Fabrication and characterization of chitosan/kefiran electrospun nanofibers for tissue engineering applications

Chitosan (CS)-based nanofibrous scaffolds are very promising in tissue engineering applications. However, electrospinning of CS is not possible unless using toxic solvents such as trifluoroacetic acid or by blending with other polymers. In the present study, we investigated CS-based nanofibers' fabrication by blending it with kefiran as a natural polysaccharide. A series of solutions with various CS to kefiran ratios were prepared and underwent electrospinning. The effects of main process parameters, including applied voltage and needle tip-to-collector distance on nanofibers' diameter and morphology, were also studied. Nanofibers containing 80% CS and 20% Kefiran with an average diameter of 81 ± 17 nm were successfully electrospun. Thermogravimetric analysis indicated the presence of both polymers in blend nanofibers. The diameter of CS/kefiran nanofibers increased with enhanced applied voltage, while needle tip-to-collector distance did not significantly affect the mean diameters. Appropriate viability of l929 cells on the obtained scaffolds was demonstrated utilizing Alamar blue assay. Also, cell attachment onto the fiber surface was confirmed by scanning electron microscopy. Results indicated that CS/kefiran nanofibrous scaffolds would be promising for tissue engineering applications.     

Mechanical properties of porous MgO substrates for membrane applications

Advanced design concepts for the application of oxygen transport ceramic membranes are based on thin layers supported by porous substrates. One suitable support material in this respect is porous MgO. However, a careful consideration of the mechanical stability is required to warrant long term performance and reliability under application relevant thermo-mechanical loads. The current work summarizes the effect of the sintering conditions on porosity and mechanical properties and gives elastic modulus and fracture stress as a function of temperature. An enhancement of the strength by the addition of boehmite to MgO was tested. Elastic moduli are determined and compared as obtained by indentation and bending tests. With respect to fracture, specimens in planar geometry are investigated using ring-on-ring bending tests; tubes are tested using an O-ring set-up. Fracture stresses are statistically analyzed. The obtained mechanical parameters are compared to that of other potential porous substrate materials.     

Mechanical properties and biodegradability of green composites based on biodegradable polyesters and lyocell fabric

Green composites composed of regenerated cellulose (lyocell) fabric and biodegradable polyesters [poly(3‐hydroxybutyrate‐co‐3‐hydroxyvarelate) (PHBV), poly(butylene succinate) (PBS), and poly(lactic acid) (PLA)] were prepared by compression‐molding method. The tensile moduli and strength of all the biodegradable polyester/lyocell composites increased with increasing fiber content. When the obtained PLA/lyocell composites were annealed at 100°C for 3 h, the tensile strength and moduli were lowered despite the increase of degree of crystallization of the PLA component. The SEM observation of the composites revealed that the surface of the annealed composite has many cracks caused by the shrinkage of the PLA adhered to lyocell fabric. Multilayered PLA/lyocell laminate composites showed considerably higher Izod impact strength than PLA. As a result of the soil viral test, although the order of higher weight loss for the single substance was lyocell > PHBV > PBS > PLA, the biodegradability of the green composites did not reflect the order of a single substance because of the structural defect of the composite. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3857–3863, 2004     

Mechanical properties of crosslinked polyurethanes

Stress–strain and stress–relaxation behavior of polyurethane elastomers based on poly(ethylene adipate), poly(ethylene maleate), polyethylene glycol, and 4,4′-diphenylmethane diisocyanate (MDI) have been studied. The elastomers were crosslinked by an excess of MDI and by dicumyl peroxide (DiCup); the latter was supposed to form additional crosslinks on the unsaturated bonds. The determined values of Young's modulus, Mooney-Rivlin elastic parameters C₁ and C₂, relaxation moduli E(10 sec) and E(100 sec), as well as relaxation speed were used to estimate the effect of MDI- and DiCup-formed crosslinks on the mechanical behavior of polyurethanes. It was found that while the elastomers crosslinked by MDI only apparently displayed viscoelastic properties, the polyurethanes additionally crosslinked by DiCup exhibited more elastic behavior. The results obtained were explained on the basis of changes in the amount of secondary bonding due to the additional network junctions formed by DiCup at nonpolar groups.     

Mechanical properties of poly lactic acid composite films reinforced with wet milled jute nanofibers

In the present study, waste jute fibers generated in textile industries, were wet pulverized to the scale of nanofibers of 50 nm diameter using high energy planetary ball milling for 3 h. The presence of water during wet pulverization found to reduce the rising temperature of mill, which prevented sticking of nanofibers on the mill wall and resulted in unimodal size distribution. In the subsequent stage, 1, 5, and 10 wt% of jute nanofibers were incorporated in poly(lactic acid) (PLA) matrix to prepare nanocomposite films by solvent casting. The reinforcement of nanofibers was investigated from the improvements in mechanical properties based on tensile tests, dynamic mechanical analysis, and differential scanning calorimetry. The maximum improvement was observed in case of 5 wt% nanocomposite film where initial modulus and tensile strength increased by 217.30% and 170.59%, respectively as compared to neat PLA film. These improvements are attributed to the increased interaction between nanofibers and matrix as well as to the increased crystallinity of PLA in composites. The improvements in load bearing capacity of nanocomposite films were significant at 60°C than 35°C, which showed ability of jute nanofibers to improve the softening temperature of PLA matrix. In the end, experimental results of Young's modulus were compared with predicted modulus of mechanical models. A good level of agreement was observed up to 5 wt% loading of jute nanofibers. POLYM. COMPOS., 34:2133–2141, 2013. © 2013 Society of Plastics Engineers     

Mechanical properties of poly(ether-ether-ketone) for engineering applications

An outline of the characteristics of PEEK and the versatility of its compositional forms (micro and macro composites) are given to illustrate its wide potential for success in engineering applications. Although it is necessary to have particular tabulations of mechanical properties for engineering design, these are seldom available and consequently it is argued that an understanding of stiffness, toughness and strength properties are required to fully exploit available manufacturer's data and thus develop the full potential of PEEK and its composites. Stiffness characteristics are considered in terms of a modulus function which is dependent on time under load and temperature. In its composite forms, whether reinforced with short or continuous fibres, stiffness anistropy can be both considerable and complex, but some empirical ground-rules are apparent. For continuous fibre composites even in the form of complex lay-ups, it is also possible to attempt some stiffness prediction from certain pseudo-elastic constants. Toughness of PEEK and its composites is described in terms of both comparative and intrinsic properties. Instrumented falling weight impact data, particularly as a function of temperature enable some insight into ductile-brittle transitions for the unreinforced material, but crack initiation and crack propagation processes for the various fibre reinforced forms. Intrinsic toughness is described in terms of linear elastic fracture mechanics theory. Strength properties are described for static and dynamic loading configurations. In particular, PEEK and its composites are evaluated for increasing test severities for strength characteristics; stress concentration, loading form and test temperature are considered.     

Mechanical and physical properties of epoxy composites reinforced by vapor grown carbon nanofibers

Epoxy/vapor grown carbon nanofiber composites (VGCF) with different proportions of VGCF were fabricated by the in situ process.The VGCFs were well dispersed in both of the low and high viscosity epoxy matrices, although occasional small aggregates were observed in a high viscosity epoxy of 20 wt.%. The dynamic mechanical behavior of the nanocomposite sheets was studied. The storage modulus and the glass transition temperature (T_g) of the polymer were increased by the incorporation of VGCFs.The electrical and mechanical properties of the epoxy-VGCFs nanocomposite sheets with different weight percentages of VGCFs were discussed. The results were that both had maximum tensile strength and Young’s modulus at 5 wt.% for both materials and reduced the fracture strain with increasing filler content. The electrical resistivity was decreased with the addition of filler content. Mechanical, electrical and thermal properties of low viscosity epoxy composites were resulted better than that of the high viscosity composites.     

Ultrathin electrospun PANI nanofibers for neuronal tissue engineering

N‐(4‐aminophenyl)aniline oxidative polymerization is optimized to produce polyaniline (PANI) free from carcinogenic and/or polluting coproducts. The resulting polymer is electrospun using polymethyl methacrylate (PMMA) as the supporting polymer, with different weight ratios (1:0, 4:1, 3:1, 2:1, 1:1, and 0.5:1 w/w PANI/PMMA). By rinsing with a selective solvent, PMMA is removed while maintaining the fibrous morphology. Ultrathin (65 ± 14 nm) and defect‐free PANI nanofiber mats are obtained for the blend containing a high relative content of PANI (2:1 w/w, namely F_2:1). Two different solvents are tested to remove PMMA, namely acetone and isopropanol, the former giving better results, as highlighted by infrared spectroscopy (FTIR). X‐ray diffraction (XRD) demonstrates that the electrospun PANI is amorphous. The thin fiber mats are robust and sterilization both by autoclave and UV irradiation can be carried out. UV irradiation is preferred since no modification of the fibrous morphology is detectable. In vitro biocompatibility of the electrospun F_2:1 fibers has been evaluated with SH‐SY5Y neuronal‐like cells. Indirect cytocompatibility tests show that no cytotoxic leachable is released by the electrospun mats at both short and longer times, while direct cytocompatibility investigations indicate that only F_2:1 fibers washed in isopropanol do not reduce cell proliferation rate with respect to controls on tissue culture plates. Globally, these results suggest that the proposed electrospun nanostructures are promising materials for neuronal tissue engineering. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43885.     

Electrospun biodegradable nanofibers scaffolds for bone tissue engineering

Many polymeric materials have been developed and introduced for bone regeneration. Especially, their nanofibrous forms are mostly applied for artificial extracellular matrices. Polymeric materials in their nanofibrous form show some potent properties such as high surface‐to‐volume ratio, tunable porosity, and ease of surface functionalization. Benefiting from the properties of their main polymer and additives, they can provide new opportunities for cell seeding, proliferation, and new 3D‐tissue formation. This article focuses on most cited polymeric nanofibrous scaffolds fabricated by electrospinning and recent achievements. They were divided into two main categories: natural (collagen, silk, keratin, gelatin, chitosan, and alginate) and synthetic (e.g., polycaprolactone, polylactic acid, and polyglycolic acid) polymers. The role of several additives like hydroxyapatite, bone morphogenetic proteins (BMPs), tricalcium phosphate, and collagen type I in improving the adhesion, differentiation, and tissue formation of stem cells were discussed. Finally, the osteogenic capacity and ability of nanofibrous scaffolds to support the growth of clinically relevant bone tissue were briefly studied. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42883.     

Polymers for medical and tissue engineering applications

Recent decades have seen great advancements in medical research into materials, both natural and synthetic, that facilitate the repair and regeneration of compromised tissues through the delivery and support of cells and/or biomolecules. Biocompatible polymeric materials have become the most heavily investigated materials used for such purposes. Naturally‐occurring and synthetic polymers, including their various composites and blends, have been successful in a range of medical applications, proving to be particularly suitable for tissue engineering (TE) approaches. The increasing advances in polymeric biomaterial research combined with the developments in manufacturing techniques have expanded capabilities in tissue engineering and other medical applications of these materials. This review will present an overview of the major classes of polymeric biomaterials, highlight their key properties, advantages, limitations and discuss their applications. © 2014 Society of Chemical Industry     

Mechanical and electrical properties of carbon nanofibers reinforced aluminum nitride composites prepared by plasma activated sintering

High density carbon nanofibers (CNFs) reinforced aluminum nitride (AlN) composites were successfully fabricated by plasma activated sintering (PAS) method. The effects of CNFs on the microstructure, mechanical and electrical properties of the AlN composites were investigated. The experimental results showed that the grain growth of AlN was significantly inhibited by the CNFs. With 2 wt.% CNFs added into the composites, the fracture toughness and flexural strength were increased, respectively to 5.03 MPa m^1/2 and 354 MPa, which were 20.9% and 13.4% higher than those of monolithic AlN. The main toughening mechanisms were CNFs pullout and bridging, and the main reason for the improvements in strength should be the fine-grain-size effect caused by the CNFs. The DC conductivity of the composites was effectively enhanced through the addition of CNFs, and showed a typical percolation behavior with a very low percolation threshold at the CNFs content of about 0.93 wt.% (1.51 vol.%).     

Study on the mechanical and thermal properties of polylactic acid/hydroxyapatite@polydopamine composite nanofibers for tissue engineering

Electrospun nanofibers have attracted tremendous attention because of their similar structure with extracellular matrix. In this work, the polydopamine (PDA) coating layer was first applied to modify hydroxyapatite (HA) nanoparticles and obtain functional HA@PDA nanoparticles. Subsequently, the polylactic acid (PLA)/HA@PDA composite nanofibers were prepared via electrospinning. The hydrophilicity and water absorption of PLA/HA@PDA composite nanofibers were larger than those of PLA and PLA/HA composite nanofibers. The thermal stability, static and dynamic mechanical properties of PLA/HA@PDA composite nanofibers significantly increased because the PDA coating layer on the surface of the HA nanoparticles acted like a glue-like transition layer, which led to an increase in interfacial adhesion between HA@PDA nanoparticles and the PLA matrix. The attachment and viability of mouse embryonic osteoblast cells (MC3T3-E1) cultured on the PLA/HA@PDA composite nanofibers were significantly increased compared with those cultured on the PLA and PLA/HA composite nanofibers. These results suggested that the PLA/HA@PDA composite nanofibers have superior mechanical and biological properties, which makes it potentially useful for tissue engineering scaffolds.     

Modelling oxygen diffusion and cell growth in a porous, vascularising scaffold for soft tissue engineering applications

Soft tissue engineering presents significant challenges compared to other tissue engineering disciplines such as bone, cartilage or skin engineering. The very high cell density in most soft tissues, often combined with large implant dimensions, means that the supply of oxygen is a critical factor in the success or failure of a soft tissue scaffold. A model is presented for oxygen diffusion in a 15-60 mm diameter dome-shaped scaffold fed by a blood vessel loop at its base. This model incorporates simple models for vascular growth, cell migration and the effect of cell density on the effective oxygen diffusivity. The model shows that the dynamic, homogeneous cell seeding method often employed in small-scale applications is not applicable in the case of larger scale scaffolds such as these. Instead, we propose the implantation of a small biopsy of tissue close to a blood supply within the scaffold as a technique more likely to be successful.     

Preparation and properties of high performance gelatin-based hydrogels with chitosan or hydroxyethyl cellulose for tissue engineering applications

High performance gelatin-based biocompatible hybrid hydrogels are developed using functionalized polyethylene glycol as a cross-linker in presence of chitosan or hydroxyethyl cellulose. Tensile test shows robust and tunable mechanical properties and reveals non-linear and J-shaped stress-strain curves similar to those found for native extracellular matrix. Degradation study demonstrates that the mass loss and change in mechanical properties are dependent on hydrogel composition and cross-linking density. Structural features of the hydrogels are confirmed by infrared spectroscopy. A preliminary biological evaluation is carried out using rat myoblasts and human fibroblasts cell lines. The results show that all hydrogels allow cell adhesion and proliferation during four days culture, hence, they might have a great potential for use in the biomedical applications.     

Mechanical properties of vapor grown carbon nanofibers

Individual as-fabricated, high temperature heat-treated and graphitized/surface oxidized vapor grown carbon nanofibers (VGCNFs), with average diameter of 150 nm were tested for their elastic modulus and their tensile strength by a MEMS-based mechanical testing platform. The elastic modulus increased from 180 GPa for as-fabricated, to 245 GPa for high temperature heat-treated nanofibers. The nominal fiber strengths followed Weibull distributions with characteristic strengths between 2.74 and 3.34 GPa, which correlated well with the expected effects of heat treatment and oxidative post-processing. As-fabricated VGCNFs had small Weibull modulus indicating a broad flaw population, which was condensed upon heat treatment. For all VGCNF grades, the nanofiber fracture surface included the stacked truncated cup structure of the oblique graphene layers comprising its backbone and cleavage of the outer turbostratic or thermally graphitized layer.     

Cardanol biocomposites reinforced with jute fiber: Microstructure,biodegradability, and mechanical properties

This work aims at studying the preparation and characterization of composites of phenolic resin (matrix) based on cashew nut shell liquid, reinforced by natural jute fibers. The fibers were chemically modified using alkaline treatment with solutions of NaOH (5 and 10%) and bleached with sodium hypochlorite NaClO/H₂0 (1:1) at 60–75°C. The microstructure was investigated by Scanning Electron Microscopy to observe the fiber surface after the treatment. As a result, there was an improvement in the thermal stability of the fiber, which was verified by Thermogravimetric Analysis. The jute fiber composites showed an improvement in their mechanical properties due to chemical treatment with 5% NaOH. Their biodegradability level depended on the employed alkali solution concentration. This study is important to evaluate the application of the fibers as renewable materials. POLYM. COMPOS., 31:1928–1937, 2010. © 2010 Society of Plastics Engineers.     

Structural and biological properties of novel Vanadium and Strontium co-doped HAp for tissue engineering applications

The development of novel bioactive materials with improved physical and biological properties is crucial for advancing tissue engineering applications. In this study, we synthesized a Vanadium and Strontium co-doped hydroxyapatite (V–Sr:HAp) nanoparticle intending to enhance the performance of pure HAp. The V–Sr:HAp nanoparticles were synthesized using a microwave-assisted reflux condensation method, and their structural and chemical characteristics were investigated using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The morphology and elemental composition of the nanoparticles were examined through scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). The XRD analysis confirmed the presence of characteristic peaks of HAp in each sample. SEM images revealed well-connected and highly agglomerated small sphere-like morphology in both pure HAp and V–Sr:HAp nanoparticles. The Vickers hardness test demonstrated the improved mechanical strength in V–Sr:HAp compared to pure HAp. Antibacterial efficacy was evaluated using an agar diffusion test, which showed enhanced antibacterial activity in the co-doped HAp samples against S. aureus and P. aeruginosa. Moreover, the Ca–P deposition rate on the surface of the co-doped HAp samples during biomineralization was higher. Hemolysis assay results have indicated compatibility of both pure HAp and V–Sr:HAp with human blood (<5% lysis). The results of cell viability tests demonstrate that the V and Sr co-doped HAp samples do not exhibit any cytotoxic effects and instead promote cell proliferation. Overall, the incorporation of V and Sr metal ions into HAp presents a promising bio-functional tool for tissue engineering applications, offering improved mechanical and antibacterial properties.