis showed the presence of crystalline ribbons with a high aspect ratio. All the polymers show single stage decomposition temperature centered around 420°C. The solvent resistivity of these materials is very high even at a low concentration of (5 wt%) amide content. POLYM. ENG. SCI., 58:361–368, 2018. © 2017 Society of Plastics Engineers     

Interference Avoidance through Pilot‐Based Spectrum Sensing Algorithm in Overlaid Femtocell Networks

Co‐channel interference between macro–femtocell networks is an unresolved problem, due to the frequency reuse phenomenon. To mitigate such interference, a secondary femtocell must acquire channel‐state knowledge about a co‐channel macrocell user and accordingly condition the maximum transmit power of femtocell user. This paper proposes a pilot‐based spectrum sensing (PSS) algorithm for overlaid femtocell networks to sense the presence of a macrocell user over a channel of interest. The PSS algorithm senses the pilot tones in the received signal through the power level and the correlation metric comparisons between the received signal and the local reference pilots. On ensuring the existence of a co‐channel macrocell user, the maximum transmit power of the corresponding femtocell user is optimized so as to avoid interference. Time and frequency offsets are carefully handled in our proposal. Simulation results show that the PSS algorithm outperforms existing sensing techniques, even at poor received signal quality. It requires less sensing time and provides better detection probability over existing techniques.     

Influence of PVP on Bi25FeO40 microcubes for Supercapacitors and Dye-Sensitized Solar Cells applications

Journal of Materials Science: Materials in Electronics - Polyvinylpyrrolidone (PVP)-assisted Bi25FeO40 microcubes have been synthesized through hydrothermal technique and the effect of morphology...