Thiol–ene ‘click’ reactions between terpenes and a four-arm thiol were utilized to produced thermoset 3D printed structures using vat photopolymerisation.

Biosourced materials are gaining interest industrially, but there are still limitations on the library of available materials suitable for advanced manufacturing, especially using photopolymerization-based processing techniques. Terpenes, such as myrcene, are naturally produced materials possessing structural features, specifically alkenes, that avail themselves for such techniques. Free-radical and anionic polymerization techniques were used to explore molecular architecture, such as branching, as well as molecular weight and dispersity on physical properties prior to the production of 3D printing photopolymer resins. The polymyrcene resins were printed into dogbones and mold templates for soft materials. Model reactions with monofunctional thiols were used to demonstrate the potential for postpolymerization and fabrication functionalization, accompanying a physical demonstration where the surface hydrophobicity of polymyrcene could be tuned from superhydrophobic when using an alkyl chain monothiol (greater than 100°water contact angle) to a hydrophilic surface displaying a water contact angle of less than 45°compared with that of the unmodified surface (∼60°). Tunable bulk and surface properties are a unique feature for 3D printing materials and demonstrate the potential of polymyrcene and other biosourced photopolymers to a wide range of research applications.

Biocompatible polymers are widely used in tissue engineering and biomedical device applications. However, few biomaterials are suitable for use as long-term implants and these examples usually possess limited property scope, can be difficult to process, and are nonresponsive to external stimuli. Here, we report a class of easily processable polyamides with stereocontrolled mechanical properties and high-fidelity shape memory behaviour. We synthesise these materials using the efficient nucleophilic thiol-yne reaction between a dipropiolamide and dithiol to yield an α,β − unsaturated carbonyl moiety along the polymer backbone. By rationally exploiting reaction conditions, the alkene stereochemistry is modulated between 35-82% cis content and the stereochemistry dictates the bulk material properties such as tensile strength, modulus, and glass transition. Further access to materials possessing a broader range of thermal and mechanical properties is accomplished by polymerising a variety of commercially available dithiols with the dipropiolamide monomer.

Green manufacturing and reducing our cultural dependency on petrochemicals have been topics of growing interest in the past decade, particularly for three-dimensional (3D) printable photopolymers where often toxic solvents and reagents have been required. Here, a simple solvent-free, free-radical polymerization is utilized to homo- and copolymerize limonene and β-myrcene monomers to produce oligomeric photopolymers (M n < 11 kDa) displaying Newtonian, low viscosities (∼10 Pa × s) suitable for thiol–ene photo-cross-linking, yielding photoset materials in a digital light processing (DLP)-type 3D printer. The resulting photosets display tunable thermomechanical properties (poly­(limonene) displays elastic moduli exceeding 1 GPa) compared with previous works focusing on monomeric terpenes as well as four-dimensional (4D) shape memory behavior. The utility of such photopolymers for biomedical applications is briefly considered on the premise of the hydrophilic nature (measured by contact angle) as well as their cytocompatibility upon seeding films with macrophages. These terpene-derived, green 4D photopolymers are shown to have promising physical behaviors suitable for an array of manufacturing and 3D printing applications.

The use of green alternatives to petrochemicals from renewable feedstocks is of great interest globally, especially within additive manufacturing efforts. To this end, the utilization of the terpenoid linalool is presented for photopolymer resins 3D printed using digital light processing (DLP) with thiol-ene click chemistry. Linalool derivatives are made from single-step modifications, providing multiple greener alternatives to current acrylate photopolymers, and are characterized based upon rheology, thermomechanical, and shape memory properties. The use of aliphatic and aromatic diisocyanates to produce tetra-functional monomers is demonstrated to provide tunability to the photoreactivity/gelation time as well as significantly enhancing the tensile properties (2–3 orders of magnitude increase in elastic modulus) and thermal properties (glass transition temperature increase from ∼12 °C for linalool to 75 °C for the isophorone diisocyanate-containing linalool urethane derivative) and 4D behavior, in this case shape memory response. Ultimately, the derivatives are shown to be better candidates for DLP-type 4D printing of complex prototypes, using a porous cubic structure to demonstrate the additive manufacturing potential of this simple material platform.

Photopolymerization has been widely used to create cross-linked photoset materials that have found wide applicability, including in 3D printing. Among the many chemistries available for these processes, thiol-ene "click" chemistry provides a rapid and efficient route to produce such materials but also leaves residual alkene groups that may be further exploited for postpolymerization functionalization. In the case of aliphatic polycarbonates, these residual functional groups are demonstrated to be suitable for controlling the thermosolvation response by modifying hydrophobicity, enhancing radiodensity and biostability through incorporation of alkylthiol chains (i.e., hexadecanethiol) or halogenation using molecular iodine, and reducing biofouling using thiolterminated poly(ethylene glycol). To further enhance the potential for postfabrication modification, we further demonstrate the concept with off-stoichiometric stereolithographic 3D printing (OSS3DP), where we can selectively leave more than 30% additional alkenes on the scaffold surface for postpolymerization functionalization in a process that could have clinical utility across a range of medical devices and therapeutics.

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