Three dimensional scaffolds of hybrid PLA/PCL/HA/silica nanocomposites for bone tissue engineering

Bone is the second most common connective tissue worldwide and more than four million bone grafts or substitutes are used annually to treat bone defects. Due to the restrictions of using these therapies, today the development of bioactive 3D scaffolds has become a major field in bone tissue engineering. The main aim of this study was to fabricate polylactic acid/ polycaprolactone bone scaffolds by freeze extraction method. In order to improve the rheological, mechanical and biological properties of these scaffolds, hydroxyapatite, silica and their mixture were used as the filler loaded into scaffolds (35 wt%). All scaffolds were fabricated in three different concentrations of 5, 6.5 and 8% w/w based on polymer to investigate the effect of polymer concentration on their properties. In this regard, to evaluate the surface morphology of scaffolds and the size of pores, SEM analysis and porosity test were used. FTIR analysis was performed to identify functional groups and possible molecular interactions in the scaffold. The degree of degradation of scaffolds was conducted when incubated in PBS and also to better investigate the mechanical properties, a compression test was performed on cylindrical specimens. SEM images indicated that the pores were interconnected in the composite scaffolds and their size varied from 23 to 114 μm. The amount of porosity of the scaffolds made in this project ranged from 62.2 to 84.1%. These values demonstrated that the scaffolds prepared by the freeze extraction method had suitable pore sizes for use in tissue engineering. Considering the morphology and porosity as well as the appropriate pore size distribution in the 6.5% hybrid sample, this scaffold was selected as the optimal scaffold. The results indicated that the hydrophilicity of the scaffold surface was improved by the addition of silica nanoparticles and hydroxyapatite. The use of HA alone improved the mechanical properties of the porous structure, but the addition of SiO₂ to HA more effectively strengthened the scaffolds. Furthermore, in samples containing silica, an increase in degradation was observed. According to the results of MTT test, the constructed scaffolds not only did not show cytotoxicity but also increased the rate of cell growth and proliferation. Pathological images showed that ECM deposition and collagen deposition were significantly higher in the hybrid groups from the third week onwards than in the other groups.