Templated Hydroxyapatite Nucleation and Growth at Physiological Conditions onto Self-assembled Elastin-Like Nanoparticles.

Abstract

Studying materials in the nanosize scale lead to develop new synthetic approaches and discover a lot of new properties, and therefore manipulating to develop new materials that are used for different applications. In the nanoscale, physics, chemistry, biology, material science and engineering converge toward the same principles and tools. In this work, nanoparticles that developed genetically have been used to form hydroxyapatites. Polymers such as elastin-like polymers can be manipulated by the bottom-up approach to form nanoparticles and also by top-down to form patterns in scales of nanometers on the polymer hydrogel. The first aim of this work is to synthesis a nanoparticles and characterizing it. These nanoparticles are synthesized from amphiphilic elastin-like copolymers that exhibit a lower critical solution temperature, (LCST), and under the effect of the environmental stimuli could show a transition from soluble phase to insoluble phase. Below this transition temperature, in aqueous solution, the polymers chains are hydrated and extended by the hydrophobic interaction. Above this transition temperature, the chains can be assembled to form a phase separated state and adopt a dynamic, regular and nonrandom structure. Due to the self-assembly properties of thess amphiphilic elastin-like polymers at low temperature, recombinant DNA genetic engineering has been used to recombine it with SNA15 fragment. The SNA15 fragment is the first fifteen amino acid from salivary protein statherin wherein the two phosphoserine amino acid residues at positions 2 and 3 have been substituted by L- aspartic acid. This fragment has a negative charge and a helical structure in all solvents that has a high affinity to nucleate and promote the crystallization of hydroxyapatites. The amphiphilic block copolymer has been recombined with three and six fragments of SNA15. These polymers have been characterized in ultra-pure deionized water by using differential scanning calorimetry and light scattering; furthermore, have been characterized in the solid state by Fourier Transform Infrared Spectroscopy (FTIR). The second aim of this work is using these nanoparticles as a template to form nanoparticles of calcium phosphates under physiological conditions. The elastin-like polymers assembled to nanoparticles that are able to form calcium phosphate in SBF at 37oC. Electron microscopy used to study the formed nanoparticles of calcium phosphate by performing electron diffraction and elemental analysis over the nanoparticles. Also, the calcium phosphates formed have been investigated using X-ray to identify the formed phases of calcium phosphate. Furthermore; the formed nanocalcium phosphates and its effect on polymer structure have been studied by FTIR spectroscopy.