Investigation of bone allografts representing different steps of the bone bank procedure using the CAM-model

Bone grafting is commonly used to treat large bone defects. Since autografts are limited and frequently associated with postoperative donor morbidity, allografts from bone banks are often used. However, vascularisation of the allograft is often impaired, resulting in inadequate bone healing and functional graft failure. In bone bank processing, tissue is stored at -80 degree Celsius and subsequently subjected to a harsh multi-step cleaning and sterilisation procedure to prevent immune rejection or transmission of diseases. To determine which step of this procedure diminishes the ability of allografts to induce or promote vascularisation, we used the chick chorioallantoic membrane (CAM) model to monitor the vascular reaction to sample bone chips representing the respective procedural steps. The CAM model monitors the angiogenic potency of xenogeneic and, hence, potentially immunogeneic materials (e.g. cells, tissues, tissue-engineered matrices). Due to the chicken embryo's lack of a fully functional immune system, it provides test conditions that are analogous to immunologically incompetent mice and is a well-suited alternative to their use. Bone chips were placed onto the CAM, and vascular reactions were quantified by image analysis after 48 h incubation. The vascular reaction was most pronounced to fresh, untreated bone chips that had been kept at +2 degree Celsius prior to the experiment. Surprisingly, storage of bone samples at -80 degree Celsius was sufficient to drastically reduce the vascular reaction. Consistent with this, samples representing different stages of the subsequent procedure showed similarly low vascular indices.