The increasing number of mastectomies results in a greater demand for breast reconstruction characterized by simplicity and a Q1 low complication profile. Reconstructive surgeons are investigating tissue engineering (TE) strategies to overcome the current surgical drawbacks. 3D bioprinting is the rising technique for the fabrication of large tissue constructs which provides a potential solution for unmet clinical needs in breast reconstruction building on decades of experience in autologous fat grafting, adipose-derived mesenchymal stem cell (ASC) biology and TE. A scaffold was bioprinted using encapsulated ASC spheroids in methacrylated gelatin ink (GelMA). Uniform ASC spheroids with an ideal geometry and diameter for bioprinting were formed, using a high-throughput non-adhesive agarose microwell system. ASC spheroids in adipogenic differentiation medium (ADM) were evaluated through live/dead staining, histology (HE, Oil Red O), TEM and RT-qPCR. Viable spheroids were obtained for up to 14 days post-printing and showed multilocular microvacuoles and successful differentiation toward mature adipocytes shown by gene expression analysis. Moreover, spheroids were able to assemble at random in GelMA, creating a macrotissue. Combining the advantage of microtissues to self-assemble and the controlled organization by bioprinting Q2 technologies, these ASC spheroids can be useful as building blocks for the engineering of soft tissue implants. IntroductionBreast cancer is the most common cancer in women worldwide, with nearly 1.7 million new cases diagnosed in 2012 (second most common cancer overall). This represents about 12% of all new cancer cases and 25% of all cancers in women [1]. Mastectomies impair the esthetic appearance, function and psychological well-being of patients. In 31 addition to breast reconstruction following mastectomy for 32 established breast cancer, an increasing number of women 33 with BRCA mutations (25%) is opting for prophylactic 34 mastectomy followed by breast reconstruction, indicating 35 the need for soft tissue implants [2]. The success of con-36 ventional implant-based breast reconstruction has been 37 hindered by complications such as capsular contracture, 38 infection, rupture, foreign body reaction and anaplastic 39 large-cell lymphoma [3]. Adipose tissue (AT), in the form 40 of a free flap, has been the preferred method of choice since 41 patients are pleased with the natural shape, consistency and 42 permanency of the superior esthetic results [4]. Despite 43 major advancements in microsurgery and transplantation, 44 reconstruction remains hindered by the availability of donor 45 sites. Even in less extensive cases, the harvest of donor 46 tissue carries a significant risk of donor site morbidity and 47

No abstract