Magnetic force-based tissue engineering and regenerative medicine

Among other biomedical applications, magnetic nanoparticles and liposomes have a vast field of applications in tissue engineering and regenerative medicine. Magnetic nanoparticles and liposomes, when introduced into cells to be cultured, maneuver the cell's positioning by the appropriate use of magnets to create more complex tissue structures than those that are achieved by conventional culture methods.This work was supported by the Portuguese Foundation for Science and Technology (FCT) and the Andalusian Initiative for Advanced Therapies (Ministry of Health of the Andalusian Regional Government). Special thanks to Dr. Vega Asensio (www.NorArte.es) and her beautiful scientific illustrations for the review. Emilio Castro thanks his postdoctoral fellowship from Health and Progress Foundation (Mobility Program for Nanomedicine)

The Fallacy of Composition

The fallacy of composition involves differing relationships of parts to wholes complicated by the problem of group ambiguity. Our discussion begins with a brief diagnosis of important features of the fallacy. We consider a common implicit assumption and the main factors that contribute to its acceptability. Our focus will be on illuminating some common strategies rather than formal material conditions for the fallacy. This is to facilitate the critical discussion of possibilities for this fallacy

Synthesis and characterization of stable dicarboxylic pegylated magnetite nanoparticles

The coating of implantable nano- or micro-objects with polyethylene glycol (PEG) enhances its biocompatibility and biodistribution. Herein, we describe a new protocol that enhances and maintains MNPs stability in biological media, simulating multiple conditions to which they would be subjected in the human body. Magnetite nanoparticles (MNPs) prepared via a facile way at room temperature by co-precipitation reaction, were coated with dicarboxylic polyethylene glycol (DCPEG) via covalent bonds. The surface of the nanoparticles was first coated with 3-aminopropyl trimethoxysilane by a silanization reaction and then linked with DCPEG of different molecular weight (Mw=5000, 10,000 and 20,000 g mol−1). The uncoated magnetite nanoparticles, with an average size of 20 nm, exhibited superparamagnetism, high saturation magnetization and a negative surface charge (with a zeta potential value of −40 mV). Increase of Mw enhances the colloidal stability of MNPs and makes them more suitable to tolerate high salt concentrations (1M NaCl) and wide pH (from 5.5 to 12) and temperature ranges (24 °C to 46 °C). The results indicate that magnetite nanoparticles coated with DCPEG with Mw=20,000 have improved properties over their counterparts, making them our best choice for biomedical studies.This work was supported by the Science and Technology Foundation (FCT) projects SUPRARELAX and PTDC/CTM-BPC/112774/2009. E. C acknowledges the Health and Progress Foundation for their financial support through the Andalusian Initiative for Advanced Therapies (Andalusian Regional Ministry of Health)

Polyethylene composites with lignocellulosic material

The aim of this chapter is to describe in detail the advances in polyethylene reinforced with lignocellulosic material. Indeed, the successful employment of natural based materials to reinforce/improve the properties of polyolefins has been growing in a wide range of applications. Firstly, basic concepts and terminology adopted in the lignocellulosic composite materials are reviewed. The objective is to bring the readerâ s attention to important issues that must to be taken into account when working in this subject as well as by providing the most appropriate references for those with interest to delve into the topic. In the context of polyethylene lignocellulosic composites, ongoing research is then summarised mainly focussing on (i) the main aspects related to the selection of the commonly used lignocellulosic materials and the potential of its main chemical constituents, (ii) the principal methods used for the improvement of interfacial adhesion and (iii) the main adopted processing routes and the composite properties. Finally, applications, new challenges and opportunities of these polyethylene-lignocellulosic composites are also discussed.(undefined)info:eu-repo/semantics/publishedVersio

Hybrid cork-polymer composites containing sisal fibre : morphology, effect of the fibre treatment on the mechanical properties and tensile failure prediction

In this study, we investigated the use of short sisal fibre with and without polyethylene-graft-maleic anhydride (PE-g-MA) as a strategy to reinforce cork–polymer composite (CPC) materials. The use of alkali treatment of sisal to improve fibre–matrix adhesion was evaluated. High density polyethylene (HDPE) was used as matrix and the composites were produced in a two-step process using twin-screw extruder followed by compression moulding. FTIR, TGA and XRD were used to confirm the sisal fibre modification. Additionally, morphology, density, diameter and tensile properties of the fibres were evaluated before processing. The hybrid composites containing cork powder (40 wt.%) and randomly distributed sisal fibres were evaluated in terms of morphology and mechanical properties. The use of a 10 wt.% sisal fibre in the presence of a 2 wt.% coupling agent based on maleic anhydride, has shown to improve the tensile and flexural properties of the composites. The higher mechanical properties were achieved by using alkali treated sisal fibres and PE-g-MA. In the presence of the coupling agent the composite morphology revealed good interfacial adhesion between the natural components and the polypropylene matrix, being in accordance with the mechanical results. Weibull cumulative distribution was successfully used to accurately predict the tensile strength failure of the hybrid CPC materials.We gratefully acknowledge to Amorim Revestimentos S.A. for the supply of cork and to Pallmann GmbH for the polymer in the grinding form. To QREN FCOMP-01-0202-FEDER-003107 financing support on the project "NovelComp". EMF acknowledge to Portuguese Foundation for Science and Technology (FCT) Grant (SFRH/BD/71561/2010)

Charged black holes: Wave equations for gravitational and electromagnetic perturbations

A pair of wave equations for the electromagnetic and gravitational perturbations of the charged Kerr black hole are derived. The perturbed Einstein-Maxwell equations in a new gauge are employed in the derivation. The wave equations refer to the perturbed Maxwell spinor $\Phi_0$ and to the shear $\sigma$ of a principal null direction of the Weyl curvature. The whole construction rests on the tripod of three distinct derivatives of the first curvature $\kappa$ of a principal null direction.Comment: 12 pages, to appear in Ap.

Enzymatic degradation behavior and cytocompatibility of silk fibroin–starch–chitosan conjugate membranes

The objective of this study was to investigate the influence of silk fibroin and oxidized starch conjugation on the enzymatic degradation behavior and the cytocompatability of chitosan based biomaterials. The tensile stress of conjugate membranes, which was at 50 Megapascal (MPa) for the lowest fibroin and starch composition (10 weight percent (wt.%)), was decreased significantly with the increased content of fibroin and starch. The weight loss of conjugates in α-amylase was more notable when the starch concentration was the highest at 30 wt.%. The conjugates were resistant to the degradation by protease and lysozyme except for the conjugates with the lowest starch concentration. After 10 days of cell culture, the proliferation of osteoblast-like cells (SaOS-2) was stimulated significantly by higher fibroin compositions and the DNA synthesis on the conjugate with the highest fibroin (30 wt.%) was about two times more compared to the native chitosan. The light microscopy and the image analysis results showed that the cell area and the lengths were decreased significantly with higher fibroin/chitosan ratio. The study proved that the conjugation of fibroin and starch with the chitosan based biomaterials by the use of non-toxic reductive alkylation crosslinking significantly improved the cytocompatibility and modulated the biodegradation, respectively.E.T. Baran thanks the Portuguese Foundation for Science and Technology for providing him a PostDoc scholarship (SFRH/BPD/30768/2006). This work was partially supported by the European Union funded STREP Project HIPPOCRATES (NMP3-CT-2003-505758)

Natural fibres as reinforcement strategy on cork-polymer composites

Cork powder, the most important sub-product of cork processing, combined with thermoplastic matrixes like, high density polyethylene (HDPE), offer a new class of cork-polymer composite (CPC) materials with high added-value. Therefore, reinforcing strategies must be considered to increase the mechanical performance, especially when high content of cork powder is added to the formulation. Coconut fibres have several advantages, such as, low density, renewable source, low cost and biodegradability. The use of these fibres on the reinforcement of CPC materials will not only contribute to improve the mechanical performance but also for increasing the amount of natural component present on the final composition. The main goal of this work was to prepare HDPE/cork (50-50 wt.%) composites reinforced with discontinuous coconut fibres (5 and 10 wt.%) with and without the addition of coupling agent (2 wt.%) by extrusion. The developed reinforced cork based composites were characterized regarding its morphology and mechanical performance. Optical micrographs have shown a homogeneous distribution of the fibres. The coupling agent effect on CPC performance was also investigated. The tensile strength and tensile modulus of the reinforced composites were significantly improved with the addition of coupling agent. The use of 10 wt.% of coconut fibres in the presence of coupling agent promote an increase on maximum tensile strength of around 41 % comparing with the HDPE/cork (50-50 wt.%) composites. Scanning electron microscopy (SEM) micrographs of the tensile fractured specimens confirmed that the use of coupling agent promoted the interfacial adhesion between the fibres and the thermoplastic matrix. Since, like cork powder, coconut fibres have good thermal and acoustic properties, we consider that the novel reinforced CPC herein described have high potential to be used in building and construction systems and other structural 3D applications.Corticeira Amorim S.G.P.S. (Portugal)Fundação para a Ciência e a Tecnologia (FCT)Project ”NovelComp”QREN FCOMP-01-0202 FEDER-00310

Conjugation of fibroin and starch to chitosan for increasing cell proliferation capacity

[Excerpt] In this study, chitosan conjugates with starch and fibroin were produced for increasing degradability in the presence of physiological enzymes and cell proliferation capacities of biomaterials. The degradation profile was monitored over prolonged time periods and characterization of chemical changes during degradation periods were investigated by spectroscopic methods. Various ratios of starch, fibroin and chitosan (%, (weight/weight)) were prepared. The in vitro cell culture studies were conducted to evaluate biocompatibility and proliferation capacities of conjugate materials. [...]info:eu-repo/semantics/publishedVersio

Novel cork-polymer composites reinforced with short natural coconut fibres : effect of fibre loading and coupling agent addition

Composites from high density polyethylene filled with cork powder and coconut short fibres, in two different ratios, were prepared in a twin-screw extruder followed by compression moulding process. The main motivation of this work was to improve the mechanical performance without compromising the use of high weight percentage of natural component used in the preparation of cork-based composites. The morphology of the hybrid composites were more homogeneous in the presence of the coupling agent (CA) displaying enhanced fibre–matrix adhesion. Moreover, the use of CA based on maleic anhydride promotes a mechanical reinforcement effect on the tensile properties, including the elongation at break. The addition of coconut fibre resulted on an increase of 27% in elastic modulus and 47% in the tensile strength when compared with the unreinforced cork-based (50–50) wt.% composite. This work clearly shows that the addition of 10 wt.% of short-coconut fibres, randomly distributed, can be effectively used as reinforcing strategy of cork-based composite materials, preferably in the presence of 2 wt.% of CA.The work was performed within the project of Corticeira Amorim S.G.P.S. on the development of new products based in/with cork. We gratefully acknowledge to Amorim Revestimentos S.A. for the supply of cork and to Amorim Isolamentos S.A. for the coconut fibres and to Pallmann GmbH for the grinding polymer. E.M.F. and V.M.C. acknowledges to Portuguese Foundation for Science and Technology (FCT) grants (SFRH/BD/71561/2010) and (SFRH/BPD/64790/2009) respectively