Hydroxyapatite-alginate composite for lead removal in artificial gastric fluid
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a Helena Rocha-Leão and Nilce C.C. da Rocha Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
Marcelo H. Prado da Silva Instituto Militar de Engenharia, Rio de Janeiro, Brazil
Alexandre Malta Rossi Centro Brasileiro de Pesquisas Fı´sicas: Centro Brasileiro de Pesquisas Fı´sicas, Fı´sica Aplicada, Rio de Janeiro 22290-18, Brazil (Received 9 January 2007; accepted 3 August 2007)
Millimetric spherical beads of a biocompatible composite were produced from sodium alginate, a natural polysaccharide, and nanostructured hydroxyapatite (HA). It was shown that the composite was effective in the removal of lead ions and lead phosphate nanoparticles from high-contaminated simulated gastric fluid. X-ray diffraction spectroscopy and scanning electron microscopy analyses performed on HA–alginate beads after the Pb2+ uptake showed that nanocrystals of a lead phosphate, [Pb10–xCax(PO4)6Cl2], were precipitated on the bead surface. The cross-linked polymer chain had a double role: (i) keep Pb2+ ions and lead phosphate nanoparticles bounded to the bead surface, preventing their bioavailability in stomach fluid; and (ii) delay HA dissolution in the acidic conditions of the stomach, assuring that an excess of Ca2+ will not be released to simulated gastric fluid. Desorption experiments in simulated enteric fluid revealed that lead remained immobilized in the calcium phosphate phase in the intestinal tract. These results indicate HA–alginate composite as a potential system for heavy metals removal from contaminated gastric and enteric human fluids, minimizing its adsorption by the human body.
I. INTRODUCTION
Lead is a widely used metal and is toxic to human beings, particularly children. Ingestion is the most common exposure route and, once ingested, Pb2+ is released into the blood stream after gastric acidic activity, causing its complexation in stomach digestive fluids. According to the United States Environmental Protection Agency,1 a child’s gastrointestinal tract absorbs 50% of total ingested Pb2+ compared to an adult uptake of 10%–15%. Once ingested, the metal is stored in bone, and the rate of elimination from bone is estimated to be several years.2 So, it is essential to find efficient alternatives to minimize the effects caused by Pb2+ ingestion.
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0419 J. Mater. Res., Vol. 22, No. 12, Dec 2007
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Alginate is a safe biocompatible polysaccharide and has been applied in many industrial products.3 Since 1980, alginate has been used in food products. Its use includes: as a safe food additive and as a base material for modeling food or dietary food. Besides, alginate composites offer several applications in many fields of regenerative medicine: as an injectable material for new bone formation4; as injectable scaffolds for tissue regeneration5; in drug delivery systems6; in antibiotics7; in proteins or genes; and as matrix for immunoisolation of transplanted cells.4 In environme
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