Long-Term Comparison between Human Normal Conchal and Microtia Chondrocytes Regenerated by Tissue Engineering on Nanofiber Polyglycolic Acid Scaffolds.

BACKGROUND: Previous regeneration studies of auricle-shaped cartilage by tissue engineering leave unresolved whether the chondrocyte phenotype from human auricular chondrocytes seeded onto polymeric scaffolds is retained over the long term and whether microtia remnants may be a viable cell source for auricular reconstruction. METHODS: Chondrocytes were isolated from human ears, either normal conchal ear or microtia cartilage remnants, expanded in vitro, and seeded onto nanoscale-diameter polyglycolic acid sheets. These tissue-engineered constructs were implanted into athymic mice for up to 40 weeks. At harvest times of 5, 10, 20, and 40 weeks, samples were documented by gross morphology, histology, and reverse transcription-quantitative polymerase chain reaction analysis. RESULTS: Neocartilages generated from the two types of surgical tissues were similar in appearance of their extracellular matrices and positive staining for elastin and proteoglycans. In the 5- to 40-week time interval, there was an increasing trend in gene expression for type II collagen, elastin, and sex determining region Y box 5, important to normal cartilage phenotype, and a decreasing trend in gene expression for type III collagen, a fibroblast and dedifferentiation marker. Over 40 weeks of implantation, the original nanoscale-diameter polyglycolic acid scaffold dimensions (1 cm × 1 cm × 80 µm) were generally maintained in tissue-engineered cartilage length and width, and thickness was statistically significantly increased. CONCLUSIONS: Auricular cartilage can be regenerated over the long term (40 weeks) from surgical remnants by tissue-engineering techniques incorporating nanoscale-diameter polyglycolic acid scaffolds. Based on the present assays, microtia neocartilage very closely resembles tissue-engineered cartilage regenerated from chondrocytes isolated from normal conchal cartilage.

Murine metapodophalangeal sesamoid bones: morphology and potential means of mineralization underlying function.

Normal murine metapodophalangeal sesamoid bones, closely associated with tendons, were examined in terms of their structure and mineralization with reference to their potential function following crystal deposition. This study utilized radiography, whole mount staining, histology, and conventional electron microscopy to establish a maturation timeline of mineral formation in 1- to 6-week-old metapodophalangeal sesamoids from CD-1 mice. An intimate cellular and structural relationship was documented in more detail than previously described between the sesamoid bone, tendon, and fibrocartilage enthesis at the metapodophalangeal joint. Sesamoid calcification began in 1-week lateral sesamoids of the murine metacarpophalangeal joint of the second digit. All sesamoids were completely calcified by 4 weeks. Transmission electron microscopy of 2-week metacarpophalangeal sesamoids revealed extensive Type I collagen in the associated tendon and fibrocartilage insertion sites and Type II collagen and proteoglycan networks in the interior of the sesamoid. No extracellular matrix vesicles were documented. The results demonstrate that murine sesamoid bones consist of cartilage elaborated by chondrocytes that predominantly synthesize and secrete Type II collagen and proteoglycan. Type II collagen and proteoglycans appear responsible for the onset and progression of mineral formation in this tissue. These data contribute to new understanding of the biochemistry, ultrastructure, and mineralization of sesamoids in relation to other bones and calcifying cartilage and tendon of vertebrates. They also reflect on the potentially important but currently uncertain function of sesamoids as serving as a fulcrum point along a tendon, foreshortening its length and altering advantageously its biomechanical properties with respect to tendon-muscle interaction.