Orthogonal experimental design of titanium dioxide - Poly(methyl methacrylate) electrospun nanocomposite membranes for photocatalytic applications

An orthogonal experimental method was designed to assess the influence of the electrospinning processing parameters on average diameter and distribution of poly(methyl methacrylate) (PMMA) fibers. Based on the orthogonal experimental design analysis, electrospun TiO2-PMMA nanocomposites were processed with the optimal polymer processing conditions to obtain thin fibers with a high overall surface area. Further it was found that the average fiber diameter decreases from 2.0 ± 0.5 down to 1.2 ± 0.2 μm with increasing photocatalyst content. Moreover, the wettability of samples was independent of the filler amount, and showed strong hydrophobic behavior. Thermogravimetric analysis showed that for polymer solutions with concentrations higher than 10 wt%, there was a loss of the photocatalytic particles during processing, being more evident for the sample with 40 wt% particles present in the solution, with a loss of 8 wt% of ceramic particles. The immobilization of the TiO2 nanoparticles in the polymer fibers led to an increase of the thermal stability. The photocatalytic performance was assessed by using methylene blue (MB). The nanocomposite electrospun fiber membranes had a remarkable photocatalytic activity, especially the one with higher amount of TiO2, with all the MB dye being removed from the solution after 100 min, under UV. The orthogonal experimental design is an efficient way to save time and materials in the production of photocatalytic membranes

Ultra-stretchable MWCNT-Ecoflex piezoresistive sensors for human motion detection applications

Ultra-stretchable sensors are highly desirable for wearable electronic applications. In this paper, we manufactured self-standing piezoresistive sensors using a simple method based on blending multiwall carbon nanotubes (MWCNTs) with a stretchable elastomeric matrix (Ecoflex). The sensors showed a low electrical percolation threshold of 0.3 wt%, with an elastic modulus as soft as the human skin in the forearm and palm dermis. An increase in the cross-linking degree of the matrix from 17.43 ± 0.20 mol/m 3 up to 28.55 ± 2.07 mol/m 3 was observed with the incorporation of MWCNTs, revealing that the conductive filler is covalently bonded to the elastomeric matrix. The piezoresistive sensors showed high stretchability with an outstanding linearity between the resistance change with the applied strain, up to 200%, with significant sensitivity which is essential to use these sensors in human motion applications, e.g. finger bending, walking or speaking, and even detecting a hot liquid poured into a cup. Finally, MWCNT-Ecoflex sensors showed remarkable mechanical and electromechanical response features which are essential for wearable applications to monitor human motion with minimal discomfort

Reusable Flexible Concentric Electrodes Coated With a Conductive Graphene Ink for Electrotactile Stimulation

Electrotactile stimulation is a highly promising technique for providing sensory feedback information for prosthetics. To this aim, disposable electrodes which are predominantly used result in a high environmental and financial cost when used over a long period of time. In addition, disposable electrodes are limited in their size and configurations. This paper presents an alternative approach based on a 3D printed reusable flexible concentric electrode coated with a conductive graphene ink. Here, we have characterized the electrode and demonstrated its effective performance in electrotactile stimulation and sensory feedback for robotic prosthetic hands

Human skin interactive self-powered wearable piezoelectric bio-e-skin by electrospun poly-l-lactic acid nanofibers for non-invasive physiological signal monitoring

Flexible and wearable piezoelectric bio e-skin (PBio-e-skin) based on electrospun poly(l-lactic acid) PLLA nanofiber membrane is demonstrated for non-invasive human physiological signal monitoring and detecting dynamic tactile stimuli. The molecular orientations of the CO dipoles by electrospinning technique result in a longitudinal piezoelectric charge co-efficient (d 33 ) value of ∼(3 ± 1) pm V -1 realized by piezoresponse force microscopy, allowing the PBio-e-skin for pressure sensing applications. The robust mechanical strength (Young\u27s modulus ∼50 MPa) of nanofiber membrane ensures PBio-e-skin\u27s superior operational stability over 375000 cycles. Owing to the superior mechanosensitivity of ∼22 V N -1 , PBio-e-skin has the ability to measure subtle movement of muscle in the internal organs such as esophagus, trachea, motion of joints and arterial pressure by recognition of strains on human skin. This flexible and light weight PBio-e-skin precisely detects vital signs and provides important clinical insights without using any external power source. Eventually, the low cost, environmental friendly PBio-e-skin will have a huge impact in a broad range of applications including self-powered wearable health care systems, human-machine interfacing devices, artificial intelligence and prosthetic skin

Strong affinity of polysulfide intermediates to multi-functional binder for practical application in lithium-sulfur batteries

Binder, one of the most important battery components, plays a critical role in lithium-sulfur batteries. Poly(vinylidene difluoride) (PVDF), a commonly used binder in lithium-sulfur batteries, does not have a strong affinity to the intermediate polysulfides, however, leading to fast capacity fading with electrochemical cycling. Herein, copolymers of vinylidene difluoride with other monomers are used as multi-functional binders to enhance the electrochemical performance of lithium-sulfur batteries. Compared to the PVDF, the copolymer, poly(vinylidene difluoride-trifluoroethylene) (P(VDF-TRFE)) binder exhibits higher adhesion strength, less porosity, and stronger chemical interaction with polysulfides, which helps to keep the polysulfides within the cathode region, thereby improving the electrochemical performance of the lithium-sulfur battery. As a result, sulfur electrode with P(VDF-TRFE) binder delivered a high capacity of 801 mA h g-1 at 0.2 C after 100 cycles, which is nearly 80% higher capacity than the corresponding sulfur cathode with PVDF binder

Mechanical fatigue performance of PCL-chondroprogenitor constructs after cell culture under bioreactor mechanical stimulus

[EN] In tissue engineering of cartilage, polymeric scaffolds are implanted in the damaged tissue and subjected to repeated compression loading cycles. The possibility of failure due to mechanical fatigue has not been properly addressed in these scaffolds. Nevertheless, the macroporous scaffold is susceptible to failure after repeated loading-unloading cycles. This is related to inherent discontinuities in the material due to the micropore structure of the macro-pore walls that act as stress concentration points. In this work, chondrogenic precursor cells have been seeded in poly-epsilon-caprolactone (PCL) scaffolds with fibrin and some were submitted to free swelling culture and others to cyclic loading in a bioreactor. After cell culture, all the samples were analyzed for fatigue behavior under repeated loading-unloading cycles. Moreover, some components of the extracellular matrix (ECM) were identified. No differences were observed between samples undergoing free swelling or bioreactor loading conditions, neither respect to matrix components nor to mechanical performance to fatigue. The ECM did not achieve the desired preponderance of collagen type II over collagen type I which is considered the main characteristic of hyaline cartilage ECM. However, prediction in PCL with ECM constructs was possible up to 600 cycles, an enhanced performance when compared to previous works. PCL after cell culture presents an improved fatigue resistance, despite the fact that the measured elastic modulus at the first cycle was similar to PCL with poly(vinyl alcohol) samples. This finding suggests that fatigue analysis in tissue engineering constructs can provide additional information missed with traditional mechanical measurements.Contract grant sponsors: FEDER Funds; Programa Operacional Regional do Norte (ON.2 - O Novo Norte); Quadro de Referencia Estrategico Nacional (QREN); Fundo Europeu de Desenvolvimento Regional (FEDER); VI National R&D&i Plan 2008-2011; Iniciativa Ingenio 2010; Consolider Program; CIBER Actions; Instituto de Salud Carlos III with assistance from the European Regional Development FundPanadero, JA.; Sencadas, V.; Silva, SCM.; Ribeiro, C.; Correia, V.; Gama, FM.; Gómez Ribelles, JL.... (2016). Mechanical fatigue performance of PCL-chondroprogenitor constructs after cell culture under bioreactor mechanical stimulus. Journal of Biomedical Materials Research Part B Applied Biomaterials. 104(2):330-338. https://doi.org/10.1002/jbm.b.33386330338104

Spray Drying: An Overview

Spray drying is a well-known method of particle production which comprises the transformation of a fluid material into dried particles, taking advantage of a gaseous hot drying medium, with clear advantages for the fabrication of medical devices. In fact, it is quite common the production of microspheres and microcapsules designed for drug delivery systems. This review describes the different stages of the mechanism of the spray-drying process: atomization, droplet-to-particle conversion and particle collection. In particular, this work addresses the diversity of available atomizers, the drying kinetics and the importance of the configuration of the drying chamber, and the efficiency of the collection devices. The final properties of the dried products are influenced by a variety of factors, namely the spray dryer design, the feed characteristics and the processing parameters. The impact of those variables in optimizing both the spray-drying process and the synthesis of dried particles with desirable characteristics is discussed. The scalability of this manufacturing process in obtaining dried particles in submicron-to-micron scale favors a variety of applications within the food, chemical, polymeric, pharmaceutical, biotechnology and medical industries

Effect of the carbon nanotube surface characteristics on the conductivity and dielectric constant of carbon nanotube/poly(vinylidene fluoride) composites

Commercial multi-walled carbon nanotubes (CNT) were functionalized by oxidation with HNO3, to introduce oxygen-containing surface groups, and by thermal treatments at different temperatures for their selective removal. The obtained samples were characterized by adsorption of N2 at -196°C, temperature-programmed desorption and determination of pH at the point of zero charge. CNT/poly(vinylidene fluoride) composites were prepared using the above CNT samples, with different filler fractions up to 1 wt%. It was found that oxidation reduced composite conductivity for a given concentration, shifted the percolation threshold to higher concentrations, and had no significant effect in the dielectric response

Single step fabrication of antimicrobial fibre mats from a bioengineered protein-based polymer

Producción CientíficaGenetically engineered protein polymers functionalized with bioactive domains have potential as multifunctional versatile materials for biomedical use. The present work describes the fabrication and characterisation of antimicrobial fibre mats comprising the antimicrobial elastin-like recombinamer (ELR) CM4-A200. The CM4-A200 protein polymer derives from the genetic fusion of the ABP-CM4 antimicrobial peptide from Bombyx mori with 200 repetitions of the pentamer VPAVG. This is the first report on non-crosslinked fibre mats fabricated with an antimicrobial ELR stable in solution. Thermal gravimetric analysis of CM4-A200 fibre mats shows one single degradation step at temperatures above 300 °C, with fibres displaying a higher thermal degradation activation. The electrospun CM4-A200 fibres display high antimicrobial activity against Gram-positive and Gram-negative bacteria with no detectable cytotoxic effects against normal human skin fibroblasts and keratinocytes, revealing the great potential of these polymers for the fabrication of biomedical materials.2018-09-10Ministerio de Economía, Industria y Competitividad (Projects MAT2013-41723-R, MAT2013- 42473-R and MAT2012-38043)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA244U13, VA313U14

Tailoring porous structure of ferroelectric poly(vinylidene fluoride-trifluoroethylene) by controlling solvent/polymer ratio and solvent evaporation rate

Ferroelectric macroporous poly(vinylidene fluoride-trifluoroethylene) membranes have been produced by isothermal crystallization from the solution at different temperatures starting from different diluted solutions of the co-polymer in dimethylformamide. In this way pore architecture, consisting in interconnected spherical pores can be obtained. The mechanism and kinetics of solvent evaporation was investigated and related to the evolution of the polymer microstructure. The mechanism underlying the pattern formation has been discussed on the light of the Flory-Huggins (FH) lattice theory, grain boundary effects and the Cahn-Hilliard equation for mass conservation systems. It was also observed that the temperature or initial concentration of the crystallization process does not affect the phase, ferroelectric transition temperature or the melting temperature of the polymer.The authors thank the Portuguese Foundation for Science and Technology (FCT) Grants PTDC/CTM-NAN/112574/2009, PTDC/CTM/73030/2006, PTDC/CTM/69316/2006 and NANO/NMed-SD/0156/2007. V.F., C.M.C. and V.S. thank the FCT for the SFRH/BD/44289/2008, SFRH/BD/68499/2010, SFRH/BPD/63148/2009 grants, respectively. JLGR acknowledge the funding from the Programa de Apoyo a la Investigacion y Desarrollo (PAID-00-09) of the Universidad Politecnica de Valencia for a short stay in Universidade do Minho, Braga, the support of the Spanish Ministry of Science through project No. MAT2010-21611-C03-01 (including the FEDER financial support) and funding for research in the field of Regenerative Medicine through the collaboration agreement from the Conselleria de Sanidad (Generalitat Valenciana), and the Institute de Salud Carlos III (Ministry of Science and Innovation). The authors wish also thank the CeNTI - Centre for Nanotechnology and Smart Materials, Rua Fernando Mesquita, 2782, 4760-034 Vila Nova de Famalicao, Portugal for allowing the use of some experimental equipment.California, A.; Cardoso, VF.; Costa, CM.; Sencadas, V.; Botelho, G.; Gómez Ribelles, JL.; Lanceros-Mendez, S. (2011). Tailoring porous structure of ferroelectric poly(vinylidene fluoride-trifluoroethylene) by controlling solvent/polymer ratio and solvent evaporation rate. EUROPEAN POLYMER JOURNAL. 47(12):2442-2450. https://doi.org/10.1016/j.eurpolymj.2011.10.005S24422450471