Judith Serra Moreno

Structured Silicon Anodes for Lithium Battery Applications

Pillar arrays fabricated on silicon substrates have been tested as potential anodes for lithium batteries. Electrodes of array characteristics, diameter 580 ′ 150 nm: fractional surface coverage 0.34: height 810 nm are reported here. Cyclic voltammetry (CV) and cyclic galvanostatic tests of alloying/dealloying of electrochemically produced lithium with silicon were carried out, and results correlated with SEM studies. Aerial current densities in the low and fractional mA cm - 2 , and voltage 25 mV to 2 V (vs. L/Li + ) were used. CV features correspond to various Zintl phase compounds (ZPCs). Structured electrodes of Si pillars maintained their structural integrity throughout cycling; planar Si electrodes showed cracks (2 μm features) after 50 cycles. A model is advanced in which lithium diffuses through a layer of ZPC to react with Si: growing ZPCs plastically deforms where necessary. Upon lithium dealloying vacancies coalesce to form voids at the ZPC/Si interface, Si rejoins the substrate. or precipitates out as a nanocrystalline material, and the voids appear as a fine pattern of cracks, looking like dried mud. The extra surface area that a pillar structure can confer on Si electrodes is essential and makes it practical to consider the possible eventual use of such anodes in integrated battery structure;.

Polypyrrole-polysaccharide thin films characteristics: electrosynthesis and biological properties.

Polypyrrole-polysaccharide thin films were electropolymerized from starting solutions containing pyrrole and a polysaccharide, namely, heparin, chondroitin-4-sulphate or hyaluronic acid. The synthesized samples showed good chemical and physicochemical properties determined by the synthesis parameters such as the current density and time. For instance, the sample morphology was strictly correlated to the current density as follows: a smooth surface morphology was observed when the current density was in the range of 100-700 microA/cm(2), whereas high current (I > 1.0 mA/cm(2)) or longer time (synthesis charge > 100 mC/cm(2)) led to rough surfaces. The presence of polysaccharide within the polymeric matrix assured proper hydrophilicity to the samples. The optimized surface chemistry due to the presence of a polysaccharide and the controllable morphology allowed positive cell/substrate interactions and these are proved by cellular tests using MC3T3-E1 osteoblast cultures.

Synthesis and Characterization of Cellulose-Based Hydrogels to Be Used as Gel Electrolytes

Cellulose-based hydrogels, obtained by tuned, low-cost synthetic routes, are proposed as convenient gel electrolyte membranes. Hydrogels have been prepared from different types of cellulose by optimized solubilization and crosslinking steps. The obtained gel membranes have been characterized by infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and mechanical tests in order to investigate the crosslinking occurrence and modifications of cellulose resulting from the synthetic process, morphology of the hydrogels, their thermal stability, and viscoelastic-extensional properties, respectively. Hydrogels liquid uptake capability and ionic conductivity, derived from absorption of aqueous electrolytic solutions, have been evaluated, to assess the successful applicability of the proposed membranes as gel electrolytes for electrochemical devices. To this purpose, the redox behavior of electroactive species entrapped into the hydrogels has been investigated by cyclic voltammetry tests, revealing very high reversibility and ion diffusivity.

Polysaccharides immobilized in polypyrrole matrices are able to induce osteogenic differentiation in mouse mesenchymal stem cells

Bone marrow mesenchymal stem cells (MSCs) have attracted considerable interest due to their ability to differentiate and contribute to the regeneration of mesenchymal tissues. The present study illustrates that the proper immobilization of heparin (Hep) and hyaluronic acid (HA) into a polypyrrole (PPy) matrix by electropolymerization results in an optimal interface for MSC differentiation towards osteoblast lineage. The obtained thin films showed good thermal stability, hydrophilicity and slow controlled polysaccharide release. The in vitro tests showed the main role of the interface chemical composition. Indeed, PPyHep and PPyHA thin films were able to induce osteogenic differentiation as determined by levels of specific early osteogenic markers (Runx2 and osterix) even in the absence of differentiating medium. Increased levels of ALP and Alizarin red staining, both indicating mineralization processes, confirmed the presence of mature osteoblasts. Copyright

Synthesis of novel pyrrolyl-indomethacin derivatives

In the present work, we report the synthesis of the novel esters of indomethacin (IDMC) and an ester of reduced IDMC. For this purpose, IDMC is covalently bound by using a spacer chain to the pyrrole (Py) in the 3-position. The innovative pyrrole-indomethacin (3-Py-IDMC) derivates show no cytotoxic effects in primary calvarial osteoblasts. The designed IDMC derivates have been studied because they could be injected locally as a component of polymeric micro-particles. In fact, the new 3-Py-IDMC derivatives will assure their further polymerization since the 2- and 5-monomer positions are free.

Evaluation of Alloys Synthesized by Mechanical Alloying as Potential Anode Materials for Lithium-Ion Batteries

Several alloys (Mg 2 Si, Li 4 Mg 2 Si, Sn 0.66 Sb 0.34 , and Li 4 Sn 0.72 Sb 0.28 ) have been synthesized by mechanical alloying and characterized for their performance as anode materials for Li-ion batteries. Sn 0.66 Sb 0.34 shows a better cycling performance than Mg 2 Si, whose higher initial capacities fade after a few cycles only. The pre-lithiated materials Li 4 Mg 2 Si and Li 4 Sn 0.72 Sb 0.28 give good cycling stabilities, however, at much smaller capacities than exhibited by their unlithiated counterparts.

Porous Hydroxyapatite Surface-Modified by Polypyrrole-Heparin Conducting Polymer

The preparation and characterization of an inorganic/organic composite scaffold is proposed in this paper. The substrate was realized by the polymerization of an electroconductive polymer, namely polypyrrole PPy, into an hydroxyapatite HAp porous support. The PPy/HAp composite was characterized by XRD, Hg porosimetry measurements, SEM-EDS and electrochemical test. The results pointed out that the PPy polymer entered into the HAp whole pores moving through the interconnected paths of the hydroxyapatite matrix. The PPy thin film doped with heparin maintained its electrochemical characteristics even in the ceramic support.