Exploiting Meltable Protein Hydrogels to Encapsulate and Culture Cells in 3D.

There is a growing realization that 3D cell culture better mimics complex in vivo environments than 2D, lessening aberrant cellular behaviors and ultimately improving the outcomes of experiments. Chemically crosslinked hydrogels which imitate natural extracellular matrix (ECM) are proven cell culture platforms, but the encapsulation of cells within these hydrogel networks requires bioorthogonal crosslinking chemistries which can be cytotoxic, synthetically demanding, and costly. Capsular antigen fragment 1 (Caf1) is a bacterial, polymeric, fimbrial protein which can be genetically engineered to imitate ECM. Furthermore, it can, reversibly, thermally interconvert between its polymeric and monomeric forms even when chemically crosslinked within a hydrogel network. It is demonstrated that this meltable feature of Caf1 hydrogels can be utilized to encapsulate neonatal human dermal fibroblasts at a range of cell densities (2 × 105 -2 × 106  cells mL-1 of hydrogel) avoiding issues with chemical cytotoxicity. These hydrogels supported cell 3D culture for up to 21 d, successfully inducing cellular functions such as proliferation and migration. This work is significant because it further highlights the potential of simple, robust, Caf1-based hydrogels as a cell culture platform.

Hydrogels of engineered bacterial fimbriae can finely tune 2D human cell culture.

Demand continues to grow for biomimetic materials able to create well-defined environments for modulating the behaviour of living cells in culture. Here, we describe hydrogels based upon the polymeric bacterial fimbriae protein capsular antigen fragment 1 (Caf1) that presents tunable biological properties for enhanced tissue cell culture applications. We demonstrate how Caf1 hydrogels can regulate cellular functions such as spreading, proliferation and matrix deposition of human dermal fibroblast cells (hDFBs). Caf1 hydrogels exploring a range of mechanical properties were prepared using copolymers featuring controlled compositions of inert wild-type Caf1 subunits and a mutant subunit displaying the RGDS peptide motif. The hydrogels showed excellent cytocompatibility with hDFBs and the ability to modulate both cell morphology and matrix deposition. Interestingly, Caf1 hydrogels displaying faster stress relaxation were demonstrated to show the highest metabolic activities of growing cells in comparison with other Caf1 hydrogel formulations. The stiffest Caf1 hydrogel impacted cellular morphology, inducing alignment of the cells. This work is significant as it clearly indicates that Caf1-based hydrogels offer tuneable biochemical and mechanical substrates conditions suitable for cell culture applications.