Abstract
Abstract Hydroxyapatite (HA) is the major component of the inorganic part in bone. Because HA has the advantages, such as excellent bio-compatibility, free of cell toxicity, and form strong bonding to bone, it has been widely studied and used. Biomaterials with anti-bacterial property will extend reservation period and applications, and will help to prevent the infection of injured. There are many methods used to synthesize HA, including chemical precipitation, solid state reaction, hydrothermal synthesis, sol-gel route, and so on. In this study, sol-gel route was applied to synthesize HA, with addition of silver or zinc ions. Synthetic mechanisms and optimal processing parameters (conditions) were investigated. Streptococcus mutans (ATCC 25175), an etiological agent of human caries and plaques, was applied in the anti-bacterial in vitro tests. In the study of synthesis of HA by sol-gel route, results showed that when Ca(NO3)2 and TEP were used as sources of calcium and phosphorus respectively, alcohol as solvent, 16 hours aging under at 80℃, 24 hours gelation and dried under 80℃, then calcined above 350℃ will lead to HA phase. When 2-methoxy ethanol is used as the solvent the calcination has to be above 650℃ to obtain HA. The major mechanisms of aging are the hydrolysis of TEP and the rearrangements of precursor. CaO impurity would be produced after samples being calcined above 550℃. Comparing the TG/DTA and XRD data lead to the formation mechanisms of intermediates and CaO. HA would be produced for samples added with silver or zinc below 20000ppm. The one with Ag：Ca=2：9 would result in a new phase that could out be indexed in existing JCPD cards. The ICP-AES data of obtained HA samples showed a lower value of Ca/P than the ideal HA. Streptococcus mutans was cultured at 37℃. When they were cultured on BHIA (brain heart infusion agar) medium the colonies showed inhibiting effects to each other. The radius of colonies ranged from 0.1mm to 4mm. In BHI medium, the doubling time was 2 hours, the maximum cell concentrations reached 109 CFU/mL. Streptococcus mutans can be preserved for tree months under 4℃. In BHI medium, sample C (20000ppm silver added) and sample F (zinc 2000ppm added) would not release silver or zinc ions obviously, and would not inhibit the growth of cells. Streptococcus mutans would reject to grow on samples C and F, but not for HA. Anti-bacterial circles can be seen when these samples (above 20000ppm silver or 2000ppm zinc) were put on BHIA medium.