Physical and Chemical Modifications of Free Radical Scavengers to Reduce their Radioprotective Potentials for Bacterial Agents
Annually, an estimated 1.2 million allografts are transplanted in the United States for repair or reconstruction of skeletal defects caused by disease, illness, or injury. Sterilization of these allografts must be performed to prevent disease transmission and reduce the inherent risk of infection. Currently, there is no single accepted sterilization technique in the bone and tissue banking industry. Gamma irradiation is the most popular and the safest form of allograft sterilization. However, to attain that level of sterility assurance, the biochemical and biomechanical integrity of the allograft is compromised, which is a serious concern since bone allografts are used in load bearing applications. Damage to allografts results in the radiolysis of water molecules during gamma irradiation. The water molecules bound to the tissue are essentially split into highly reactive, damaging free radical molecules. These free radicals cleave the collagen molecules in bone allograft tissues. One method to control the formation of these free radicals is to add a free radical scavenger to the bone allograft before gamma irradiation sterilization. However, while the free radical scavenger is protecting the collagen, is there the unintended consequence that the free radical scavenger is also protecting the pathogenetic organisms that should be eradicated? It was hypothesized that small, positively charged, globularly shaped free radical scavengers will protect bacteria more efficiently because the scavenger will be able to penetrate the intracellular space of the cell and thus scavenger for the free radicals that should be killing the bacteria. To test this hypothesis, viability tests were preformed with E. coli. Free radical scavengers were selected based on their charge, size, and shape. Solutions of these scavengers were added to E. coli suspended in media and incubated at time points of 0, 10, 20, and 40 hours and then subsequently irradiated to a dose of 500Gy. Results showed that positively charged scavengers protected E. coli from the harmful effects of irradiation, p<0.05. Results also indicated that a globular shaped scavenger protects E. coli, p<0.05. Additionally, a medium sized molecular weight molecule protected the E. coli, however, it may be possible that this protection was based more on chemical specificity than actual size of the molecule. The global conclusion of this study is: the addition of a scavenger has proven to alleviate biochemical and biomechanical stress to a bone allograft. However, selection of the proper scavenger is essential. From the results of this study, it would be advantageous to select a scavenger with a molecular weight greater than 250Da, but smaller than 350Da to penetrate the fabric of bone, additionally, to select a scavenger that is linear in shape and has an overall net positive charge. Allograft tissues gamma irradiated in the presence of such a scavenger could be treated with excess doses of irradiation for an elevated level of sterility assurance without worry of biochemical and biomechanical degradation.
School:University of Toledo
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:allograft sterilization gamma irradiation bone grafting homografts
Date of Publication:01/01/2005