Temporal regulation of chondrocyte metabolism in agarose constructs subjected to dynamic compression

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Abstract

The temporal response of chondrocyte metabolism in agarose constructs subjected to different dynamic compression regimes was investigated. The current study explored the effects of continuous or intermittent compression using various duty cycles of dynamic compressive loading, over a 48 h culture period. For the continuous compression experiments, duty cycles ranged from 5400 to 172,800 and intermittent compression delivered a total of 86,400 cycles. Large numbers of duty cycles significantly stimulated proteoglycan synthesis with maximal levels obtained for constructs subjected to 12 h of intermittent compression. The shortest duration of intermittent compression suggested that further cycles are inhibitory for cell proliferation. Nitrite release was independent of the length or type of compressive regime applied. The uncoupled nature of the metabolic response determined in this study suggests that mechanical conditioning regimes may be fine tuned to selectively stimulate key metabolic parameters of relevance to cartilage tissue engineering.

Section snippets

Preparation of chondrocyte/agarose constructs

Full depth slices of cartilage were removed from the metacarpalphalangeal joints of 18-month-old steers. The cartilage slices were washed, diced finely using a scalpel, and incubated at 37 °C on rollers for 1 h in Dulbecco’s minimal essential medium supplemented with 20% foetal calf serum, 2 μM l-glutamine, 5 μg ml−1 penicillin, 5 μg ml−1 streptomycin, 20 mM Hepes buffer, and 0.85 μM l-ascorbic acid (DMEM + 20% FCS) + 700 U ml−1 pronase and for a further 16 h at 37 °C in DMEM + 20% FCS supplemented with 100 U ml−1

Effects of continuous compression on chondrocyte/agarose constructs

The effects of continuous dynamic compressive strain on 35SO4 incorporation, [3H]thymidine incorporation, and nitrite release within unstrained constructs and constructs subjected to dynamic compressive strain are summarised in Table 1. The corresponding normalised strained values, presented as a percentage of the unstrained controls, are illustrated in Fig. 2. In unstrained constructs, mean 35SO4 incorporation values measured from individual experiments ranged from 0.0248 to 0.0361 μmol/h/μg

Discussion

A number of studies, previously published by the authors, have demonstrated that 15% compressive strain amplitude, applied in a static or dynamic manner, will induce distinct metabolic responses, in full depth chondrocytes and cells isolated from surface and deep zones of articular cartilage, when applied continuously over a 48 h test period to chondrocytes seeded in agarose constructs [12], [18], [19], [27]. Previous studies have demonstrated that low amplitude dynamic compression-induced

Acknowledgements

This study was supported by a Framework V European grant, “Imbiotor,” Project No. GRD1-2000-25394.

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