Periodic Reporting for period 1 - PhotoPolyCarb (Biodegradable bottlebrush polycarbonates with benzophenone groups for the preparation of tissue engineering scaffolds)
Période du rapport: 2022-01-24 au 2024-01-23
Photoreactive monomers and polymers have emerged as key components in the preparation of resin formulations for 3D printing (3DP). Techniques such as stereolithography (SLA) and digital light printing (DLP) have gained increasing attention to light assisted polymerisation, most likely on account of their high resolution and fast printing speed. However, the number of resins for use in SLA and DLP remains limited and most commercially available ones are based on acrylates and epoxides, which are commonly produced from fossil sources - non-sustainable. Besides, undesired toxicity and non-degradability restrict the use of acrylated-based prototypes in the medical field. To overcome these challenges, a new platform that allows the printing of degradable, non-toxic and additive-free 3D objects is needed. Initially, the main goal of this project was to investigate the modification of cyclic carbonates with photoactive benzophenones to obtain photoreactive resins, allowing the crosslinking of materials through C-H-insertion without the addition of additives. However, the developed system showed certain complexity and could not be easily translated into 3D printing. With this in mind, a new system was developed to attend the current demands of commercial resins for 3DP. For this, renewable resins based on terpenes and multi-arm thiol were designed to access materials with a wide range of thermomechanical properties. Although the project followed a different direction, the main objectives remained the same: 1. Synthesis of novel photocrosslinkable resins. 2. Investigate the effect of resin architecture on the mechanical properties of the crosslinked materials. 3. Resin formulation for 3DP using the polymers/copolymers designed in step 1 and 2. The last objective involving the evaluation of the biological properties of the designed prints was not performed, as this was not a priority considering the remaining time of the project.
Initially, aliphatic polycarbonates bearing different functional groups (PEG and carbonates containing different number of pendent methylene groups) were synthesised according to literature procedures. In order to copolymerise these with photoactive carbonates, a synthetic procedure was carried out to attach benzophenone groups into a 6-membered cyclic carbonate (CC). For this, a CC containing carboxylic acid functionality was coupled with benzophenones via CDI coupling. Although the products could be obtained in high conversions, the monomers were not stable through the purification methods and hydrolised in the tested conditions. To address this issue, post-polymerisation strategies were developed to add benzophenone groups to the side chain of polycarbonate copolymers. This way, benzophenone containing azide groups could be introduced into the polymer backbone via alkyne-azide cycloaddition (post-polymerisation modification) by the reaction between the benzophenone and an alkyne-functional CC. Given the monomer instability and difficulties into translation the developed systems into 3DP, a new photoactive resin system based on natural monomers and thiol-chemistry was prepared. These new monomers could be synthesised from renewable sources following green chemistry protocols, to prepare highly reactive resins that underwent fast photocuring. These materials were susceptible to DLP printing and were able to form structures with adjustable thermomechanical properties. The results of this study have been submitted to an open access journal and are currently under revision. Besides, the progress of the project has been also disseminated via 2 oral presentations: in 2022 at Recent Appointees in Polymer Science (RAPS 2022) and in 2023 at the Society of Polymer Science Japan International Polymer Conference (SPSJ IPC, Sapporo, Japan).
The global 3D printing plastic market showed significant growth rates over the past years and is projected to reach $1,907 million by 2027 at a compound annual growth rate of 25.0% from 2022 to 2027. Although successful, 3D printed objects are still limited by the type of chemistry and the properties of the final materials, and most available resins contain toxic additives in their composition. This project aimed to utilise a method that can address this issue by delivering a resin with only one component and no additives: a photoreactive polycarbonate that undergoes curing by itself. Although unsuccessful in designing cyclic carbonates containing functional benzophenone group, a new route to access non-toxic resins has proven to be effective. This new material platform could provide great additions in the field of photocurable materials and their translation to 3DP. We believe that the ongoing work has a potential as an additive free resin, in addition to the synthetic procedure already being reproducible and scalable. The most prevailing societal impact would be the identification of a new chemistry to be employed in 3D printing systems, more specifically the ones using VAT photopolymerization, to improve the sustainability, biocompatibility and mechanical performance of 3DP materials.