Influence of Morphology on Hydroxyapatite Surface Functionalization
A.N. Vasiliev, E. Zlotnikov, J.G. Khinast and R.E. Riman
Rutgers University, US
Hybrid organic/inorganic materials, hydroxyapatite, surface, amines
Novel hybrid organic/inorganic materials containing different amines on calcium hydroxyapatite (CaHAP) surface were synthesized. In our studies, we used CaHAP with different morphologies. For the preparation of spherical CaHAP we stirred a mixture of triethylphosphate with water solution of Ca(NO3)2 and NH4OH in a reactor-autoclave. The particles are relatively small and consist of randomly packed tiny platelets (10-15 nm). For hexagonal samples NH4OH was replaced on KOH, and EDTA was added to the reactional mixture. These samples consist of much bigger hexagonal particles with different aspect ratios. We used N-[3-(trimethoxysilyl)propyl]-ethylenediamine, 2-(2’-pyridyl)-ethyltrimethoxysilane and 3-aminopropyltrimethoxysilane for synthesis of hybrid materials. Their immobilization was carried out by refluxing suspended CaHAP in toluene solutions of correspondent amines. The highest loading of organic modifiers was achieved for the spherical CaHAP. In the hexagonal samples, the loading decreases with an increase of the aspect ratio the chemisorbed amount is reduced. Thus, the different faces of the crystal are not equally reactive, and it can be concluded that end faces are more reactive and can be used to immobilize a higher loading of organic modifiers. Amino-modified CaHAP might serve as intermediates for grafting compounds of different types on the surface.
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