عزیزالله نودهی

Biocompatible cellulosic polymer hydrogels are used in in-situ forming injectable scaffolds for bone regeneration. The hydrogels، however، generally suffer from their inherent weak mechanical properties. Calcium phosphate particles are used to enhance the mechanical strength and to improve the bone tissue regeneration capability of the scaffolds. In this study، hydroxypropyl methylcellulose (HPMC) was utilized as a polymeric matrix and β-tricalcium phosphate (β-TCP) and hydroxyapatite (HAp) nanoparticles were used to improve the mechanical properties. β-TCP Nanoparticles with plate-like morphology was synthesized through a wet chemical precipitation method. The morphology of the particles was confirmed using scanning electron microscope (SEM). Because the gelation temperature of the HPMC solution was above the temperature of normal human body، different concentrations of sodium sulphate (Na2SO4) were incorporated into the HPMC solutions to examine and adjust the gelation temperature. The cloud point and gelation temperature of the hydrogels were measured using UV/Vis spectroscopy and oscillatory rheometry، respectively. The injectability of the hydrogels، with different inorganic contents، was also measured using a universal testing machine. The results indicated that the cloud point and the gelation temperature of the hydrogels dropped with increase in the sodium sulphate concentration due to Hofmeister effect. The rheology measurements also revealed that β-tricalcium phosphate was more effective than hydroxyapatite in reducing the gelation temperature and enhancement of the modulus and viscosity of the hydrogels. The HPMC hydrogels containing β-tricalcium phosphate and hydroxyapatite nanoparticles were injectable at room temperature. The hydrogels based on HPMC matrix and the calcium phosphate nanoparticles provided promising hydrogels applicable as in-situ forming injectable scaffolds.

Hollow microspheres or microballoons are gas-filled spherical particles with diameters between 1 to 1000 micrometers. The wall material may be made from glass, ceramic oxides, polymers or even metals. The typical thickness of the wall is in the range of 1 to 10% of the outer diameter of the sphere. Hollowmicrospheres have low density and high specific surface. They are widely used as toners, immobilization carriers, chromatographic packings, and sound dampening or adsorption materials. Thermally expandable microspheres are hollow balloons that consist of a thermoplastic shell with a liquid blowing agent as the core. These microspheres are expanded by applying temperatures higher than the glass transition temperature of the thermoplastic shell. The particles expand due to the evaporation of the encapsulated solvent which causes an internal pressure. In this study the primary expandable particles were synthesized via suspension polymerization of methacrylate monomers in the presence of pentane as a blowing agent and benzoyl peroxide as a thermal initiator. In the second step, the particles consisting of PMMA shell and pentane core were expanded at elevated temperature to obtain microballoons with a very low density. Morphology of the particles was studied using scanning electron microscopy. The results showed that the process successfully resulted in formation of spherical microballoons. The mean diameter of unexpanded particles was about 30 μm and thickness of the shell was about 2 μm while, their mean diameter after expansion was about 90 μm and the thickness of the shell decreased to 400 nm. The diameter to wall thickness ratio of expanded particles was about 1:200 which provided particles with a very low density of 0.05 g/cm3.