Synthesis and characterization of nanocrystalline Zn, Mg substituted hydroxyapatite

Hydroxyapatite (HA) is the most important bioceramic material for hard tissue replacement in human bodies. Recently, cation substituted HA has been a research focus in order to further enhance HA bioactivity and to adapt various application requirements. Magnesium and zinc are potentially the elements to partially substitute calcium in the HA for improving osteointegration, because Mg and Zn are the most important minor and trace elements respectively in human hard tissues. Magnesium depletion affects all stages of skeletal metabolism adversely, causing cessation of bone growth, decreasing osteoblastic and osteoclastic activity, osteopenia, and bone fragility. Zn can promote bone metabolism and growth, increase bone density and prevent bone loss. Mg, Zn substitutions in the crystal structure of HA are expected to have excellent biocompatibility and biological properties. Previous researches showed no direct evidence to prove that Zn/Mg successfully substituted partial Ca in the apatite lattice but not just absorbed on the apatite surface. The apatite structural changes after substitution even the maximum amount of Mg and Zn substitution for Ca are still in controversy. Nanocrystalline Mg, Zn substituted HA particles with various Mg and Zn substitution amount were synthesized by wet chemical method. Diffraction, spectroscopy, microscopy characterization techniques were employed to investigate the substituted apatites. Especially the X-ray diffraction Rietveld Refinement method was used to examine the effects of Mg and Zn substitution on crystal structure changes. Experimental results showed that Mg, Zn successfully substituted Ca in HA. The substitution limit was between 15~20 at. % Zn and different new phases presented over this limit. While Mg substitution was rather limited (less than 5 at.%)，various non apatite phases came out when the Mg/(Mg+Ca) atomic ratio was over 15 at. % in aqueous solution. Both Zn and Mg increased the resistance of HA crystallization. After substitution, the crystallite size and crystallinity decreased. Pure HA was well crystallized and in regular shape. With the substitution content increasing, crystallites were smaller, shorter, more irregular and formed serious agglomerates. Also both Mg and Zn substitution destabilized the apatite structure and reduced the decomposition temperature of HA. The lattice parameters a and c decreased up to 10at. % in solution and then started to slightly increase

Ab initio simulation on the crystal structure and elastic properties of carbonated apatite

Ab initio quantum mechanical (QM) calculations were employed to study the crystal structure and elastic properties of carbonated apatite (CAp). Two locations for the carbonate ion in the apatite lattice were considered: carbonate substituting for OH- ion (type-A), and for PO43- ion (type-B) with possible charge compensation mechanisms. A combined type-AB substitution (two carbonate ions replacing one phosphate group and one hydroxyl group, respectively) was also investigated. The results show that the most energetically stable substitution is type-AB, followed by type-A and then type-B. The most stable configuration of type-A has its carbonate triangular plane almost parallel to c-axis at z=0.46. The lowest energy configuration of type-B is that with a sodium ion substituting for a calcium ion for charge balance and the carbonate lying on the b/c-plane of apatite. Lattice parameter changes after carbonate substitution in hydroxyapatite (HA) agree with reported experimental results qualitatively: for type-A, lattice parameter a increases but c decreases; and for type-B, lattice parameter a decreases but c increases. Using the calculated CAp stable structures, we also calculated the elastic properties of CAp and compared them with those of HA and biological apatites. (C) 2013 Elsevier Ltd. All rights reserved

Infrared spectroscopic characterization of carbonated apatite: A combined experimental and computational study

A combined experimental and computational approach was employed to investigate the feasibility and effectiveness of characterizing carbonated apatite (CAp) by infrared (IR) spectroscopy. First, an experimental comparative study was conducted to identify characteristic IR vibrational bands of carbonate substitution in the apatite lattice. The IR spectra of pure hydroxyapatite (HA), carbonate adsorbed on the HA surface, a physical mixture of HA and sodium carbonate monohydrate, a physical mixture of HA and calcite, synthetic CAps prepared using three methods (precipitation method, hydrothermal route, and solid-gas reaction at high temperature) and biological apatites (human enamel, human cortical bone, and two animal bones) were compared. Then, the IR vibrational bands of carbonate in CAp were calculated with density functional theory. The experimental study identified characteristic IR bands of carbonate that cannot be generated from surface adsorption or physical mixtures and the results show that the bands at approximate to 880, 1413, and 1450 cm(-1) should not be used as characteristic bands of CAp since they could result from carbonate adsorbed on the apatite crystals surface or present as a separate phase. The combined experimental and computational study reveals that the carbonate v(3) bands at approximate to 1546 and 1465 cm(-1) are, respectively, the IR signature bands for type A CAp and type B CAp. (c) 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 496-505, 2014

Molecular dynamics simulation of protein effects on interfacial energy between HA surfaces and solutions

Proteins play an important role in apatite formation in physiological environments. The effects of proteins partially result from changing apatite interfacial energy, and in turn, promoting or inhibiting apatite precipitation in physiological environment. The interfacial energies of hydroxyapatite (HA) crystallographic planes in aqueous solutions containing proteins and calcium and phosphate ions were calculated by molecular dynamics simulations. It provided reference interfacial energies for comparative study of protein effects that both acidic Human serum albumin and basic Lysozyme reduces the interfacial energy of HA (001) and HA (100). The simulations provide information to achieve better understanding of protein effects on the biomineralization process at atomic level. (c) 2014 Elsevier B.V. All rights reserved

Molecular dynamics simulation of protein effects on interfacial energy between HA surfaces and solutions

a b s t r a c t Proteins play an important role in apatite formation in physiological environments. The effects of proteins partially result from changing apatite interfacial energy, and in turn, promoting or inhibiting apatite precipitation in physiological environment. The interfacial energies of hydroxyapatite (HA) crystallographic planes in aqueous solutions containing proteins and calcium and phosphate ions were calculated by molecular dynamics simulations. It provided reference interfacial energies for comparative study of protein effects that both acidic Human serum albumin and basic Lysozyme reduces the interfacial energy of H

Chitosan/bovine serum albumin co-micropatterns on functionalized titanium surfaces and their effects on osteoblasts

Chitosan (CS)/bovine serum albumin (BSA) micropatterns were prepared on functionalized Ti surfaces by micro-transfer molding (mu-TM). mu-TM realized the spatially controlled immobilization of cells and offered a new way of studying the interaction between micropatterns and cells. Two kinds of micropatterns were produced: (1) microgrooves representing a discontinuously grooved co-micropattern, with the rectangular CS region separated by BSA walls; (2) microcylinders representing a continuously interconnected co-micropattern, with the net-like CS region separated by BSA cylinders. A comparison of cell behaviors on the two types of micropatterns indicated that the shape rather than the size had a dominant effect on cell proliferation. The micropattern size in the same range of cell diameters favored cell proliferation. However, cell differentiation was more sensitive to the size rather than to the shape of the micropatterns. In conclusion, cell behavior can be regulated by micropatterns integrating different materials