Synthesis of amorphous aliphatic polyester-ether homo- and copolymers by radical polymerization of ketene acetals

Amphiphilic Block Copolymers PEG-b-PMTCs: Synthesis, Self-Assembly, Degradation Properties and Biocompatibility

As a hydrophilic cyclic ketene acetal (CKA), 2-methylene-1,3,6-trioxocane (MTC) has recently attracted a lot of attention owing to its ability to promote a quicker (bio)degradation as compared to other heavily studied CKAs. Here, we prepared amphiphilic block copolymers based on poly-MTC with varying chain lengths by radical ring opening polymerization. Self-assemblies of these amphiphiles were performed in PBS buffer to generate nanoparticles with sizes from 40 to 105 nm, which were verified by dynamic light scattering, electron microscopy, and static light scattering (Zimm plots). Subsequently, fluorescence spectroscopy was applied to study the enzymatic degradation of Nile red-loaded nanoparticles. By performing a point-by-point comparison of fluorescence intensity decline patterns between nanoparticles, we demonstrated that lipase from Pseudomonas cepacia was very efficient in degrading the nanoparticles. Hydrolysis degradations under basic conditions were also carried out, and a complete degradation was achieved after 4 h. Additionally, cytotoxicity assays were carried out on HEK293 cells, and the results affirmed cell viabilities over 90% when incubated with up to 1 mg/mL nanoparticles for 24 h. These biodegradable and biocompatible nanoparticles hence hold great potential for future applications such as drug release.

Current Standing on Radical Ring-Opening Polymerizations of Cyclic Ketene Acetals as Homopolymers and Copolymers with one another

Radical Ring-opening polymerization (RROP) of cyclic ketene acetals (CKAs) emerges to be a valuable polymerization technique. In attracting more attention, RROP has seen a new spike in publications, which the authors will put into perspective. This review will hence address the progress made on the number of available CKAs and the synthetic strategies to get them. In grouping, the available monomers into distinct categories, the enormous variety of available CKAs will be highlighted. Polymerizations of CKAs without vinylenes have the potential to yield fully biodegradable polymers, which is why this kind of polymerization is the focus of this review. Detailing the current understanding of the mechanism, the various side reactions will be noted and also their effect on the overall properties of the final polymers. Current attempts to control the ring-retaining and branching reactions will be discussed as well. In addition to the polymerization itself, the available materials will be discussed as well as homopolymers, copolymers of CKAs, and block-copolymers with pure CKA-blocks have significantly widened the range of possible applications of materials from RROP. Altogether this review highlights the progress in the entire field of RROP just of CKAs to give a holistic overview of the field.

Increasing the Hydrophilicity of Cyclic Ketene Acetals Improves the Hydrolytic Degradation of Vinyl Copolymers and the Interaction of Glycopolymer Nanoparticles with Lectins

Radical ring-opening polymerization (rROP) of cyclic ketene acetals (CKAs) with traditional vinyl monomers allows the synthesis of degradable vinyl copolymers. However, since the most commonly used CKAs are hydrophobic, most degradable vinyl copolymers reported so far degrade very slowly by hydrolysis under physiological conditions (phosphate-buffered saline, pH 7.4, 37 °C), which can be detrimental for biomedical applications. Herein, to design advanced vinyl copolymers by rROP with high CKA content and enhanced degradation profiles, we reported the copolymerization of 2-methylene-1,3,6-trioxocane (MTC) as a CKA with vinyl ether (VE) or maleimide (MI) derivatives. By performing a point-by-point comparison between the MTC/VE and MTC/MI copolymerization systems, and their counterparts based on 2-methylene-1,3-dioxepane (MDO) and 5,6-benzo-2-methylene-1,3-dioxepane (BMDO), we showed negligible impact on the macromolecular characteristics and similar reactivity ratios, suggesting successful substitution of MDO and BMDO by MTC. Interestingly, owing to the hydrophilicity of MTC, the obtained copolymers exhibited a faster hydrolytic degradation under both accelerated and physiological conditions. We then prepared MTC-based glycopolymers, which were formulated into surfactant-free nanoparticles, exhibiting excellent colloidal stability up to 4 months and complete degradation under enzymatic conditions. Importantly, MTC-based glyconanoparticles also showed a similar cytocompatibility toward two healthy cell lines and a much stronger lectin affinity than MDO-based glyconanoparticles.

Mechanistic investigation of cyclic ketene acetal radical ring-opening homo- and co-polymerization and preparation of PEO graft copolymers with tunable composition

Radical ring-opening polymerization of cyclic ketene acetals (CKAs) led to homogeneous ester insertion during semi-batch reactions with N-vinyl pyrrolidone (NVP). Investigation of CKA radical transfer allowed for CKA–NVP graft copolymer preparation.

100th Anniversary of Macromolecular Science Viewpoint: Degradable Polymers from Radical Ring-Opening Polymerization: Latest Advances, New Directions, and Ongoing Challenges

Radical ring-opening polymerization (rROP) allows facile incorporation of labile groups (e.g., ester) into the main chain of vinyl polymers to obtain (bio)degradable materials. rROP has focused a lot of attention especially since the advent of reversible deactivation radical polymerization (RDRP) techniques and is still incredibly moving forward, as attested by the numerous achievements in terms of monomer synthesis, macromolecular engineering, and potential biomedical applications of the resulting degradable polymers. In the present Viewpoint, we will cover the latest progress made in rROP in the last ∼5 years, such as its recent directions, its remaining limitations, and the ongoing challenges. More specifically, this will be achieved through the three different classes of monomers that recently caught most of the attention: cyclic ketene acetals (CKA), thionolactones, and macrocyclic monomers.

A comprehensive kinetic study of the conventional free-radical polymerization of seven-membered cyclic ketene acetals

The current study reports on the kinetic analysis of the free-radical polymerization of several seven-membered cyclic ketene acetal monomers.

Efficient synthesis of 2-methylene-4-phenyl-1,3-dioxolane, a cyclic ketene acetal for controlling the NMP of methyl methacrylate and conferring tunable degradability

The efficient and reliable synthesis of 2-methylene-4-phenyl-1,3-dioxolane (MPDL) was reported and MPDL was used as a controlling comonomer for nitroxide-mediated polymerization of methyl methacrylate to give degradable copolymers.

Adjustable degradation properties and biocompatibility of amorphous and functional poly(ester-acrylate)-based materials

Tuning the properties of materials toward a special application is crucial in the area of tissue engineering. The design of materials with predetermined degradation rates and controlled release of degradation products is therefore vital. Providing a material with various functional groups is one of the best ways to address this issue because alterations and modifications of the polymer backbone can be performed easily. Two different 2-methylene-1,3-dioxepane/glycidyl methacrylate-based (MDO/GMA) copolymers were synthesized with different feed ratios and immersed into a phosphate buffer solution at pH 7.4 and in deionized water at 37 °C for up to 133 days. After different time intervals, the molecular weight changes, mass loss, pH, and degradation products were determined. By increasing the amount of GMA functional groups in the material, the degradation rate and the amount of acidic degradation products released from the material were decreased. As a result, the composition of the copolymers greatly affected the degradation rate. A rapid release of acidic degradation products during the degradation process could be an important issue for biomedical applications because it might affect the biocompatibility of the material. The cytotoxicity of the materials was evaluated using a MTT assay. These tests indicated that none of the materials demonstrated any obvious cytotoxicity, and the materials could therefore be considered biocompatible.

Copolymerization of 2-methylene-1,3-dioxepane and glycidyl methacrylate, a well-defined and efficient process for achieving functionalized polyesters for covalent binding of bioactive molecules

The understanding of cell-material interactions is important for creating personalized implants for tissue engineering. This has resulted in an interest in developing polymers with functional groups with the possibility of controlling the macromolecular surface. We have in a one-pot reaction synthesized a series of amorphous and degradable polyester-based copolymers with active functional groups by copolymerization of 2-methylene-1,3-dioxepane and glycidyl methacrylate. The properties of the final polymers were varied by varying the feed ratios of the monomers, and it was seen that it was possible to control the amount of active functional groups. The resulting epoxy-functionalized polyester was further modified by covalent immobilization of heparin. The heparinization was done in order, in a future aspect, to enhance the osteogenic differentiation of mesenchymal stem cells. Heparin binds directly with the growth factor bone morphogenetic protein-2 and helps to retain its activity. The molecular structure of the copolymers was characterized by nuclear magnetic resonance, size exclusion chromatography, and Fourier transform infrared spectroscopy. Differential scanning calorimetry and tensile testing showed that the monomer feed ratio had a great influence on the properties of the final polymer and that it thus was possible to control the mechanical properties to suit an intended application. The presence of heparin was verified by toluidine blue staining, and all of the films tested showed positive signals for heparin.