Biomedical subjects

Quanzu Yang

Publications and source records attributed to Quanzu Yang.

3 recordsLinked to original sources

PubMed2002

Sol-gel hydroxyapatite coatings on stainless steel substrates.

Thin film hydroxyapatite deposits onto sandblasted 316L stainless steel substrates were prepared using water-based sol-gel technique recently developed in our lab. The coatings were annealed in air at 375 degrees C, 400 degrees C, and 500 degrees C. Phase formation, surface morphology, interfacial microstructure, and interfacial bonding strength of the coatings were investigated. Apatitic structure developed within the coatings while annealing at temperatures > or = 400 degrees C, while those heat-treated at 375 degrees C showed poor crystallinity. The coatings were dense and firmly attached to the underlying substrates, reaching an average bonding strength (as determined through the pull-out test) of 44 MPa. Nano-porous structure was found for the coatings annealed at 500 degrees C, believed to result from grain growth, and causing a slight decrease in the bonding strength. Surface microcracking, although not extensive, occurred after annealing at temperatures > or = 400 degrees C, and was linked to non-uniform thickness of the coating due to roughness of the substrate. A contraction of the coatings as a result of sintering, and phase transition from amorphous (or poor crystalline) to reasonably good crystalline apatite, may be responsible for the loss of structural integrity of the thicker sections of the coatings. It seems quite promising that a dense and adhesive apatite coating can be achieved through water-based sol gel technology after short-term annealing at around 400 degrees C in air.

Bone Substitutes↗

PubMed2002

Structural evolution of sol-gel-derived hydroxyapatite.

Structural evolution upon transformation of sol to gel, and gel to final ceramic during the synthesis of hydroxyapatite is investigated using Fourier transform infrared (FTIR) analysis, X-ray diffraction (XRD), thermal behavior (DTA and TGA), and electron microscopy examination (SEM/TEM). The sol was first thermally aged at 45 C for various time periods up to 120 min. The colloidal sol, which may have an oligomeric structure, was relatively stable against coagulation. Upon drying, the sol particles consolidated into dry gel through van der Waals attraction, and showed X-ray amorphous phosphate structure. The solid gels showed a particulate microstructure, composed of primary particles of about 8-10 nm in diameter. The amorphous gel transformed into crystalline apatite at temperatures > 300 C. The calcined gels showed a nano-scale microstructure, with grains of 20-50 nm in diameter. Through an appropriate heat treatment between 300 and 400d degrees C. the apatite prepared using current process exhibits a nano-scale, low-crystallinity, carbonated apatitic structure, which closely resembles that of human bone apatite.

Biocompatible Materials↗

PubMed2002

Influence of apatite seeds on the synthesis of calcium phosphate cement.

This preliminary study explores the seeding effect (using crystalline hydroxyapatite particles) on the setting time, compressive strength, phase evolution, and microstructure of calcium phosphate cements (CPC) based on monocalcium phosphate monohydrate and calcium hydroxide. Experimental results showed that the setting time varies from 5 to about 30 min, as the seed concentration increased from 0 to 20 wt%. The compressive strength of CPC increased from 4 to 17 MPa, followed by decrease to 12 MPa, for the same range of seeds content. The CPC transformed to predominantly apatitic structure within 24 h for all the samples, with or without the seeds. However, increase of the seed concentration improved the final crystallinity of the apatite phase, suggesting nucleation and growth effects during precipitation of CPC from the precursor solution. The microstructure of the resulting apatitic cement showed a change from essentially featureless (or glass-like) to thin, elongated plate-like morphology, as seeds concentration increased. Correlation between microstructural evolution and corresponding compressive strength of seeded CPC is investigated.

Apatites↗