Due to increasing numbers of critical size bone defects, bone replacement materials are gaining importance. Since autologous material is limited in amount, the use of allogenic bone is highly favorable. Complex processing steps are required in order to provide a cell-free and sterile allograft. To date, mainly chemical and physical methods are used in allograft processing. Methods like these are known to impair biomechanical properties of bone tissue and thereby compromise successful reconstruction of load-bearing areas. In contrast, high hydrostatic pressure (HHP)-technology is able to effectively devitalize tissue while maintaining the biomechanical tissue properties. This study aimed to evaluate the inactivation of microorganisms by means of high hydrostatic pressure to provide sterile allografts.

Two model microorganisms (Escherichia coli and Micrococcus luteus), harvested the in exponential or stationary growth phase, were treated with different pressure levels of 250 MPa, 350 MPa, 450 MPa and 600 MPa for 10 min. Inactivation was quantified by determining the colony forming units (CFU) of treated E. coli (24 h) and M. luteus (48 h). Significant differences were analyzed by ANOVA and Dunnett’s post-hoc tests.

Results showed that the extent to which bacterial growth is reduced correlated with the applied pressure load and the growth phase of the bacterium. Especially in the exponential growth phase, HHP treatment induced killing of bacteria. In the case of E. coli, a significant reduction in CFU was observed at a treatment pressure of 250 MPa (1 log cycle), while for M. luteus this only became apparent at 450 MPa (1.5 log cycles). In the stationary phase, treatments with higher pressures were required to achieve a reduction in the CFU. A significant reduction was observed for E. coli at 350 MPa, whereas for M. luteus this was only attained at 600 MPa.

The conducted studies on the decontamination efficiency of HHP indicated that the viable cells of Gram-negative and Gram-positive model organisms can be reduced by HHP treatment. Thus, apart from the proven devitalization HHP might also aid the sterilization of bone allografts. Further investigations with a contamination model in bone are required to verify the results from the bacterial suspensions.