In the year 2010, over 52 million women and men aged 50 and over will be affected by osteoporosis and this number will climb to over 61 million by the year 2020 [1]. Bone grafting is used to promote bone fussing in fully detached fractures, in arthrodesis of joint, and to fill defects or cavities in bone. Grafts involve transplantation of bone from either another part of person’s body (auto graft), from another human patient (allograft), or even an animal (xenograft).

Biomaterials may provide a solution to these problems; an ideal bone substitute should be tolerated by the host tissue without any adverse reaction. It should promote bone formation, have appropriate mechanical strength, be malleable and resorbs after it has fulfilled its function [2]. The purpose of a biomaterial is to replace part or perform function of the body in a safe, reliable, economic and physiologically acceptable manner

Complex forms based on natural structures that can mimic natural scaffolds offer an exciting range of avenues for the construction of a bone analog for tissue engineering taking the advantage of tridimensional constructs to deliver vital cells to the damaged sites [3].

Marine corals act as bioactive natural materials because they are biocompatible, biodegradable and osteoconductive materials. Corals from various sources have been shown to have cell attachment, spread, proliferation and differentiation [4]. Although having strength perse, it is a biodegradable material that bonds tightly to bone without surface apatite layer. On other hand, natural corals provide mechanical interlocking bonding provided by the anchoring effect of the newly formed bone into the surface roughness could be considered as a major factor in bone bonding. Both ß- Tricalcium phosphate (ß-TCP) and natural calcite do not have apatite formation on their surfaces in SBF [5, 6] but despite of this, they bond to living bone. These results may be related to the high resorbability of these materials. In contrast, natural abalone shell forms apatite form on its surface in SBF [7] but does not bond to living bone which might be attributed to antibody reaction to protein in the shell.

It was thought to beneficially modify corals by impregnating them with ions such as Silver (Ag⁺ )which is reported to induce antibacterial and antimicrobial effect upon substitution with hydroxyapatite ceramics. While Strontium (Sr²⁺ )and Zinc ( Zn²⁺ )are proved as bone seeking elements.

Various investigations have been performed to develop antibacterial surface coating. Among them Kim, T. N., used the antimicrobial ceramics based on HA with additions of AgNO₃, Cu (NO₃)₂. 3H₂O and Zn (NO₃)₂. 6H₂O. He proved that Ag⁺ HA exhibited complete inhibition of the growth of E. coli after 20h incubation. In contrast to Ag⁺ HA, the Cu²⁺ and Zn²⁺ HA didn't show any antimicrobial effect in his experiment. This implied that the Ag⁺ HA plays an important role in the inhibition of the growth of E. coli [8]. Also Abou Neel, E. A. et al. used copper oxide (CuO) – containing phosphate based glass fibers (PGF) for potential uses in wound healing with several concentrations of CuO (0, 1, 5, 10 mole %). They found that the addition of CuO into the glass fibers was effective in reducing the number of bacteria attached to the fiber and fibers with 10%mole CuO were most effective in delivering sufficient amounts of antibacterial Cu²⁺ to prevent colonization and reduce the number of viable bacteria in the local environment [9]. However, Heidenau, F, made a comparative study about the antibacterial potential of different metal ions Cu²⁺, Ag⁺, Co²⁺, Zn²⁺, Al³⁺ and Hg²⁺with respect to both cytotoxicity (tissue cell toxicity) and antibacterial properties. He reported that the growth inhibition tests proved that Ag⁺ as well as Zn²⁺ and Hg²⁺ ions exhibit very strong cytotoxicity at low concentration but Co²⁺ showed intermediate mode whereas tissue cells tolerated relatively high concentration of Cu²⁺ and Al³⁺. These results are similar for bacteria, except the fact that Co²⁺ and Zn²⁺ exhibited no significant antibacterial effect at the investigated concentrations and that Cu²⁺ ions were significantly more effective against bacteria, staphylococcus epidermis, than toxic for tissue cells. The concentration reported for each ion was (Ag⁺ = 3. 5×10^-3, Zn²⁺ = 3. 6×10^-3, Hg²⁺ = 4. 2×10^-3, Cu²⁺ = 2. 3×10^-1, Co²⁺ = 3. 4×10^-2 and Al³⁺ = 1. 8×10^-2 mmol/L). So copper ions prove most adequate to equip implant surfaces with antibacterial properties without decreasing their biocompatibility in a significant manner [10]. However, none of them followed the consequent effect on the apatite deposition.

In a previous work deprotinated corals were impregnated with Cu²⁺ in various mole concentrations between 0. 5 to2. 0 and proved that the higher Cu²⁺ concentration affect the more dense surface biolayer formation [11].

In several reports as early as 1991, it was proposed that the essential requirements for an arjpgicial material to bond to living bone is the formation of bone like apatite on its surface when implanted in the living body, and that this in vivo apatite formation can be reproduced in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma [12 ]. This means that the in vivo bone bioactivity of a material can be predicted from the apatite formation on its surface in SBF. Since then, in vitro bone bioactivity of various types of materials have been evaluated through apatite formation in SBF. However, the validity of this method has not been systematically assessed. So to investigate the mechanism of the material/ tissue reaction in vitro examination, with SBF has been developed [13]. In 2003, Conventional SBF with the refined recipe was proposed to the technical Committee ISO/TC150 of International Organization for standardization for in the vitro measurement of apatite forming ability of implant materials and is being discussed by the committee [14].

The aim of the present work is dealing with the impregnation of corals with either of Ag⁺, Zn²⁺ or Sr²⁺ ions in 2 moles concentrations each. The assessment of ions mobility and therefore, biocompatibility of corals in biological solutions was followed through AC electrical conductivity measurements using Conductance Bridge. Spectrophotometer and chemical Kits were used to analyze biological solutions pre and post immersion up to72 h. The results are supposed to reflect ion mobility and subsequent biolayer formation on coral surfaces. The validity of AC electrical conductivity using conductance bridge and ion mobility of saline or SBF as a tool for studying the kinetics of bioactive layer formed compared to spectral analysis using biochemical kits was verified. Moreover, the formation of carbonated hydroxyapatite biolayer and other phosphates on the surface are studied by Scanning Electron microscope equipped with X-ray analysis (SEM and EDX)for the samples post 72 h immersion.

1. The conductivity values of saline proved dissolution in a reverse trend to SBF proving ionic deposition from the latter in favor biomimetic deposition.
2. As conductivity was saturated as early as 20h for Sr/corals, the immersion for such time is recommended for biolayer deposition. Saturation was recorded at 32 and 45 hrs for Ag and Zn respectively.
3. The presence of Sr²⁺ in corals lead to higher iP release from coral which would invite bone forming process involving Ca²⁺ precipitation.