Tuning the Functionality of Self-Assembled 2D Platelets in the Third Dimension.

The decoration of 2D nanostructures using heteroepitaxial growth is of great importance to achieve functional assemblies employed in biomedical, electrical, and mechanical applications. Although the functionalization of polymers before self-assembly has been investigated, the exploration of direct surface modification in the third dimension from 2D nanostructures has, to date, been unexplored. Here, we used living crystallization-driven self-assembly to fabricate poly(ε-caprolactone)-based 2D platelets with controlled size. Importantly, surface modification of the platelets in the third dimension was achieved by using functional monomers and light-induced polymerization. This method allows us to selectively regulate the height and fluorescence properties of the nanostructures. Using this approach, we gained unprecedented spatial control over the surface functionality in the specific region of complex 2D platelets.

Self-Healing Hydrogel Scaffolds through PET-RAFT Polymerization in Cellular Environment.

Photo electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) has emerged as a powerful reversible-deactivation radical polymerization technique, enabling oxygen-tolerant polymerizations with exquisite spatiotemporal control through irradiation with visible light. In contrast to traditional free radical photo-polymerization, which often requires the use of DNA-damaging UV irradiation, PET-RAFT offers a more cytocompatible alternative for the preparation of polymeric materials in cell culture environments. Herein, we report the use of PET-RAFT for the fabrication of self-healing hydrogels using commercially available monomers, reaching high monomer conversions and cell encapsulation efficiencies. Our hydrogels showed the expected rheological and mechanical properties for the systems considered, together with excellent cytocompatibility and spatiotemporal control over the polymerization process. Moreover, hydrogels prepared through this method could be cut and healed again by simply adding further monomer and irradiating the system with visible light, even in the presence of mammalian cells. This study demonstrates for the first time the potential of PET-RAFT polymerization as a viable methodology for the synthesis of self-healing hydrogel scaffolds for cell encapsulation.

Aliphatic Polycarbonates from Cyclic Carbonate Monomers and Their Application as Biomaterials.

Aliphatic polycarbonates have gained increased attention as biomaterials largely owing to their biocompatibility and tunable degradation. Moreover, the ability to introduce functional handles in the polymer backbone through careful design of cyclic carbonate monomers or copolymerization with other biodegradable polymers has significantly contributed to the interest in exploiting this class of materials for biomedical applications. Such investigations have enabled their utility to be expanded to a wide variety of applications in the biomedical field, from drug delivery to tissue regeneration and the design of vascular grafts. Herein, we review the synthesis, degradation, and studies into biomedical applications of aliphatic polycarbonates obtained by ring-opening polymerization of cyclic carbonate monomers (ring sizes between 6 and 8). While all synthetic methods will be covered, particular emphasis will be given to materials that have been exploited for therapeutic applications in vitro and in vivo.

Ultra-Tough Elastomers from Stereochemistry-Directed Hydrogen Bonding in Isosorbide-Based Polymers.

The remarkable elasticity and tensile strength found in natural elastomers are challenging to mimic. Synthetic elastomers typically feature covalently cross-linked networks (rubbers), but this hinders their reprocessability. Physical cross-linking via hydrogen bonding or ordered crystallite domains can afford reprocessable elastomers, but often at the cost of performance. Herein, we report the synthesis of ultra-tough, reprocessable elastomers based on linear alternating polymers. The incorporation of a rigid isohexide adjacent to urethane moieties affords elastomers with exceptional strain hardening, strain rate dependent behavior, and high optical clarity. Distinct differences were observed between isomannide and isosorbide-based elastomers where the latter displays superior tensile strength and strain recovery. These phenomena are attributed to the regiochemical irregularities in the polymers arising from their distinct stereochemistry and respective inter-chain hydrogen bonding.

Organocatalytic Synthesis of Alkyne-Functional Aliphatic Polycarbonates via Ring-Opening Polymerization of an Eight-Membered-N-Cyclic Carbonate.

The synthesis of well-defined propargyl-functional aliphatic polycarbonates is achieved via the organocatalytic ring-opening polymerization of prop-2-yn-1-yl 2-oxo-1,3,6-dioxazocane-6-carboxylate (P-8NC) using a wide variety of commercially available or readily made, shelf-stable organocatalysts. The resulting homopolymers show low dispersities and end-group fidelity, with the versatility of the system being demonstrated by the synthesis of telechelic copolymers and block copolymers with molar mass up to 40 kDa.

Selective Chemical Upcycling of Mixed Plastics Guided by a Thermally Stable Organocatalyst.

Chemical recycling of plastic waste represents a greener alternative to landfill and incineration, and potentially offers a solution to the environmental consequences of increased plastic waste. Most plastics that are widely used today are designed for durability, hence currently available depolymerisation methods typically require harsh conditions and when applied to blended and mixed plastic feeds generate a mixture of products. Herein, we demonstrate that the energetic differences for the glycolysis of BPA-PC and PET in the presence of a protic ionic salt TBD:MSA catalyst enables the selective and sequential depolymerisation of these two commonly employed polymers. Employing the same procedure, functionalised cyclic carbonates can be obtained from both mixed plastic wastes and industrial polymer blend. This methodology demonstrates that the concept of catalytic depolymerisation offers great potential for selective polymer recycling and also presents plastic waste as a "greener" alternative feedstock for the synthesis of high added value molecules.

3D Printing for the Clinic: Examining Contemporary Polymeric Biomaterials and Their Clinical Utility.

The advent of additive manufacturing offered the potential to revolutionize clinical medicine, particularly with patient-specific implants across a range of tissue types. However, to date, there are very few examples of polymers being used for additive processes in clinical settings. The state of the art with regards to 3D printable polymeric materials being exploited to produce novel clinically relevant implants is discussed here. We focus on the recent advances in the development of implantable, polymeric medical devices and tissue scaffolds without diverging extensively into bioprinting. By introducing the major 3D printing techniques along with current advancements in biomaterials, we hope to provide insight into how these fields may continue to advance while simultaneously reviewing the ongoing work in the field.

Engineering the Mammalian Cell Surface with Synthetic Polymers: Strategies and Applications.

Manipulating the surface of living cells represents a powerful tool by which to control cell behavior and provides a unique strategy to modulate cellular function and cell-cell interactions. Recent progress in this area has seen the development of robust and elegant approaches to selectively decorate the cell surface, leading to unprecedented advances in cellular manipulation and cell-based therapies. Despite some impressive in vitro results, several obstacles remain to the broader application of some of these strategies, including their limited translation in vivo. In this review, the leading techniques used to introduce polymers at the plasma membrane of mammalian cells are discussed, focusing on strategies that generate a stable and homogeneous distribution of polymeric chains at the cell surface. Application of these strategies to control cell behavior and deliver cell-based therapies to targeted tissues are highlighted.

Poly(Pentafluorophenyl Methacrylate)-Based Nano-Objects Developed by Photo-PISA as Scaffolds for Post-Polymerization Functionalization.

The preparation of a functional fluorine-containing block copolymer using reversible addition-fragmentation chain-transfer dispersion polymerization in DMSO as a "platform/scaffold" is explored. The nanostructures, comprised of poly(ethyleneglycol)-b-poly(pentafluorophenyl methacrylate) or PEG-b-P(PFMA), are formulated via photo-initiated polymerization-induced self-assembly (PISA) followed by post-polymerization modification using different primary amines. A combination of light scattering and microscopy techniques are used to characterize the resulting morphologies. It is found that upon varying the degree of polymerization of the core-forming block of PFMA, only uniform spheres (with textured surfaces) are obtained. These nanostructures are subsequently modified by cross-linking using a non-responsive and a redox-responsive diamine, thus imparting stability to the particles in water. In response to intracellular glutathione (GSH) concentration, destabilization of the micelles occurs as evidenced by dynamic light scattering. The well-defined size, inherent reactivity of the nanoparticles toward nucleophiles, and GSH-responsiveness of the nanospheres make them ideal scaffolds for drug delivery to intracellular compartments with reductive environments.

Catalytically Active N-Heterocyclic Carbene Release from Single-Chain Nanoparticles Following a Thermolysis-Driven Unfolding Strategy.

The need for efficient, tailor-made catalysts has inspired chemists to design synthetic macromolecular architectures for selective catalysis. To this purpose, herein the synthesis and in-depth characterization of Ag(I)-crosslinked single-chain nanoparticles (SCNPs) is reported and their application as catalysts is demonstrated. Specifically, a copolymer of styrenic benzimidazolium chloride is synthesized as a linear precursor via reversible addition-fragmentation chain-transfer polymerization. Metalation of the benzimidazolium moieties by Ag(I) resulted in the intramolecular cross-linking of single chains via the formation of silver-N-heterocyclic carbene (Ag-NHC) linkages under dilute conditions. The successful formation of well-defined, robust SCNPs is evidenced by size-exclusion chromatography, dynamic light scattering, nuclear magnetic resonance spectroscopy, and transmission electron microscopy. Finally, it is demonstrated that the Ag-SCNPs can be used as NHC pre-catalysts, by first indirectly evidencing the formation of the corresponding unfolded NHC-CS2 polybetaine and then organocatalysing a benzoin condensation reaction.

Nonswelling Thiol-Yne Cross-Linked Hydrogel Materials as Cytocompatible Soft Tissue Scaffolds.

A key drawback of hydrogel materials for tissue engineering applications is their characteristic swelling response, which leads to a diminished mechanical performance. However, if a solution can be found to overcome such limitations, there is a wider application for these materials. Herein, we describe a simple and effective way to control the swelling and degradation rate of nucleophilic thiol-yne poly(ethylene glycol) (PEG) hydrogel networks using two straightforward routes: (1) using multiarm alkyne and thiol terminated PEG precursors or (2) introducing a thermoresponsive unit into the PEG network while maintaining their robust mechanical properties. In situ hydrogel materials were formed in under 10 min in PBS solution at pH 7.4 without the need for an external catalyst by using easily accessible precursors. Both pathways resulted in strong tunable hydrogel materials (compressive strength values up to 2.4 MPa) which could effectively encapsulate cells, thus highlighting their potential as soft tissue scaffolds.

pH-Responsive, Functionalizable Spyrocyclic Polycarbonate: A Versatile Platform for Biocompatible Nanoparticles.

Polymeric nanoparticles are widely investigated to enhance the selectivity of therapeutics to targeted sites, as well as to increase circulation lifetime and water solubility of poorly soluble drugs. In contrast to the encapsulation of the cargo into the nanostructures, the conjugation directly to the polymer backbone allows better control on the loading and selective triggered release. In this work we report a simple procedure to create biodegradable polycarbonate graft copolymer nanoparticles via a ring opening polymerization and subsequent postpolymerization modification strategies. The polymer, designed with both pH-responsive acetal linkages and a norbornene group, allows for highly efficient postpolymerization modifications through a range of chemistries to conjugate imaging agents and solubilizing arms to direct self-assembly. To demonstrate the potential of this approach, polycarbonate-based nanoparticles were tested for biocompatibility and their ability to be internalized in A549 and IMR-90 cell lines.

Hydrogel scaffolds for differentiation of adipose-derived stem cells.

Natural extracellular matrices (ECMs) have been widely used as a support for the adhesion, migration, differentiation, and proliferation of adipose-derived stem cells (ADSCs). However, poor mechanical behavior and unpredictable biodegradation properties of natural ECMs considerably limit their potential for bioapplications and raise the need for different, synthetic scaffolds. Hydrogels are regarded as the most promising alternative materials as a consequence of their excellent swelling properties and their resemblance to soft tissues. A variety of strategies have been applied to create synthetic biomimetic hydrogels, and their biophysical and biochemical properties have been modulated to be suitable for cell differentiation. In this review, we first give an overview of common methods for hydrogel preparation with a focus on those strategies that provide potential advantages for ADSC encapsulation, before summarizing the physical properties of hydrogel scaffolds that can act as biological cues. Finally, the challenges in the preparation and application of hydrogels with ADSCs are explored and the perspectives are proposed for the next generation of scaffolds.

Precision Epitaxy for Aqueous 1D and 2D Poly(ε-caprolactone) Assemblies.

The fabrication of monodisperse nanostructures of highly controlled size and morphology with spatially distinct functional regions is a current area of high interest in materials science. Achieving this control directly in a biologically relevant solvent, without affecting cell viability, opens the door to a wide range of biomedical applications, yet this remains a significant challenge. Herein, we report the preparation of biocompatible and biodegradable poly(ε-caprolactone) 1D (cylindrical) and 2D (platelet) micelles in water and alcoholic solvents via crystallization-driven self-assembly. Using epitaxial growth in an alcoholic solvent, we show exquisite control over the dimensions and dispersity of these nanostructures, allowing access to uniform morphologies and predictable dimensions based on the unimer-to-seed ratio. Furthermore, for the first time, we report epitaxial growth in aqueous solvent, achieving precise control over 1D nanostructures in water, an essential feature for any relevant biological application. Exploiting this further, a strong, biocompatible and fluorescent hydrogel was obtained as a result of living epitaxial growth in aqueous solvent and cell culture medium. MC3T3 and A549 cells were successfully encapsulated, demonstrating high viability (>95% after 4 days) in these novel hydrogel materials.

Poly(oligo(ethylene glycol) vinyl acetate)s: A Versatile Class of Thermoresponsive and Biocompatible Polymers.

Polymers with a thermally triggered phase transition are important in the design of materials for biological applications, where their behavior can be used to trigger release or (dis)assembly events. Despite their advantages, a system with tunable thermal response, end-group reactive sites, low toxicity, and controlled main-chain degradability has not been realized, yet this would be a significant advance. The versatile new poly(oligo(ethylene glycol) vinyl acetate)s are presented with excellent control over their molecular properties obtained through RAFT/MADIX polymerization. Furthermore, we demonstrate structure-controlled thermal transitions, conjugation to human lysozyme through the retained end-group, and moreover show that this class of polymers can uniquely be copolymerized with 2-methylene-1,3-dioxepane (MDO) to generate polymers in which the degradability and cloud point can be independently tuned to create materials that display the same cloud point but degrade differently.

Copper(II) binding properties of hepcidin.

Hepcidin is a peptide hormone that regulates the homeostasis of iron metabolism. The N-terminal domain of hepcidin is conserved amongst a range of species and is capable of binding Cu(II) and Ni(II) through the amino terminal copper-nickel binding motif (ATCUN). It has been suggested that the binding of copper to hepcidin may have biological relevance. In this study we have investigated the binding of Cu(II) with model peptides containing the ATCUN motif, fluorescently labelled hepcidin and hepcidin using MALDI-TOF mass spectrometry. As with albumin, it was found that tetrapeptide models of hepcidin possessed a higher affinity for Cu(II) than that of native hepcidin. The log K 1 value of hepcidin for Cu(II) was determined as 7.7. Cu(II) binds to albumin more tightly than hepcidin (log K 1 = 12) and in view of the serum concentration difference of albumin and hepcidin, the bulk of kinetically labile Cu(II) present in blood will be bound to albumin. It is estimated that the concentration of Cu(II)-hepcidin will be less than one femtomolar in normal serum and thus the binding of copper to hepcidin is unlikely to play a role in iron homeostasis. As with albumin, small tri and tetra peptides are poor models for the metal binding properties of hepcidin.

Functional characterization of fluorescent hepcidin.

Hepcidin is a peptide hormone that regulates homeostasis in iron metabolism. It binds to the sole known cellular iron exporter ferroportin (Fpn), triggers its internalization, and thereby modulates the efflux of iron from cells. This functional property has been adopted in this study to assess the bioactivity and potency of a range of novel fluorescent hepcidin analogues. Hepcidin was selectively labeled with 6-carboxyfluorescein (CF) and 6-carboxytetramethylrhodamine (TMR) using Fmoc solid phase peptide chemistry. Internalization of Fpn by hepcidin was assessed by high-content microscopic analysis. Both K18- and M21K-labeled hepcidin with TMR and CF exhibited measurable potency when tested in cultured MDCK and T47D cells expressing human ferroportin. The bioactivity of the labeled hepcidin varies with the type of fluorophore and site of attachment of the fluorophores on the hepcidin molecule.

Enhanced drug delivery to cancer cells through a pH-sensitive polycarbonate platform.

Polymer-drug conjugates are widely investigated to enhance the selectivity of therapeutic drugs to cancer cells, as well as increase circulation lifetime and solubility of poorly soluble drugs. In order to direct these structures selectively to cancer cells, targeting agents are often conjugated to the nanoparticle surface as a strategy to limit drug accumulation in non-cancerous cells and therefore reduce systemic toxicity. Here, we report a simple procedure to generate biodegradable polycarbonate graft copolymer nanoparticles that allows for highly efficient conjugation and intracellular release of S-(+)-camptothecin, a topoisomerase I inhibitor widely used in cancer therapy. The drug-polymer conjugate showed strong efficacy in inhibiting cell proliferation across a range of cancer cell lines over non-cancerous phenotypes, as a consequence of the increased intracellular accumulation and subsequent drug release specifically in cancer cells. The enhanced drug delivery towards cancer cells in vitro demonstrates the potential of this platform for selective treatments without the addition of targeting ligands.

Uniform segmented platelet micelles with compositionally distinct and selectively degradable cores.

The creation of nanoparticles with controlled and uniform dimensions and spatially defined functionality is a key challenge. The recently developed living crystallization-driven self-assembly (CDSA) method has emerged as a promising route to one-dimensional (1D) and 2D core-shell micellar assemblies by seeded growth of polymeric and molecular amphiphiles. However, the general limitation of the epitaxial growth process to a single core-forming chemistry is an important obstacle to the creation of complex nanoparticles with segmented cores of spatially varied composition that can be subsequently exploited in selective transformations or responses to external stimuli. Here we report the successful use of a seeded growth approach that operates for a variety of different crystallizable polylactone homopolymer/block copolymer blend combinations to access 2D platelet micelles with compositionally distinct segmented cores. To illustrate the utility of controlling internal core chemistry, we demonstrate spatially selective hydrolytic degradation of the 2D platelets-a result that may be of interest for the design of complex stimuli-responsive particles for programmed-release and cargo-delivery applications.