Authors: Luis M. Rodríguez-Lorenzo, Blanca Vázquez, Julio San Román
Abstract: Hydroxyapatite has been frequently described as an osteoconductive but not
osteoinductive material based on failure to observe bone formation in nonbony sites.
Bisphosphonates (BPs) are stable pyrophosphate analogs, that enhance the proliferation, differentiation and bone forming activity of osteoblasts and are potent inhibitors of bone resorption.
In this paper, the modification of a calcium hydroxyfluor carbonate apatite with sodium alendronate and (4-(aminomethyl)benzene)bisphosphonic acid is described. The surface modification is carried out by refluxing the apatite in a bisphosphonate acetone solution. Modified particles are characterized by thermal analysis, ATR-IR spectroscopy and contact angle between other techniques. A weight loss between 150 and 500°C can be observed for the modified apatites. IR
spectra show the appearance of bisphosphonate bands on modified powders. The surface energy of the modified apatite is reduced up to a 74% from the total apatite value after the alendronate surface modification with a decrease of 58% of the polar component main responsible of the cellular interaction of biomaterials.
357
Authors: E.S. Thian, Jie Huang, Serena Best, Zoe H. Barber, William Bonfield
Abstract: 0.8 wt.% silicon-containing hydroxyapatite (Si-HA) thin films of thickness 600 nm have been successfully developed using a magnetron co-sputtering technique, through careful selection and control of the processing conditions. These films were immersed in simulated body fluid (SBF) to investigate the nucleation and growth of an apatite layer on their surfaces. A newly-formed apatite layer with similar characteristics to that of the biological bone apatite, was observed after 4 days of
immersion in SBF. X-ray diffraction and infrared analyses confirmed this layer to be calciumdeficient micro-crystalline carbonate HA. These results demonstrated that the novel Si-HA films were highly bioactive and the time frame required for apatite formation was reduced by approximately 76 % (from 17 days to 4 days).
445
Authors: Hai Long Yang, Shouichi Somegawa, Ying Jie Yang, Zhi Chen Luo
617
Authors: Racquel Z. LeGeros, John P. LeGeros
Abstract: Plasma-sprayed ‘HA’ coatings on commercial orthopedic and dental
implants were developed to combine the strength of the metal (Ti or Ti alloy) and the
bioactivity of the hydroxyapatite (HA). Several studies have shown that ‘HA’-coated
implants provided greater amount of bone attachment, higher bone-implant interfacial
strength and accelerated skeletal attachment. However, some reports on implant
failures have been attributed to coating delamination and coating early resorption of
the plasma sprayed ‘HA’ coating. This paper reviews studies on characterization and
degradation of plasma-sprayed ‘HA’ coatings on orthopedic and dental implants and
offers alternatives to plasma-spray method of providing calcium phosphate coating.
X-ray diffraction analyses showed that plasma-sprayed HA coating consists principally
of HA and amorphous calcium phosphate (ACP) with minor amounts of other
resorbable calcium phosphates (α- or β-tricalcium phosphates, tetracalcium
phosphate), sometimes calcium oxide. The HA/ACP ratios were found to range from
20HA/80ACP to 70HA/30ACP in coated implants from different manufacturers. In vitro
initial dissolution rates in acidic buffer (pH 6, 37oC) increased with decreasing HA/ACP
ratios in the coating because of the preferential dissolution of the ACP phase. These
results suggest that coating with very low HA/ACP ratio may result in the premature
resorption of the coating before the bone can attach to the implant thus causing
loosening and eventual failure of the implant.
Alternatives to plasma-sprayed ‘HA’ are implant surface modifications and low
temperature calcium phosphate coatings using electrochemical deposition method or
precipitation method.
203
Authors: Shihori Yamane, Takeshi Yabutsuka, Mitsuhiro Hibino, Takeshi Yao
Abstract: Apatite nuclei were precipitated in the pores of silicagel microspheres by raising pH of simulated body fluid (SBF). By a soak in SBF, hydroxyapatite (HAp) was induced from the apatite nuclei and spread over whole surface area of the silicagel microspheres. Then encapsulated silicagel microspheres with HAp were fabricated.
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