Enhanced Degradability of Thiol-ene Based Composite Networks Through the Inclusion of Isosorbide-based Polycarbonates

Open reduction internal fixation (ORIF) metal plates and screws represent the standard-of-care for complex fracture fixation; however, they have drawbacks such as soft-tissue adhesions, lack of degradation and poor customization, which may necessitate a second removal surgery.<br/>One of our strategies for overcoming these issues is to replace metal plates with a triazine trione (TATO) based composite patch fixated to the bone either with metal screws or through chemical adhesion by priming the bone surface. The composite contains allyl- and thiol-containing monomers with a high percentage of hydroxyapatite, and is rapidly cured on demand via high-energy visible-light-induced thiol–ene coupling chemistry.^1,2 <i>In vivo</i> studies showed that this bone-like composite patch did not induce soft-tissue adhesions. The customization, bone-like nature and soft-tissue repelling properties of the composite fixation patch are highly compelling features that traditional metal implants lack. Moreover, in contrast to some commercial bone glues, the composite is applied topologically over the bone fracture as opposed to being inserted in the cross-section of the bone, which allows for bone healing without interference from the composite.¹<br/>Thus far, the composites that we have developed have not shown degradability over time. However, it is our hypothesis that degradation can be achieved by adding degradable polymers to the composite formulation. These degradable polymers introduce hydrolysable linkages into the system while reacting covalently with the rest of monomers thanks to the presence of allyl functionalities. Aliphatic polycarbonates and polyesters are good examples of such degradable polymers that provide controlled degradation rates and are therefore widely used in the medical field as degradable agents.^3,4 In this work, we present the development of novel composite systems that include polycaprolactone and polycarbonates. The impact of these polymers with respect to degradation and mechanical properties of the final composites will be described thoroughly. Finally, the best candidates will be used as demonstrators for comminuted fracture fixators in wet and dry conditions, using synthetic bones as a substrate.<br/><br/><i>References:</i><br/><br/>1. Hutchinson, D.J; Granskog, V.; Kieseritzky, J.; Alfort, H.; Stenlund, P.; Zhang, Y.; Malkoch, M. Highly Customizable Bone Fracture Fixation through the Marriage of Composites and Screws. Avd. Funct. Mater. <b>2021</b>, 2105187.<br/><br/>2. Arseneault, M.; Granskog, V.; Khosravi, S.; Heckler I.M.; Mesa-Antunez, P.; Hult, D.; Zhang, Y; Malkoch, M. The Dawn of Thiol-Yne Triazine Triones Thermosets as a New Material Platform Suited for Hard Tissue Repair. Adv. Mater. <b>2018</b>, 30, 1804966.<br/><br/>3. Hult, D.; García-Gallego, S.; Ingverud, T.; Andren, O.; Malkoch, M. Degradable high Tg sugar-derived polycarbonates from isosorbide and dihydroxyacetone. <i>Polym. Chem</i>., <b>2018</b>, 9, 2238-2246.<br/><br/>4. Juan, P.-K.; Fan, F.-Y.; Lin, W.-C.; Liao, P.-B.; Huang, C.-F.; Shen, Y.-K.; Ruslin, M.; Lee, C.-H. Bioactivity and Bone Cell Formation with Poly-"-Caprolactone/Bioceramic 3D Porous Scaffolds. Polymers, <b>2021</b>, 13, 2718.