Three-Dimentionally Interconnected BCP/(PCL-Silica) Hybrid Scaffolds with Controlled Microstructure for Biomedical Implant

Abstract

Porous bioceramics with aligned pores has been widely studied in bone tissue engineering field since they provide proper environment for bone cells to attach and grow, and three-dimentionally interconnected pore structures enable them to penetrate. Furthermore, porous bioceramic with adequate strength could be used as a supporting framework that can sustain loads as tissues grow. Among various methods of producing porous bioceramics, freeze casting has attracted great interest, as it can produce interconnected pore channels formed by freezing vehicles. The freezing vehicles can be easily removed by sublimation of frozen phase which in turn leaves pores in the ceramic body. This present study reports novel, simple way of creating porous BCP bioceramic scaffold with three-dimentionally interconnected pore structure by camphene-based freeze casting achieved by our recent works and suggests the potential application as biomedical implant by coating with organic/inorganic compound. First, porous BCP ceramic with unidirectional pore channels were produced by extruding frozen ceramic/camphene body through reduction die at room temperature. This simple extrusion process enabled the formation of aligned porous BCP ceramics as a replica of the camphene dendrites which were removed by freeze drying. The preferential orientation of pore structure was attributed to the extrusion process, which induced unidirectional elongation of camphene dendrite. Furthermore, for further application with diverse shapes of porous ceramic, fabrication of versatile designs of porous BCP ceramics were suggested by extruding frozen BCP/camphene body assembled with camphene rod as a shell and core, respectively. For the purpose of microstructure control, initial BCP contents and post-treatment time were changed, and the pore structure such as porosity, densification of BCP walls, pore size, and pore alignment were investigated. However, the prepared porous BCP ceramics showed significantly enhanced mechanical strength in the parallel direction of pore alignment, but exhibited brittle fracture, due to the brittle nature of ceramic and porous structure. Therefore, our strategy is to coat the porous BCP ceramics with hybrid solution not only to enhance mechanical properties but also to provide biocompatible environment for promising material that could be used in biomedical applications. The BCP/(PCL-silica) hybrid scaffolds could provide superior functions to conventional materials. In that point of view, we demonstrated fabrication of organic/inorganic hybrid composites. Poly(e-caprolactone) was chosen as a biopolymer, which is most widely used polymer that can be degraded in human body and with biocompatibility. For inorganic compound in hybrid solution, sol-gel derived silica, which possesses the mesoporous structure, was used to improve bioactivity of the hybrid material. The PCL/sol-gel derived silica membrane with controlled pore structure were fabricated, characterized, and evaluated in assess of microstructure, wettability, and biological properties. The capability of antibiotic and protein loading was assessed for further applications in this work. The potential of the BCP/(PCL-silica) hybrid scaffolds as the biomedical implant was examined by coating the porous BCP bioceramic scaffolds with prepared PCL/silica solution. Bone morphogenetic protein-2 (BMP-2) was loaded in the hybrid solution before coating the porous BCP bioceramic. The BCP(PCL-silica) hybrid scaffolds showed significantly improved fracture behavior, which could be used in load bearing part in biomedical field and the enhanced bioactivity of BCP(PCL-silica) hybrid scaffolds was examined by the in vitro cellular test using osteoblast-like cells. Furthremore, in vivo animal study was performed and ossteointegration was examined using rat tibial defect model. These results suggested that improved mechanical properties and enhanced biocompatibility could be achieved by PCL/silica solution coating on the porous BCP ceramic scaffold. Fabrication of antibiotic and grow-factor eluting material with controlled pore structure is another advantage of this work since in-situ loading of biomolecules to the coating solution is possible. The prepared BCP(PCL-silica) hybrid scaffolds by extrusion and coating process could be a promising material in biomedical applications.