Tailoring the assembly of collagen fibers in alginate microspheres

The application of microspheres instead of bulk hydrogels in cell-laden biomaterials offers multiple advantages such as a high surface-to-volume-ratio and, consequently, a better nutrition and oxygen transfer to and from cells. The preparation of inert alginate microspheres is facile, quick, and well-established and the fabrication of alginate-collagen microspheres has been previously reported. However, no detailed characterization of the collagen fibrillogenesis in the alginate matrix is available. We use second-harmonic imaging microscopy reflection microscopy and turbidity assay to study assembly of collagen in alginate microspheres. We show that the assembly of collagen fibers in a gelled alginate matrix is a complex process that can be aided by addition of small polar molecules, such as glycine and by a careful selection of the gelling buffer used to prepare alginate hydrogels. HighlightsO_LIIn situ characterization of collagen fiber assembly in a gelled alginate matrix using collagen-specific second harmonic generated microscopy C_LIO_LICollagen fibrillogenesis is positively influenced by the presence of small molecules in the solution prior microsphere preparation C_LIO_LIThe ratio and amount of calcium, sodium and chloride ions used for the alginate gelling has also a crucial impact on the development of a collagen fiber network C_LI