Bulk collagen incorporation rates into knitted stiff fibre polymer in tissue-engineered scaffolds: the rate-limiting...

Fabrication of tissue-engineered constructs in vitro relies on sufficient synthesis of extracellular matrix (ECM) by cells to form a material suitable for normal function in vivo. Collagen synthesis by human dermal fibroblasts grown in vitro on two polymers, polyethylene terephthalate (PET) and polyglycolic acid (PGA), was measured by high-performance liquid chromatography (HPLC). Cells were either cultured in a dynamic environment, where meshes were loaded onto a pulsing tube in a bioreactor, or in a static environment without pulsing. Collagen synthesis by cells cultured on a static mesh increased by six-fold compared to monolayer culture, and increased by up to a further 5.4-fold in a pulsed bioreactor. However, little of the collagen synthesized was deposited onto the meshes, almost all being lost to the medium. The amount of collagen deposited onto meshes was highest when cells were cultured dynamically on PET meshes (17.6 microg), but deposition still represented only 1.4% of the total synthesized. Although total collagen synthesis was increased by the use of 3D culture and the introduction of pulsing, the results suggest that the limiting factor for fabrication of a tissue-engineered construct within practical timescales is not the amount of collagen synthesized but the quantity retained (i.e. deposited) within the construct during culture. This may be enhanced by systems which promote or assemble true 3D multi-layers of cells.