Study of self-assembling block co-polymer templated hydroxyapatite nanocomposites gel by urease enzymetic urea hydrolysis

• Main Author: Li, Mowen
• Format: Dissertation
• Language: English
• Subjects: engineering, materials science
• ISBN: 0549997296; 9780549997290

This study aimed to develop a biomimetic approach to achieve the natural biomineralization of bone. Temperature and pH-sensitive self-assembling tri- and pentablock co-polymer templated Hydroxyapatite (Ca5(PO 4)3OH) (HAp) nanocomposite hydrogels were synthesized, and enzyme-catalyzed urea decomposition was used to increase pH gradually and homogeneously. XRD, SEM, TEM and EDS analysis confirmed the formation of HAp. The hydrogels showed the existence of amorphous HAp. The inorganic phase exhibited thin sheet-like structure with a length of hundreds nanometers, and only 5-10 nm thick. Both high-resolution TEM and scanning TEM microimages, electron diffraction and SEM confirmed the nano-crystalline phase of HAp in dry state. The nano HAp sheets assembled to form clusters in the presence of polymer. The inorganic components account for 4-6 wt% of the total hydrogels. It is also proved by NMR that organic and inorganic components intimately associated with each other that formed nanocomposites. Samples prepared with Pluronic at 37oC showed smaller nanocomposite size than PAA.
It is also found that by the same urea-urease method without polymer, low inorganic ion concentrations (0.2M and 0.4M) and low temperatures (room T and 37°C), resulted in mainly calcium carbonate (CaCO 3, calcite) whereas for higher Ca2+ and PO4 3- concentrations and temperatures (i.e., 1.0M and 1.5M at 60°C), HAp was the dominant phase. The urease activity has been confirmed to be affected by high concentration of buffer phosphate solution. Low phosphate concentration may facilitate the urea hydrolysis to release CO2 at a faster rate which reacts with Ca2+ to form CaCO3.