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Fluorescence ANALYSIS OF BIOMEDICAL POLYMERS:

Introduction to Polymer Analysis. Methodology & Instrumentation. Thermoresponisve polymers. Solvatochromic methods. Fluorescence methods. Publications.

This research has been part-funded (2003-2008) by Science Foundation Ireland as part of a Principal Investigator award (02/IN.1/M231) and fully from 2007-2010 by Science Foundation Ireland as part of a Research Frontiers Programme Grant (MASF423).

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introduction :

The use of functional coatings based on micrometre thick hydrophilic polymer films is becoming more widespread in medical devices and pharmaceutical formulations.  These functional polymer coatings can serve as aids to improve implanted device compatibility and/or as reservoirs for local drug delivery.  In one such example, coronary stents, manufacturers are developing stents coated with drug-eluting polymers, with a view to achieve local delivery of potential anti-restenosis therapies.  These polymer coatings are relatively thin (20-100 µm) and formed on small and complex geometries (the typical size of a coronary stent is 15 x 3 mm) and this combination generates significant problems for in-situ polymer film analysis.  The drug elution rate, long-term storage, device efficacy, and hence regulatory issues are all dependant on the physicochemical properties of the polymer film. 
Understanding these properties in detail is important from the standpoint of fully understanding how thin polymer films will behave in many biomedical applications.  For example, changes in polymer polarity will have significant impact on the water uptake and retention rates, which in turn affect the mechanical and chemical properties.
The analysis of thin polymer films for biomedical applications typically involves the analysis of two separate domains, the polymer surface, and the bulk film.  For in-situ analysis of the bulk properties of polymer films, various optical techniques can be employed including vibrational, fluorescence, and UV-Visible absorption spectroscopy.  In particular, fluorescence spectroscopy has received considerable interest due to its high sensitivity, selectivity, and non-destructive characteristics.  However, for fluorescence methods to be useful for characterising polymer films one must overcome problems such as photobleaching, excitation source instabilities, and local variations in a probe concentration.
Our research is focused on developing robust analytical methods for the analysis of hydrophilic polymers such as those used in medical device manufacturing and healthcare.

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Methodology & INSTRUMENTATION :

The key methods that we use are Fluorescence and UV-visible absorption spectroscopies. The key requirement is that the methods we develop are non-contact, non-destructive, and can be practically implemented. 

One of our most heavily used pieces of instrumentation is the controlled humidity chamber. 

The research is being carried out by Boguslaw Szczupak and Cheryl Morris.

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Theromresponsive polymers : 

We are mainly working on pNIPAM and its pNTBA co-polymers.

Solvatochromic Methods :

A method has been developed to charaterise hydrophilic polymers using solvatochromic probes.  This gives information about the polarizability, hydrogen bonding donor and acceptor ability of polymers.

Measuring the micro-polarity and hydrogen-bond donor/acceptor ability of thermoresponsive N-isopropylacrylamide/N-tert-butylacrylamide copolymer films using solvatochromic indicators. B. Szczupak, A.G. Ryder, D.M. Togashi, Y.A. Rotchev, A. Gorelov, and T.J. Glynn, Applied Spectroscopy, 63(4), 442-449, (2009).
Online at: Ingenta.  

fluorescence Methods :

We have been using novel ESIPT probes to characterise these polymers.  More details to come.

Publications :  

1. Study of water adsorption in Poly(N-isopropylacrylamide) thin films using fluorescence emission of 3-hydroxyflavone probes.  C. Morris, B. Szczupak, A.S. Klymchenko, and A.G. Ryder. Macromolecules , 43(22), 9488-9494, ( 2010). 
   DOI:  10.1021/ma102152j .
   
2. Polarity assessment of thermoresponsive poly(NIPAM-co-NtBA) copolymer films using fluorescence methods.  B. Szczupak, A.G. Ryder, D.M. Togashi, Y.A. Rotchev, A.S. Klymchenko, A. Gorelov, and T.J. Glynn,  Journal of Fluorescence, 20(3), 719-731, ( 2010).
   DOI: 10.1007/s10895-010-0613-5
3. Measuring the micro-polarity and hydrogen-bond donor/acceptor ability of thermoresponsive N-isopropylacrylamide/N-tert-butylacrylamide copolymer films using solvatochromic indicators. B. Szczupak, A.G. Ryder, D.M. Togashi, Y.A. Rotchev, A. Gorelov, and T.J. Glynn, Applied Spectroscopy, 63(4), 442-449, ( 2009).
   Online at: Ingenta.
4. A fluorescence methodology for assessing the polarity and composition of novel thermoresponsive hydrophilic/hydrophobic copolymer system.  (Invited Paper), A.G. Ryder, B. Szczupak, Y.A. Rotchev, A.S. Klymchenko, A. Gorelov, and T.J. Glynn.  Proc SPIE Int. Soc. Opt. Eng., 5826, 1-11, ( 2005). [Invited,  full paper] DOI:10.1117/12.605117

International Presentations:

1. The Effect of Humidity on the Emission Properties of Poly(N-isopropylacrylamide) films doped with 3-Hydroxyflavone derivatives.  C. Morris, A.G. Ryder, B. Szczupak, and A.S. Klymchenko, 11th Conference on Methods and Applications of Fluorescence: Spectroscopy, Imaging and Probes, Budapest, Hungary, 6 – 9 Sept., 2009.
   
2. Determination of empirical polarity parameters of thermoresponsive N-Isopropylacrylamide/N-Tert-Butylacrylamide copolymer films using solvatochromic indicators.  B. Szczupak, A.G. Ryder, D.M. Togashi, Y.A. Rochev, A. Gorelov, and T.J. Glynn. XXII IUPAC Symposium on Photochemistry, Gotenburg, Sweden, 28 July – 01Aug. 2008.
3. Fluorescence Studies of Rhodamine B in PVA Thin Films.  E. Joyce, B. Szczupak, D.M. Togashi, A.G. Ryder. Europtrode IX, Dublin, March 30th - April 2nd 2008.
4. Thermoresponsive copolymers for tissue engineering and drug delivery.  A. Gorelov, A. Ryder, W. Carroll, and Y. Rochev.  8th Annual Meeting of Tissue Engineering Society International, Shanghai, China, 22-25 Oct. 2005.
5. A fluorescence methodology for assessing the polarity and composition of novel thermoresponsive hydrophylic/hydrophobic copolymer system (Invited Paper), A.G. Ryder, B. Szczupak, Y.A. Rotchev, A.S. Klymchenko, A. Gorelov, T.J. Glynn.  OptoIreland, RDS Dublin, Ireland, 4-6 April, 2005.
6. A fluorescence methodology for assessing the polarity of hydrophilic polymers. B. Szczupak, A.G. Ryder, Y.A. Rochev, A.S. Klymchenko, A. Gorelov, and T.J. Glynn.  Polymer Networks 2004, Bethesda, MD, USA, 15-19 August, 2004.

National Presentations:

1. Humidity effects on the emission of 4’-diethylamino-3-hydroxyflavone fluorophores in Poly(N-isopropylacrylamide) thin films.  C. Morris, B. Szczupak, and A.G. Ryder. 61st Annual Chemistry Colloquium, Dublin Institute of Technology, Dublin, 17-19 June, 2009.
   
2. The Effect of Humidity on the Emission Properties of 4’-diethylamino-3-hydroxyflavone doped Poly(N-isopropylacrylamide) films.  C. Morris, B. Szczupak, and A.G. Ryder. 60th Annual Chemistry Colloquium, UCC, Cork, 11-13 June, 2008.
3. Polymer polarity measurements using fluorescence techniques.  B. Szczupak, A.G. Ryder, Y.A. Rochev, A.V. Gorelov, & T.J. Glynn. BioNet 2003, GMIT, Galway, 16-17 Dec., 2003.

 

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