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David Pickles
09-12-1994, 10:04 PM
This is a second summary of responses to my request for info about the
effects on the biomechanical properties of human tissue of different
methods of sterilization... I evidently jumped the gun with my previous
post!

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From: Robert Day

We have looked at the effect of sterilising doses of gamma irradiation on
human cortical bone for the Perth Bone and Tissue bank, in order to
quantify the degredation induced in material destined for human
allografts. This is usually subjected to 2.5 Mrad, accepted as the
sterilising dose for all organisms with a reasonable margin for error.
1.5 Mrad will drop the microbial load to a reasonable level in medical
devices sterilised by gamma, but this is unreliable for killing HIV I in
allograft bone.

There is little literature on the effect on gamma irradiation on bone, as
you will have found. Turner and Bassett of the National Naval Medical
Research Centre in Maryland first reported the use of 60Co in the '50s.
Triantafyllou reported a 25-50% reduction in 3 point bending failure
stress at 3 Mrads in BOVINE bone. (197?, I don't have the exact
references in front of me, but can look them up if you want.)

The only human bone studies we found were Bright who reported no change
at 2.5 Mrad, and Komender who reported a 30% reduction in flexural
strength at 6 Mrad and 20% at 5 Mrad. I don't know if I would trust
either of these papers, as the methods are not documented.

We have looked at the effect of gamma irradiation on flexural strength,
compressive strength, indentation hardness and fracture toughness of
cotrical bone from human femurs taken from our bone bank. This bone is
harvested under sterile conditions, stripped of muscle etc. and stored at
-80 degrees C. There is a body of work to show that this freezing does
not change anything significantly, and it is the standard way to store
all banked bone. We used 0, 1.5, 2.5 & 5.0 Mrad 60Co irradiation.

Mean reduction of flexural strength ( 3 point bending ) was 5.7 % @ 1.5,
22.6 % @ 2.5 and 30% @ 5 Mrad. All were significant @ p