This study examines the tissue engineering of a human ear model through use of bovine chondrocytes isolated from four different cartilaginous sites (nasoseptal, articular, costal, and auricular) and seeded onto biodegradable poly(l-lactic acid) and poly(L-lactide-epsilon-caprolactone) (50 : 50) polymer ear-shaped scaffolds. After implantation in athymic mice for up to 40 weeks, cell/scaffold constructs were harvested and analyzed in terms of size, shape, histology, and gene expression. Gross morphology revealed that all the tissue-engineered cartilages retained the initial human auricular shape through 40 weeks of implantation. Scaffolds alone lost significant size and shape over the same period. Quantitative reverse transcription-polymerase chain reaction demonstrated that the engineered chondrocyte/scaffolds yielded unique expression patterns for type II collagen, aggrecan, and bone sialoprotein mRNA. Histological analysis showed type II collagen and proteoglycan to be the predominant extracellular matrix components of the various constructs sampled at different implantation times. Elastin was also present but it was found only in constructs seeded with auricular chondrocytes. By 40 weeks of implantation, tissue-engineered cartilage of costal origin became calcified, marked by a notably high relative gene expression level of bone sialoprotein and the presence of rigid, nodular protrusions formed by mineralizing rudimentary cartilaginous growth plates. The collective data suggest that nasoseptal, articular, and auricular cartilages represent harvest sites suitable for development of tissue-engineered human ear models with retention over time of three-dimensional construct architecture, gene expression, and extracellular matrix composition comparable to normal, nonmineralizing cartilages. Calcification of constructs of costal chondrocyte origin clearly shows that chondrocytes from different tissue sources are not identical and retain distinct characteristics and that these specific cells are inappropriate for use in engineering a flexible ear model.

Human middle phalanges were tissue-engineered with midshaft scaffolds of poly(L-lactide-epsilon-caprolactone) [P(LA-CL)], hydroxyapatite-P(LA-CL), or beta-tricalcium phosphate-P(LA-CL) and end plate scaffolds of bovine chondrocyte-seeded polyglycolic acid. Midshafts were either wrapped with bovine periosteum or left uncovered. Constructs implanted in nude mice for up to 20 weeks were examined for cartilage and bone development as well as gene expression and protein secretion, which are important in extracellular matrix (ECM) formation and mineralization. Harvested 10- and 20-week constructs without periosteum maintained end plate cartilage but no growth plate formation. They also consisted of chondrocytes secreting type II collagen and proteoglycan, and they were composed of midshaft regions devoid of bone. In all periosteum-wrapped constructs at like times, end plate scaffolds held chondrocytes elaborating type II collagen and proteoglycan and cartilage growth plates resembling normal tissue. Chondrocyte gene expression of type II collagen, aggrecan, and bone sialoprotein varied depending on midshaft composition, presence of periosteum, and length of implantation time. Periosteum produced additional cells, ECM, and mineral formation within the different midshaft scaffolds. Periosteum thus induces midshaft development and mediates chondrocyte gene expression and growth plate formation in cartilage regions of phalanges. This work is important for understanding developmental principles of tissue-engineered phalanges and by extension those of normal growth plate cartilage and bone.

Results give insight into construct processes of tissue regeneration and development and suggest more complete tissue-engineered cartilage, bone, and tendon models. These should have significant future scientific and clinical applications in medicine, including their use in plastic surgery, orthopaedics, craniofacial reconstruction, and teratology.