The clinical relevance of perichondrium was recognized more than a century ago. In children and adolescents, perichondrium is essential for the formation and growth of the cartilaginous part of craniofacial features and must be considered during reconstructive surgery in the head and neck area. Also in adults, perichondrium must be preserved during surgical intervention for adequate postoperative healing and cartilage maintenance. Furthermore, the regenerative function of perichondrium in the ribs enables the harvesting of the rib cartilage tissue for reconstruction of craniofacial features. With the advancement of tissue engineering, renewed attention has been focused on the perichondrium, because without this crucial tissue, the function of cartilage engineered for craniofacial reconstruction is incomplete and may not be suitable for long-term reconstructive goals. Furthermore, interest in the perichondrium was revived owing to its possible role as a microenvironment containing stem and progenitor cells. Here we will revisit seminal studies on the perichondrium and review the current literature to provide a holistic perspective on the importance of this tissue in the context of regenerative medicine. We will also highlight the functional significance of perichondrium for cartilage tissue engineering. Impact statement: All adult cartilage tissues, with the exception of articular and fibrocartilage, are lined by a stratified tissue called the perichondrium. The perichondrium contributes to growth, structural stability, and regeneration and maintenance of the organ, but the cellular mechanisms underlying these processes are not well understood. This review provides a comprehensive summary of past and recent studies on perichondrium from the vantage point of tissue engineering and regenerative medicine. Of particular relevance is the evidence that perichondrium might contain chondrogenic progenitor cells. Cartilage tissue engineering holds great promise for novel treatments of craniofacial defects, and a better understanding of the function and structure of the perichondrium could contribute to improved therapies for head and neck reconstructive surgery and beyond.

The gold standard of auricular reconstruction involves manual graft assembly from autologous costal cartilage. The intervention may require multiple surgical procedures and lead to donor‐site morbidity, while the outcome is highly dependent on individual surgical skills. A tissue engineering approach provides the means to produce cartilage grafts of a defined shape from autologous chondrocytes. The use of autologous cells minimizes the risk of host immune response; however, factors such as biomaterial compatibility and in vitro maturation of the tissue‐engineered (TE) cartilage may influence the engraftment and shape‐stability of TE implants. Here, this work tests the biocompatibility of bioprinted autologous cartilage constructs in a rabbit model. The TE cartilage is produced by embedding autologous auricular chondrocytes into hyaluronan transglutaminase (HATG) based bioink, previously shown to support chondrogenesis in human auricular chondrocytes in vitro and in immunocompromised xenotransplantation models in vivo. A drastic softening and loss of cartilage markers, such as sulfated glycosaminoglycans (GAGs) and collagen type II are observed. Furthermore, fibrous encapsulation and partial degradation of the transplanted constructs are indicative of a strong host immune response to the autologous TE cartilage. The current study thus illustrates the crucial importance of immunocompetent autologous animal models for the evaluation of TE cartilage function and compatibility.

Tissue engineering (TE) techniques offer solutions for tissue regeneration but require large quantities of cells. For microtia patients, TE methods represent a unique opportunity for therapies with low donor-site morbidity and reliance on the surgeon’s individual expertise. Microtia-derived chondrocytes and perichondrocytes are considered a valuable cell source for autologous reconstruction of the pinna. The aim of this study was to investigate the suitability of perichondrocytes from microtia patients for autologous reconstruction in comparison to healthy perichondrocytes and microtia chondrocytes. Perichondrocytes were isolated via two different methods: explant culture and enzymatic digestion. The isolated cells were analyzed in vitro for their chondrogenic cell properties. We examined migration activity, colony-forming ability, expression of mesenchymal stem cell markers, and gene expression profile. We found that microtic perichondrocytes exhibit similar chondrogenic properties compared to chondrocytes in vitro. We investigated the behavior in three-dimensional cell cultures (spheroids and scaffold-based 3D cell cultures) and assessed the expression of cartilage-specific proteins via immunohistochemistry, e.g., collagen II, which was detected in all samples. Our results show that perichondrocytes from microtia patients are comparable to healthy perichondrocytes and chondrocytes in terms of chondrogenic cell properties and could therefore be a promising cell source for auricular reconstruction.

Microtia is a congenital condition of abnormal development of the outer ear. Tissue engineering of the ear is an alternative treatment option for microtia patients. However, for this approach, the identification of high regenerative cartilage progenitor cells is of vital importance. Raman analysis provides a novel, non-invasive, label-free diagnostic tool to detect distinctive biochemical features of single cells or tissues. Using micro-Raman spectroscopy, we were able to distinguish and characterize the particular molecular fingerprints of differentiated chondrocytes and perichondrocytes and their respective progenitors isolated from healthy individuals and microtia patients. We found that microtia chondrocytes exhibited lower lipid concentrations in comparison to healthy cells, thus indicating the importance of fat storage. Moreover, we suggest that collagen is a useful biomarker for distinguishing between populations obtained from the cartilage and perichondrium because of the higher spectral contributions of collagen in the chondrocytes compared to perichondrocytes from healthy individuals and microtia patients. Our results represent a contribution to the identification of cell markers that may allow the selection of specific cell populations for cartilage tissue engineering. Moreover, the observed differences between microtia and healthy cells are essential for gaining better knowledge of the cause of microtia. It can be useful for designing novel treatment options based on further investigations of the discovered biochemical substrate alterations.