Radiation sterilisation dose determination for lyophilised amnion membranes and lyophilised bone grafts

Radiation sterilisation of medical products is now well established in commercial scale and at present there are more than two hundred irradiation facilities in operation throughout the world. It is a cold sterilisation process without toxic chemical residues, high degree of safety and easy to control, so that it is a safe technology to sterilise human tissue grafts. According to ISO (International Organisation of Standard) No. 11137, radiation sterilisation dose should be established based on the number of product's bioburden (number of product's contaminated microbes before irradiation). Bioburden of lyophilised amnion membranes and lyophilised bone grafts produced by Batan Research Tissue Bank (BRTB) have been determined since 1990 and 1994 consecutively by using 100 up to 120 pieces of samples per year. Results show that the average bioburden of the amnion membranes were 1.4 ( 0.2 x 103; 1.2 (0.2 x 103; 1.2 ( 1.2 x 103; 4.5 ( 0.5 x 102; 1.8 ( 0.9 x 102; 2.4 ( 2.3 x 102; 1.7(l.5 x 102; 1.5 ( 1.7 x 102 cells per sample, calculated in 1990 to 1997 consecutively and the average bioburden of the bonegrafts were 1.5 (0.4x 101; 0.25 (0.12 x 101; 0; 0 cells per sample, calculated in 1994 to 1997 consecutively. Morphological of those contaminants were found to be Gram positive coccoid forms (98%) and Gram positive vegetative rod (2%) with the D10 - values of 0.25 to 0.50 kGy. No spore forming bacteria and Gram negative bacteria were found in those contaminations. The highest bioburden of lyophilised amnion membranes and lyophilised bone grafts were found to be 4900 and 80 cells per sample consecutively, and the lowest was found to be 0 cell per sample in both of materials observed. According to ISO 11137 radiation sterilisation doses for amnion membranes were ranging between 21 to 25 kGy and for bone grafts was around 15 kGy with the Sterility Assurance Level (SAL) of 106. Since 1990, radiation sterilisation dose used for lyophilised amnion membranes produced by BRTB was 25 kGy and 15 kGy for lyophilised bone grafts. All of those doses used are still in the range of the determination doses