Tuning the Mechanical Properties of Multiarm RAFT-Based Block Copolyelectrolyte Hydrogels via Ionic Cross-Linking for 3D Cell Cultures.

Hydrogels that serve as native extracellular matrix (ECM) mimics are typically naturally derived hydrogels that are physically cross-linked via ionic interactions. This means rapid gelation of synthetic polymers, which give control over the chemical and physical cues in hydrogel formation. Herein, we combine the best of both systems by developing a synthetic hydrogel with ionic cross-linking of block copolyelectrolytes to rapidly create hydrogels. Reversible addition-fragmentation chain-transfer (RAFT) polymerization was used to synthesize oppositely charged polyelectrolyte molecules and, in turn, modulate the mechanical property of stiffness. The mechanical stiffness of a range of 900-3500 Pa was tuned by varying the number of charged ionic groups, the length of the polymer arms, and the polymer concentration. We demonstrate the synthetic polyelectrolyte hydrogel as an ECM mimic for three-dimensional (3D) in vitro cell models using MCF-7 breast cancer cells.

A Covalently Crosslinked Ink for Multimaterials Drop-on-Demand 3D Bioprinting of 3D Cell Cultures.

In vitro 3D cell models have been accepted to better recapitulate aspects of in vivo organ environment than 2D cell culture. Currently, the production of these complex in vitro 3D cell models with multiple cell types and microenvironments remains challenging and prone to human error. Here, a versatile ink comprising a 4-arm poly(ethylene glycol) (PEG)-based polymer with distal maleimide derivatives as the main ink component and a bis-thiol species as the activator that crosslinks the polymer to form the hydrogel in less than a second is reported. The rapid gelation makes the polymer system compatible with 3D bioprinting. The ink is combined with a novel drop-on-demand 3D bioprinting platform, designed specifically for producing 3D cell cultures, consisting of eight independently addressable nozzles and high-throughput printing logic for creating complex 3D cell culture models. The combination of multiple nozzles and fast printing logic enables the rapid preparation of many complex 3D cell cultures comprising multiple hydrogel environments in one structure in a standard 96-well plate format. The platform's compatibility for biological applications is validated using pancreatic ductal adenocarcinoma cancer (PDAC) and human dermal fibroblast cells with their phenotypic responses controlled by tuning the hydrogel microenvironment.

Porous Graphene Oxide Films Prepared via the Breath-Figure Method: A Simple Strategy for Switching Access of Redox Species to an Electrode Surface.

Porous materials can be modified with physical barriers to control the transport of ions and molecules through channels via an external stimulus. Such capability has brought attention toward drug delivery, separation methods, nanofluidics, and point-of-care devices. In this context, gated platforms on which access to an electrode surface of species in solution can be reversibly hindered/unhindered on demand are appearing as promising materials for sensing and microfluidic switches. The preparation of a reversible gated device usually requires mesoporous materials, nanopores, or molecularly imprinted polymers. Here, we show how the breath-figure method assembly of graphene oxide can be used as a simple strategy to produce gated electrochemical materials. This was achieved by forming an organized porous thin film of graphene oxide onto an ITO surface. Localized brushes of thermoresponsive poly(N-isopropylacrylamide) were then grown to specific sites of the porous film by in situ reversible addition-fragmentation chain-transfer polymerization. The gating mechanism relies on the polymeric chains to expand and contract depending on the thermal stimulus, thus modulating the accessibility of redox species inside the pores. The resulting platform was shown to reversibly hinder or facilitate the electron transfer of solution redox species by modulating temperature from the room value to 45 °C or vice versa.