Comparative study of bone substitute materials on transplanted tissue in a rat model of vascularized composite allograft

Vascularized composite allotransplantation (VCA) enables the reconstruction of extensive craniofacial and extremity defects but carries a higher risk of rejection than solid organ transplantation, primarily due to the immunogenicity of the skin and composite tissues. Although bone substitutes are widely used in craniofacial surgery, their immunological effects in the setting of VCA remain inadequately investigated.In this study, fifteen Sprague–Dawley rats underwent reciprocal abdominal wall flap allotransplantation, with flaps exchanged between paired animals. Reconstruction was performed under five conditions: control, titanium mesh, polycaprolactone (PCL), poly-L-lactic acid with unsintered hydroxyapatite (PLLA-uHA), and silicone. All recipients received cyclosporine-based immunosuppressive therapy. Graft survival, collagen matrix deposition, and immunohistochemical expression of interleukin-1β, tumor necrosis factor-α, and interferon-γ were evaluated over eight weeks.All silicone grafts failed within 3 weeks as a result of hematoma and vascular compromise. In surviving groups, collagen deposition and pro-inflammatory cytokine expression were significantly greater in the control and titanium groups than in the PCL and PLLA-uHA groups (p < 0.01). Titanium supported stable matrix deposition without persistent cytokine elevation, whereas absorbable substitutes elicited chronic inflammation and impaired tissue integration.These findings suggest that titanium provides the most reliable skeletal support in craniofacial VCA, ensuring favorable collagen deposition with minimal immune activation.