Plastic Surgery Research Council
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Presenter: Dan Wang, DMD
Co-Authors: Gilbert JR; Shakir S; Shaw MA; Kubala AA; Losee JE; Billiar TR; Cooper GM
University of Pittsburgh

Background and Purpose: Autologous bone graft remains the gold standard for the calvarial repair. The synthesis and deposition of extracellular bone matrix and the osteogenic potential of cellular components have been observed to play a role in bone repair. It has only been appreciated recently that excellular matrix and cell necrosis induce an inflammatory response that has an established role in promoting tissue repair. TLR2 and TLR4 are members of a highly conserved receptor family and are critical activators of the innate immune response after tissue injury. Here we tested the hypothesis that calvarial healingafter cellular and accellular bone components implantation would be influenced by the absence of TLR2 and TLR4.

Methods: celluar-enriched suspension and matrix-enriched suspension were obtained from two femurs and two tibias of WT mice. 1 ml PBS was prepared as control solution . Each suspension was mixed with fibrinogen and thrombin, before surgery. Circular bone defects were made in the parietal bones using a 1.8mm outer diameter trephine in WT (n=15), TLR2-/- mice (n=15), and TLR4-/- mice (n=11). Three groups were implanted on WT, TLR2-/- and TLR4-/- mice. Calvarial bone and surrounding soft tissues (e.g. skin and brain) were harvested and bone healing was assessed at postoperative day 28 using radiographic and histologic analyses.

Results: Radiographic and histomorphometric analyses demonstrated that 1) increased bone healingwas observed in the matrix-enriched group of WT mice compared to all other groups; 2) in TLR2-/- mice, matrix-enriched group showed more bone formation compared to cellular-enriched and control groups; 3) similar amounts of bone healing were observed in TLR4-/- mice after three implantation groups.

Conclusions: These data are consistent with the hypothesis that bone matrix implantation assists in calvarial healing; furthermore, TLR2 and TLR4 activation will influence the effect of autologous bone implantation on calvarial healing in mice. Further work is required to determine if this is due to different inflammatory responses driven by TLR2 and TLR4 activation.

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