Francisco Balas

Publications (44) View all

• Source

  Available from: Francisco Balas

  Article: Surface functionalization for tailoring the aggregation and magnetic behaviour of silica-coated iron oxide nanostructures.

  A G Roca, D Carmona, N Miguel-Sancho, O Bomatí-Miguel, F Balas, C Piquer, J Santamaría
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  ABSTRACT: We report here a detailed structural and magnetic study of different silica nanocapsules containing uniform and highly crystalline maghemite nanoparticles. The magnetic phase consists of 5 nm triethylene glycol (TREG)- or dimercaptosuccinic acid (DMSA)-coated maghemite particles. TREG-coated nanoparticles were synthesized by thermal decomposition. In a second step, TREG ligands were exchanged by DMSA. After the ligand exchange, the ζ potential of the particles changed from -10 to -40 mV, whereas the hydrodynamic size remained constant at around 15 nm. Particles coated by TREG and DMSA were encapsulated in silica following a sol-gel procedure. The encapsulation of TREG-coated nanoparticles led to large magnetic aggregates, which were embedded in coalesced silica structures. However, DMSA-coated nanoparticles led to small magnetic clusters inserted in silica spheres of around 100 nm. The final nanostructures can be described as the result of several competing factors at play. Magnetic measurements indicate that in the TREG-coated nanoparticles the interparticle magnetic interaction scenario has not dramatically changed after the silica encapsulation, whereas in the DMSA-coated nanoparticles, the magnetic interactions were screened due to the function of the silica template. Moreover, the analysis of the AC susceptibility suggests that our systems essentially behave as cluster spin glass systems.
  Nanotechnology 03/2012; 23(15):155603. · 3.98 Impact Factor
• Article: In vitro structural changes in porous HA/beta-TCP scaffolds in simulated body fluid.

  S Sánchez-Salcedo, F Balas, I Izquierdo-Barba, M Vallet-Regí
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  ABSTRACT: Porous scaffolds of biphasic calcium phosphate (hydroxyapatite/beta-tricalcium phosphate (beta-TCP)) have been fabricated and changes induced both in phase composition and porous architecture by immersion in simulated body fluid (SBF) under static and orbital stirring conditions have been studied. The starting porous scaffolds exhibit a low and randomized micro- and mesoporosity, an interconnected macroporosity centered at 100 and 0.6microm, a fractal connectivity of D=2.981 and total percent porosity of ca. 80%. After immersion for up to 60days the micro- and mesoporosity increase slightly, which could be attributed to dissolution of the beta-TCP phase confirmed by transmission electron microscopy. The effects of the change in the porous framework with SBF immersion time favor the bioactive behavior of the tested materials, inducing a nucleation and growth of a nanocrystalline apatite phase as the interconnected macroporosity centered at 0.6microm is reduced. The macroporosity centered at 100microm is still stable after 60days in SBF. Therefore, these biphasic calcium phosphate porous scaffolds combine bioactive behavior with the stability of interconnected macroporosity over large periods of soaking time in SBF under static and orbital stirring conditions.
  Acta biomaterialia 04/2009; 5(7):2738-51. · 3.98 Impact Factor
• Article: Functionalization of different polymers with sulfonic groups as a way to coat them with a biomimetic apatite layer.

  I B Leonor, H-M Kim, F Balas, M Kawashita, R L Reis, T Kokubo, T Nakamura
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  ABSTRACT: Covalent coupling of sulfonic group (-SO 3H) was attempted on different polymers to evaluate efficacy of this functional group in inducing nucleation of apatite in body environment, and thereupon to design a simple biomimetic process for preparing bonelike apatite-polymer composites. Substrates of polyethylene terephthalate (PET), polycaprolactam (Nylon 6), high molecular weight polyethylene (HMWPE) and ethylene-vinyl alcohol co-polymer (EVOH) were subjected to sulfonation by being soaked in sulfuric acid (H2SO4) or chlorosulfonic acid (ClSO 3H) with different concentrations. In order to incorporate calcium ions, the sulfonated substrates were soaked in saturated solution of calcium hydroxide (Ca(OH)2). The treated substrates were soaked in a simulated body fluid (SBF). Fourier transformed infrared spectroscopy, thin-film X-ray diffraction, and scanning electron microscopy showed that the sulfonation and subsequent Ca(OH)2 treatments allowed formation of -SO3H groups binding Ca2+ ions on the surface of HMWPE and EVOH, but not on PET and Nylon 6. The HMWPE and EVOH could thus form bonelike apatite layer on their surfaces in SBF within 7 d. These results indicate that the -SO3H groups are effective for inducing apatite nucleation, and thereby that surface sulfonation of polymers are effective pre-treatment method for preparing biomimetic apatite on their surfaces.
  Journal of Materials Science Materials in Medicine 11/2007; 18(10):1923-30. · 2.32 Impact Factor
• Article: Surface modification of organic polymers with bioactive titanium oxide without the aid of a silane-coupling agent.

  F Balas, T Kokubo, M Kawashita, T Nakamura
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  ABSTRACT: Polyethylene (PE), polyethylene terephthalate (PET), ethylene-vinyl alcohol copolymer (EVOH), and poly(epsilon-caprolactam) (Nylon 6) were successfully modified with a thin crystalline titanium oxide layer on their surfaces by a simple dipping into a titanium alkoxide solution and a subsequent soak in hot HCl solution, without the aid of a silane-coupling agent. The surface modified polymers formed a bone-like apatite layer in a simulated body fluid (SBF) within a period of 2 days. PE, PET, and Nylon 6 formed an apatite layer faster and had a higher adhesive strength to the apatite. Three-dimensional fabrics with open spaces in various sizes containing such surface modified polymer fibers are expected to be useful as bone substitutes, since they may be able to form apatite on their constituent fibers in the living body, and thus, integrate with living bone.
  Journal of Materials Science Materials in Medicine 07/2007; 18(6):1167-74. · 2.32 Impact Factor
• Source

  Available from: Luis Esquivias

  Article: Structural characterization of nanosized silica spheres

  F. Balas, M. Rodriguez-Delgado, C. Otero-Arean, F. Conde, E. Matesanz, L. Esquivias, J. Ramirez-Castellanos, J. Gonzalez-Calbet, M. Vallet-Regi
  Solid State Sciences. 01/2007; 9(5):351-356.