Over the past two decades, deep eutectic solvents (DESs) have captured significant attention as an emergent class of solvents that have unique properties and applications in differing fields of chemistry. One area where DES systems find utility is the design of polymeric gels, often referred to as “eutectogels,” which can be prepared either using a DES to replace a traditional solvent, or where monomers form part of the DES themselves. Due to the extensive network of intramolecular interactions (e.g., hydrogen bonding) and ionic species that exist in DES systems, polymeric eutectogels often possess appealing material properties—high adhesive strength, tuneable viscosity, rapid polymerization kinetics, good conductivity, as well as high strength and flexibility. In addition, non‐covalent crosslinking approaches are possible due to the inherent interactions that exist in these materials. This review considers several key applications of polymeric eutectogels, including organic electronics, wearable sensor technologies, 3D printing resins, adhesives, and a range of various biomedical applications. The design, synthesis, and properties of these eutectogels are discussed, in addition to the advantages of this synthetic approach in comparison to traditional gel design. Perspectives on the future directions of this field are also highlighted.

Alginate (Alg) polymers have received much attention due to the mild conditions required for gel formation and their good bio‐acceptability. However, due to limited interactions with cells, many drugs, and biomolecules, chemically modified alginates are of great interest. Sulfated alginate (S–Alg) is a promising heparin‐mimetic that continues to be investigated both as a drug molecule and as a component of biomaterials. Herein, the S–Alg literature of the past five years (2017–2023) is reviewed. Several methods used to synthesize S–Alg are described, with a focus on new advances in characterization and stereoselectivity. Material fabrication is another focus and spans bulk materials, particles, scaffolds, coatings, and part of multicomponent biomaterials. The new application of S–Alg as an antitumor agent is highlighted together with studies evaluating safety and biodistribution. The high binding affinity of S–Alg for various drugs and heparin‐binding proteins is exploited extensively in biomaterial design to tune the encapsulation and release of these agents and this aspect is covered in detail. Recommondations include publishing key material properties to allow reproducibility, careful selection of appropriate sulfation strategies, the use of cross–linking strategies other than ionic cross–linking for material fabrication, and more detailed toxicity and biodistribution studies to inform future work.

Surface modification of biomaterials is a strategy used to improve cellular and in vivo outcomes. However, most studies do not evaluate the lifetime of the introduced surface layer, which is an important aspect affecting how a biomaterial will interact with a cellular environment both in the short and in the long term. This study evaluated the surface layer stability in vitro in buffer solution of materials produced from poly(lactic-co-glycolic acid) (50:50) and polycaprolactone modified by hydrolysis and/or grafting of hydrophilic polymers using grafting from approaches. The data presented in this study highlight the shortcomings of using model substrates (e.g., spun-coated films) rather than disks, particles, and scaffolds. It also illustrates how similar surface modification strategies in some cases result in very different lifetimes of the surface layer, thus emphasizing the need for these studies as analogies cannot always be drawn.

Solvent‐free photopolymerization of vinyl monomers to produce high modulus materials with applications in 3D printing and photoswitchable materials is demonstrated. Polymerizable eutectic (PE) mixtures are prepared by simply heating and stirring various molar ratios of N‐isopropylacrylamide (NIPAM), acrylamide (AAm) and 2‐hydroxyethyl methacrylate (HEMA). The structural and thermal properties of the resulting mixtures are evaluated by 1D and 2D NMR spectroscopy as well as differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). UV photocuring kinetics of the PE mixtures is evaluated via in situ photo‐DSC and photorheology measurements. The PE mixtures cure rapidly and display storage moduli that are orders of magnitude greater than equivalent copolymers cured in an aqueous medium. The versatility of these PE systems is demonstrated through the addition of a photoswitchable spiropyran acrylate monomer, as well as applying the PE formulation as a stereolithography (SLA)‐based 3D printing resin. Due to the hydrogen‐bonding network in PE systems, 3D printing of the eutectic resin is possible in the absence of crosslinkers. The addition of a RAFT agent to reduce average polymer chain length enables 3D printing of materials which retain their shape and can be dissolved on demand in appropriate solvents.

Over the past five years, there has been a notable increase in the application of three-dimensional (3D) printing techniques mediated by reversible addition–fragmentation chain-transfer (RAFT) polymerization. This increasing interest is due in part to the associated benefits that RAFT 3D printing systems provide, including tighter control over macromolecular network structures and the ability to easily prepare multifunctional materials. In parallel, deep eutectic solvents that feature polymerizable components, called polymerizable eutectics, have also been gaining attention for their outstanding properties and ease of manufacture of functional polymer materials. In this work, we develop polymerizable eutectic resins that contain RAFT agents and are suitable for application to visible-light induced vat 3D printing. The combination of the polymerizable eutectic components and a Z-connected bis-RAFT agent in the resin provides the resulting materials with excellent properties derived from both the eutectic components and the degenerative chain transfer mechanism of RAFT polymerization. While the base (non-RAFT) polymerizable eutectic materials display high modulus and adhesive strength on their own, the inclusion of RAFT agents provides materials with higher adhesive strength while retaining their high strength to higher temperatures. Moreover, the selection of N-isopropylacrylamide as one of the eutectic components provides these materials with reversible thermoresponsive behavior in water. The high shape fidelity and ease of preparation of these materials could be of potential use in the design of 3D printable biomaterials and actuators.

The preparation of interpenetrating polymer networks (IPNs) and semi-interpenetrating polymer networks (semi-IPNs) is reported via a solvent-free approach using a binary polymerizable eutectic. N-Isopropylacrylamide (NIPAM) and ε-caprolactone (CL) were mixed in various mole ratios to prepare viscous polymerizable liquids that were stable at room temperature, based on solid–liquid equilibrium phase diagrams from differential scanning calorimetry (DSC) data. The strong degree of association between NIPAM and CL within these mixtures was confirmed via 1D and 2D NMR spectroscopy. Using an appropriate UV photoinitiator and ring opening polymerization catalyst, the orthogonal polymerization (either in a sequential or simultaneous fashion) of each component within the eutectic was achieved, with enhanced reaction kinetics for the ring opening polymerization compared to a traditional solvent (DMSO). Through the incorporation of diacrylate and bis(carbonate) crosslinkers into the resin mixture, IPNs and semi-IPNs were realised in a one-pot two-step approach from polymerizable eutectics for the first time. These networks possessed thermoresponsive swelling behaviour in water, and retained their structural integrity in good solvents for both phases. This binary eutectic was also shown to be suitable as a resin for stereolithography 3D printing on a benchtop printer through the inclusion of a RAFT agent, achieving semi-IPN printed objects in a two-step approach.