Co-reporter:Guillermo R. Alas, Rachit Agarwal, David M. Collard, Andrés J. García
Acta Biomaterialia 2017 Volume 59(Volume 59) pp:
Publication Date(Web):1 September 2017
DOI:10.1016/j.actbio.2017.06.033
The modification of the surface of surgical implants with cell adhesion ligands has emerged as a promising approach to improve biomaterial-host interactions. However, these approaches are limited by the non-specific adsorption of biomolecules and uncontrolled presentation of desired bioactive ligands on implant surfaces. This leads to sub-optimal integration with host tissue and delayed healing. Here we present a strategy to grow non-fouling polymer brushes of oligo(ethylene glycol) methacrylate by atom transfer radical polymerization from dopamine-functionalized clinical grade 316 stainless steel. These brushes prevent non-specific adsorption of proteins and attachment of cells. Subsequently, the brushes can be modified with covalently tethered adhesive peptides that provide controlled cell adhesion. This approach may therefore have broad application to promote bone growth and improvements in osseointegration.Statement of SignificanceStainless steel (SS) implants are widely used clinically for orthopaedic, spinal, dental and cardiovascular applications. However, non-specific adsorption of biomolecules onto implant surfaces results in sub-optimal integration with host tissue. To allow controlled cell-SS interactions, we have developed a strategy to grow non-fouling polymer brushes that prevent protein adsorption and cell adhesion and can be subsequently functionalized with adhesive peptides to direct cell adhesion and signaling. This approach has broad application to improve osseointegration onto stainless steel implants in bone repair.Download high-res image (83KB)Download full-size image
Co-reporter:Pranav P. Kalelkar, Guillermo R. Alas, and David M. Collard
Macromolecules 2016 Volume 49(Issue 7) pp:2609-2617
Publication Date(Web):March 31, 2016
DOI:10.1021/acs.macromol.5b02431
The ring-opening copolymerization of 3,6-bis(chloromethyl)-1,4-dioxane-2,5-dione and l-lactide affords a chloro-substituted polylactide copolymer (chloro-PL). Base-promoted dehydrochlorination of chloro-PL provides a copolymer (ene-PL) that contains electrophilic α,β-unsaturated ester units. The copolymer undergoes conjugate addition with a variety of thiols in solution under mildly basic conditions and also in the presence of AIBN. Reaction on the surface of films of the unsaturated copolyester is demonstrated by the addition of a thiol-substituted fluorescent dye.
Co-reporter:Dr. Bradley E. Carson;Trent M. Parker;Dr. Edward G. Hohenstein;Dr. Glen L. Brizius;Whitney Komorner; Rollin A. King; David M. Collard; C. David Sherrill
Chemistry - A European Journal 2015 Volume 21( Issue 52) pp:19168-19175
Publication Date(Web):
DOI:10.1002/chem.201502363
Abstract
The structural and electronic consequences of π–π and CH/π interactions in two alkoxy-substituted 1,8-bis- ((propyloxyphenyl)ethynyl)naphthalenes are explored by using X-ray crystallography and electronic structure computations. The crystal structure of analogue 4, bearing an alkoxy side chain in the 4-position of each of the phenyl rings, adopts a π-stacked geometry, whereas analogue 8, bearing alkoxy groups at both the 2- and the 5-positions of each ring, has a geometry in which the rings are splayed away from a π-stacked arrangement. Symmetry-adapted perturbation theory analysis was performed on the two analogues to evaluate the interactions between the phenylethynyl arms in each molecule in terms of electrostatic, steric, polarization, and London dispersion components. The computations support the expectation that the π-stacked geometry of the alkoxyphenyl units in 4 is simply a consequence of maximizing π–π interactions. However, the splayed geometry of 8 results from a more subtle competition between different noncovalent interactions: this geometry provides a favorable anti-alignment of CO bond dipoles, and two CH/π interactions in which hydrogen atoms of the alkyl side chains interact favorably with the π electrons of the other phenyl ring. These favorable interactions overcome competing π–π interactions to give rise to a geometry in which the phenylethynyl substituents are in an offset, unstacked arrangement.
Co-reporter:Dr. Sukrit Mukhopadhyay;Dr. Subodh P. Jagtap;Dr. Veaceslav Coropceanu; Jean-Luc Brédas; David M. Collard
Angewandte Chemie 2012 Volume 124( Issue 46) pp:11797-11800
Publication Date(Web):
DOI:10.1002/ange.201205738
Co-reporter:Dr. Sukrit Mukhopadhyay;Dr. Subodh P. Jagtap;Dr. Veaceslav Coropceanu; Jean-Luc Brédas; David M. Collard
Angewandte Chemie International Edition 2012 Volume 51( Issue 46) pp:11629-11632
Publication Date(Web):
DOI:10.1002/anie.201205738
Co-reporter:Kathy B. Woody, Benjamin J. Leever, Michael F. Durstock, and David M. Collard
Macromolecules 2011 Volume 44(Issue 12) pp:4690-4698
Publication Date(Web):May 18, 2011
DOI:10.1021/ma200084z
A synthetic approach is established to provide a monofunctional telechelic poly(3-octylthiophene) (P3OT) bearing a single bromine-substituted end group that is of potential use in the preparation of well-defined block copolymers. Telechelic P3OT was prepared via a chain growth process by a catalyst-transfer condensation polymerization (CTCP) of 5-bromo-4-octyl-2-thienylmagnesium iodide initiated by a phenylnickel(II) initiator. Optimization of the conditions for quenching the reaction allowed for the installation an α-bromo functionality at the terminus of the polymer. We demonstrate the utility of this well-defined monofunctional polymer, Ph–P3OT–Br, by coupling it to a poly(quinoxaline) (PQ) bearing boronate ester end groups to provided a new class of donor–acceptor–donor (D–A–D) triblock copolymers. The formation of the triblock copolymers was confirmed by gel-permeation chromatography (GPC) and 1H NMR spectroscopy. The optical properties of the polymers were investigated using UV–visible absorption and fluorescence spectroscopy. Efficient quenching of the fluorescence from the individual blocks of the triblock copolymers is consistent with the occurrence of electron transfer. AFM images illustrate a nanoscale phase separation of the electron-rich P3OT and electron-poor PQ blocks.
Co-reporter:Kathy B. Woody, Elizabeth M. Henry, Subodh Jagtap, and David M. Collard
Macromolecules 2011 Volume 44(Issue 23) pp:9118-9124
Publication Date(Web):November 10, 2011
DOI:10.1021/ma201347z
A majority of conjugated organic polymers are electron-rich materials, with far fewer electron-poor (i.e., electron accepting) analogues. Here we report the synthesis and preliminary characterization of new class of electron-poor poly(arylene ethynylene)s (PAEs) that contain 5,8-quinoxaline ethynylene repeat units. While various PAE copolymers consisting of alternating electron-rich and electron-poor units display lower bandgaps than poly(phenylene ethynylene)s, the poly(5,8-quinoxaline ethynylene) (PQE) reported in this study has a higher electron affinity and lower bandgap (2.25 eV) than many of these donor–acceptor materials. In comparison to poly(5,8-quinoxaline)s (PQs), which do not have an ethynylene linkage between the quinoxalines, the PQE has a red-shifted absorption spectrum that is consistent with a more highly conjugated and planar backbone. In addition, the PQE has a lower electrochemical reduction potential than both a corresponding PQ and a donor–acceptor alternating PAE copolymer that contains the quinoxaline unit as the electron-poor component.
Co-reporter:Subodh P. Jagtap
Journal of the American Chemical Society 2010 Volume 132(Issue 35) pp:12208-12209
Publication Date(Web):August 16, 2010
DOI:10.1021/ja104696e
Interchain interactions between π-systems have a strong effect on the electronic structure of conjugated organic materials. This influence has previously been explored by the spectroscopic and electrochemical characterization of molecules in which pairs of conjugated oligomers are held in a stacked fashion by attachment to a rigid scaffold. We have prepared a new polymer which uses a pseudo-geminal disubstituted [2.2]paracyclophane scaffold to hold 1,4-bis(phenylethynyl)-2,5-dialkoxybenzene (PE3) chomophores in a π-stacked fashion over their entire length and in an extended multitier arrangement. Solutions of this new polymer display a Stokes shift of 171 nm, compared to just ca. 30 nm for previous models in which only the terminal phenyl rings of the PE3 chromophore are held in a stacked arrangement. This suggests that interchain interactions of π-systems over their entire length in a multitier assembly provides for relaxation of the excited state to a stable “phane” electronic state which is responsible for emission. This stabilization is not available in the stacked dimer or other regioisomers of the polymer which possess lesser degrees of overlap. Thus, the architecture of the soluble polymer mimics that of segments of conjugated polymers in semiconducting thin films and will provide a platform for the exploration of the nature of charge carriers and excitons in these important materials.
Co-reporter:Jenny E. Raynor, Timothy A. Petrie, Kenan P. Fears, Robert A. Latour, Andrés J. García and David M. Collard
Biomacromolecules 2009 Volume 10(Issue 4) pp:
Publication Date(Web):March 9, 2009
DOI:10.1021/bm8011924
Attaining control over the surface chemistry of titanium is critical to its use in medical implants, especially to address complications such as infection and loosening of implants over time, which still present significant challenges. The surface-initiated atom transfer radical polymerization (SI-ATRP) of a saccharide-substituted methacrylate, 2-gluconamidoethyl methacrylate (GAMA), affords dense polymer brushes that resist protein adsorption and cell adhesion. We further tailored the nature of the surfaces by covalent attachment of an adhesion peptide to afford control over cell adhesion. Whereas unmodified poly(GAMA) brushes prevent cell adhesion, brushes with a tethered GFOGER-containing peptide sequence promote the deposition of confluent well-spread cells. The presentation of adhesion proteins on a robust bioresistive background in this fashion constitutes a versatile approach to the development of new biomaterials.
Co-reporter:Rakesh Nambiar, Kathy B. Woody, Josh D. Ochocki, Glen L. Brizius and David M. Collard
Macromolecules 2009 Volume 42(Issue 1) pp:43-51
Publication Date(Web):December 15, 2008
DOI:10.1021/ma802215y
Poly(2,5-disubstituted-1,4-phenylene ethynylene)s, PPEs, are generally synthesized by Pd-catalyzed coupling polymerizations of appropriately substituted 1,4-diiodobenzenes and 1,4-diethynylbenzenes (i.e., condensation polymerization of A−A and B−B type monomers). If the monomers are not symmetrically substituted, this results in an irregular substitution pattern of the side chains along the polymer backbone. As with other classes of conjugated polymers, the relative placement of side chains along the backbone should influence the properties of the materials. We report a new synthetic approach to prepare regioregular unsymmetrically substituted PPEs by polymerization of 4-iodophenylacetylenes (i.e., a condensation polymerization of a single A−B type monomer). We have synthesized both the regiorandom and regioregular PPEs from unsymmetrically substituted monomers. We provide a detailed discussion of various approaches to the synthesis of PPEs with different regioregularities and provide a preliminary description of the differences between regioregular and regiorandom analogues.
Co-reporter:Kathy B. Woody, Rakesh Nambiar, Glen L. Brizius and David M. Collard
Macromolecules 2009 Volume 42(Issue 21) pp:8102-8111
Publication Date(Web):September 10, 2009
DOI:10.1021/ma901442j
New poly(1,4-phenylene ethynylenes)s (PPEs), in which each phenylene unit is substituted with both semifluoroalkoxy (−O(CH2)m(CF2)nF) and dodecyloxy (−O(CH2)12H) groups, are amphiphilic by virtue of the self-aggregating properties of the dissimilar side chains. Sonogashira polymerization of 4-iodophenylacetylenes bearing semifluoroalkoxy and alkoxy groups in the 2- and 5-positions, respectively, affords polymers with regular relative placement of the dissimilar side chains (i.e., “regioregular” materials containing only “head-to-tail” diads). This provides a Janus type structure. The assembly of these polymers was studied as a function of the length of the fluoroalkyl segment in the side chain by X-ray diffraction, differential scanning calorimetry, and UV−vis spectroscopy. The properties of these polymers were compared to analogues with random relative placement of side chains (i.e., materials containing a mixture of “head-to-head”, “tail-to-tail” and “head-to-tail” diads), and to a nonfluorinated analogue. In contrast to the highly ordered and oriented solid phases formed by alkyl/semifluoroalkyl substituted poly(bithiophene)s, and despite their defined molecular structure, the amphiphilicity of the new semifluoro PPEs impedes their crystallization. While the overall structure of the regioregular polymer is amphiphilic, in which the dissimilar side chains are expected to segregate, we ascribe the lack of crystallinity to the disruption of side chain crystallization by virtue of having the alkyl and fluoroalkyl segments within a single side chain. These side chain cannot pack in an interdigitated fashion by virtue of the disparate segments, thereby leading to poorly ordered, or amorphous, solid materials.
Co-reporter:David E. Noga, Timothy A. Petrie, Anjli Kumar, Marcus Weck, Andrés J. García and David M. Collard
Biomacromolecules 2008 Volume 9(Issue 7) pp:
Publication Date(Web):June 25, 2008
DOI:10.1021/bm800292z
A polylactide copolymer with pendant benzyloxy groups has been synthesized by the copolymerization of a benzyl-ether substituted monomer with lactide. Debenzylation of the polymer to provide pendant hydroxyl groups followed by modification with succinic anhydride affords the corresponding carboxylic acid functionalized copolymer that is amenable to standard carbodiimide coupling conditions to attach amine-containing biological molecules. An amino-substituted biotin derivative was coupled to the carboxyl functional groups of copolymer films as proof-of-concept. In a demonstration of the function of these new materials, an RGD-containing peptide sequence was tethered to copolymer films at various densities and was shown to enhance the adhesion of epithelial cells. This strategy provides the opportunity for the attachment of a variety of ligands, allowing for the fabrication of a versatile class of biodegradable, biocompatible materials.
Co-reporter:J. E. Raynor;D. M. Collard;T. A. Petrie;A. J. García
Advanced Materials 2007 Volume 19(Issue 13) pp:1724-1728
Publication Date(Web):25 MAY 2007
DOI:10.1002/adma.200602129
A monolayer of 11-(2-bromo-2-methyl)propionyloxy)undecenyldimethylchlorosilane on titanium serves as an initiator for surface-initiated atom-transfer polymerization of (oligoethylene glycol) methacrylate (OEGMA) to prepare poly(OEGMA) brushes. The polymer brush affords resistance to adhesion of osteoblastic cells. Treatment of the brush-modified surface with 4-nitrophenyl chloroformate followed by a GFOGER-containing peptide promotes cell adhesion, thereby representing a strategy to impart biofunctionality to titanium (see figure) and thereby promote osseointegration.
Co-reporter:R. R. Nambiar;G. L. Brizius;D. M. Collard
Advanced Materials 2007 Volume 19(Issue 9) pp:1234-1238
Publication Date(Web):4 APR 2007
DOI:10.1002/adma.200602902
Regioregular and regiorandom analogues of a dialkoxy-substituted poly(1,4-phenylene ethynylene) (PPE) bearing a pair of dissimilar side chains (dodecyloxy and methoxy) on each ring have been prepared to explore how the relative placement of substituents (see figure) can be used to modify the properties of this class of conjugated polymers. A preliminary study of the effect of regioregularity on properties is presented in which regiorandom and regioregular polymers are compared.
Co-reporter:David A. Schiraldi;Genara S. Andrade
Macromolecular Chemistry and Physics 2005 Volume 206(Issue 14) pp:1373-1381
Publication Date(Web):18 JUL 2005
DOI:10.1002/macp.200500004
Summary: The successful incorporation of hydroquinone in thermal polyesterifications to prepare rigid linear copolyesters is hindered by the leaving group ability of phenols in nucleophilic acyl substitution reactions, the low nucleophilicity of phenols relative to aliphatic alcohols, and its volatility. To overcome these obstacles, with particular regard to improving the properties of poly(ethylene terephthalate), PET, we chose an approach whereby dyad-based AB-type mono(acetoxyphenyl) terephthalate monomers are transesterified into PET. In contrast to attempts to copolymerize terephthalic acid, ethylene glycol (EG) and hydroquinone, the transterification of small amounts (<10 mol-%) of the preformed dyad in the absence of aliphatic diol, provides homogeneous random copolymers. Incorporation of larger amounts of aromatic diol gave only partly soluble materials. NMR analysis of the soluble fraction (in 20 vol.-% TFA:CHCl3) indicated that the copolymers are substantially random. Transesterification of mono(4-acetoxyphenyl) terephthalate (hydroquinone-terephthalic acid, 1) and mono(3-acetoxyphenyl) terephthalate (resorcinol-terephthalic acid, 2) into PET allows us to further explore the effect of mesogen structure on the development of liquid crystalline copolyesters.
Co-reporter:Robert M. Kriegel;David A. Schiraldi;Katie L. Saliba;Genay Jones
Macromolecular Chemistry and Physics 2005 Volume 206(Issue 15) pp:1479-1487
Publication Date(Web):29 JUL 2005
DOI:10.1002/macp.200500063
Summary: The chain extension of anthracene end-capped oligoesters by reaction with bismaleimides constitutes a rapid route to high molecular weight polyesters. Polytransesterification of bis(2-hydroxyethyl) terephthalate in the presence of a small amount of 2-hydroxyethyl 2-anthracenecarboxylate provides low molecular weight anthracene-terminated macromers with anthracene end group functionality (fAN) of 1.66–1.85. These are subject to rapid chain extension with di(4-maleimidophenyl)methane by Diels-Alder cycloadditions resulting in consumption of the anthracene and maleimide end groups to generate polymers with > 2.0 × 104 g · mol−1. Thus, generation of the polymeric structure is achieved rapidly by addition reactions rather than sluggish transesterification reactions in which a condensate must be removed from the viscous polymer melt.
Co-reporter:L. Li;K. E. Counts;S. Kurosawa;A. S. Teja;D. M. Collard
Advanced Materials 2004 Volume 16(Issue 2) pp:
Publication Date(Web):29 JAN 2004
DOI:10.1002/adma.200305333
Co-reporter:L. Li;K. E. Counts;S. Kurosawa;A. S. Teja;D. M. Collard
Advanced Materials 2004 Volume 16(Issue 6) pp:
Publication Date(Web):22 MAR 2004
DOI:10.1002/adma.200490019
Co-reporter:Jeremy Holtzclaw;Michael R. Hibbs;Richard Y. F. Liu;Anne Hiltner;Eric Baer;David A. Schiraldi
Journal of Polymer Science Part A: Polymer Chemistry 2004 Volume 42(Issue 7) pp:1668-1681
Publication Date(Web):9 FEB 2004
DOI:10.1002/pola.11075
The synthesis and properties of poly(ethylene terephthalate) (PET) copolymers containing four bisester diamide structural units are reported. Two of the bisester diamides consist of three para-substituted aromatic rings, and the other two consist of three meta-substituted aromatic rings. The copolymers have been characterized by nuclear magnetic resonance, differential scanning calorimetry, and dilute solution viscometry. Three of the copolymers can be compression-molded into amorphous films for oxygen barrier testing, and one of these three films can be oriented for additional barrier testing. The three amorphous films all have lower permeabilities than unoriented PET. However, this difference diminishes upon the orientation of the polymer films. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1668–1681, 2004
Co-reporter:F. Salhi;D.M. Collard
Advanced Materials 2003 Volume 15(Issue 1) pp:
Publication Date(Web):10 JAN 2003
DOI:10.1002/adma.200390018
Co-reporter:Marian Vargas;Robert M. Kriegel;David A. Schiraldi
Journal of Polymer Science Part A: Polymer Chemistry 2002 Volume 40(Issue 19) pp:3256-3263
Publication Date(Web):20 AUG 2002
DOI:10.1002/pola.10414
Dimethyl 2,6-anthracene dicarboxylate is used as a comonomer in the synthesis of functional copolymers that are subject to modification with Diels–Alder reactions. The formation of poly(ethylene terephthalate-co-2,6-anthracenate), containing less than 20 mol % of the anthracene-2,6-dicarboxylate structural units, provides materials that are tractable and soluble. The anthracene units of the copolymers undergo Diels–Alder reactions with N-substituted maleimides. The grafting of N-alkylmaleimides affords soluble, hydrophobic polymers, whereas grafting with maleimide-terminated poly(ethylene glycol) affords hydrophilic polymers. Because this reaction proceeds below the melting point of the copolymers, the procedure can be applied to thin films, whereby the surface properties are modified. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3256–3263, 2002
Co-reporter:Daniel M. Connor;Charles L. Liotta;Scott D. Allen;David A. Schiraldi
Journal of Applied Polymer Science 2001 Volume 80(Issue 14) pp:2696-2704
Publication Date(Web):5 APR 2001
DOI:10.1002/app.1384
Small amounts of dimethyl-4,4′-biphenyldicarboxylate, 2,7-dimethyl-4,5,9,10-tetrahydropyrenedicarboxylate, and dimethyl-2,7-pyrenedicarboxylate have been copolymerized into poly(ethylene) terephthalate (PET). The thermal transitions of the copolymers have been characterized, and the crystallization rates have been measured isothermally. Avrami analysis indicates that all the copolymers crystallized at a slower rate than that of the PET homopolymer. Addition of perylene to the copolymers containing pyrene enhanced the rate of crystallization, which could be the consequence of stacked arene assemblies serving as templates for crystal formation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2696–2704, 2001
Co-reporter:Daniel M. Connor;Robert M. Kriegel;Charles L. Liotta;David A. Schiraldi
Journal of Polymer Science Part A: Polymer Chemistry 2000 Volume 38(Issue 8) pp:1291-1301
Publication Date(Web):9 MAR 2000
DOI:10.1002/(SICI)1099-0518(20000415)38:8<1291::AID-POLA13>3.0.CO;2-1
Diacids of fused arenes have been prepared for use as covalently bound fluorescent optical brightening agents in condensation polymers. The monomers: dimethyl 1,6-pyrene dicarboxylate, dimethyl 1,8-pyrenedicarboxylate, dimethyl 2,7-pyrenedicarboxylate, 1,8-bis(2-carboxybenzoyl)pyrene dimethyl ester, dimethyl 2,6-anthracenedicarboxylate, dimethyl 2,7-anthracenedicarboxylate and dimethyl 9,10-anthracenedicarboxylate are copolymerized with poly(ethylene terephthalate) and their optical properties are assessed. All of the polymers give blue fluorescence, with the copolymer containing dimethyl 1,6-pyrenedicarboxylate being the brightest. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1291–1301, 2000
Co-reporter:David M. Collard;Charles L. Liotta;David A. Schiraldi;Marian Vargas
Journal of Polymer Science Part A: Polymer Chemistry 2000 Volume 38(Issue 12) pp:2167-2176
Publication Date(Web):18 MAY 2000
DOI:10.1002/(SICI)1099-0518(20000615)38:12<2167::AID-POLA50>3.0.CO;2-7
1,4-Phenylene bis(acrylic acid) is a thermally stable diacid, which can be incorporated into polyesters. The phenylene bisacrylate structural units undergo rapid photochemical reaction in the solid state to form crosslinks. This constitutes a feasible approach to polyesters, which can be photochemically thermoset after fabrication as films and fibers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2167–2176, 2000
Co-reporter:Daniel M Connor, David M Collard, Charles L Liotta, David A Schiraldi
Dyes and Pigments 1999 Volume 43(Issue 3) pp:203-206
Publication Date(Web):October 1999
DOI:10.1016/S0143-7208(99)00060-1
Dimethyl esters of four pyrene dicarboxylic acids were synthesized and incorporated into poly(ethylene terephthalate). The spectroscopic properties of the polymers and monomers are assessed for their effectiveness and potential as covalently-bound fluorescent brightening agents.
