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Pseudo-simulated body fluids (SBFs) were used in in vitro experiments to promote chitosan porous membrane calcification. Common SBFs, which had concentrations of phosphate or calcium ions doubled, were so named because they do not replicate, by rigor, a genuine body fluid ion concentration. The objective of using such calcification fluids was to study the influence of phosphate and calcium excess in solution on mineralization deposit characteristics. SEM-EDS analyses showed that morphology and composition of deposits varies depending on which ion (phosphate or calcium) is in excess; x-ray diffractograms show that deposits are poorly crystalline (like biological apatites) but still show better crystallinity in deposits generated from P-rich SBF. This result, added to previous ones [such as those reported by Beppu and Santana Mater. Res. 5, 47 (2002)] where a difference in the interconnectivity of the inorganic and organic (matrix) phases was stressed, suggests different deposition processes for each situation.

I. INTRODUCTION

Calcification or mineralization, defined as the formation of calcium phosphate or other calcium compounds, is a phenomenon that is a prominent subject for researchers for many reasons. From the biomaterials point of view, there is a need to better understand how to control mineralization because this may be useful for some processes, as in osteogenic implants, or conversely, completely undesired in others as it is the major reason for many medical device failures, as in cardiac devices.2 For material scientists, in situ deposition is an alternative to avoid the usual difficulties found in sol-gel processes, such as particle aggregation. In these state-of-the-art and so-called biomimetic processes, the inorganic phase is obtained under an organic matrix control, which regulates the shape, size, and orientation of deposits and hence determines the structural and mechanical characteristics of the final material. Interest in chitosan can be measured by the exponential growth of the number of scientific articles related to its characterization and uses that has occurred during the last five years. Part of the attention that has been directed a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0410 J. Mater. Res., Vol. 20, No. 12, Dec 2005

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toward chitosan is attributed to its renewable, biodegradable, and biocompatible character. It also presents good versatility, as it can be shaped into several forms and has amino and hydroxyl groups that can be easily reacted and functionalized.3 Our laboratory has been studying the potential of chitosan as a biomaterial and for bioseparation processes since 1997. Our main field of exploration with chitosan has been as an organic matrix to produce composites using biomimetic processes. In the present study, we expanded recently published results on the mechanisms of in vitro calcification of chitosan extracted from crab shells.4 Previously, we mentioned that por