Esperanza Díaz

In vitro degradation of Poly(caprolactone)/nHA composites

The degradation behavior and mechanical properties of polycaprolactone/nanohydroxyapatite composite scaffolds are studied in phosphate buffered solution (PBS), at 37°C, over 16 weeks. Under scanning electron microscopy (SEM), it was observed that the longer the porous scaffolds remained in the PBS, the more significant the thickening of the pore walls of the scaffold morphology was. A decrease in the compressive properties, such as the modulus and the strength of the PCL/nHA composite scaffolds, was observed as the degradation experiment progressed. Samples with high nHA concentrations degraded more significantly in comparison to those with a lower content. Pure PCL retained its mechanical properties comparatively well in the study over the period of degradation. After the twelfth week, the results obtained by GPC analysis indicated a significant reduction in their molecular weight. The addition of nHA particles to the scaffolds accelerated the weight loss of the composites and increased their capacity to absorb water during the initial degradation process. The addition of these particles also affected the degradation behavior of the composite scaffolds, although they were not effective at compensating the decrease in pH prompted by the degradation products of the PCL.

Physical gelation of polystyrene-b-poly(ethylene/butylene)-b-polystyrene in several paraffinic oils

The thermoreversible gelation of a triblock copolymer polystyrene-b-poly(ethylene/butylene)-b-polystyrene in three paraffinic oils was studied. The paraffinic oils used (Norpar 12, Norpar 13 and Norpar 15) are selective solvents for the middle PEB block of the copolymer. The three oils are chemically similar and they only differ in the average carbon number. Thus the solvent influence on the sol-gel transition and on the mechanical properties of the gels was analysed. The sol-gel transition temperature increased with the copolymer concentration and the average carbon number of the paraffinic oil. The mechanical properties of the gels were examined through oscillatory shear and compressive stress relaxation measurements. The concentration dependences of the elastic storage modulus were established, and were similar for the three paraffinic oils with exponents close to those expected for systems in good solvents (2.25) that possess a structure close to that of chemical networks. The relaxation rates observed were extremely high suggesting a considerable mobility in the gel over the measurement time. The relaxation rate increased as the oil carbon number decreased. The swelling behavior was also examined. All gels swelled significantly. The swelling equilibrium ratios varied linearly with the copolymer preparation concentration. The gels formed in Norpar 13 and Norpar 15 show a similar swelling behavior whereas the gels formed in Norpar 12 show a swelling capability markedly lower.

In Vitro Degradation of PLCL/nHA Biodegradable Scaffolds

We investigated the effect of bioactive nanoparticles on the in-vitro degradation of PLCL and PLCL/nHA composite scaffolds. The concentration of nanohydroxyapatite significantly affected the degradation rate. An increase in the crystallinity of the amorphous portion of the polymer was observed. This increased crystallinity was more pronounced in the pure PLCL samples than in those with more nHA. During the degradation process, we observed the appearance of multiple micropores on the scaffold walls as the hydrolysis process progressed and, by the sixth week, the remains of the degradation products were visible on the pore walls. GRAPHICAL ABSTRACT

Morphology and Mechanical Properties of PLLA and PCL Scaffolds

Human tissue engineering, comprising methods and tools to create implants, is a promising although as yet a very underdeveloped field of research into the regeneration of specific damaged or necrotic tissue. Porous scaffolds play an important role in tissue engineering. The porous cell culture scaffolds in this study were produced through thermally induced phase separation (lyophilization). This technique yields considerable variations in scaffold microstructures (pore size and morphology) as a function of the polymer, solvent and thermal processing. PLLA and PCL were used with chloroform, 1,4-dioxane and water as solvent. We observed a decrease in mechanical properties with increasing pore size in the two polymers under study. However, we found that PLLA, which possesses larger pore sizes than PCL, showed superior mechanical properties, which we explain in terms of crystallinity.

The Influence of Copolymer Composition on PLGA/nHA Scaffolds´ Cytotoxicity and In Vitro Degradation

The influence of copolymer composition on Poly(Lactide-co-Glycolide)/nanohydroxyapatite (PLGA/nHA) composite scaffolds is studied in the context of bone tissue engineering and regenerative medicine. The composite scaffolds are fabricated by thermally-induced phase separation and the effect of bioactive nanoparticles on their in vitro degradation in phosphate-buffered solution at 37 °C is analyzed over eight weeks. The indirect cytotoxicity evaluation of the samples followed an adaptation of the ISO 10993-5 standard test method. Based on the measurement of their molecular weight, molar mass, pH, water absorption and dimensions, the porous scaffolds of PLGA with a lower lactide/glycolide (LA/GA) molar ratio degraded faster due to their higher hydrophilicity. All of the samples without and with HA are not cytotoxic, demonstrating their potential for tissue engineering applications.

Magnetic composite scaffolds of polycaprolactone/nFeHA, for bone-tissue engineering

ABSTRACT Magnetic composite scaffolds of polycaprolactone/Fe doped nanohydroxyapatite (PCL/nFeHA) with different composition ratios have been fabricated lyophilization for the purpose of bone-tissue engineering. Magnetic measurements reveal some interaction between the Fe particles that decreases steadily as the nFeHA is diluted in the polymer. All the scaffolds were characterized before and after in vitro degradation for over 28 weeks. The nFeHA nanoparticles decreased the initiation rate of hydrolytic degradation. After 16 weeks degradation, thermograms of the first heating revealed two melting peaks, which could be attributed to the presence of crystals of two different sizes. GPC results indicated that Mw and Mn were unaffected by the degradation with no cleavage of the macromolecular chains. GRAPHICAL ABSTRACT

The Effects of Bioactive Nanoparticles on the Degradation of DLGA

The effect of bioactive nanoparticles on the in vitro degradation of DLGA composite scaffolds is investigated. Fabricated by thermally induced phase separation, the scaffolds present a high porosity (>90%). In vitro degradation is performed by immersing the scaffolds in a phosphate buffered saline solution, to evaluate water absorption, pH change, and weight loss. Chain scission by hydrolysis reduces the average molecular weight and increases the polydispersity index. The incorporation of modified hydroxyapatite nanoparticles significantly affects the DLGA degradation process, inducing appreciable changes in the morphology of the material, but not in its percentage of porosity. Nanohydroxyapatite blocks the entry of water, reducing the degradation rates. GRAPHICAL ABSTRACT

Development of Magnetically Active Scaffolds for Bone Regeneration

This work reports on the synthesis, with the thermally induced phase separation (TIPS) technique, of poly (l-lactide) (PLLA) scaffolds containing Fe-doped hydroxyapatite (FeHA) particles for bone regeneration. Magnetization curves and X-ray diffraction indicate two magnetic particle phases: FeHA and magnetite Fe3O4. Magnetic nanoparticles (MNPs) are approximately 30 ± 5 nm in width and 125 ± 25 nm in length, and show typical ferromagnetic properties, including coercivity and rapid saturation magnetization. Scanning electron microscopy (SEM) images of the magnetic scaffolds reveal their complex morphology changes with MNP concentration. Similarly, at compositions of approximately 20% MNPs, the phase separation changes, passing from solid–liquid to liquid–liquid as revealed by the hill-like structures, with low peaks that give the walls in the SEM images a surface pattern of micro-ruggedness typical of nucleation mechanisms and growth. In vitro degradation experiments, carried out for more than 28 weeks, demonstrated that the MNPs delay the scaffold degradation process. Cytotoxicity is appreciated for FeHA content above 20%.

Importing Nautical Knowledge: Nineteenth-century specialized journalism in Spain

In Spain, the advancement of science in the nineteenth century was hindered by political instability within the country. Very little domestic scientific production took place, and even less was done to keep abreast of the advances taking place abroad. In scientific and technical disciplines, knowledge transfer occurs primarily through specialized journals, whose readers may effectively track the spread of new ideas. This paper discusses the relevance of nineteenth-century Spanish nautical journalism in communicating advances in maritime knowledge, which it reviews through the spread of ‘new astronomical navigation,’ one of the key advances in nautical positioning of that century.

A Study of Poly(L-Lactide) Complexes in Solution with Cu2+

The present paper describes the synthesis of different poly(Llactide)/copper complexes (PLLA/Cu) in solution using distilled chloroform as a solvent. A polymer-metal complex is a coordination complex resulting from the reaction of a ligand function anchored to a macromolecular matrix with a metal ion. The structural environment of the ligand function is one of the key factors that determines the complexing ability of polymeric ligands with metal ions. By applying viscometric techniques, the study has successfully determined the intermolecular interactions established between the polymer and the metal cation at 298 and 338 K and at different copper concentrations using four PLLA samples, each with a different molar mass.