Coating nanothickness degradable films on nanocrystalline hydroxyapatite particles to improve the bonding strength between nanohydroxyapatite and degradable polymer matrix

Abstract

Hydroxyapatite (HA) nanoparticles are similar to bone apatite in size, phase composition, and crystal structure. When compared with micron-size HA particles, nano-HA possesses improved mechanical properties and superior bioactivity for promoting bone growth and regeneration. However, scaffolds fabricated from nano-HA alone cannot meet the mechanical requirements for direct-loading applications. A number of studies suggest that nanostructured composites may offer surface and/or chemical properties of native bone, and therefore represent ideal substrates to support bone regeneration. However, a common problem with nanohydroxyapatite (nano-HA)-polymer composites is the weak binding strength between the nano-HA filler and the polymer matrix since they are two different categories of materials and cannot form covalent bonds between them during the mixing process. Often, the mechanical strength of the composite is compromised due to the phase separation of the HA filler from the polymer matrix during the tissue repair process. To overcome this problem, an ultrathin degradable polymer film was grafted onto the surface of nano-HA using a radio-frequency plasma polymerization technology from acrylic acid monomers. The treated nano-HA powders are expected to bind to the polymer matrix via covalent bonds, thus enhancing the mechanical properties of the resultant composites. High-resolution transmission electron microscopy (HRTEM) experiments showed that an extremely thin polymer film (2 nm) was uniformly deposited on the surfaces of the nanoparticles. The HRTEM results were confirmed by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (TOFSIMS). Tensile tests performed on the specimens revealed that the degradable coating had improved elastic and strength properties when compared with the nondegradable and uncoated controls. XPS and TOSIMS data revealed that more functional carboxyl groups were formed on degradable coatings than cross-linked nondegradable coatings. Cytocompatibility assay demonstrated that both the degradable and nondegradable coatings are cytocompatible.

Nanodimensional and Nanocrystalline Calcium Orthophosphates

“…These examples emphasize that nanophase materials deserve more attention in improving orthopedic implant failure rates. However, to reduce surface energy, all nano-sized materials tend to agglomerate and, to avoid self-aggregation of calcium orthophosphate nano-sized particles [195][196][197][198], special precautions might be necessary [54,60,120,[199][200][201][202].…”

Nanodimensional and Nanocrystalline Apatites and Other Calcium Orthophosphates in Biomedical Engineering, Biology and Medicine

“…To prepare nanodimensional and/or nanocrystalline apatites, methods of wet chemical precipitation [62,71,73,86,119,121,155,156,157,160,166,186,187,237,246,258,259,260,261,262,263,264,265,266,267,268,269,270,271,272,273,274,275,276,277,278,279,280,281,282,283,284,285,286,287,288], sol-gel synthesis [30,176,210,211,242,288,289,290,291,292,293,294,295,296,297,298,299], co-precipitation [243,300…”

Biodegradable Polymeric Nanoparticles as Templates for Biomimetic Mineralization of Calcium Phosphate

“…nanoHAP surface by using radio-frequency plasma polymerization to improve the adhesion within the PLGA matrix for better mechanical properties has been described. [18] Several other interesting methods for fabricating porous composite scaffolds using biodegradable polymers have also been reported. [19] As biomimetic routes offer better organic/inorganic interface integrity as well as the feasibility to control shape, size, crystal structure, and orientation of the inorganic materials, biomimetic approaches have been postulated to mineralize polymeric scaffolds.…”