Wettability influences cell behavior on superhydrophobic surfaces with different topographies

Surface wettability and topography are recognized as critical factors influencing cell behavior on biomaterials. So far only few works have reported cell responses on surfaces exhibiting extreme wettability in combination with surface topography. The goal of this work is to study whether cell behavior on superhydrophobic surfaces is influenced by surface topography and polymer type. Biomimetic superhydrophobic rough surfaces of polystyrene and poly(l-lactic acid) with different micro/nanotopographies were obtained from smooth surfaces using a simple phase-separation based method. Total protein was quantified and showed a less adsorption of bovine serum albumin onto rough surfaces as compared to smooth surfaces of the same material. The mouse osteoblastic MC3T3-E1 cell line and primary bovine articular chondrocytes were used to study cell attachment and proliferation. Cells attached and proliferate better in the smooth surfaces. The superhydrophobic surfaces allowed cells to adhere but inhibited their proliferation. This study indicates that surface wettability, rather than polymer type or the topography of the superhydrophobic surfaces, is a critical factor in determining cell behavior

Changes on surface morphology of corn starch blend films

This study aims at evaluating the influence of enzymatic degradation solution on the surface morphology and thermal properties of a poly(ethylene-vinyl alcohol) copolymer-corn starch thermoplastic blend (SEVA-C), as a function of immersion time. To perform this study, three different batches were assessed using SEVA-C samples of different thicknesses and a fixed weight of 1.6 g, immersed in alpha-amylase (50 u/L) up to 90 days at 37 degrees C. TGA, contact angle measurements, scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques were used. Three degradation mechanisms are considered in these systems: namely, mass loss due to plasticizer leaching (glycerol), starch enzymatic cleavage, and synthetic polymer fractions degradation. Enzymatic hydrolysis of the starch fraction and subsequent leaching from the internal bulk structure led to an increase in surface porosity, pore size, roughness, and to the development of small pits throughout the surface, as observed by SEM and AFM

Morphology, mechanical characterization and in vivo neo-vascularization of chitosan particle aggregated scaffolds architectures

The present study intended to evaluate the performance of chitosan-based scaffolds produced by a particle aggregation method aimed to be used in tissue engineering applications addressing key issues such as morphological characteristics, mechanical performance and in vivo behaviour. It is claimed that the particle aggregation methodology may present several advantages, such as combine simultaneously a high interconnectivity with high mechanical properties that are both critical for an in vivo successful application. In order to evaluate these properties, micro-Computed Tomography (micro-CT) and Dynamical Mechanical Analysis (DMA) were applied. The herein proposed scaffolds present an interesting morphology as assessed by micro-CT that generally seems to be adequate for the proposed applications. At a mechanical level, DMA has shown that chitosan scaffolds have an elastic behaviour under dynamic compression solicitation, being simultaneously mechanically stable in the wet state and exhibiting a storage modulus of 4.21 ! 1.04 MPa at 1 Hz frequency. Furthermore, chitosan scaffolds were evaluated in vivo using a rat muscle-pockets model for different implantation periods (1, 2 and 12 weeks). The histological and immunohistochemistry results have demonstrated that chitosan scaffolds can provide the required in vivo functionality. In addition, the scaffolds interconnectivity has been shown to be favourable to the connective tissues ingrowth into the scaffolds and to promote the neo-vascularization even in early stages of implantation. It is concluded that the proposed chitosan scaffolds produced by particle aggregation method are suitable alternatives, being simultaneously mechanical stable and in vivo biofunctional that might be used in load-bearing tissue engineering applications, including bone and cartilage regeneration.The authors would like to acknowledge the Portuguese Foundation for Science and Technology for the PhD Grant to Patricia B Malafaya (SFRH/BD/11155/2002). This work was partially supported and carried out under the scope of the European STREP Project HIPPOCRATES (NMP3-CT-2003-505758) and European NoE EXPERTISSUES (NMP3-CT-2004-500283). The authors also thank Prof. Heinz Redl for the collaboration in the in VIVO Studies, as well as Bernhard Horing for the surgical procedures both from LBI, Austria and Joao Oliveira from 3B's Research Group, Portugal for the initial assistance with the DMA equipment

Occurence Probabilities of Stochastic Paths

An analytical formula for the occurence probability of Markovian stochastic paths with repeatedly visited and/or equal departure rates is derived. This formula is essential for an efficient investigation of the trajectories belonging to random walk models and for a numerical evaluation of the `contracted path integral solution' of the discrete master equation [Phys. Lett. A 195, 128 (1994)].Comment: For related work see http://www.theo2.physik.uni-stuttgart.de/helbing.htm

Stimulatory effects of inorganic ions on osteogenesis in vitro

Introduction: Several studies demonstrated the effect of silicate ions (Si) on differentiation of bone precursor cells1,2, although its exact role in processes related to bone formation and remodeling is still incompletely understood. The focus of this work is to explore the effect of calcium and silicate ions on growth and osteogenic differentiation of human mesenchymal stem cells (hMSCs). This strategy may reduce the need for growth factors required to stimulate bone formation in regenerative approaches, decreasing the associated costs and overcoming stability issues. Materials and Methods In order to define the range of Si concentrations that are not toxic to cells, we performed a preliminary study varying Si concentrations from 0.00357mM to 4mM. The concentration of the Ca ions was selected based on the earlier study by Barradas et. al3. Cell culture media were supplemented by using sodium silicate (Na2SiO3) and/or calcium chloride dehydrate (CaCl2*2H2O) as Si and Ca precursors, respectively. hMSCs derived from bone marrow were seeded at a seeding density of 2.000 cells/cm2 and allowed to adhere overnight. Then, the medium was replaced by the appropriate supplemented medium and cells were cultured for 3, 7, 14 and 18 days. Basic and osteogenic media were used as negative and positive controls. Cell proliferation was evaluated by DNA quantification. hMSCs osteogenic gene expression was evaluated by Q-PCR. Results DNA quantification indicated an increase in cell number during the culture time for all the conditions. Results obtained by Q-PCR revealed a significantly higher expression of osteocalcin (OC) and bone morphogenetic protein-2 (BMP2) in cells cultured in media supplemented by both ions, as compared to media containing either Ca or Si alone. Discussion and Conclusions DNA quantification studies indicated that none of the selected concentrations had a negative influence on cell proliferation. The increase in osteogenic gene expression for cells cultured with both Ca and Si suggested a synergistic effect of the two ions on osteogenic differentiation of hMSCs. We further showed that cells cultured in the medium with the highest concentration of Ca (7.8mM) revealed a higher expression of the selected genes, which is in accordance with the earlier results by Barradas et al3. The obtained results suggest the importance of combining both ions, Ca and Si, for promoting the osteogenic differentiation of hMSCs. References 1. Hoppe A, Biomaterials 32: 2757-2774, 2011. 2. Beck Jr GR, Nanomedicine: Nanotechnology, Biology, and Medicine,1-11, 2011 3. Barradas AMC et al., Biomaterials 3205-3215, 2012. Acknowledgments The author thanks the Portuguese Foundation for Science and Technology (FCT) for the grant (SFRH/BD/69962/2010). Disclosures The authors have nothing to disclose

ESBies: safety in the tranches

It is well known that rational bubbles can be sustained in balanced growth path of a deterministic economy when the return to capital r is equal to the growth rate g. When there is a lack of stores of value, bubbles can implement an e¢ cient allocation. This paper considers a world where r áuctuates over time due to shocks to the marginal productivity of capital. Then, bubbles further e¢ ciency, though they cannot implement Örst best. While bubbles can only be sustained when r = g in a deterministic economy, r > g "on average" in a stochastic economy. Fiscal policy improves welfare by adding an extra asset. Where only the elderly contribute to shifting resources between investment and consumption in a bubbly economy, Öscal policy allows part of that burden to be shifted to the young. Contrary to common wisdom, trade in bubbly assets implements intergenerational transfers, while Öscal policy implements intragenerational transfers. Hence, while bubbles and Öscal policy are perfect substitutes in the deterministic economy, Öscal policy dominates bubbles in a stochastic economy. For plausible parameter values, a higher degree of dynamic ine¢ ciency should lead to a higher sovereign debt

Regeneration of the intervertebral disc

Degeneration of intervertebral disc (IVD) seems to be one of the main causes associated to lower back pain (LBP), one of the most common painful conditions that lead to work absenteeism, medical visits, and hospitalization in actual society [1,2]. This complex fibro-cartilaginous structure is composed by two structures, an outer multilayer fiber structure (annulus fibrosus, AF) and a gel-like inner core (nucleus pulposus, NP), which are sandwiched in part between two cartilage endplates (CEP) [1]. Existing conservative and surgical treatments for LBP are directed to pain relief and do not adequately restore disc structure and mechanical function [2]. In the last years, several studies have been focusing on the development of tissue engineering (TE) approaches aiming to substitute/regenerate the AF or NP, or both by developing an artificial disc that could be implanted in the body thus replacing the damaged disc [3]. TE strategies aiming to regenerate NP tissue often rely on the use of natural hydrogels, due to the number of advantages that these highly hydrated networks can offer. Nevertheless, several of the hydrogel systems developed still present numerous problems, such as variability of production, and inappropriate mechanical and degradation behaviour. Recently, our group has proposed the use of gellan gum (GG) and its derivatives, namely the ionic- and photo-crosslinked methacrylated gellan gum (GG-MA) hydrogels, as potential injectable scaffolds for IVD regeneration [4,5]. Work has been conducted regarding the improvement of GG mechanical properties either by chemically modifying the polymer (allowing to better control in situ gelation and hydrogel stability) [4] or by reinforcing it with biocompatible and biodegradable GG microparticles (enabling the control of degradation rate and cell distribution) [5]. Another strategy currently under investigation relies on the development of a biphasic scaffold that mimics the total disc by using a reverse engineering approach

Discovery of a missing disease spreader

This study presents a method to discover an outbreak of an infectious disease in a region for which data are missing, but which is at work as a disease spreader. Node discovery for the spread of an infectious disease is defined as discriminating between the nodes which are neighboring to a missing disease spreader node, and the rest, given a dataset on the number of cases. The spread is described by stochastic differential equations. A perturbation theory quantifies the impact of the missing spreader on the moments of the number of cases. Statistical discriminators examine the mid-body or tail-ends of the probability density function, and search for the disturbance from the missing spreader. They are tested with computationally synthesized datasets, and applied to the SARS outbreak and flu pandemic.Comment: in pres