Interfacial Interactions between Calcined Hydroxyapatite Nanocrystals and Substrates

Abstract

Interfacial interactions between calcined hydroxyapatite (HAp) nanocrystals and surface-modified substrates were investigated by measuring adsorption behavior and adhesion strength with a quartz crystal microbalance (QCM) and a contact-mode atomic force microscope (AFM), respectively. The goal was to develop better control of HAp-nanocrystal coatings on biomedical materials. HAp nanocrystals with rodlike or spherical morphology were prepared by a wet chemical process followed by calcination at 800 degrees C with an antisintering agent to prevent the formation of sintered polycrystals. The substrate surface was modified by chemical reaction with a low-molecular-weight compound, or graft polymerization with a functional monomer. QCM measurement showed that the rodlike HAp nanocrystals adsorbed preferentially onto anionic COOH-modified substrates compared to cationic NH2- or hydrophobic CH3-modified substrates. On the other hand, the spherical nanocrystals adsorbed onto NH2- and COOH-modified substrates, which indicates that the surface properties of the HAp nanocrystals determined their adsorption behavior. The adhesion strength, which was estimated from the force required to move the nanocrystal in contact-mode AFM, on a COOH-grafted substrate prepared by graft polymerization was almost 9 times larger than that on a COOH-modified substrate prepared by chemical reaction with a low-molecular-weight compound, indicating that the long-chain polymer grafted on the substrate mitigated the surface roughness mismatch between the nanocrystal and the substrate. The adhesion strength of the nanocrystal bonded covalently by the coupling reaction to a Si(OCH3)-grafted substrate prepared by graft polymerization was approximately 1.5 times larger than that when adsorbed on the COOH-grafted substrate.

Hydroxylapatite nanoparticles: fabrication methods and medical applications

“…To coat well-crystallized HAp on a broad range of substrates, the nanocrystal coating has been developed [346][347][348][349][350][351][352][353][354][355]. This approach involves four steps: (i) preparation of calcined HAp nanocrystals (see section 2.2.6), (ii) surface modification of the substrate to react with HAp surfaces, (iii) adsorption of HAp nanocrystals onto the modified substrate, and (iv) reaction at the interface between the HAp nanoparticle and the substrate (figure 3).…”

“…The surface modification of the substrate is essential to determine the bonding strength of HAp [354]. In the nanocrystal coating method, the substrates were modified by graft polymerization of functional monomers having alkoxysilyl, isocyanate or carboxyl groups.…”

“…For example, alkoxysilyl groups (silane coupling agents) [210,366] and isocyanate groups [367] can covalently react with surface hydroxyl groups of HAp, and carboxyl groups can interact ionically with calcium ions on the HAp surfaces. Polymer and metal substrates have been used [346][347][348][349][350][351][352][353][354][355]. After adsorption of HAp nanocrystals and reaction at the interface between HAp nanocrystals and substrate surfaces, the HAp-nanocrystal-coated substrates retained the mechanical properties of the substrates and showed improved cell adhesion properties owing to the presence of HAp crystals on the surface [349][350][351][352][353]355].…”

Nanodimensional and Nanocrystalline Calcium Orthophosphates

“…Furthermore, nanophase HA appeared to have ~ 11% more proteins of fetal bovine serum adsorbed per 1 cm2 than submicron-sized HA [160]. Interfacial interactions between calcined HA nano-sized crystals and various substrates were studied and a bonding strength appeared to be influenced not only by the nature of functional groups on the substrate but also by matching of surface roughness between the nano-sized crystals and the substrate [161]. More to the point, incorporating of nanodimensional particles of HA into polyacrylonitrile fibers were found to result in their crystallinity degree rising by about 5% [162].…”

Medical Application of Calcium Orthophosphate Bioceramics

“…Ideally, a strong bond will be formed between the implant and surrounding tissues [54]. A detailed study on interfacial interactions between calcined HA and substrates have been performed recently [641], where the interested readers are referred for further details.…”