Matrix Production in Large Engineered Cartilage Constructs Is Enhanced by Nutrient Channels and Excess Media Supply

Cartilage tissue engineering is a promising approach to resurfacing osteoarthritic joints. Existing techniques successfully engineer small-sized constructs with native levels of extracellular matrix (glycosaminoglycans [GAG] or collagen). However, a remaining challenge is the growth of large-sized constructs with properties similar to those of small constructs, due to consumption and transport limitations resulting in inadequate nutrient availability within the interior of large constructs. This study employed system-specific computational models for estimating glucose requirements of large constructs, with or without channels, to enhance nutrient availability. Based on glucose requirements for matrix synthesis in cartilage constructs, computational simulations were performed to identify the media volume (MV) and the number of nutrient channels (CH) needed to maintain adequate glucose levels within tissue constructs over the 3-day period between media replenishments. In Study 1, the influence of MV (5, 10, 15 mL/construct) and number of nutrient channels (CH: 0, 3, 7, 12 per construct) on glucose availability was investigated computationally for ∅10 × 2.34 mm cylindrical constructs. Results showed that the conventionally used MV 5 led to deleterious glucose depletion after only 40 h of culture, and that MV 15 was required to maintain sufficient glucose levels for all channel configurations. Study 2 examined experimentally the validity of these predictions, for tissue constructs cultured for 56 days. Matrix elaboration was highest in MV 15/CH 12 constructs (21.6% ± 2.4%/ww GAG, 5.5% ± 0.7%/ww collagen, normalized to wet weight (ww) on day 0), leading to the greatest amount of swelling (3.0 ± 0.3 times day-0 volume), in contrast to the significantly lower matrix elaboration of conventional culture, MV 5/CH 0 (11.8% ± 1.6%/ww GAG and 2.5% ± 0.6%/ww collagen, 1.6 ± 0.1 times day-0 volume). The computational analyses correctly predicted the need to increase the conventional media levels threefold to support matrix synthesis in large channeled engineered constructs. Results also suggested that more elaborate computational models are needed for accurate predictive tissue engineering simulations, which account for a broader set of nutrients, cell proliferation, matrix synthesis, and swelling of the constructs.