Plastic Surgery Research Council

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The Development Of A Customized 3d-printed Nanocomposite Polyurethane Implant For Auricular Cartilage Reconstruction
Michelle Griffin, MBChB MSc MRes MRCS PhD1,2, Deepak Kalaskar, PhD1, Peter Butler, Sr., MD FRCS1,2.
1University College London, London, United Kingdom, 2Royal Free Hospital, London, United Kingdom.

Purpose
Children born with a small or absent ear undergo surgical reconstruction to create a suitable replacement using rib cartilage. To overcome the donor site morbidity and long-term pain of harvesting rib cartilage, synthetic materials can be a useful alternative. Medpor, is the currently used synthetic polyethylene material to replace missing facial cartilage but unfortunately it has high levels of surgical complications including infection and extrusion, making it an unsuitable replacement. The development of alternative biocompatible biomaterials for auricular reconstruction is needed to improve the surgical outcomes of microtia reconstruction. Previously, we have demonstrated that nanocomposite polyurethane manufactured using a salt-leaching technique can provide auricular reconstructive surgeons with an alternative alloplastic biomaterial. Herein, we fabricate polyurethanes auricular cartilage replacements using 3D-printing to provide more anatomic and customized features.
Methods
Nanocomposite polyurethane biomaterial was manufactured and developed into 3D-printing filament. Customized nanocomposites polyurethane auricular implants (3D-PU) were designed and 3D-printed using fused deposition modeling technology (FDM) on a purpose build 3D-printer. The in vitro and in vivo response of 3D-PU was compared to Medpor implants. The adhesion and proliferation of human dermal fibroblasts (HDFs) and endothelial cells (ECs) was compared in vitro over 14-days. The formation of extracellular matrix (ECM) by HDFs and ECs was compared in vitro using RT-qPCR, immunocytochemistry and western blotting. Both implants were implanted into rats and pigs and explanted after 6 months (n=6) to assess for tissue integration, angiogenesis and immune response.
Results
3D-PU showed no difference in compressive or tensile properties compared to human cartilage. 3D-PU enhanced the adhesion and proliferation of HDFs and ECs compared Medpor over 14-days (p<0.05). 3D-PU upregulated the protein and gene expression of collagen type I, elastin and fibronectin of HDFs using RT-qPCR, immunocytochemistry and western blotting compared to Medpor over 14-days (p<0.05). 3D-PU enhanced the protein and gene expression of vascular endothelial-cadherin and von Willebrand factor (VWF) by the ECs compared to Medpor over 14 days (p<0.05). Both implants retained their shape and mechanical properties after 6-months in vivo. Medpor showed a 20% extrusion rate in small animal studies without any infections whereas 3D-PU showed no extrusion or infection complications in both small and large animal studies. 3D-PU showed significantly greater tissue integration after 6-months of subcutaneous implantation compared to Medpor using H&E and collagen staining (90% vs 75%, p=0.034). Vessel formation by immunohistochemistry staining of CD31 and α-SMA was also enhanced with 3D-PU than Medpor (143 vs 52 respectively, p=0.03). Both implants did not cause any immune response over the 6-months as shown by CD45 and CD68 immunohistochemistry staining.
Conclusion
We have shown that 3D-PU is a biocompatible and safe alternative for replacing auricular cartilage for microtia reconstruction. Small and large animal studies demonstrate that 3D-PU provides enhanced tissue integration and angiogenesis than currently available Medpor implants. 3D-printed nanocomposites polyurethane implants provides customized implants for auricular reconstruction that can overcome the infection and extrusion complications of current available alloplastic materials.


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