Fabrication of Reduction-Sensitive Amphiphilic Cyclic Brush Copolymer for Controlled Drug Release

Nanoscale polymer discs, toroids and platelets: a survey of their syntheses and potential applications

Polymer self-assembly has become a reliable and versatile workhorse to produce polymeric nanomaterials. With appropriate polymer design and monomer selection, polymers can assemble into shapes and morphologies beyond well-studied spherical and cylindrical micellar structures. Steadfast access to anisotropic polymer nanoparticles has meant that the fabrication and application of 2D soft matter has received increasing attention in recent years. In this review, we focus on nanoscale polymer discs, toroids, and platelets: three morphologies that are often interrelated and made from similar starting materials or common intermediates. For each morphology, we illustrate design rules, and group and discuss commonly used self-assembly strategies. We further highlight polymer compositions, fundamental principles and self-assembly conditions that enable precision in bottom-up fabrication strategies. Finally, we summarise potential applications of such nanomaterials, especially in the context of biomedical research and template chemistry and elaborate on future endeavours in this space.

Recent Advances in the Application of ATRP in the Synthesis of Drug Delivery Systems

Advances in atom transfer radical polymerization (ATRP) have enabled the precise design and preparation of nanostructured polymeric materials for a variety of biomedical applications. This paper briefly summarizes recent developments in the synthesis of bio-therapeutics for drug delivery based on linear and branched block copolymers and bioconjugates using ATRP, which have been tested in drug delivery systems (DDSs) over the past decade. An important trend is the rapid development of a number of smart DDSs that can release bioactive materials in response to certain external stimuli, either physical (e.g., light, ultrasound, or temperature) or chemical factors (e.g., changes in pH values and/or environmental redox potential). The use of ATRPs in the synthesis of polymeric bioconjugates containing drugs, proteins, and nucleic acids, as well as systems applied in combination therapies, has also received considerable attention.

Chemistry and engineering of brush type polymers: Perspective towards tissue engineering

In tissue engineering, it is imperative to control the behaviour of cells/stem cells, such as adhesion, proliferation, propagation, motility, and differentiation for tissue regeneration. Surfaces that allow cells to behave in this way are critical as support materials in tissue engineering. Among these surfaces, brush-type polymers have an important potential for tissue engineering and biomedical applications. Brush structure and length, end groups, bonding densities, hydrophilicity, surface energy, structural flexibility, thermal stability, surface chemical reactivity, rheological and tribological properties, electron and energy transfer ability, cell binding and absorption abilities for various biological molecules of brush-type polymers were increased its importance in tissue engineering applications. In addition, thanks to these functional properties and adjustable surface properties, brush type polymers are used in different high-tech applications such as electronics, sensors, anti-fouling, catalysis, purification and energy etc. This review comprehensively highlights the use of brush-type polymers in tissue engineering applications. Considering the superior properties of brush-type polymer structures, it is believed that in the future, it will be an effective tool in structure designs containing many different biomolecules (enzymes, proteins, etc.) in the field of tissue engineering.

Molecular polymer bottlebrushes in nanomedicine: therapeutic and diagnostic applications

Molecular polymer bottlebrushes are densely grafted, individual macromolecules with nanoscale proportions. The last decade has seen an increased focus on this material class, especially in nanomedicine and for biomedical applications. This Feature Article provides an overview of major developments in this area to highlight the many opportunities that these polymer architectures bring to nano-bio research. The article covers aspects of bottlebrush synthesis and summarises their use in drug and gene delivery, imaging, as theranostics and as prototype materials to correlate nanoparticle structure and composition to biological function and behaviour. Areas for future research in this area are discussed.

Biomaterials applications of cyclic polymers

Cyclic polymers are an intriguing class of polymers due to their lack of chain ends. This unique architecture combined with steric constraints adorn cyclic polymers as well as nano-, micro- and macro-scale materials containing cyclic polymers with distinctive physicochemical properties which can have a profound effect on the performance of these materials in a wide range of applications. Within a biomedical context, biomaterials based on cyclic polymers have shown very distinct properties in terms of biodistribution, pharmacokinetics, drug/gene delivery efficiency and surface activity. This review summarizes the applications of cyclic polymers in the field of biomaterials and highlights their potential in the biomedical field as well as addressing future challenges in this area.

Effect of side-chain length on solute encapsulation by amphiphilic heterografted brush copolymers

Anisotropic nanomaterials are non-spherical structures that possess unique shape-dependent physicochemical properties and functionalities. Inspired by the abundance of filamentous entities in nature, cylindrical nanostructures have gained significant attention due to their unique performance. Herein, we discuss the effect of side-chain length on the encapsulation properties of amphiphilic heterografted bottlebrushes. We observed that by grafting a long hydrophilic block to the double-brush, we were able to restrict solute-induced conformational changes, thus producing drug-loaded anisotropic carriers. Unimolecular encapsulation in brushes was solute-dependent as shown here for probucol and rose bengal lactone. Stabilization with an amphiphilic diblock copolymer-consisting of the same type of blocks as those comprising the heterografted brush-served to explain the solute-dependent behavior observed for brushes, suggesting that solutes with a higher propensity to nucleation could be more effectively stabilized by the anisotropic carrier in a unimolecular worm-like construct.

Synthesis of cyclic graft polymeric prodrugs with heterogeneous grafts of hydrophilic OEG and reducibly conjugated CPT for controlled release

Fabrication of cyclic graft (cg) copolymer-based polymeric prodrugs by conjugation of drug molecules to cg copolymers via a dynamic covalent bond capable of responding to biorelevant signals integrates simultaneously the merits of cg copolymers and polymeric prodrugs for enhanced stability of nanocarriers and precise modulation of drug release kinetics. To completely eliminate the compromised drug conjugation efficiency due to the steric hindrance of hydrophilic grafts, it will be useful to develop cg polymeric prodrugs with heterogeneous grafts composed of hydrophilic polymers and drug species, respectively. For this purpose, we reported in this study the synthesis of cyclic graft polymeric prodrugs with heterogeneous grafts of hydrophilic oligo (ethylene glycol) (OEG) and reducibly conjugated camptothecin (CPT), cg-poly(oligo(ethylene glycol) monomethyl ether methacrylate)-b-poly((2-hydroxyethyl methacrylate)-disulfide link-camptothecin) (cg-P(OEGMA)-b-P(HEMA-SS-CPT), cg-prodrugs), via an integrated strategy of a previously reported diblock copolymer-based template and post-polymerization intermolecular click conjugation of a reducible CPT prodrug. The micelles self-assembled from cg-prodrugs on one hand had sufficient salt stability due to the branched cg structure, and on the other hand showed a reduction-triggered cleavage of the disulfide link for a promoted CPT release. Most importantly, we uncovered two interesting phenomena of the cg-based polymeric prodrugs as delivery vehicles: (i) the dimensions of both self-assemblies formed by the cg and bottlegraft (bg) polymers depend substantially on the molecular size of the cg and bg polymers likely due to the steric hindrance of the grafted structures of the cg and bg molecules and relatively low aggregation number of the self-assembled structures, and (ii) cg-prodrug-based micelles exhibited greater in vitro cytotoxicity against cancer cells despite the lower drug loading content (DLC) than the bg-based analogues, which results primarily from the faster reduction-triggered degradation and drug release as well as the greater cellular uptake efficiency of the former micelle prodrugs. Taken together, the developed cg-prodrugs provide great potential for chemotherapy, and the aforementioned interesting results will definitely inspire more upcoming studies on the future design and development of novel cg polymers for biomedical applications.

Topological Polymer Chemistry Enters Materials Science: Expanding the Applicability of Cyclic Polymers

Polymer-topology effects can alter technologically relevant properties when cyclic macromolecules are applied within diverse materials formulations. These include coatings, polymer networks, or nanostructures for delivering therapeutics. While substituting linear building blocks with cyclic analogues in commonly studied materials is itself of fundamental interest, an even more fascinating observation has been that the introduction of physical or chemical boundaries (e.g., a grafting surface or cross-links) can amplify the topology-related effects observed when employing cyclic polymer-based precursors for assembling multidimensional objects. Hence, the application of cyclic polymers has enabled the fabrication of coatings with enhanced biorepellency and superior lubricity, broadened the tuning potential for mechanical properties of polymer networks, increased the thermodynamic stability, and altered the capability of loading and releasing drugs within polymeric micelles.

Amphiphilic multicomponent molecular brushes

Multicomponent molecular brushes containing amphiphilic polymer moieties are promising objects of research of macromolecular chemistry. The development of stimulus-responsive systems sensitive to changes in environmental parameters, based on the molecular brushes, opens up new possibilities for their applications in medicine, biochemistry and microelectronics. The review presents the current understanding of the structures of main types of amphiphilic multicomponent brushes, depending on the chemical nature and type of coupling of the backbone and side chains. The approaches to the controlled synthesis of multicomponent molecular brushes of different architecture are analyzed. Self-assembly processes of multicomponent molecular brushes in selective solvents are considered.

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Exploiting scaling laws for designing polymeric bottle brushes: a theoretical coarse-graining for homopolymeric branched polymers

Bottle brushes are polymeric macromolecules made of a linear polymeric backbone grafted with side chains. The choice of the grafting density σg, the length ns the grafted side chains and their chemical nature fully determines the properties of each macromolecule, such as its elasticity and its folding behaviour. Typically, experimental bottle brushes are systems made of tens of thousands of monomeric units, rendering a computational approach extremely expensive, especially in the case of bottle brush solutions. A proper coarse graining description of these macromolecules thus appears essential. We present here a theoretical approach able to develop a general, transferable and analytical multi-scale coarse graining of homopolymeric bottle brush polymers under good solvent conditions. Starting from scaling theories, each macromolecule is mapped onto a chain of tethered star polymers, whose effective potential is known from scaling predictions, computational and experimental validations and can be expressed as a function of the number of arms f, and the length na of each arm. Stars are then tethered to one another and the effective potential between them is shown to only depend on the key parameters of the original bottle brush polymer (σg, ns). The generalised form of the effective potential is then used to reproduce properties of the macromolecules obtained both with scaling theories and with simulations. The general form of the effective potentials derived in the current study allows a theoretical and computational description of the properties of homopolymeric bottle brush polymers for all grafting densities and all lengths of both backbone and grafted arms, opening the path for a manifold of applications.

Fabrication of theranostic amphiphilic conjugated bottlebrush copolymers with alternating heterografts for cell imaging and anticancer drug delivery

We reported the first example of polyfluorene (PF)-backboned bottlebrush (bb) copolymers with alternating POEGMA/PCL hetero brushes for cancer theranostics.