Real time responses of fibroblasts to plastically compressed fibrillar collagen hydrogels

In vitro reconstituted type I collagen hydrogels are widely utilized for tissue engineering studies. However, highly hydrated collagen (HHC) gels exhibit insufficient mechanical strength and unstable geometrical properties, thereby limiting their therapeutic application. Plastic compression (PC) is a simple and reproducible approach for the immediate production of dense fibrillar collagen (DC) scaffolds which demonstrate multiple improvements for tissue engineered constructs including extracellular matrix (ECM)-like meso scale characteristics, increased mechanical properties (modulus and strength), enhanced cell growth and differentiation, and reduced long-term scaffold deformation. In order to determine at which stage these benefits become apparent, and the underlying mechanisms involved, the immediate response of NIH/3T3 fibroblasts to PC as well as longer-term cell growth within DC scaffolds were examined herein. The real time three-dimensional (3D) distribution of fluorescently labelled cells during PC was sequentially monitored using confocal laser scanning microscopy (CLSM), observing excellent cell retention and negligible numbers of expelled cells. Relative to cells grown in HHC gels, a significant improvement in cell survival within DC scaffolds was evident as early as day 1. Cell growth and metabolic activity within DC gels were significantly increased over the course of one week. While cells within DC scaffolds reached confluency, an inhomogeneous distribution of cells was present in HHC gels, as detected using x-ray computed micro-tomography analysis of phosphotungstic acid labelled cells and CLSM, which both showed a significant cell loss within the HHC core. Therefore, PC generates a DC gel scaffold without detrimental effects towards seeded cells, surpassing HHC gels as a 3D scaffold for tissue engineering.