New sterilization process shows no effect on allografts’ biomechanical properties

Fresh-frozen allografts were initially less stiff than sterilized, but all were similar within 10 cycles.

Issue: July 2006

HOLLYWOOD, Fla. – The proprietary Biocleanse tissue sterilization process does not affect the baseline biomechanical properties of allografts, according to a recent study.

Robert A. Pedowitz, MD, PhD, of the University of California, San Diego, presented the study results on the low temperature chemical process here at the Arthroscopy Association of North America 25th Annual Meeting.

“The process itself is effective to sterilize against viruses and spores and bacteria … as far as my review of literature,” Pedowitz said.

Robert A. Pedowitz, MD, PhD [photo]
Robert A. Pedowitz

To study baseline properties, Pedowitz and his residents measured creep, stiffness, failure load and failure stress of 12 fresh-frozen, 12 irradiated and 12 Biocleanse allografts (Regeneration Technologies Inc.).

Study method

Surgeons treated 12 allografts with the Biocleanse process as follows:

a low-temperature chemical sterilization;
tissue submerged in cleaning solutions;
large pressure/vacuum fluctuations to perfuse the tissue;
fluid exchanges to remove cells, bacteria, viruses, fungi and spores; and
rinse cycles to remove residual chemicals.

The result is “very pearly white tissue,” Pedowitz said.

To measure graft cross-sectional area for all allografts, researchers doubled the tibialis anterior allografts, measured the diameter with a sizer and sutured the trailing ends. They next looped the allografts over a rod and clamped the sutured ends, leaving 10 cm of tissue for loading, Pedowitz said.

Researchers pretensioned the allografts to 10 N for two minutes and loaded them between 50 N and 300 N at 0.5 Hz for 1000 cycles. Stiffness measurements were performed at cycles one, 10 and 1000. All results, including creep, stiffness, failure load and failure stress, were compared to a one-way ANOVA (P<.05).

No significant differences

“[Biocleanse] appears to have paralleled the normal biologic process, but I think more work needs to be done.”
— Robert A. Pedowitz, MD, PhD

Researchers found no significant differences between the three groups for creep, failure load or failure stress.

Further, “the diameters of the grafts were similar between the three groups,” Pedowitz said. “There was no relationship we could call out between graft size and failure load, but the problem is that all these groups had a fairly tight graft size. I wouldn’t expect to see much of a difference based upon graft diameter.”

Graft diameter findings were as follows: fresh-frozen, 7.4±0.7 mm; irradiated, 6.9±0.4 mm; and Biocleanse, 7.4±0.7 mm. Researchers found the following results for creep during pre-load – again no significant difference: fresh-frozen, 0.35±0.15 mm; irradiated, 0.29±0.09 mm; and Biocleanse, 0.34±0.14 mm.

“In terms of ultimate load to failure … these groups are nearly identical,” Pedowitz continued. Failure load findings were as follows: 1665+/-291 N in the fresh-frozen group, 1672+/-290 N in the irradiated group and 1652+/-377 N in the Biocleanse group.

One significant difference: fresh-frozen allografts were significantly less stiff than the Biocleanse and irradiated allografts in the first cycle (P<.005). Fresh-frozen allografts had a stiffness of 117.8±15.7 N/mm, while irradiated and Biocleanse allografts had a stiffness of 144.7±17.7 N/mm and 146.5±28.2 N/mm, respectively. But all groups showed similar stiffness within 10 cycles.

“From other studies, tissue remodeling after Biocleanse appears to have paralleled the normal biologic process, but I think more work needs to be done,” Pedowitz said.

Regeneration Technologies Inc. provided the soft tissue for the study. Researchers received support from Stryker.

chart
Researchers found only one significant difference between the fresh-frozen, irradiated and Biocleanse allografts. Fresh-frozen allografts showed significantly less stiffness in the first cycle only, but all allografts showed similar stiffness in subsequent cycles.

Source: Pedowitz RA

For more information:
Pedowitz R, Mahar A, Schmizzi A. Effects of novel sterilization process on soft tissue mechanical properties for anterior cruciate ligament repair. #SS-55. Presented at the Arthroscopy Association of North America 25th Annual Meeting. May 18-21, 2006. Hollywood, Fla.