Phosphatidylserine and antibiotic coatings for allograft bone

Abstract

Osteosarcoma is the most common type of primary bone tumor in humans. Treatment usually involves both surgical resection of the tumor and chemotherapy. Limb sparing often necessitates the use of massive bone allografts, however patients on anticancer drug regimens are at increased risk of infection, non-union and mechanical failure. The purpose of this work was to develop and test antibiotic eluting phospholipid coatings for massive bone allografts which may be useful in revision surgery for patients with osteomyelitis infection. This project was motivated by previous research performed on coatings of the phospholipid 1,2-dioleoyl-sn-glycero-3-phospho-l-serine (DOPS) and the antibiotic Gentamicin Sulfate (GS) applied to metallic implants. The potential of these coatings to combat infection and enhance osseointegration was evaluated in vivo using massive femoral allografts in a murine model with a well established osteomyelitis infection. Phospholipid coatings were applied to decellularized mouse femur segments using an electrospray method. Antibiotic was incorporated between two DOPS layers. The presence of both DOPS and GS was verified by examining the treated allografts with a scanning electron microscope (SEM). Allografts were then prepared and implanted into 50 mice in seven different treatment groups. In four of these treatment groups the mice were deliberately infected with osteomyelitis one week prior to allograft implantation using a genetically modified bioluminescent strain of Staphylococcus aureus that enabled tracking of the infection in vivo. Mice were sacrificed at 28 days post allograft implantation and allografts were evaluated histologically. After completing the in vivo portion of the study, the antibiotic eluting characteristics of the coatings were analyzed in vitro with a total sink elution method and antibiotic in the eluent was quantified using an agar diffusion test. Results showed that mice receiving antibiotic coated allografts displayed significantly reduced infection up to fifteen days post allograft implantation. Measurable infection remained until the end of the study however and none of the infected mice exhibited any osseointegration with the allograft. These results were most likely due to the severity of the osteomyelitis infection and the rapid elution of the antibiotic from the allografts, as confirmed by the in vitro elution study. Osseointegration was observed in the uninfected mice however no statistically significant differences were found between the DOPS coated treatment groups and the uncoated control group. This was attributed to the small sample size of the uninfected groups and the small number of histological sections, and was perhaps exacerbated by inconsistent host-graft apposition. Further research is therefore necessary to validate the potential of DOPS/GS allograft coatings to fight infection and enhance osseointegration.