"Engineering live cell surfaces with functional polymers via cytocompatible controlled radical polymerization"
Authors: Niu, J., Lunn, D. J., Pusuluri, A., Yoo, J. I., O'Malley, M. A., Mitragotri, S., Soh, H. T., Hawker, C. J.
The capability to graft synthetic polymers onto the surfaces of live cells offers the potential to manipulate and control their phenotype and underlying cellular processes. Conventional grafting-to strategies for conjugating preformed polymers to cell surfaces are limited by low polymer grafting efficiency. Here we report an alternative grafting-from strategy for directly engineering the surfaces of live yeast and mammalian cells through cell surface-initiated controlled radical polymerization. By developing cytocompatible PET-RAFT (photoinduced electron transfer-reversible addition-fragmentation chain-transfer polymerization), synthetic polymers with narrow polydispersity (Mw/Mn < 1.3) could be obtained at room temperature in 5 minutes. This polymerization strategy enables chain growth to be initiated directly from chain-transfer agents anchored on the surface of live cells using either covalent attachment or non-covalent insertion, while maintaining high cell viability. Compared with conventional grafting-to approaches, these methods significantly improve the efficiency of grafting polymer chains and enable the active manipulation of cellular phenotypes.
Authors: Diaz, Y. J., Page, Z. A., Knight, A. S., Treat, N. J., Hemmer, J. R., Hawker, C. J., Read de Alaniz, J.
The utility of Meldrum's activated furan (MAF) for the colorimetric detection of sub ppm levels of amines in solution, on solid supports, and as vapors is reported. MAF is synthesized in one step from inexpensive and commercially available starting materials and exhibits high selectivity for primary and secondary amines in the presence of competing nucleophiles. The reaction between activated furans and amines results in a distinct color change, discernable by the naked eye. UV/Vis absorption spectroscopy was utilized to monitor reactions in solution and determine detection limits. Additionally, solutions of MAF were useful as stains for thin layer chromatography and for monitoring solid-phase synthesis of peptides and peptidomimetics. Finally, MAF was used to detect volatile amines released from fish samples, demonstrating potential for food spoilage applications.
Authors: Murakami, T., Schmidt, B. V. K. J., Brown, H. R., Hawker, C. J.
We describe a one-pot strategy for the fabrication of novel slide-ring (SR) gels based on supramolecular polyrotaxane structures with cyclodextrin-derived cross-links and additional free cyclodextrin ring spacers co-threaded onto the polymer backbones. Photoinitiated thiol-yne click coupling leads to facile hydrogel fabrication from pseudo-polyrotaxanes prepared in situ from β-cyclodextrin derivatives and bifunctional polyethylene glycol (PEG). The obtained SR gels were characterized by NMR spectroscopy using a polyrotaxane model compound with the ratio of cyclodextrin sliding spacers to PEG backbone controlled by adjusting the feed ratio of the starting materials. This structural tuning leads to dramatic changes in the rheological properties, mechanical properties, and swelling behavior of the SR gels. In addition, the coupling of simple synthetic procedures with enhanced properties offers a versatile approach to novel elastomeric materials.
"Direct Access to Functional (Meth)Acrylate Copolymers ThroughTransesterification with Lithium Alkoxides"
Authors: Fleischmann, C., Anastasaki, A., Gutekunst, W. R., McGrath, A. J., Hustad, P. D., Clark, P. G.,Laitar, D. S., Hawker, C. J.
A straightforward and efficient synthetic method that transforms poly(methyl methacrylate) (PMMA) into value-added materials is presented. Specifically, PMMA is modified by transesterification to produce a variety of functional copolymers from a single starting material. Key to the reaction is the use of lithium alkoxides, prepared by treatment of primary alcohols with LDA, to displace the methyl esters. Under optimized conditions, up to 65% functionalization was achieved and copolymers containing alkyl, alkene, alkyne, benzyl, and (poly)ether side groups could be prepared. The versatility of this protocol was further demonstrated through the functionalization of both PMMA homo and block copolymers obtained through either radical polymerization (traditional and controlled) or anionic procedures. The scope of this strategy was illustrated by extension to a range of architectures and polymer backbones.
"Dual-pathway chain-end modification of RAFT polymers using visible light and metal-free conditions"
Authors: Discekici, E. H., Shankel, S. L., Anastasaki, A., Oschmann, B., Lee, I. H., Niu, J., McGrath, A. J., Clark, P. G., Laitar, D. S., Read de Alaniz, J., Hawker, C. J., Lunn, D. J.
We report a metal-free strategy for the chain-end modification of RAFT polymers utilizing visible light. By turning the light source on or off, the reaction pathway in one pot can be switched between either complete desulfurization (hydrogen chain-end) or simple cleavage (thiol chain-end), respectively. The versatility of this process is exemplified by application to a wide range of polymer backbones under mild, quantitative conditions using commercial reagents.
Authors: Lunn, D. J., Discekici, E. H., Read de Alaniz, J., Gutekunst, W. R., Hawker, C. J.
The development of “controlled” and “living” polymerization processes with high end-group fidelity has enabled an unprecedented range of polymeric materials with specific chain-end functionality to be prepared. This highlight provides an overview of available strategies and evaluation of recent approaches for the chain-end functionalization of polymers prepared through controlled chain-growth polymerizations. As a tribute to Professor Robert B. Grubbs on the occasion of his 75th birthday, we also take this opportunity to highlight methods for the chain-end modification of polymers prepared by ring-opening metathesis polymerization within the broader context of functional group tolerant, living polymerizations. Finally, we focus attention toward new directions in polymer chain-end modifications, describing existing gaps in current strategies, and detailing recently reported protocols that show significant improvements over traditional methods.
"Universal Conditions for the Controlled Polymerization of Acrylates, Methacrylates, and Styrene via Cu(0)-RDRP"
Authors: Whitfield, R., Anastasaki, A., Nikolaou, V., Jones, G. R., Engelis, N. G., Discekici, E. H., Fleischmann, C., Willenbacher, J., Hawker, C. J., Haddleton, D. M.
Atom transfer radical polymerization (ATRP) typically requires various parameters to be optimized in order to achieve a high degree of control over molecular weight and dispersity (such as the type of initiator, transition metal, ligand, solvent, temperature, deactivator, added salts, and reducing agents). These components play a major role when switching monomers, e.g., from acrylic to methacrylic and/or styrenic monomers during the synthesis of homo- and block copolymers as the stability and reactivity of the carbon centered propagating radical dramatically changes. This is a challenge for both “experts” and nonexperts as choosing the appropriate conditions for successful polymerization can be time-consuming and overall an arduous task. In this work, we describe one set of universal conditions for the efficacious polymerization of acrylates, methacrylates and styrene (using an identical initiator, ligand, copper salt, and solvent) based on commercially available and inexpensive reagents (PMDETA, IPA, Cu(0) wire). The versatility of these conditions is demonstrated by the near quantitative polymerization of these monomer families to yield well-defined materials over a range of molecular weights with low dispersities (∼1.1–1.2). The control and high end group fidelity is further exemplified by in situ block copolymerization upon sequential monomer addition for the case of methacrylates and styrene furnishing higher molecular weight copolymers with minimal termination. The facile nature of these conditions, combined with readily available reagents, will greatly expand the access and availability of tailored polymeric materials to all researchers.
"Simple Benchtop Approach to Polymer Brush Nanostructures Using Visible-Light-Mediated Metal-Free Atom Transfer Radical Polymerization"
Authors: Discekici, E. H., Pester, C. W., Treat, N. J., Lawrence, J., Mattson, K. M., Narupai, B., Toumayan, E. P., Luo, Y., McGrath, A. J., Clark, P. G., Read de Alaniz, J., and Hawker, C. J.
The development of an operationally simple, metal-free surface-initiated atom transfer radical polymerization (SI-ATRP) based on visible-light mediation is reported. The facile nature of this process enables the fabrication of well-defined polymer brushes from flat and curved surfaces using a “benchtop” setup that can be easily scaled to four-inch wafers. This circumvents the requirement of stringent air-free environments (i.e., glovebox), and mediation by visible light allows for spatial control on the micron scale, with complex three-dimensional patterns achieved in a single step. This robust approach leads to unprecedented access to brush architectures for nonexperts.
Authors: Minehara, H., Pitet, L. M., Kim, S., Zha, R. H., Meijer, E. W., Hawker, C. J.
A library of Y-shaped poly(dimethylsiloxane) (PDMS)-b-poly(d,l-lactide) (PLA) diblock copolymers and their corresponding linear counterparts were synthesized, and their morphologies and feature sizes in bulk and thin films were compared using small-angle X-ray scattering (SAXS), scanning force microscopy (SFM), and grazing incidence small-angle X-ray scattering (GI-SAXS). For macromolecular isomers with approximately the same molecular weights and volume fractions (PLA fL: 0.20 and 0.35), different thin film morphologies were obtained for the Y-shaped PDMS-b-PLA derivatives when compared to the corresponding linear derivatives. These data also gave us the option to determine some of the key parameters of these block copolymers. A relatively high χ value of 0.24 was found for these PDMS-b-PLA systems and was shown to be influenced by architecture.
"Vitronectin-based, biomimetic encapsulating hydrogel scaffolds support adipogenesis of adipose stem cells "
Authors: Clevenger, T. N., Hinman, C. R., Rubin, Ashley, R. K., Smither, K., Burke, D. J., Hawker, C. J., Messina, D., Van Epps, D., Clegg, D. O.
Soft tissue defects are relatively common, yet currently used reconstructive treatments have varying success rates, and serious potential complications such as unpredictable volume loss and reabsorption. Human adipose-derived stem cells (ASCs), isolated from liposuction aspirate have great potential for use in soft tissue regeneration, especially when combined with a supportive scaffold. To design scaffolds that promote differentiation of these cells down an adipogenic lineage, we characterized changes in the surrounding extracellular environment during adipogenic differentiation. We found expression changes in both extra-cellular matrix (ECM) proteins, including increases in expression of collagen-IV and vitronectin, as well as changes in the integrin expression profile, with an increase in expression of integrins such as αVβ5 and α1β1. These integrins are known to specifically interact with vitronectin and collagen-IV, respectively, through binding to an Arg-Gly-Asp (RGD) sequence. When three different short RGD containing peptides were incorporated into 3D hydrogel cultures it was found that an RGD containing peptide derived from vitronectin provided strong initial attachment, maintained the desired morphology and created optimal conditions for in vitro 3D adipogenic differentiation of ASCs. These results describe a simple, nontoxic encapsulating scaffold, capable of supporting the survival and desired differentiation of ASCs for the treatment of soft tissue defects.
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