A peptide functionalized poly(ethylene glycol) (PEG) hydrogel for investigating the influence of biochemical and biophysical matrix properties on tumor cell migration.

To address the challenges associated with defined control over matrix properties in 3D cell culture systems, we employed a peptide functionalized poly(ethylene glycol) (PEG) hydrogel matrix in which mechanical modulus and adhesive properties were tuned. An HT-1080 human fibrosarcoma cell line was chosen as a model for probing matrix influences on tumor cell migration using the PEG hydrogel platform. HT-1080 speed varied with a complex dependence on both matrix modulus and Cys-Arg-Gly-Asp-Ser (CRGDS) adhesion ligand concentration, with regimes in which motility increased, decreased, or was minimally altered being observed. We further investigated cell motility by forming matrix interfaces that mimic aspects of tissue boundaries that might be encountered during invasion by taking advantage of the spatial control of the thiol-ene photochemistry to form patterned regions of low and high cross-linking densities. HT-1080s in 100 Pa regions of patterned PEG hydrogels tended to reverse direction or aggregate at the interface when they encountered a 360 Pa boundary. In contrast, HT-1080s were apparently unimpeded when migrating from the stiff to the soft regions of PEG peptide hydrogels, which may indicate that cells are capable of "reverse durotaxis" within at least some matrix regimes. Taken together, our results identified matrix regimes in which HT-1080 motility was both positively and negatively influenced by cell adhesion or matrix modulus.

A quantitative comparison of human HT-1080 fibrosarcoma cells and primary human dermal fibroblasts identifies a 3D migration mechanism with properties unique to the transformed phenotype.

Here, we describe an engineering approach to quantitatively compare migration, morphologies, and adhesion for tumorigenic human fibrosarcoma cells (HT-1080s) and primary human dermal fibroblasts (hDFs) with the aim of identifying distinguishing properties of the transformed phenotype. Relative adhesiveness was quantified using self-assembled monolayer (SAM) arrays and proteolytic 3-dimensional (3D) migration was investigated using matrix metalloproteinase (MMP)-degradable poly(ethylene glycol) (PEG) hydrogels ("synthetic extracellular matrix" or "synthetic ECM"). In synthetic ECM, hDFs were characterized by vinculin-containing features on the tips of protrusions, multipolar morphologies, and organized actomyosin filaments. In contrast, HT-1080s were characterized by diffuse vinculin expression, pronounced ß1-integrin on the tips of protrusions, a cortically-organized F-actin cytoskeleton, and quantitatively more rounded morphologies, decreased adhesiveness, and increased directional motility compared to hDFs. Further, HT-1080s were characterized by contractility-dependent motility, pronounced blebbing, and cortical contraction waves or constriction rings, while quantified 3D motility was similar in matrices with a wide range of biochemical and biophysical properties (including collagen) despite substantial morphological changes. While HT-1080s were distinct from hDFs for each of the 2D and 3D properties investigated, several features were similar to WM239a melanoma cells, including rounded, proteolytic migration modes, cortical F-actin organization, and prominent uropod-like structures enriched with ß1-integrin, F-actin, and melanoma cell adhesion molecule (MCAM/CD146/MUC18). Importantly, many of the features observed for HT-1080s were analogous to cellular changes induced by transformation, including cell rounding, a disorganized F-actin cytoskeleton, altered organization of focal adhesion proteins, and a weakly adherent phenotype. Based on our results, we propose that HT-1080s migrate in synthetic ECM with functional properties that are a direct consequence of their transformed phenotype.

Photodegradable, Photoadaptable Hydrogels via Radical-Mediated Disulfide Fragmentation Reaction.

Various techniques have been adopted to impart a biological responsiveness to synthetic hydrogels for the delivery of therapeutic agents as well as the study and manipulation of biological processes and tissue development. Such techniques and materials include polyelectrolyte gels that swell and deswell with changes in pH, thermosensitive gels that contract at physiological temperatures, and peptide cross-linked hydrogels that degrade upon peptidolysis by cell-secreted enzymes. Herein we report a unique approach to photochemically deform and degrade disulfide cross-linked hydrogels, mitigating the challenges of light attenuation and low quantum yield, permitting the degradation of hydrogels up to 2 mm thick within 120 s at low light intensities (10 mW/cm(2) at 365 nm). Hydrogels were formed by the oxidation of thiol-functionalized 4-armed poly(ethylene glycol) macromolecules. These disulfide cross-linked hydrogels were then swollen in a lithium acylphosphinate photoinitiator solution. Upon exposure to light, photogenerated radicals initiate multiple fragmentation and disulfide exchange reactions, permitting and promoting photodeformation, photowelding, and photodegradation. This novel, but simple, approach to generate photoadaptable hydrogels portends the study of cellular response to mechanically and topographically dynamic substrates as well as novel encapsulations by the welding of solid substrates. The principles and techniques described herein hold implications for more than hydrogel materials but also for photoadaptable polymers more generally.