Complex relationship between alumina and selenium-doped carbonated hydroxyapatite as the ceramic additives to electrospun polycaprolactone scaffolds for tissue engineering applications

The future of nanomedicine belongs to composite nanostructures with complex and precisely tailored synergistic interactions between individual components. A composite scaffold was fabricated by electrospinning epsilon-polycaprolactone microfibers containing dispersed alumina and selenite-doped carbonated hydroxyapatite (Se-CHAP). The effects of the two coexisting ceramic components were investigated by testing the composites using a range of experimental techniques, including diffractometric, vibrational spectroscopic, porosimetric, mechanical and biological ones. No preferential orientation of the microfibers in the scaffolds was detected, but the fiber diameters increased and their curliness decreased as a function of the weight ratio between alumina and Se-CHAP. Synergistic breaking of the polymeric structure occurred due to the interaction of alumina and Se-CHAP in the polymeric matrix. The density of the composites decreased as Se-CHAP replaced alumina, but porosity was maximal in the material containing equal amounts of the two ceramic components, reiterating the complex synergistic interaction between them. Mechanical properties exhibited an equally complex relationship, with the composition containing alumina and Se-CHAP in 3:1 wt ratio displaying the highest toughness and strain at break and the composition containing alumina and Se-CHAP in 1:1 weight ratio exhibiting the lowest tensile strength and Young's modulus, lower than the materials supplemented with only alumina and only Se-CHAP. In-vitro cell studies on the human fibroblast HFB4 cell line demonstrated that the cells grew and spread on all polymeric scaffolds, but the adhesion, spread and infiltration increased in direct proportion with the Se-CHAP phase content. Also, although no significant loss of viability was detected in cells grown on any of the composite matrices, thus proving their biocompatibility, the lowest viability was detected on the matrices supplemented with the two ceramic additives in 1:1 weight ratio. Overall, no single composition proved most optimal for all the properties analyzed - microstructural, porosimetric, mechanical, biological. Rather, a compromise must be made between these different properties in search of the composition with the most optimal performance, with the caveat that fine changes in the weight ratio between alumina and Se-CHAP could produce significant repercussions at the level of material properties. The variable weight ratio between the two ceramic additives, however, allows for the tuning of the material properties for the desired application. This fundamental principle can be taken advantage of in the further optimization of this and similar materials for clinical use. (C) 2019 Elsevier B.V. All rights reserved.