Tissue engineering by molecular disassembly and reassembly: biomimetic retention of mechanically functional aggrecan in hydrogel.

In vitro assembly of key functional extracellular matrix constituents for tissue-engineered constructs may provide a tool to modulate the retention of proteoglycan (PG) aggregates, which are crucial to compressive biomechanical properties of connective tissues. This study tested the hypotheses that (1) biomimetic molecular reassembly of PG aggregates (native aggrecan [AGC] with hyaluronan [HA] ± link protein [LP]) affects AGC retention kinetics in hydrogel constructs, (2) the compressive properties of such hydrogel constructs are related to the content of retained AGC, and (3) the reassembly method is compatible with chondrocytes. Addition of HA to AGC in hydrogel constructs increased AGC retention in a dose-dependent manner, and the addition of LP to AGC + HA further enhanced AGC retention. The level of AGC retention, in turn, was associated with increased equilibrium compressive stress of the constructs. Chondrocytes could be included in the process, and maintained expression of the chondrogenic phenotype, secreting type II collagen but little type I collagen. Thus, by altering the assembly of PG aggregates with HA ± LP, which affects AGC retention, it may be possible to achieve the targeted levels of PG components to modulate the mechanical properties of the engineered construct for cartilage as well as other tissues containing PG and PG aggregates.