Evaluation of novel biphasic nanocomposite biomeaterials for bone tissue engineering

Abstract

The design and application of nanoparticles in both single and composite forms have gained particular interest in bone tissue engineering. Ideally, the physicochemical properties of individual nanoparticles should mimic the bone apatite while the composite nanoparticles (nanocomposite scaffold) should also mimic the bone structural and functional properties with mimetic porosity. In this context, controlling the porosity and hydrophilicity parameters of bone scaffolds is critical because of their direct impact on scaffold permeability which in turn affects protein adsorption and cellular behaviors.

This thesis aims to address the current challenges in the production of nanoparticles and nanocomposite scaffold for bone tissue engineering. Biphasic nanoparticles with optimized physicochemical properties were first synthesized using an alternative approach based on the modified wet mechanochemical method and solid state synthesis. After, these nanoparticles were used for the production of the novel nanocomposite in a collagen/nBCP scaffold through a novel integrated manufacturing approach involving a modified freeze-drying and chemical-foaming method. Various processing variables were extensively explored to control and optimize the porosity and hydrophilicity of the scaffold. In particular, the application of “Tween” and “vitamin E” in different ratios were evaluated as potential foaming agents and porogens, as well as different quenching rates, and collagen/nBCP ratios. Detailed physicochemical characteristics, porosimetry, and the initial biocompatibility of the produced biomaterials were analyzed using various methods including; X-ray diffractometry (XRD), fourier transform infrared spectrophotometry (FTIR), particle size analysis (PSA), thermogravimetric analysis (TGA), micro-CT, swelling test, mechanical test, scanning electron microscopy (SEM), and Alamar blue test.

The results confirmed production of a highly biomimetic calcium-deficient carbonate-substituted nano biphasic calcium phosphate (nBCP) bioceramic consisting of nano hydroxyapatite and β-tricalcium phosphate (nHA/nβ-TCP). Compared to control and standard samples, these nanoparticles displayed a higher crystallinity and homogeneity with a reduced particle agglomeration size which in turn would improve their biological behaviors. The composition ratio of nHA/nβ-TCP can be further modified through careful control of the calcination process which in turn influences the biodegradation rate and bioactivity of these nanoparticles. Furthermore, the developed nanocomposite scaffold exhibited various ranges of controllable pore size and shape, high pore interconnectivity, high hydrophilicity, and a springiness property. These features are aimed to facilitate early vascularization, bone regeneration, and the physical adaptation into small bone defect sites with the ability to rebound on insertion to fill the defect. The initial in vitro study and biocompatibility analysis also confirmed the higher biological performances of these scaffolds.

We have successfully synthesized biomimetic nanoparticles (nBCP) for production of nanocomposite scaffold (collagen/nBCP) with multimodal gradient porosity and controllable properties. This could be either through control of the physicochemical characteristics of individual nanoparticles (e.g., nHA/ nβ-TCP ratio) or by modification of nanocomposite scaffold through control of production variables which in turn yield in different degree of porosity and hydrophilicity. Furthermore, considering the potential of applied surfactants (Tween and vitamin E), their application as a porogen as well as a potential drug carrier could be a promising approach in tissue engineering. The detailed cellular and pre-clinical studies are required for further evaluation.