Effects of cell concentration and growth period on articular and ear chondrocyte transplants for tissue engineering

This study determined the effects of chondrocyte source, cell concentration , and growth period on cartilage production when isolated porcine cells are injected subcutaneously in a nude mouse model. Chondrocytes were isolated from both car and articular cartilage and were suspended in Ham's F-12 medi um at concentrations of 10, 20,40, and 80 million cells per cubic centimete r. Using the nude mouse model, each concentration group was injected subcut aneously in 100-mul aliquots and was allowed to incubate for 6 weeks in viv o. In addition, cells suspended at a fixed concentration of 40 million cell s per cubic centimeter were injected in 100-mul aliquots and were incubated for 1, 2, 3, 4, 5, 6, 9, and 12 weeks. Each concentration or time period s tudied contained a total of eight mice, with four samples harvested per mou se for a final sample size of 32 constructs. All neocartilage samples were analyzed by histologic characteristics, mass, glycosaminoglycan level, and DNA content. Control groups consisted of native porcine ear and articular c artilage. Specimen mass increased with increasing concentration and incubation time. Ear neocartilage was larger than articular neocartilage at each concentrati on and time period. At 40 million cells per cubic centimeter, both ear and articular chondrocytes produced optimal neocartilage, without limitations i n growth. Specimen mass increased with incubation time up to 6 weeks in bot h ear and articular samples. No significant variations in glycosaminoglycan content were found in either articular or ear neocartilage, with respect t o variable chondrocyte concentration or growth period. Although articular s amples demonstrated no significant trends in DNA content over time, car spe cimens showed decreasing values through 6 weeks, inversely proportional to increase in specimen mass. Although both articular and ear sources of chond rocytes have been used in past tissue-engineering studies with success, thi s study indicates that a suspension of ear chondrocytes injected into a sub cutaneous location will produce biochemical and histologic data with greate r similarity to those of native cartilage. The authors believe that this ph enomenon is attributable to the local environment in which isolated chondro cytes from different sources are introduced. The subcutaneous environment o f native ear cartilage accommodates subcutaneously injected ear chondrocyte transplants better than articular transplants. Native structural and bioch emical cues within the local environment are believed to guide the prolifer ation of the differentiated chondrocytes.