Bioengineering of elastic cartilage with aggregated porcine and human auricular chondrocytes and hydrogels containing alginate, collagen, and kappa-elastin

Transplantation of isolated chondrocytes has long been acknowledged as a potential method for rebuilding small defects in damaged or deformed cartilages. Recent advances in tissue engineering permit us to focus on production of larger amounts of cartilaginous tissue, such as might be needed for reconstructive surgery of the entire auricle. In this report we describe modification of the basic techniques that lead to production of a large amount of elastic cartilage originated from porcine and human isolated chondrocytes. Small fragments of auricular cartilage were harvested from children undergoing ear reconstruction for microtia or extirpation of preauricular tags and from ears of juvenile pigs. Enzymatically isolated elastic chondrocytes were then agitated in suspension to form the chondronlike aggregates, which were further embedded in molded hydrogel constructs made of alginate and type I collagen augmented with kappa-elastin. The constructs were then implanted in nude mice and harvested 4 and 12 weeks after heterotransplantation. The resulting neocartilage closely resembled native auricular cartilage at the gross, microscopic, and ultrastructural levels. Immunohistochemistry and electron microscopy additionally confirmed that the newly produced cartilage contained the major components of the elastic cartilage-specific matrix, including collagen type II, proteoglycans, and well-assembled elastic fibers.

Bone formation by isolated calvarial osteoblasts in syngeneic and allogeneic transplants: light microscopic observations

Taking advantage of recently developed methods for osteoblast isolation, we used these cells to study bone morphogenesis in syngeneic and allogeneic intramuscular transplants. Syngeneic osteoblasts from fetal rat calvaria produced small islands of bone by the third day after transplantation. These islands increased in size and began to fuse after about 14 days. At the surface of the woven bone laid down first, lamellar bone developed. The amount of this bone increased, and in 56-day-old transplants solid blocks of bone were present. Osteoclasts were scarce, and the woven bone remained unresorbed. Bone marrow was absent. The structure of bone in transplants differed from that of mature calvarial bones in which only remnants of woven bone remained and bone marrow was well developed. The scarcity of osteoclasts in transplants could be caused by their relative paucity among the injected cells, since these cells responded strongly to added parathyroid hormone by increased production of cyclic adenosine monophosphate (cAMP) but only weakly to calcitonin. Osteoblasts isolated from the surface of calvarial lamellar bone of 28-day-old rats formed woven bone similar to the bone formed by fetal cells. This suggests that the type of bone produced does not depend on the intrinsic properties of the osteoblasts. Bone formed in an allogeneic system was surrounded by infiltrations containing lymphocytes, macrophages, and osteoclastlike cells in 14-day-old transplants. Osteoblasts at the bone periphery were destroyed and bone matrix was resorbed by infiltrating cells. Numerous bone lacunae were enlarged, suggesting the occurrence of osteocytic osteolysis. Isolated osteoblasts cultured for three population doublings or longer did not form bone after transplantation, although they retained some reactivity toward parathyroid hormone.

Synthesis of proteoglycans, collagen, and elastin by cultures of rabbit auricular chondrocytes--relation to age of the donor

Chondrocytes were isolated from the auricular cartilage of rabbits, aged 1 week to 30 months, and grown in short-term cell culture. The cells from the 1-week animals were small, polygonal, and mononucleated, while the chondrocytes from the older animals were larger, rounded, and frequently binucleated. The synthesis of proteoglycans, collagen, and elastin was determined by isotope incubation. Chemical characterization of the proteoglycans was also performed. The production of the matrix macromolecules showed a clear age dependence with peak synthesis occurring at different ages. Proteoglycans were actively synthesized by chondrocytes from all age groups with a broad maximum between 2 weeks and 5 months followed by a sharp decline to about 50% of the 1-week level at 12-30 months. Collagen synthesis peaked at 2 weeks, declining progressively thereafter to about 60% of the 1-week level at 30 months. Elastin synthesis was highest in the 1-week cultures and thereafter fell quickly to very low levels. In all age groups the chondrocytes synthesized predominantly cartilage-typic proteoglycans, i.e., large aggregate forming molecules containing chondroitin sulfate. Monomers and aggregates showed a size maximum at 2-8 weeks. The degree of sulfation of the chondroitin sulfate and the proportion of 6-sulfate increased with age. These findings support the concept of "age programs" for the biosynthesis and turnover of different matrix macromolecules.

The elastogenetic process in transplants and cultures of isolated auricular chondrocytes

Chondrocytes isolated from auricular cartilage of rabbits in the early postnatal period were transplanted intramuscularly into closely related animals and the reconstruction of cartilage and formation of elastic fibers monitored. Elastogenesis was most produced in transplants from younger donors. Auricular chondrocytes from 7 day old rabbits also produced elastic fibers in tissue culture, undergoing morphological changes similar to those occurring in vivo. The ability to form elastic fibers declined after prolonged cultivation.

In situ aging of auricular chondrocytes is not due to the exhaustion of their replicative potential

Multiplication of chondrocytes during growth of rabbit auricular cartilage was estimated on the basis of total DNA determination and compared with the population doubling level reached by these chondrocytes in vitro. The results indicate that the in situ aging of auricular chondrocytes is caused by factors other than the intrinsic depletion of their growth potential.

Maturation of rabbit auricular chondrocytes grown in vitro in monolayer culture

Chondrocytes isolated from auricular cartilage of 7-day-old rabbits were grown in vitro until the onset of phase III, occurring after 10-14 population doublings (PD). The size of cells and their dry mass were measured at various PD levels. These data were compared with results of analogous measurements of chondrocytes freshly isolated from 28-day-old rabbits. Both in vivo, during cartilage growth, and in vitro, some of the chondrocytes increased considerably in size and acquired two nuclei. Chondrocytes cultured in vitro for 4 population doublings were still capable of depositing elastic fibers in culture and forming cartilage after intramuscular transplantation. After longer periods of cultivation the ability of cells to produce a cartilage matrix declined. It is suggested that the auricular chondrocytes may represent a convenient model for comparative studies of cell aging in culture and in vivo, owing to the simplicity of matching senescent cells arising in both these situations.