A Protein-Adsorbent Hydrogel with Tunable Stiffness for Tissue Culture Demonstrates Matrix-Dependent Stiffness Responses.

Although tissue culture plastic has been widely employed for cell culture, the rigidity of plastic is not physiologic. Softer hydrogels used to culture cells have not been widely adopted in part because coupling chemistries are required to covalently capture extracellular matrix (ECM) proteins and support cell adhesion. To create an in vitro system with tunable stiffnesses that readily adsorbs ECM proteins for cell culture, we present a novel hydrophobic hydrogel system via chemically converting hydroxyl residues on the dextran backbone to methacrylate groups, thereby transforming non-protein adhesive, hydrophilic dextran to highly protein adsorbent substrates. Increasing methacrylate functionality increases the hydrophobicity in the resulting hydrogels and enhances ECM protein adsorption without additional chemical reactions. These hydrophobic hydrogels permit facile and tunable modulation of substrate stiffness independent of hydrophobicity or ECM coatings. Using this approach, we show that substrate stiffness and ECM adsorption work together to affect cell morphology and proliferation, but the strengths of these effects vary in different cell types. Furthermore, we reveal that stiffness mediated differentiation of dermal fibroblasts into myofibroblasts is modulated by the substrate ECM. Our material system demonstrates remarkable simplicity and flexibility to tune ECM coatings and substrate stiffness and study their effects on cell function.

Fibroblast clearance of damaged tissue following laser ablation in engineered microtissues.

Although the mechanisms underlying wound healing are largely preserved across wound types, the method of injury can affect the healing process. For example, burn wounds are more likely to undergo hypertrophic scarring than are lacerations, perhaps due to the increased underlying damage that needs to be cleared. This tissue clearance is thought to be mainly managed by immune cells, but it is unclear if fibroblasts contribute to this process. Herein, we utilize a 3D in vitro model of stromal wound healing to investigate the differences between two modes of injury: laceration and laser ablation. We demonstrate that laser ablation creates a ring of damaged tissue around the wound that is cleared by fibroblasts prior to wound closure. This process is dependent on ROCK and dynamin activity, suggesting a phagocytic or endocytic process. Transmission electron microscopy of fibroblasts that have entered the wound area reveals large intracellular vacuoles containing fibrillar extracellular matrix. These results demonstrate a new model to study matrix clearance by fibroblasts in a 3D soft tissue. Because aberrant wound healing is thought to be caused by an imbalance between matrix degradation and production, this model, which captures both aspects, will be a valuable addition to the study of wound healing.

Click Chemistry-Based DNA Labeling of Cells for Barcoding Applications.

Cell labeling and tracking methodologies can play an important role in experiments aimed at understanding biological systems. However, many current cell labeling and tracking techniques have limitations that preclude their use in a variety of multiplexed and high-throughput applications that could best represent the heterogeneity and combinatorial complexity present in physiologic contexts. Here, we demonstrate an approach for labeling, tracking, and quantifying cells using double-stranded DNA barcodes. These barcodes are introduced to the outside of the cell membrane, giving the labeled cells a unique identifier. This approach is compatible with flow cytometric and PCR-based identification and relative quantification of the presence of barcode-labeled cells. Further, utilizing this strategy, we demonstrate the capacity for sorting and enrichment of barcoded cells from a bulk population. In addition, we illustrate the design and utility of a range of orthogonal barcode sequences, which can enable the use of multiple independent barcodes to track, sort, and enrich multiple cell types and/or cells receiving distinct treatments from a pooled sample. Overall, this method of labeling cells has the potential to track multiple populations of cells in both high-throughput in vitro and physiologic in vivo settings.