Precultivation of Engineered Human Nasal Cartilage Enhances the Mechanical Properties Relevant for Use in Facial Reconstructive Surgery

Autologous cartilage grafts are frequently used in reconstructive and esthetic surgery of the nose. The main disadvantages of this approach are the limited availability of tissue, morbidity at the donor site1,2 and time-consuming surgery. Indeed, the external ear and nasal septum provide only limited quantities of cartilage, and harvesting larger amounts of costal cartilage may lead to acute or delayed complications such as pneumothorax or chest wall deformities.3 Tissue engineering offers the possibility of producing large quantities of cartilage of autologous origin, starting from a small tissue biopsy and thus with minimal donor site morbidity. Recent studies have shown that human nasal chondrocytes released form a tissue biopsy and de-differentiated by expansion in monolayers, have the capacity to redifferentiate and generate cartilaginous tissue structures when cultured at high density (eg, in micromasses or pellets4,5) or in a variety of porous scaffolds.6,7 To be used in a clinical setting for nasal reconstructive surgery, engineered cartilage grafts need to have sufficient mechanical integrity (ie, suture retention strength) at the time of implantation, to allow for reliable suturing at the recipient site, and sufficient mechanical stability (ie, tensile and bending stiffness) when fixation is typically removed (ie, 2 weeks after implantation), to resist contraction by scar tissue formation and by exposure to local or external forces in the recipient bed. So far, however, both native cartilage tissue and engineered cartilage grafts have been mostly characterized biomechanically in terms of compressive stiffness,7–9 which would be of limited relevance for nasal reconstruction. Another important issue to be addressed toward the clinical use of engineered cartilage grafts is the extent of precultivation of cell-scaffold constructs prior to their implantation. In this context, previous studies indicated that precultivated engineered cartilage tissues not only reach a superior quality, but display a higher capacity to further develop upon implantation than scaffolds implanted directly after seeding,10,11 possibly due to less fibrous tissue and blood vessel ingrowth. However, an independent study reported that in vitro culture time had only a minor influence on construct development7: the issue is thus still controversial and is likely related to the scaffold used and the specific precultivation conditions. Based on the above design considerations, the aim of this study was to investigate if precultivation of human tissue engineered nasal cartilage grafts of clinically relevant size would increase the suture retention strength before implantation and the tensile and bending stiffness at 2 weeks postimplantation. To address this question, the selected model system consisted of human nasal chondrocytes, de- and redifferentiated using previously identified culture medium supplements,4,10 and loaded into nonwoven meshes made of esterified hyaluronic acid (Hyaff-11, Fidia Advanced Biopolymers, Abano Terme, Italy), already in clinical use for the repair of articular cartilage.12 The in vivo model consisted of ectopic implantation in nude mice, in a pocket between excised muscle fascia and subcutaneous tissue, resembling the environment where nasal cartilage grafts would be clinically implanted (ie, highly vascularized mucosal tissue on one side, and thin layer of subcutaneous tissue on the other side).