Postfabrication Functionalization of 4D-Printed Polycarbonate Photopolymer Scaffolds

Abstract

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.

Ring-Opening Copolymerization of Four-Dimensional Printable Polyesters Using Supramolecular Thiourea/Organocatalysis

“…By comparison, differential scanning calorimetry (DSC) thermograms revealed T g values of 40–50 °C for molecular weights greater than 1 kDa (DP greater than ∼5) (Figure S24 in the Supporting Information). This difference in T g values is expected, as such discrepancies have been found to be dependent on heating/cooling rates, as well as differences between methods relating to probing the molecular motion …”

4D Photopolymers Derived From Ring-Opening Copolymerization of Cyclic Anhydrides and Limonene Oxide

“…A porous rectangular prism with internal porosity was printed using DLP methods (Figure ). Synthetic polyesters have been demonstrated as being feasible to process into porous geometries with internal, continuous struts without corners. − ,, However, the limonene oxide-derived polyesters were difficult to ultimately process despite their rapid gelation under photorheology testing. The desired structure could be achieved; however, overcuring was found even at minimal exposure times, as noted by the loss of resolution and formation of small film wisps (Figure B,C), and even loss of geometry (Figure D).…”

3D Printing of Green and Renewable Polymeric Materials: Toward Greener Additive Manufacturing

“…Photopolymers used in SLA, DLP, and similar methods are traditionally required to be Newtonian fluids with low viscosities and high reactivity rates. − This allows for the resin to flow around the solid, gelled parts during photoirradiation and then to flow out of the negative space as the stage is raised (when the light source is off) but rapidly solidify upon irradiation. However, this restriction to liquid resins still encompasses a variety of achievable thermal and mechanical characteristics, and there are some advances that are broadening the material library …”

“…Among natural and naturally derived materials, terpenes and terpenoids are some of the most useful in polymer synthesis and applications, such as the production of degradable polyesters, high T g and performance polymers, and 3DP. − These monomers are widely available from sources such as essential oils, tree sap and materials, and citrus fruit, as byproducts from other manufacturing processes, or simply through the processing of citrus fruits and other renewable resources. ,, The alkene and other functional groups inherent to terpenes make them great candidates for sustainably sourced photoresins (Figures and ). These alkenes are useful in thiol–ene “click” and radical photopolymerizations, and the variation in structure and substitution means that residual alkenes may remain without requiring off-stoichiometric imbalances or uncured materials. ,,,− For example, Weems et al demonstrated the use of the terpenes limonene, terpinene, geraniol, nerol, and linalool to create photoresins for stereolithography (SLA) 3DP via thiol–ene photoclick reactions (Figure ), making use of these natural functional handles, but requiring a two-step prepolymerization process similar to those used in polyurethane foam synthesis. ,− Weems et al further demonstrated poly­(β-myrcene) as a viable photoresin, while Constant et al expanded upon this concept through copolymerization of limonene and myrcene as a means of tailoring the resultant thermoset material properties while still achieving DLP-3D printing (Figure ). …”