Water dispersible hydroxyapatite nanoparticles functionalized by a family of aminoalkyl phosphates

A series of aminoalkyi phosphates（AAP-n,with carbon number n ranging from 2 to 6） are used as surface modifiers to prepare hydroxyapatite hydrocolloids.The resulting nanoparticles（Cn-HA） possess a coreshell structure where an ionized layer of calcium-（AAP-n） complex[^＋H3N-（CH2）n-OPO3Ca]encapsulates each hydroxyapatite core.Long-term colloidal stability is achieved due to the electrostatic repulsion among the suspending particles.The incorporation of AAP-n results in a preferential crystal growth along c-axis,showing an increasing aspect ratio of particles from C2-HA to C6-HA.Preliminary cell culture using osteoblast-like MG63 cells shows no cytotoxicity associated with the as-prepared Cn-HA particles.The functional amino groups around the nanoparticles could be used to graft various organic chains to prepare homogeneous HA/polymer composites as bone grafting materials.

Synthesis of poly(ethylene glycol)-functionalized hydroxyapatite organic colloid intended for nanocomposites

Traditional modifications to hydroxyapatite （HA） nanoparticles usually occurred after HA synthesis and thus are insufficient to avoid particle agglomeration. In this study, a new heterofunctional poly（ethylene glycol） （PEG） with phosphoric acid and carboxyl end groups, Le., a-（N-2-phosphoethyl phosphoric acid）- amide, w-carboxyl-bismethyoxy poly（ethylene glycol） （ADP-PEG-COOH）, was synthesized as an in situ surface modifier to HA nanoparticles. The resulting modified HA （ADP-PEG-HA） can disperse in methanol, forming a colloid stabilized by peripheral carboxyl-endcapped PEG chains. The colloidal particles resembled nanospheres which agglomerated to some extent under examination by transmission electron microscope. This highly dispersible HA nanoparticles in organic solvent might find application in preparing new HA nanocomposites.

Acid dissociation constants and cytotoxicity test of a series of omega-aminoalkyl phosphates

We synthesised a series of ω-aminoalkyl sodium hydrogen phosphates （AAP-n-Na, n =3, 4, 5, 6, purity 〉 99%）, which have potential applications as bioactive cosmetic ingredients and surface modifiers of bone minerals （i.e. hydroxyapatites）. Results from Fourier transformed infrared （FTIR）, nuclear magnetic resonance （NMR） and high resolution mass spectroscopy, and elemental analysis all matched their chemical structures. The acid dissociation constants （pKa＇s） of each AAP-n （acid form of AAP-n-Na, n ; 2-6） were measured by potentiometric titration, showing a general increasing trend with an increase in the chain length of AAP-n. However, the pKa3 constant, which corresponds to the deprotonation of the ammonium group in AAP-n-Na, displayed an unusual decrease when n = even. This odd-even effect can be explained by the pairwise self-association of AAP-n-Na molecules in water where intermolecular hydrogen bonding in case of n=even is weaker than that in case of n=odd. All AAP-n-Na at concentrations up to 0.1% （w/v） were non-toxic to L929 fibroblasts and MG 63 osteoblast-like cells in terms of cell growth and morphology, These basic data were important for applications of AAP-n and their salts in biomedical engineering.