Acid Scavenger Free Synthesis of Oligo(Poly(Ethylene Glycol) Fumarate) Utilizing Inert Gas Sparging.

The macromolecule oligo(poly(ethylene glycol) fumarate) (OPF) exhibits promising attributes for creating suitable three-dimensional hydrogel environments to study cell behavior, deliver therapeutics, and serve as a degradable, nonfouling material. However, traditional synthesis techniques are time consuming, contain salt contaminants, and generate significant waste. These issues have been overcome with an alternative, one-pot approach that utilizes inert gas sparging. Departing from previous synthetic schemes that require acid scavengers, inert gas sparging removes byproducts in situ, eliminating significant filtration and postprocessing steps, while allowing a more uniform product. Characterized by nuclear magnetic resonance, gel permeation chromatography, and differential scanning calorimetry, nitrogen sparge synthesis yields an OPF product with greater polymer length than traditional acid scavenger synthesis methods. Furthermore, nitrogen-sparged OPF readily crosslinks using either ultraviolet or thermal initiator methods with or without the addition of short-chain diacrylate units, allowing for greater tunability in hydrogel properties with little to no cytotoxicity. Overall, inert gas sparging provides a longer chain and cleaner polymer product for hydrogel material studies while maintaining degradable characteristics. Impact statement Using nitrogen sparging, we have demonstrated that oligo(poly(ethylene glycol) fumarate) (OPF) can be produced with decreased postprocessing, increased product purity, greater oligomerization, and cell viability. These properties lead to greater tunability in mechanical properties and a more versatile hydrogel for biomedical applications. The simplification of synthesis and elimination of impurities will expand the utility of OPF as a degradable hydrogel for cell culture, tissue engineering, regenerative medicine, and therapeutic delivery, among other applications.

Optimization of electrospun poly(N-isopropyl acrylamide) mats for the rapid reversible adhesion of mammalian cells.

Poly(N-isopropyl acrylamide) (pNIPAM) is a "smart" polymer that responds to changes in altering temperature near physiologically relevant temperatures, changing its relative hydrophobicity. Mammalian cells attach to pNIPAM at 37 °C and detach spontaneously as a confluent sheet when the temperature is shifted below the lower critical solution temperature (∼32 °C). A variety of methods have been used to create pNIPAM films, including plasma polymerization, self-assembled monolayers, and electron beam ionization. However, detachment of confluent cell sheets from these pNIPAM films can take well over an hour to achieve potentially impacting cellular behavior. In this work, pNIPAM mats were prepared via electrospinning (i.e., espNIPAM) by a previously described technique that the authors optimized for cell attachment and rapid cell detachment. Several electrospinning parameters were varied (needle gauge, collection time, and molecular weight of the polymer) to determine the optimum parameters. The espNIPAM mats were then characterized using Fourier-transform infrared, x-ray photoelectron spectroscopy, and scanning electron microscopy. The espNIPAM mats showing the most promise were seeded with mammalian cells from standard cell lines (MC3T3-E1) as well as cancerous tumor (EMT6) cells. Once confluent, the temperature of the cells and mats was changed to ∼25 °C, resulting in the extremely rapid swelling of the mats. The authors find that espNIPAM mats fabricated using small, dense fibers made of high molecular weight pNIPAM are extremely well-suited as a rapid release method for cell sheet harvesting.