Concentrated collagen hydrogels: A new approach for developing artificial tissues

Abstract

Collagen's unique properties are ideal for creating tissue and organ equivalents. Rapid development of methods for creating such objects has revealed that collagen biomaterials have poor mechanical properties, which complicates their use. A potential solution is increasing the collagen concentration in the initial solution; however, there is little data on the behavior of cells cultured inside concentrated collagen hydrogels for an extended period. Therefore, we assessed the cell behavior of human dermal fibroblasts (hDFs) cultured for 28 days inside collagen hydrogels of various densities (5, 10, and 30 mg/mL). In addition collagen hydrogels seeded with spheroids of human dermal papilla cells (hDPCs) has been implanted subcutaneously to mice. The RT-qPCR and immunohistochemistry results revealed no significant difference between the study groups regarding changes in cell morphology, viability, and expression of specialized markers, extracellular matrix proteins, and MMPs/TIMPs. However, matrix density influenced cell proliferation and contractile capacity. Rheological studies supplemented by time-lapse imaging revealed an inverse correlation between hydrogel density and cell motility. The hDFs constantly interacted with the matrix, changing its physical properties, which was confirmed by examining the rheological characteristics of cell-laden collagen gels over different periods (1, 14, and 28 days). The hDPCs inside 30 mg/mL collagen hydrogels maintained viability after 28 days, while 5 and 10 mg/mL hydrogels were completely biodegraded and no human cells could be found at the site of transplantation. The long-term stability of 30 mg/mL collagen hydrogels provide a basis for using concentrated collagen solutions to create new biomaterials for artificial tissue development.