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3d-printed Poly-4-hydroxybutyrate (p4hb) "Nipple" Scaffold Maintains Stable And Long-term (1 Year) Projection In Nipple Reconstruction
Xue Dong, MD, PhD1, Sabrina Shih, BA2, Ishani Premaratne, MD1, Kemal Sariibrahimoglu, PhD3, Skander Limem, PhD3, Jason Spector, MD1.
1Weill Cornell Medical College, New York, NY, USA, 2Columbia University Vagelos College of Physicians and Surgeons, New York, NY, USA, 3Tepha, Inc, Lexington, MA, USA.

Purposes: Nipple reconstruction is usually the final step of breast reconstruction after total mastectomy. However, nearly all local autologous tissue techniques are subject to scar contracture and loss of neo-nipple projection. P4HB is a biodegradable polymer with a long track record of use in mesh which promotes persistent healthy tissue ingrowth. We hypothesized that 3D-printed P4HB scaffolds with an interior reticular structure would foster the formation of healthy and permanent tissue that mimics the biomechanical properties of native nipples and protect the regenerated tissue from contracture as it matures. Methods: Nipple scaffolds were designed and 3D-printed using P4HB in 1.0cm diameter x 1.0cm height, with an internal 3D latticework of P4HB filaments (rebar) (filament diameter: 0.2mm), achieving 75.0% porosity. Wall porosity was incorporated into the scaffolds (2mm diameter pores). All the 3D-P4HB scaffolds were subcutaneously implanted in nude rats using a CV flap technique. P4HB scaffolds without the internal latticework were implanted as a control. The constructs were explanted after 12 months in vivo for further study. Results: 3D-P4HB nipple reconstructions were well preserved in diameter and projection after 12 months. Compared to the empty 3D-P4HB group, the rebar group demonstrated a slight loss of projection at 6 (85.8% vs 96.0%, p<0.05) and 12 months (74.3% vs 93.3%, p<0.05). A mostly inflammatory cell infiltrate was noted in both groups at 1 month, and over time, the inflammatory tissue was replaced by stable adipose containing fibrovascular tissue at 12 months. The rebar scaffold appeared superior to the empty scaffold due to the reliable, fast, and uniform tissue ingrowth, which 100% of the interior space in the rebar group was filled as early as at 1 month, while only 35% of the interior space in the empty group was filled at first 3 months. Because of rapid cell infiltration/ revascularization, rebar scaffolds demonstrated faster material absorption overtime, which was verified by SEM as demonstrated by widespread pitting on the scaffold surface and the loss of P4HB structural integrity before 12 months. Elastic modulus of both rebar and empty groups closely mimicked that of human native nipples after 12 months (0.28 and 0.32 Mpa). Conclusions: Using 3D-P4HB scaffolds with an interior latticework, we have engineered nipples that maintain projection and volume over time, while simultaneously allowing for the formation and maturation of an internal structure of adipose containing fibrovascular tissue that is biomechanically similar to that of native nipples. Although the scaffold eventually loses structural integrity, the adipose fibrovascular tissue formed inside prior to that time allows the engineered nipple to maintain proper shape and volume without resultant scar contracture. With continued optimization of the interior reticular structure, we believe that this novel 3D-P4HB nipple scaffold will be readily translatable to the clinic.




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