17,095 research outputs found
Cork composites and their role in sustainable development
AbstractWith the current challenges that the industrial world faces regarding the unavoidable environmental impact of manufacturing goods, companies have been turning to sustainable design in order to reduce this impact and to minimize the damage to the environment while at the same time reaping the marketing bonus that is the claim of a greener product. This reduction of environmental impact is being done at multiple levels and especially at the design stage and one of the ways taken by companies to reduce this impact is to replace fuel-based materials such as polymers with natural materials. But in order for this replacement to take place, engineers and designers need to know the behavior of these materials. With that idea a set of mechanical tests and studies, namely bending and compression tests, have been performed on cork composites. Those composites were chosen for its importance to the Portuguese economy and its peculiar growth cycle and harvesting techniques, in order to ascertain the mechanical properties of cork composites and how it stands against polymers
Porous bioactive composites from marine origin based in chitosan and hydroxylapatite particles
An optimal carrier for bone tissue engineering should be both a controlled release system
and a scaffold. In the former role, the carrier must prevent rapid factor clearance and ideally meter
out the growth factor in a predictable manner, allowing therapeutic doses to stimulate target cells for
the appropriate duration. In the latter role, the material should act as a permissive environment into
which bone cells would be attracted to migrate and begin the process of depositing bone matrix.
Therefore the direct incorporation of growth factor in porous scaffolds should be a desirable goal.
The inclusion of a bioactive ceramic on the scaffold design will confer to the systems a bone
bonding behaviour that will guide bone formation. This work reports the development of composite
chitosan/HA (from algal origin) porous structures produced by means of freeze-drying processing
routes that can be further loaded with a biologically active agent. The developed bioactive 3D
structures (completely from marine origin) have potential application as tissue engineering scaffolds
and drug delivery systems due to their morphological and bioactive properties.(undefined
Bilayered chitosan-based scaffolds for osteochondral tissue engineering : influence of hydroxyapatite on in vitro cytotoxicity and dynamic bioactivity studies in a specific double-chamber bioreactor
Osteochondral tissue engineering presents a current research challenge due to the necessity of combining both bone and cartilage
tissue engineering principles. In the present study, bilayered chitosan-based scaffolds are developed based on the optimization of both
polymeric and composite scaffolds. A particle aggregation methodology is proposed in order to achieve an improved integrative
bone–cartilage interface needed for this application, since any discontinuity is likely to cause long-term device failure. Cytotoxicity
was evaluated by the MTS assay with the L929 fibroblast cell line for different conditions. Surprisingly, in composite scaffolds using
unsintered hydroxyapatite, cytotoxicity was observed in vitro. This work reports the investigation that was conducted to overcome
and explain this behaviour. It is suggest that the uptake of divalent cations may induce the cytotoxic behaviour. Sintered hydroxyapatite
was consequently used and showed no cytotoxicity when compared to the controls. Microcomputed tomography (micro-CT) was carried
out to accurately quantify porosity, interconnectivity, ceramic content, particle and pore sizes. The results showed that the developed
scaffolds are highly interconnected and present the ideal pore size range to be morphometrically suitable for the proposed applications.
Dynamical mechanical analysis (DMA) demonstrated that the scaffolds are mechanically stable in the wet state even under dynamic compression.
The obtained elastic modulus was, respectively, 4.21 ± 1.04, 7.98 ± 1.77 and 6.26 ± 1.04 MPa at 1 Hz frequency for polymeric,
composite and bilayered scaffolds. Bioactivity studies using both a simulated body fluid (SBF) and a simulated synovial fluid (SSF) were
conducted in order to assure that the polymeric component for chondrogenic part would not mineralize, as confirmed by scanning electron
microscopy (SEM), inductively coupled plasma-optical emission spectroscopy (ICP) and energy-dispersive spectroscopy (EDS) for
different immersion periods. The assays were carried out also under dynamic conditions using, for this purpose, a specifically designed
double-chamber bioreactor, aiming at a future osteochondral application. It was concluded that chitosan-based bilayered scaffolds produced
by particle aggregation overcome any risk of delamination of both polymeric and composite parts designed, respectively, for chondrogenic
and osteogenic components that are mechanically stable. Moreover, the proposed bilayered scaffolds could serve as alternative,
biocompatible and safe biodegradable scaffolds for osteochondral tissue engineering applications
Optimization of chitosan-based composite and bi-layered scaffolds produced by particles aggregation for osteochondral tissue engineering: Influence of hydroxylapatite
[Excerpt] Osteochondral tissue engineering presents a challenge to the present research due to requirements’ combination of both bone and cartilage tissue engineering. In the present study, bilayered
chitosan scaffolds are proposed based in the optimization of polymeric and composite scaffolds. µ-CT was carried out for accurate morphometric characterization quantifying porosity, interconnectivity,
ceramic content, particles and pores size. The results showed that the developed scaffolds are highly interconnected and present ideal pore size range, being morphometrically adequate for
the proposed applications. [...]info:eu-repo/semantics/publishedVersio
Mechanical behavior of basalt fibers in a basalt-UP composite
AbstractWith the increasing interest in sustainable solutions in material design in the last decade, research on natural materials (animal, vegetal or mineral) has increased at a rapid pace. Of these materials, Basalt Fibers for composite construction provide an interesting set of mechanical properties, equal or above to those of Glass Fibers, with advantages in terms of cost effectiveness and production to vegetable based Natural Fibers. Basalt fibers offer some advantages versus current materials, it is fireproof, requires no material addition, has better mechanical properties than most types of E-Glass, and it is cheaper than Carbon Fiber. This paper studies the mechanical properties of a Basalt Fiber composite in an Unsaturated Polyester matrix produced by Resin Transfer Molding (RTM), with the composites subjected to tensile, compression, shear and flexural tests. The results aligned with the predicted values by using the mixing rule, albeit with a high coefficient of variation, which microscopic analysis confirmed to arise from production issues with RTM
Sodium silicate gel as a precursor for the in vitro nucleation and grow of a bone-like apatite coating in compact and porous polymeric structures
In the present work, a new methodology to produce bioactive coatings on the surface of starch-based biodegradable polymers or other polymeric biomaterials is proposed. A sodium silicate gel is employed as an alternative nucleating agent to the more typical bioactive glasses for inducing the formation of a calcium-phosphate (Ca-P) layer. The method has the advantage of being able to coat efficiently both compact materials and porous 3D architectures aimed at being used on tissue replacement applications and as tissue engineering scaffolds. By means of this treatment, it is possible to observe the formation of an apatite-like layer, only after 6 hours of simulated body fluid immersion. For the porous materials, this layer could also be observed inside the pores, clearly covering the cell walls. Furthermore, an increase of the surface hydrophilicity (higher amount of polar groups in the surface) might contribute to the formation of silanol groups that also act as apatite inductors. After 30 days of SBF immersion, the apatite-like films exhibit a partially amorphous nature and the Ca/P ratios became much closer to the value attributed to hydroxyapatite (1.67). The obtained results are very promising for the development of cancellous bone replacement materials and for pre-calcifying bone tissue engineering scaffolds
Simulations of Time-Resolved X-Ray Diffraction in Laue Geometry
A method of computer simulation of Time-Resolved X-ray Diffraction (TRXD) in
asymmetric Laue (transmission) geometry with an arbitrary propagating strain
perpendicular to the crystal surface is presented. We present two case studies
for possible strain generation by short-pulse laser irradiation: (i) a
thermoelastic-like analytic model; (ii) a numerical model including effects of
electron-hole diffusion, Auger recombination, deformation potential and thermal
diffusion. A comparison with recent experimental results is also presented.Comment: 9 pages, 11 figure
Starch-based microspheres produced by emulsion crosslinking with a potential media dependent responsive behavior to be used as drug delivery carriers
This paper describes the development and characterization
of starch microspheres for being used as drug
delivery carriers in tissue engineering applications. The developed
starch microspheres can be further loaded with specific
growth factors and immobilized in scaffolds, or administrated
separately with scaffolds. Furthermore and due to
the processing conditions used, it is expected that these microspheres
can be also used to encapsulate living cells. The
aim of this study was to evaluate the efficacy of this methodology
for further studies with biologically active agents or
living cells. The starch microspheres were prepared using
an emulsion crosslinking technique at room temperature to
allow for the loading of biologically active agents. A preliminary
study was performed to evaluate the incorporation of
a model drug (nonsteroidal anti-inflammatory drug-NSAID)
and investigate its release profile as function of changes in
the medium parameters, such as ionic strength and pH. The
developed starch-based drug delivery system has shown to be
dependent on the ionic strength of the release medium. From
preliminary results, the release seems to be pH-dependent
due to the drug solubility. It was found that the developed
microspheres and the respective processing route are appropriate
for further studies. In fact, and based in the processing
conditions and characterization, the developed system
present a potential for the loading of different growth factors or even living cells on future studies with these systems
for improving bone regeneration in tissue engineering, especially
because the crosslinking reaction of the microspheres
takes place at room temperature
Brachial Artery Constriction during Brachial Artery Reactivity Testing Predicts Major Adverse Clinical Outcomes in Women with Suspected Myocardial Ischemia: Results from the NHLBI-Sponsored Women's Ischemia Syndrome Evaluation (WISE) Study
Background:Limited brachial artery (BA) flow-mediated dilation during brachial artery reactivity testing (BART) has been linked to increased cardiovascular risk. We report on the phenomenon of BA constriction (BAC) following hyperemia.Objectives:To determine whether BAC predicts adverse CV outcomes and/or mortality in the women's ischemic Syndrome Evaluation Study (WISE). Further, as a secondary objective we sought to determine the risk factors associated with BAC.Methods:We performed BART on 377 women with chest pain referred for coronary angiography and followed for a median of 9.5 years. Forearm ischemia was induced with 4 minutes occlusion by a cuff placed distal to the BA and inflated to 40mm Hg > systolic pressure. BAC was defined as >4.8% artery constriction following release of the cuff. The main outcome was major adverse events (MACE) including all-cause mortality, non-fatal MI, non-fatal stroke, or hospitalization for heart failure.Results:BA diameter change ranged from -20.6% to +44.9%, and 41 (11%) women experienced BAC. Obstructive CAD and traditional CAD risk factors were not predictive of BAC. Overall, 39% of women with BAC experienced MACE vs. 22% without BAC (p=0.004). In multivariate Cox proportional hazards regression, BAC was a significant independent predictor of MACE (p=0.018) when adjusting for obstructive CAD and traditional risk factors.Conclusions:BAC predicts almost double the risk for major adverse events compared to patients without BAC. This risk was not accounted for by CAD or traditional risk factors. The novel risk marker of BAC requires further investigation in women. © 2013 Sedlak et al
Natural-origin polymers as carriers and scaffolds for biomolecules and cell delivery in tissue engineering applications
The present paper intends to overview a wide range of natural–origin polymers with special focus on proteins and polysaccharides (the systems
more inspired on the extracellular matrix) that are being used in research, or might be potentially useful as carriers systems for active biomolecules
or as cell carriers with application in the tissue engineering field targeting several biological tissues. The combination of both applications into a
single material has proven to be very challenging though. The paper presents also some examples of commercially available natural–origin
polymers with applications in research or in clinical use in several applications. As it is recognized, this class of polymers is being widely used due
to their similarities with the extracellular matrix, high chemical versatility, typically good biological performance and inherent cellular interaction
and, also very significant, the cell or enzyme-controlled degradability. These biocharacteristics classify the natural–origin polymers as one of the
most attractive options to be used in the tissue engineering field and drug delivery applications
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