Effects of hydroxyapatite filler on long-term hydrolytic degradation of PLLA/PCL

[EN] Poly(L-lactic acid)(PLLA)/poly(epsilon-caprolactone)(PCL)/hydroxyapatite(HAp) composites appear as promising materials for healing large bone defects. Highly porous PLLA/PCL scaffolds, 80/20, 20/80 weight ratios, porosity >85%, were prepared by a dual technique of freeze extraction and porogen leaching, with and without HAp. A double pore structure was obtained, with interconnected macroporosity together with interconnected microporosity. Subsequent long-term (78 weeks = 1.5 years) hydrolytic degradation behavior was investigated in terms of the samples' mechanical properties, molecular weight (M-w), mass changes, thermal characteristics, X-ray Diffraction and Thermogravimetric Analysis. Elastic modulus and yield strength of as-synthesized scaffolds were higher for PLLA rich blends and including the inorganic phase does not lead to a mechanical strengthening in these materials. Nevertheless, after 30 weeks of degradation, PLLA rich scaffolds lost more than half of their strength and rigidity. On the contrary, the densification modulus of the PLLA based blends increased with degradation time, whereas PCL-based blends had a relatively constant densification modulus. PCL-based samples showed lower hydrolysis coefficients k than PLLA-based samples, as expected from the higher density of ester bonds in the latter. Interestingly, although including HAp leads to a lower hydrolysis coefficient k in PCL rich samples, it increases k in the PLLA-based sample, which is consistent with the other results obtained.The authors are grateful for the support of the Biomedical Research Networking Center in Bioengineering, Biomaterials, and Nanomedicine, an initiative funded by the VI National R&D&i Plan 2008-2011, Iniciativa Ingenio 2010, and Consolider Program. J. Rodenas-Rochina acknowledges the funding of his PhD by the Valencian Generality through VALi+d grant.Ródenas Rochina, J.; Vidaurre, A.; Castilla Cortázar, MIC.; Lebourg ., MM. (2015). Effects of hydroxyapatite filler on long-term hydrolytic degradation of PLLA/PCL. Polymer Degradation and Stability. 119:121-131. doi:10.1016/j.polymdegradstab.2015.04.01512113111

Morphology, Crystallinity, and Molecular Weight of Poly(E-caprolactone)/Graphene Oxide Hybrids

[EN] A study was carried out to determine the effects of graphene oxide (GO) filler on the properties of poly(epsilon-caprolactone) (PCL) films. A series of nanocomposites were prepared, incorporating different graphene oxide filler contents (0.1, 0.2, and 0.5 wt%) by the solution mixing method, and an in-depth study was made of the morphological changes, crystallization, infrared absorbance, molecular weight, thermal properties, and biocompatibility as a function of GO content to determine their suitability for use in biomedical applications. The infrared absorbance showed the existence of intermolecular hydrogen bonds between the PCL's carbonyl groups and the GO's hydrogen-donating groups, which is in line with the apparent reduction in molecular weight at higher GO contents, indicated by the results of the gel permeation chromatography (GPC), and the thermal property analysis. Polarized optical microscopy (POM) showed that GO acts as a nucleating point for PCL crystals, increasing crystallinity and crystallization temperature. The biological properties of the composites studied indicate that adding only 0.1 wt% of GO can improve cellular viability and that the composite shows promise for use in biomedical applications.This work was supported by Projects GV/2016/067 of the Generalitat Valenciana and MAT2016-76039-C4-3-R of the Spanish Ministry of Economy and Competitiveness (MINECO). The authors are grateful to M. Monleon-Pradas for his helpful comments and G. Vilarino-Feltrer for his valuable advice on the cell culture experiments. A. Vidaurre would also like to express her gratitude for the support received from CIBER-BBN, an initiative funded by the VI National R&D&i Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program, CIBER Actions financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund. SEM, TEM and AFM were conducted by the authors at the Microscopy Service of the Universitat Politecnica de Valencia, whose advice is greatly appreciated.Castilla Cortázar, MIC.; Vidaurre, A.; Marí, B.; Campillo Fernandez, AJ. (2019). Morphology, Crystallinity, and Molecular Weight of Poly(E-caprolactone)/Graphene Oxide Hybrids. Polymers. 11(7):1-19. https://doi.org/10.3390/polym11071099S119117Hummers, W. S., & Offeman, R. E. (1958). Preparation of Graphitic Oxide. Journal of the American Chemical Society, 80(6), 1339-1339. doi:10.1021/ja01539a017Stankovich, S., Piner, R. D., Nguyen, S. T., & Ruoff, R. S. (2006). Synthesis and exfoliation of isocyanate-treated graphene oxide nanoplatelets. Carbon, 44(15), 3342-3347. doi:10.1016/j.carbon.2006.06.004Dreyer, D. R., Park, S., Bielawski, C. W., & Ruoff, R. S. (2010). The chemistry of graphene oxide. Chem. Soc. Rev., 39(1), 228-240. doi:10.1039/b917103gKonios, D., Stylianakis, M. M., Stratakis, E., & Kymakis, E. (2014). 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A comparative study on Poly(ε-caprolactone) film degradation at extreme pH values

The present paper studies the effect of pH on hydrolytic degradation of Poly(ε-aprolactone) (PCL) Degradation of the films was performed at 37 C in 2.5 M NaOH solution (pH 13) and 2.5 M HCl solution (pH 1). Weight loss, degree of swelling, molecular weight, and calorimetric and mechanical properties were obtained as a function of degradation time. Morphological changes in the samples were carefully studied through electron microscopy. At the start of the process the degradation rate of PCL films at pH 13 was faster than at pH 1. In the latter case, there was an induction period of around 300 h with no changes in weight loss or swelling rate, but there were drastic changes in molecular weight and crystallinity. The changes in some properties throughout the degradation period, such as crystallinity, molecular weight and Young s modulus were lower in degradations at higher pH, highlighting differences in the degradation mechanism of alkaline and acid hydrolysis. Along with visual inspection of the degraded samples, this suggests a surface degradation at pH 13, whereas bulk degradation may occur at pH 1.The authors would like to acknowledge the support of the Spanish Ministry of Science and Education through the MAT2013-46467-C4-1-R Project. A. Vidaurre would also like to acknowledge the support from CIBER-BBN, an initiative funded by the VI National R&D&i Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program, CIBER Actions financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund.Sailema-Palate, GP.; Vidaurre Garayo, AJ.; Campillo Fernández, AJ.; Castilla Cortázar, MIC. (2016). A comparative study on Poly(ε-caprolactone) film degradation at extreme pH values. Polymer Degradation and Stability. 130:118-125. https://doi.org/10.1016/j.polymdegradstab.2016.06.005S11812513

Biomimetic Growth of Hydroxyapatite in Hybrid Polycaprolactone/Graphene Oxide Ultra-Porous Scaffolds

[EN] This paper reports the preparation and character-ization of hybrid scaffolds composed of polycaprolactone (PCL) and different graphene oxide (GO) amounts, intending to incorporate the intrinsic characteristics of their constituents, such as bioactivity and biocidal effect. These materials were fabricated by a solvent-casting/particulate leaching technique showing a bimodal porosity (macro and micro) that was around 90%. The highly interconnected scaffolds were immersed in a simulated body fluid, promoting the growth of a hydroxyapatite (HAp) layer, making them ideal candidates for bone tissue engineering. The growth kinetics of the HAp layer was influenced by the GO content, a remarkable result. Furthermore, as expected, the addition of GO neither significantly improves nor reduces the compressive modulus of PCL scaffolds. The thermal behavior of composites was investigated by differential scanning calorimetry, showing an increase in crystallinity as the addition of GO raised, which implies that GO nanosheets can act as seeds to induce the crystallization of PCL. The improved bioactivity was demonstrated by the deposition of an HAp layer on the surface of the scaffold with GO, especially with a 0.1% GO content.The authors are grateful for the support of the Spanish Ministry of Science, Innovation and Universities through (i) PID2021-126612OB-I00 and (ii) PID2019-106099RB-C41. Also, this research was supported by (iii) CIBER -Consorcio Centro de Investigación Biomédica en Red- (CB06/01/1026), Instituto de Salud Carlos III, Ministerio de Ciencia e Innovación and (iv) H2020 FET-OPEN grant 964562. FESEM images were taken by the authors at the Microscopy Service of the Universitat Politecnica ̀ de Valencia, ̀ whose advice is greatly appreciated.Fuster-Gómez, S.; Castilla Cortázar, MIC.; Vidaurre, A.; Campillo-Fernández, AJ. (2023). Biomimetic Growth of Hydroxyapatite in Hybrid Polycaprolactone/Graphene Oxide Ultra-Porous Scaffolds. ACS Omega. 8:7904-7912. https://doi.org/10.1021/acsomega.2c0765679047912

Production and enzymatic degradation of poly (epsilon-caprolactone)/graphene oxide composites

[EN] Poly(epsilon-caprolactone) (PCL) based composites containing different graphene oxide (GO) contents (0.1, 0.2 and 0.5 wt%) were produced by the solution mixing method followed by compression molding and enzymatically degraded in a pH 7.4 phosphate buffer solution containing Pseudomonas lipase at 37 degrees C. Morphological changes, molecular weight, calorimetric and mechanical properties were analyzed according to graphene oxide content. The study of tensile properties showed that the composites increased their Young's modulus, while tensile strength and elongation at break decreased to significantly less than that of neat PCL. PCL composite crystallinity was evaluated by differential scanning calorimetry (DSC). It was found that incorporating GO can reduce nucleation activity as well as crystallization rates, from 67.6% for neat PCL to 50.6% for a composite with 0.5 wt% GO content. For enzymatic degradation, the weight loss data showed that incorporating GO into the PCL significantly altered enzymatic degradation. The presence of GO did not alter PCL's hydrolysis mechanism, but did slow down composite enzymatic degradation in proportion to the percentage of filler content.I. Castilla-Cortazar and A. J. Campillo-Fernandez are grateful for the support of the Spanish Ministry of Science, Innovation and Universities, through RTE2018-095872-13-C22/ERDF. A. Vidaurre would like to express her gratitude for the support of the Spanish Ministry of Science and Education, through the MAT2016-76039-C4-1-R Project, and also the support from CIBER-BBN, an initiative funded by the Sixth National R&D&i Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program, CIBER Actions financed by the Institute de Salud Carlos III with assistance from the European Regional Development Fund. The FESEM, TEM and mechanical tests were conducted by the authors at the Microscopy Service of the Universitat Politecnica de Valencia, whose advice is greatly appreciated,Martínez-Ramón, V.; Castilla Cortázar, MIC.; Vidaurre, A.; Campillo Fernandez, AJ. (2020). Production and enzymatic degradation of poly (epsilon-caprolactone)/graphene oxide composites. Materials Express. 10(6):866-876. https://doi.org/10.1166/mex.2020.1702S86687610

Poly(epsilon-caprolactone)/Graphene oxide composite systems: a comparative study on hydrolytic degradation at extreme pH values

[EN] Polycaprolactone/Graphene oxide (PCL/GO) composites are shown to be promising substrates for tissue engineering as their degradation behavior is a key aspect in this type of application. The present paper studies the effect of different GO contents (0.1, 0.2 and 0.5 wt%) of PCL/GO composites on accelerated hydrolytic degradation at pH 13 and pH 1. Degradation kinetics at pH 13 is strongly affected by GO content, and speed up at higher percentages. The composite with 0.5 wt% of GO was completely degraded in 72 hours, while degradation at pH 1 presents a different profile and seems to have an induction period that lasts more than 1500 hours. Morphological changes, molecular weight distribution, weight loss, degree of swelling and calorimetric properties were obtained as a function of degradation time. According to the results obtained, the addition of small percentages of GO significantly influences the degradation behavior of the composites acting as degradation modulators.Isabel Castilla-Cortazar and Alberto J. Campillo-Fernandez are grateful for the support of the Spanish Ministry of Science, Innovation and Universities, through RTI2018-095872-B-C22/ERDE Ana Vidaurre would like to express her gratitude for the support of the Spanish Ministry of Science and Education, through the MAT2016-76039-C4-1-R Project, and also the support from CIBER-BBN, an initiative funded by the Sixth National R&D&i Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program, CII3ER Actions financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund.Campillo Fernandez, AJ.; González-Reed, P.; Vidaurre, A.; Castilla Cortázar, MIC. (2020). Poly(epsilon-caprolactone)/Graphene oxide composite systems: a comparative study on hydrolytic degradation at extreme pH values. Materials Express. 10(6):892-902. https://doi.org/10.1166/mex.2020.1728S89290210

Influence of the achromatic grating orientation (vertical-horizontal) in the vision of interleaved sequences

With horizontal and vertical full contrast achromatic gratings, used as a background in the vision of two sequences (one red and the other one blue), it is studied the relationship between the frequency of the gratings and the Bezold effect, produced in the vision of the sequences. The results tell us that with the horizontal orientation of the grating, the Bezold effect is greater than with the vertical; in both orientations this effect is greater with the blue sequenceMontalvá Colomer, J.; Tortajada Montañana, I.; Castilla Cortázar, MIC.; Martínez Bazán, ML.; Aguilar Rico, M. (2010). Influencia de la orientación (vertical-horizontal) de redes acromáticas en la visión de secuencias intercaladas. Óptica Pura y Aplicada. 43(4):213-217. http://hdl.handle.net/10251/62930S21321743