Fabrication and evaluation of nanoclay-enriched calcium phosphate granules for bone regeneration

Fabrication and evaluation of nanoclay-enriched calcium phosphate granules for bone regeneration
Neda Eskandari,^1,* Seyedeh Sara Shafiei,²
1. Department of Stem cell and Regenerative Medicine, Institute of Medical Biotechnology, National Institute of Genetic Engineering and Biotechnology, Tehran 14965/161, Iran
2. Department of Stem cell and Regenerative Medicine, Institute of Medical Biotechnology, National Institute of Genetic Engineering and Biotechnology, Tehran 14965/161, Iran
Introduction: Tissue engineering is an essential field that provides alternative solutions for organ transplants, and contributes dramatic potential improvement in human health. Several types of bone graft materials have been used to restore damaged bones, including different types of porous materials, such as ceramics, polymers and metals have been developed in the field of tissue engineering. For the last few decades, calcium phosphate ceramics have attracted the attention of biomaterial scientists due to their osteoconductivity, biodegradability and biocompatibilities. One of the most important challenges facing tissue engineering researches is the scaffold design with optimum physical and mechanical properties for growth and proliferation of cells and tissue formation. CaPs materials such as β-tricalcium phosphate (Ca3(PO4)2, β-TCP) and hydroxyapatite (Ca10(PO4)6(OH)2, HA) are similar to those found in human bone; therefore, they are the most commonly used ceramics in the biomedical fields. Among these bioceramics, β-TCP has been widely used instead of apatites for oral plastic surgery and bone tissue engineering due to their excellent biodegradability so it can be resorbed and replaced by new formed bone tissues and there is no need for a second surgical operation to remove the device after healing occurrence. However, both of these ceramics have a number of drawbacks that have reduced their clinical performance. The biodegradation of HA was shown to be very low, which prevented optimal bone formation. On the other hand, β-TCP was reported to be a mechanically weak ceramic, so its biomedical applications for bone tissue reconstruction have been largely limited by their poor mechanical properties The aim of this study was to produce a novel nanocomposite containing β-tricalcium phosphate and nanoclay and then analyzing the capacity of osteogenic activity. To our knowledge, nanoclays have not been incorporate previously with β-tricalcium phosphate for fabrication of granules for bone grafting. Also this study is the first report on the effects of nanoclay on the mechanical properties and porosity of granules.
Methods: In this paper, nanocomposite powders were synthesized by precipitation processes. Then, the porous ceramic granules were prepared by the polyurethane sponge replication method. In this study four kinds of β-TCP granules with different nanoclay contents (ranging from 0.1 wt.% to 10 wt.%) have been prepared. X-Ray Diffraction (XRD) and Scanning Electron Microscope/Energy Dispersive X-ray spectroscopy (SEM/EDX) techniques were used in order to study the phase and element structure, morphology, and determination of functional groups of granules. Afterwards, the morphology, mechanical behavior, porosity of granules were evaluated and the effects of nanocomposites on attachment, viability and proliferation of human mesenchymal stem cells were also investigated.
Results: Physiochemical characterizations demonstrated that the chemical composition and microstructure of the granules were similar to the natural spongy bone. Interconnected macro pores ranging over 200 to 500μm were observed for all kinds of granules. SEM micrograph images showed that human mesenchymal stem cells attached to the surfaces of the granules and were well proliferated. The results warranted that, the synthesized granules exhibit good biocompatibility and in vitro biomineralization. Porosity is an essential factor for bone tissue engineering. The results of porosimetry analysis indicated that adding nanoclay to β-TCP granules resulted in no significant change on the porosity percentage and according to SEM images, macropores and their interconnectivity was also maintained. The mechanical test proved that increasing the weight percentage of nanoclay to β-TCP granules caused an increase in compressive modulus. So, by increasing the nanoclay concentrations up to 10%, compressive strength was enhanced and the porosity has not been affected significantly
Conclusion: Based on the results of compressive strength and porosity tests, the most suitable type of granule is β-TCP + 10% nanoclay with 75±5% porosity, with a compressive modulus of 230 MPa, which can be utilized in bone tissue engineering. It is considerable that high porosity β-TCP granules with high initial strength have the advantage of immediate postoperative weight bearing. Therefore, this granule have great potential for bone defects regeneration and tissue engineering applications.
Keywords: Tissue engineering - β-tricalcium phosphate - nanoclay- granule-bone grafts