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RSC Advances View Article Online PAPER View Journal | View Issue Shape memory polymers with visible and near- infrared imaging modalities: synthesis, Cite this: RSC Adv.,2017,7, 19742 characterization and in vitro analysis† A. C. Weems, a J. E. Raymond,b A. D. Easley,a M. A. Wierzbicki,a T. Gustafson, b M. B. B. Monroea and D. J. Maitland *a Shape memory polymers (SMPs) are promising for non-invasive medical devices and tissue scaffolds, but are limited by a lack of visibility under clinical imaging. Fluorescent dyes are an alternative to radiocontrast agents in medical applications, they can be utilized in chemical sensors and monitors and may be anti-microbial agents. Thus, a fluorescent SMP could be a highly valuable biomaterial system. Here, we show that four fluorescent dyes (phloxine B (PhB), eosin Y (Eos), indocyanine green (IcG), and calcein (Cal)) can be crosslinked into the polymer backbone to enhance material optical properties without alteration of shape memory and thermomechanical properties. Examinations of Creative Commons Attribution 3.0 Unported Licence. the emission wavelengths of the materials compared with the dye solutions showed a slight red shift in the peak emissions, indicative of crosslinking of the material. Quantitative analysis revealed that PhB enabled visibility through 1 cm of blood and through soft tissue. We also demonstrate the utility of these methods in combination with radio-opaque microparticle additives and the use of laser- induced shape recovery to allow for rapid shape recovery below the glass transition temperature. The Received 13th December 2016 crosslinking of fluorescent dyes into the SMP enables tuning of physical properties and shape Accepted 19th March 2017 memory and independently of the fluorescence functionality. This fluorescent SMP biomaterial DOI: 10.1039/c6ra28165f system allows for use of multiple imaging modalities with potential application in minimally invasive rsc.li/rsc-advances medical devices. This article is licensed under a Introduction modality is X-ray angiography using uoroscopy.13–17 Previously, we incorporated radio-opaque microparticle additives and Open Access Article. Published on 04 April 2017. Downloaded 10/2/2021 1:47:35 AM. Shape memory polymers (SMPs) show promise for use as demonstrated an enhancement in SMP foam X-ray opacity minimally invasive medical materials.1–10 SMPs can be pro- superior to that of a commercially-available endovascular cessed into a variety of geometries, including highly porous, occlusion device, a platinum Guglielmi detachable coil (GDC).12 ultra-low density foams.1,2 A range of SMPs have been proposed While X-ray uoroscopy is a powerful technique, it poses for use in medical applications, and polyurethane SMPs are of signicant patient and technician risks due to the use of – particular interest due to their excellent biocompatibility.3–10 ionizing radiation.13 17 The development of medical materials – Polyurethane SMP foams have demonstrated rapid, stable that do not rely on uoroscopy can reduce these risks.13 17 blood clot formation, superior immune response compared Fluorescence-guided procedures are widely used in with polypropylene and silk, and tunable shape recovery for ophthalmic examinations, such as retinal angiography. They void lling.10,11 These foams have been proposed for use in have been shown to improve clinical outcomes and are gaining – several medical device applications, including aneurysm popularity in a variety of applications.18 22 Fluoresceins and occlusion, peripheral occlusion, and vascular and coronary near-infrared (NIR) dyes have been utilized clinically for uo- gras.3–10 While SMP foams show signicant promise, a draw- rescent imaging applications, and demonstrated excellent – back of polymer biomaterial systems is the limitations on in vivo biocompatibility and clearance by the body.23 25 We investigated imaging.5,12 Clinically, the most frequently used imaging two imaging methods, NIR uorescence (700–1000 nm) and visible light uorescence, due to the transparency windows of human tissues to certain light wavelengths. Namely, the uo- aBiomedical Device Laboratory, Dept of Biomedical Engineering, Texas A&M rescence spectra reported for aqueous phloxine B (PhB) has University, College Station, TX, 77860, USA. E-mail: [email protected] emission peaks between 530 nm and 570 nm. Eosin Y (Eos) has bLaboratory for Synthetic-Biologic Interface, Dept of Chemistry, Texas A&M University, emission peaks between 515 nm and 540 nm. These emission College Station, TX, 77860, USA † Electronic supplementary information (ESI) available. See DOI: tails (600 nm) correspond to wavelengths that have reasonable 10.1039/c6ra28165f transmission through so tissue and blood. NIR dyes, such as 19742 | RSC Adv.,2017,7, 19742–19753 This journal is © The Royal Society of Chemistry 2017 View Article Online Paper RSC Advances indocyanaine green (IcG, emission at +800 nm), offer another Materials and methods method of optically viewing SMPs in the body, as there is an optical window of minimal absorption in human tissue from Materials approximately 700 nm to 900 nm.26–31 All chemicals were purchased from Sigma Aldrich and used Inclusion of uorescent moieties can potentially enhance without modication or cleaning, unless otherwise stated. additional functionalities, such as antimicrobial properties, N,N,N0,N0-Tetrakis(2-hydroxypropyl)ethylenediamine (HPED, sensing, or medical device analysis. PhB and Eos are two inex- 99%), triethanolamine (TEA, 98%, Alfa Aesar), and 2,2,4-tri- pensive uorescein derivatives that possess reactive sites, and methyl hexamethylene diisocyanate (TMHDI, TCI America, they are used as cosmetic and drug additives in the United a mixture of 2,2,4 and 2,4,4 monomers) were used as mono- States and as food additives in Japan. These dyes have been mers. Ethyl isocyanate (98%, Sigma) was used for conrming found to be antimicrobial due to the halogenation of the ben- urethane syntheformation. Fluorescent monomers, shown in zoic acid moiety and the production of singlet oxygen and Fig. 1, PhB (99%), Eos (99%), IcG (95%), and Cal (99%) (Chem- reactive oxygen species with light interaction.32–34 The use of Impex Int'l Inc.) were identied as having functional groups photodynamic treatments with these molecules has been that react with isocyanate groups similarly to alcohol groups, shown to reduce both antibiotic-susceptible and methicillin- and were added without modication. All reactive monomers resistant Staphylococcus aureus (MRSA) cultures, which are of are shown in Fig. 1. The additives barium sulphate (BaSO4, 35–41 m concern for device-transmitted infections. IcG has also been particle size of 3 m, 99%), zirconium oxide (ZrO2, particle size demonstrated as an antimicrobial dye, and has been utilized of 5 mm, 99%), and tungsten (W, particle size > 1 mm, 99.95%, with polyurethanes as a method of reducing MRSA infection. Alfa Aesar) were used without modication. Additionally, uorescein molecules have been indicated for their antioxidant roles in preventing the development of reac- Synthesis tive oxygen species predecessors. TEA, HPED and TMHDI were reacted to form a prepolymer Creative Commons Attribution 3.0 Unported Licence. Fluorescence has found use in polymer systems for – mixture with an excess of isocyanates, in a process described temperature/chemical sensors and imaging particles.42 45 elsewhere.2,42 The prepolymer was later reacted with residual Despitetheuseofuorescent dyes in a range of applications, alcohols and the uorescent monomers during the foaming they have not been widely utilized in SMPs for medical devices. process.50,51 The uorescent monomers were added at 1.000, In such devices, the enhanced uorescence could allow for 0.500, 0.050, 0.010 and 0.001 wt%. For the composite materials, imaging through blood/solid tissue, as well as for self-cleaning physical additives were added with the nal alcohols and uo- and degradation resistance. Previous efforts to include uo- rescent monomers (0.050 wt% uorescent monomer). Physical rescent molecules into biomaterial systems via physical additives were added at 1 and 4 vol%, as well as 10 vol% for dispersion into the bulk polymer have resulted in inconsistent This article is licensed under a ZrO . Foams were evaluated for homogenous pores before dye dispersion. Scaffolding techniques, such as electro- 2 cleaning and processing. Aer cleaning, foams were dried and spinning, have been shown to reduce dispersion issues.12 stored with desiccant in a sealed container. Previously, Torbati et al. reported the synthesis of uorescent To conrm the formation of urethanes, stoichiometric Open Access Article. Published on 04 April 2017. Downloaded 10/2/2021 1:47:35 AM. SMPs in an electrospun web by physically adding IcG to the amounts of dyes and ethyl isocyanates were allowed to react polymer.12 The use of high speed mixing can promote homo- overnight; urethane formation was conrmed by NMR (Mercury geneous dispersion of dye throughout polymeric materials 300, Varian Inc, Palo Alto, CA). prior to foaming without the need for additional processing steps, as has been previously shown with nanocomposites.46 Our group previously physically incorporated IcG dyes into Bulk material characterization – SMPs to enable laser shape memory actuation.47 49 However, Bulk foam characteristics were quantied and compared with the incorporation of IcG into polyurethane foams, even when nonuorescent (control containing no uorescent molecules in well-dispersed in the polymer, has been